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INTRODUCTION

May 23, 2013 — The pathophysiology of subarachnoid hemorrhage and the physical principles of CT explain the change in sensitivity of CT in detecting subarachnoid hemorrhage with time from ictus. X Ray techniques including CT produce tissue contrast because of the proportion of the incident X ray beam that is stopped (attenuated) by the tissue. This relies on two factors: the amount of tissue traversed by the beam and the attenuation coefficient of the tissue. The attenuation coefficient bears a direct relation to the electron density of the tissue. Fresh haemorrhage has the same electron density as brain and other soft tissues and so hyperacute (within 2 hours of ictus) subarachnoid hemorrhage may not be seen directly on CT. As reabsorption of serum from a haematoma progresses the local packed cell volume, and hence electron density, increases making acute subarachnoid hemorrhage visible as a high attenuating “white” area. With the passage of further time subarachnoid hemorrhage becomes less visible on CT principally because of two processes. Firstly, CSF circulation redistributes focal subarachnoid hemorrhage into other parts of the subarachnoid space and ventricular system. The resulting dilution reduces the conspicuity on CT. Secondly, reabsorption of serum is followed by reabsorption of the protein component, which also leads to reduced conspicuity. Consequently the sensitivity of CT to subarachnoid hemorrhage falls drastically over the first 14 days from ictus. [4]

Magnetic resonance imaging does not directly rely on the electron density of substances for its contrast resolution. The MR signal principally relies on proton (hydrogen nuclei) density, and T1 and T2* (which includes the T2 component) relaxation times. The different physical and chemical states of iron within haemorrhage have profound effects on the MR signal. [14] Standard spin echo MR sequences are considered to be insensitive in detecting acute haemorrhage; however, MR imaging offers two possibilities for improved detection of subarachnoid hemorrhage, both of which depend on the appearance of haemoglobin and its breakdown products.

The protein component produces high T2 signal which is swamped by the bright T2 signal from CSF on a conventional T2 weighted image. FLAIR sequences suppress the CSF signal and allow the signal from globin and its breakdown products to be seen. FLAIR has been reported to be a sensitive test for subarachnoid hemorrhage in the subacute phase. [7]

Iron in the form of Fe3+ or Fe2+ is paramagnetic. The presence of paramagnetic species in the CSF leads to localised perturbations in the magnetic field “seen” by the MR visible hydrogen nuclei. This leads to an increase in the precession rate in the immediate vicinity of Fe ions on the atomic scale and hence a faster dephasing and loss of T2* signal. Gradient echo sequences with significant T2* weighting are particularly sensitive to this localised change and are thus suited to detecting subarachnoid hemorrhage, even in the acute stage.

Figure 1. MRI T1 image showing a precontrast hyperintensity in the right parieto-occipital region and in the 4th ventricle due to the presence of methemoglobin in the subarachnoid spaces secondary to subarachnoid hemorrhage

The combination of lumbar puncture and CT is sensitive and specific for acute subarachnoid hemorrhage. CT suffers from a loss of sensitivity to subarachnoid hemorrhage in the subacute phase. MRI, particularly FLAIR and T2*, may be able to supplement CT in this situation. Both FLAIR and T2* can be performed on standard MR scanners.

Appropriately selected MR sequences are sensitive and specific in the detection of subarachnoid hemorrhage. This is by contrast with the widespread view in the clinical neuroscience literature, although some reports [7] show the value of FLAIR in detecting subarachnoid hemorrhage. one practical point of view in this chapter is that MR using FLAIR and T2* sequences together is a valuable tool in the detection of subarachnoid hemorrhage.

Figure 2. An acute subarachnoid hemorrhage. Brain CT was performed on the day of the haemorrhage; MR scans were taken 48 hours later. (A) CT shows blood in the interhemispheric fissure which is not seen on a comparable MR cut with (B) a T1 weighting sequence or (C) a fast spin echo T2 weighting sequence. (D) subarachnoid hemorrhage is seen on the gradient echo T2* image as an area of low signal. Lower cuts on the same patient show interhemispheric, sylvian, and cisternal blood on (E) CT and (F) T2* MR.

• Conclusions

Sensitivity to subarachnoid hemorrhage varied among the five MR sequences studied from 50% to 94% in acute subarachnoid hemorrhage and from 33% to 100% in subacute subarachnoid hemorrhage. The most sensitive sequences were FLAIR and T2* with T2* performing slightly better than FLAIR. The sensitivity of T2* was 94% under 4 days from the ictus and 100% between 4 and 14 days.

Fluid-attenuated inversion recovery (FLAIR) is the most sensitive MRI pulse sequence for the detection of subarachnoid hemorrhage (subarachnoid hemorrhage). On FLAIR images, subarachnoid hemorrhage appears as high signal-intensity (white) in normally low signal-intensity (black) CSF spaces. In cases of subarachnoid hemorrhage, FLAIR and CT scanning have similar findings. T2- and T2*-weighted images can potentially demonstrate subarachnoid hemorrhage as low signal-intensity in normally high signal-intensity subarachnoid spaces. On T1-weighted images, acute subarachnoid hemorrhage may appear as intermediate-intensity or high-intensity signal in the subarachnoid space.

MRA may be useful for evaluating aneurysms and other vascular lesions that cause subarachnoid hemorrhage. The low sensitivity for aneurysms smaller than 5 mm, the inability to evaluate small aneurysm contour irregularities, and difficulty in obtaining high-quality images in patients who are agitated or confused limits the utility of MRI in the diagnosis of acute subarachnoid hemorrhage.

Figure 3. A subtle subacute subarachnoid hemorrhage. (A) Brain CT was done 7 days after the haemorrhage and shows abnormal isointense material in the suprasellar cistern and along the path of the left middle cerebral artery towards the sylvian fissure. (B) A comparable slice of FLAIR MR imaging done 24 hours after the CT. It shows the abnormality more clearly as high signal material in the left side of the suprasellar cistern and left sylvian fissure (arrows) in keeping with subacute subarachnoid hemorrhage. (C) The same area shows as low signal on T2* MR imaging (arrow). (D) One slice down from C illustrates a problem with the T2* images. The low signal arising from the boundary between tissues of differing susceptibility—in this case the surface of the right lesser sphenoid wing (arrow)—obscures any additional low signal due to blood in the sylvian fissure and could be misinterpreted as blood. This is one reason why we regard the FLAIR and T2* sequences as complementary rather than alternatives.

Degree of confidence of FLAIR images

In vivo and in vitro studies suggest that FLAIR MRI is as sensitive as or more sensitive than CT scanning in the evaluation of acute subarachnoid hemorrhage; however, compared with lumbar puncture, FLAIR MRI cannot exclude subarachnoid hemorrhage. Relative to CT scanning, MRI is often more valuable in the subacute phase of subarachnoid hemorrhage, in which the density of hemorrhage on CT scans decreases. In patients with equivocal findings on CT scanning or angiography or in those patients who cannot undergo CT scanning or conventional angiography, MRI and/or MRA may provide clinically useful information.

Figure 4. A CT negative subarachnoid hemorrhage as confirmed by lumbar puncture. (A) Brain CT taken 4 days after the onset of headache is normal. The MR scans were done within 1 hour of the CT. (B) The T2* image closest to the slice of A. It shows an area of low signal (arrow). (C) The corresponding FLAIR image shows high signal from the same area (arrow). Note the different angulation used for CT and MR images.

False positives/negatives of Flair images

Magnetic field inhomogeneity can lead to artifactual increase in signal intensity in sulci over the cerebral convexities on FLAIR images, which can mimic subarachnoid hemorrhage. CSF flow artifacts can mimic the appearance of subarachnoid hemorrhage on either T1- or T2-weighted images. Intracranial thrombus can appear similar in signal to flowing blood on time-of-flight (TOF) gradient-echo (GRE) MRA. In uncooperative patients, motion artifacts may produce images that can lead to either false-positive or false-negative interpretations.

Hyperintensity in the subarachnoid space on FLAIR images can also be secondary to other pathologies, such as meningitis or meningeal carcinomatosis. It is important to know whether recent contrast-enhanced MRIs have been performed, as delayed leakage of gadolinium into the subarachnoid space can result in hyperintense signal on FLAIR images. This has been reported to result from contrast studies performed 24-48 hours before MRI scanning in patients without renal failure and without abnormalities known to disrupt the blood-brain barrier. Substantial increases in subarachnoid FLAIR signal have also been reported in patients receiving 100% supplemental oxygen.

References

1.Vermeulen M, van Gijn J (1990) The diagnosis of subarachnoid haemorrhage. J Neurol Neurosurg Psychiatry 53:365–372.

2. Morgenstern LB, Luna-Gonzales H, Huber JC, Jr, et al. (1998) Worst headache and subarachnoid hemorrhage: prospective, modern computed tomography and spinal fluid analysis. Ann Emerg Med 32:297–304.

3. Sidman R, Connolly E, Lemke T (1996) Subarachnoid hemorrhage diagnosis: lumbar puncture is still needed when the computed tomography scan is normal. Acad Emerg Med 3:827–831.

4. van Gijn J, van Dongen KJ (1982) The time course of aneurysmal haemorrhage on computed tomograms. Neuroradiology 23:153–156.

5. van Gijn J, van Dongen KJ (1980) Computed tomography in the diagnosis of subarachnoid haemorrhage and ruptured aneurysm. Clin Neurol Neurosurg 82:11–24.

6. Vermeulen M, Hasan D, Blijenberg BG, et al. (1989) Xanthochromia after subarachnoid haemorrhage needs no revisitation. J Neurol Neurosurg Psychiatry 52:826–828.

7. Noguchi K, Ogawa T, Inugami A, et al. (1994) MR of acute subarachnoid hemorrhage: a preliminary report of fluid-attenuated inversion-recovery pulse sequences. AJNR Am J Neuroradiol 15:1940–1943.

8. Singer MB, Atlas SW, Drayer BP (1998) Subarachnoid space disease: diagnosis with fluid-attenuated inversion-recovery MR imaging and comparison with gadolinium-enhanced spin-echo MR imaging-blinded reader study. Radiology 208:417–422.

9. Noguchi K, Ogawa T, Seto H, et al. (1997) Subacute and chronic subarachnoid hemorrhage: diagnosis with fluid-attenuated inversion-recovery MR imaging. Radiology 203:257–262.

10. Noguchi K, Ogawa T, Inugami A, et al. (1995) Acute subarachnoid hemorrhage: MR imaging with fluid-attenuated inversion recovery pulse sequences. Radiology 196:773–777.

11. Kates R, Atkinson D, Brant-Zawadzki M (1996) Fluid-attenuated inversion recovery (FLAIR): clinical prospectus of current and future applications. Top Magn Reson Imaging 8:389–396.

12. Chrysikopoulos H, Papanikolaou N, Pappas J, et al. (1996) Acute subarachnoid haemorrhage: detection with magnetic resonance imaging. Br J Radiol 69:601–609.

13. Ogawa T, Inugami A, Fujita H, et al. (1995) MR diagnosis of subacute and chronic subarachnoid hemorrhage: comparison with CT. AJR Am J Roentgenol 5:1257–1262.

14. Vymazal J, Brooks RA, Baumgarner C, et al. (1996) The relation between brain iron and NMR relaxation times: an in vitro study. Magn Reson Med 35:56–61.

15. Mikami T, Saito K, Okuyama T, et al. (1996) FLAIR images of subarachnoid hemorrhage. No Shinkei Geka 24:1087–1092, . (In Japanese.).

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INTRODUCTION

March 13, 2013 — Thesis section: Role of Oxidative Stress in the pathogenesis of neurodegenerative disorders

This master degree thesis was presented by Dr. David kamel and supervised by Professor Yasser Metwally. The thesis discusses the subject of “Role of Oxidative Stress in the pathogenesis of neurodegenerative disorders”, The thesis can be viewed online or downloaded in PDF format

Click here to download thesis in PDF format (1020 KB)

Lecture 1. View thesis online…Thesis section: Role of Oxidative Stress in the pathogenesis of neurodegenerative disorders

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References

1. Metwally, MYM: Textbook of neuroimaging, A CD-ROM publication, (Metwally, MYM editor) yassermetwally.com corporation, version 14.1 January 2013 [Click to have a look at the home page]

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INTRODUCTION

March 2, 2013 — The Egyptian geographic magazine is a slideshow-based digital publication that contains too may images and too little words because I always regarded pictures as pieces of information that are even more informative than words. This publication is about Egypt that will ultimately describe every thing about Egypt in photos rather than words. Images are grouped in flash-dependent slideshows to maximize the interest of the reader on one hand and the ease of use on the other hand. You need adobe flash player (which must be installed in your computer) to be able to play the slideshows. The downloadable version is a limited one and to keep this version as small as possible, it will not contains any more data, it contains only basic information (Click to download…44 MB). The CD-ROM version contains much more slideshows about Egypt than the downloadable one and it is free of charge and will always be. If you are interested to get your CD-ROM version, please contact the author.

The online version probably contains all slideshows present in the CD-ROM version and it is free of charge. However some slideshows that can not be played online are only present in the CD-ROM version.

Figure 1. The Egyptian geographic Magazine

The Egyptian geographic magazine has three versions

1- An online version (Click to view)
2- A downloadable version (Click to download…44 MB)
3- The CD-ROM version

Both the Online version and the CD-ROM version are ever growing publications that is to say "more and more data and slideshows are added on regular basis". Please contact the author every few month to get the latest CD-ROM version of the publication, it is always free of charge.

Please note that The CD-ROM and the downloadable publications are supplied as is without any warranty whatsoever, either publications are not designed to fit any of your purposes or to meet any of your requirement. The downloadable version can be distributed free of charge without the need for any permissions.

Your opinion is very much important to me. Never hesitate to contact me for suggestions.
System requirement: Windows XP,VISTA,7 OR 8, with 1MB of RAM or more

The author
Professor Yasser Metwally
www.yassermetwally.com

The online version | My web site | Email the author

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INTRODUCTION

February 15, 2013 — Definition of Some conventional EEG terminologies. While inspecting an EEG record, have you ever asked your self what exactly is meant by sharp wave, spike, spike/wave discharge, hypsarrhythmia, triphasic waves, etc…?

In this slide show Professor Yasser Metwally discusses the Definition of Some conventional EEG terminologies.

Click here to download file in PDF format

Click here to download file in PDF format

1. Metwally, MYM: Textbook of neuroimaging, A CD-ROM publication, (Metwally, MYM editor) yassermetwally.com corporation, version 14.1 January 2013 [Click to have a look at the home page]

2. The secrets of conventional EEG (Click to download in PDF format]

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INTRODUCTION

February 13, 2013 — Thesis section: Current status of Quantitative EEG

This master degree thesis was presented by Dr. Ayman Amin and supervised by Professor Yasser Metwally. The thesis discusses the subject of “Current status of Quantitative EEG”, The thesis can be viewed online or downloaded in PDF format

Click here to download thesis in PDF format (3200 KB)

Lecture 1. View thesis online…Thesis section: Current status of Quantitative EEG

Click here to download thesis in PDF format (3200 KB)

References

1. Metwally, MYM: Textbook of neuroimaging, A CD-ROM publication, (Metwally, MYM editor) yassermetwally.com corporation, version 14.1 January 2013 [Click to have a look at the home page]

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INTRODUCTION

February 12, 2012 — Radiological pathology of Radiological pathology of multisystem atrophy

In this topic Professor Yasser Metwally discusses the pathology and pathogenesis of multisystem atrophy and its radiological picture.

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Lecture 1. View topic online…Topic of the month: Radiological pathology of multisystem atrophy

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1. Metwally, MYM: Textbook of neuroimaging, A CD-ROM publication, (Metwally, MYM editor) yassermetwally.com corporation, version 14.1 January 2013 [Click to have a look at the home page]

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INTRODUCTION

February 11, 2013 — Hydatidosis in humans occurs when the eggs of Echinococcus granulosus from canine faeces are accidentally ingested. The eggs loose their enveloping layer in the stomach, releasing the larvae. The larvae pass through the wall of the gut into the portal system and are carried to the liver where 65% of the larval load is filtered. Of the rest, 25% are trapped in the lungs (second filter) and less than 10% reach various organs through the systemic circulation [2].

Hydatid disease is caused by two echinococcus organisms. Most are caused by Echinococcus granulosus and less frequently by Echinococcus multilocularis. E. granulosus has a dog or other carnivore as its definite host, and a sheep or other ruminant as the intermediate host. The organism resides within the intestine of the definite host and is anchored to the mucosa by hooklets. The distal aspect of the organism, called the proglottid, contains numerous amounts of eggs, which get excreted in the feces after they detach themselves from the proglottid. Grazing animals ingest the eggs, and after ingestion, the protective chitinous layer of the egg releases the embryo, which moves through the bowel wall into the portal venous or lymphatic system. The liver is the most involved organ in hydatid disease. After establishing itself in the liver, the embryo matures into a cyst. When the intermediate host dies, its organs are eaten by the definite host, and the life cycle is completed. Human infection occurs by contact with the definite host or by drinking or eating contaminated water or vegetables.

• E. granulosus

The cyst formed by E. granulosus has three layers. The host’s reaction and formation of the fibrous capsule form the outer layer, or pericyst. The size of the fibrous capsule varies between the different infected organs; in the liver, the capsule is thicker than those formed in the brain. The pericyst layer, containing blood vessels, provides nutrients for the parasite. The middle layer, a laminated membrane, is acellular and permits the flow of nutrients inward but does not allow the parasite to cross the membrane. Infection occurs when the middle layer is disrupted. The inner germinal layer produces the middle laminated layer and produces the scolex or larval stage. The scolices may also be manufactured by brood capsules (small spheres of disrupted germinal membrane) and can persist attached to the germinal membrane or combine with free-floating brood capsules to form hydatid sand or white sediment. The fluid contained within the cyst is a clear, antigenic, transudative serum-containing protein. Cyst rupture can occur and may produce no symptoms or symptoms ranging from eosinophilia to anaphylaxis.

Most hydatid cysts are acquired in childhood but are not diagnosed until the 20s or 30s. Ten percent to 25% may present in childhood. 1 Many cysts are found incidentally, but most symptomatic cysts have ruptured and may be secondarily infected. The most commonly affected organ systems are the liver (65% to 75%) and lung (15% to 20%) with the remaining 5% to 20% encompassing the entire body. Central nervous system involvement occurs in 5% of cases.

Cardiac contraction provides an unfavorable environment for the cysts in the heart, thus cardiac implantation is uncommon. The majority of patients with cardiac hydatidosis are asymptomatic and present due to embolic dissemination of hydatid cysts elsewhere. In a case report by Turgut et al the patient presented with cerebral hydatidosis and acute vascular occlusion of the right femoral and left internal carotid arteries, consequent to embolic dissemination from a left ventricular hydatid cyst. [3]. Trehan et al reported a case, which presented with a left basal ganglionic infarct secondary to a left atrial hydatid cyst [2]. However, sudden death resulting from anaphylactic shock and cardiac tamponade due to rupture of cysts into the blood stream or pericardium respectively has been reported. Location wise the left ventricle (75%), right ventricle (18%) and interventricular septum (7%) are the usual sites. Two-dimensional echocardiography is the best diagnostic procedure for demonstration of cardiac hydatid cysts [2].

Orbital hydatid cysts typically present with gradually progressive proptosis and diminished extra ocular motility. MR and CT imaging characteristics are non-specific, and the differential diagnosis includes congenital cysts like colobomatous cysts, optic nerve sheath meningoceles and hematic cysts. Colobomatous cysts are usually associated with micropthalmia while a hematic cyst contains blood and has a typical appearance on MRI. An optic nerve sheath meningoceles may occur primarily or secondarily (in association a optic nerve pilocytic astrocytoma or meningioma). These meningoceles can be associated with empty sella or enlarged subarachnoid cistern, such as gasserian cistern. [4] In a hydatid endemic area, a unilateral intraconal cystic mass in the presence of a positive hydatid serology should prompt a diagnosis of orbital hydatid cyst [5].

Intracranial hydatid cysts are classified as primary or secondary. The primary cysts, which are the commoner variety, are formed as a result of direct infestation of the larvae in the brain without demonstrable involvement of other organs and are mostly solitary. Supratentorial location is most frequent with a preference for the parietal lobe. These primary cysts are fertile as they contain scolices and brood capsules, hence rupture of primary cyst (e.g. during surgery) can result in dissemination. The secondary cysts on the other hand are less common and are always multiple. They arise from the rupture of a primary hydatid cyst (which may be intracranial or extra cranial). These cysts lack brood capsule and scolices and therefore are infertile and the resultant risk of recurrence after their rupture is negligible. However, recurrent secondary cysts formation can occur from repeated embolic phenomenon from a viable primary source. In the case report by Turgut et al [3], the patient underwent 5 surgeries over a period of 8 years for recurrent multiple intracranial hydatid cysts before the primary cardiac source was detected. Thus, it is essential to look for a primary source in case of multiple intracerebral hydatidosis, as only by eradicating the primary cysts will a cure be achieved.

MR and CT cannot distinguish primary from secondary cysts. Generally, multiplicity of the cysts strongly favors the diagnosis of secondary cysts and should prompt a search for a primary source elsewhere. Both modalities characteristically show hydatid cyst as a spherical, well-defined, non-enhancing cystic lesion without peripheral edema[6,7]. The fluid density is generally equal to that of CSF on both CT and MR scan. A fine rim of peripheral enhancement with perilesional edema may be seen in the presence of active inflammation [8] MR scan may show a low density cyst wall [7] and relations with surrounding structures are better delineated than on CT scan [6,7]. Kohli et al [8] performed in vivo and in vitro MR spectroscopy (MRS) studies in a patient of intracranial hydatid cyst. Besides lactate, alanine and acetate, a large resonance for pyruvate was observed. MRS pattern appeared different from the other cystic lesions of brain and they suggested MRS as an adjunct to imaging in the differential diagnosis of intracranial hydatid. Role of MRS in monitoring drug therapy was also discussed.

Figure 1. A, Contrast enhanced CT scan of the orbits demonstrating a large non-enhancing intraconal cystic mass on the left side displacing the globe outwards. C,D, Contrast enhanced CT scan of the brain demonstrating multiple non-enhancing, varying sized, water density cysts without perifocal edema. Observe the mild effacement of the surrounding sulci.

• Conclusion

In conclusion, multiple hydatid cysts in the central nervous system are invariably secondary. A primary source should always be looked for. A cure can be achieved only by eradicating the primary source. An occult cardiac source can be overlooked and hence it is important to think about this possibility when dealing with central nervous system hydatidosis.

Figure 2. Postcontrast CT scan showing a huge fronto-parietal hydatid cyst, notice absence of wall enhancement, mural nodules, multiloculations or perifocal edema

Figure 3. CT scan (A) and TI -weighted (B) and T2-weighted (C) MR images demonstrate a large cystic mass in a patient with a suspected brain tumor. Note the lack of surrounding edema. On the T2 image there is a thin, low signal intensity rim, representing the capsule.

Table 1. Characteristic radiological picture of hydatid disease

• Absence of wall enhancement

• Absence of perilesional edema

• Absence of mural nodule

• T2-weighted MR images, the best for imaging these lesions, shows a thin, low signal intensity rim, representing the capsule, surrounding a hyperintense lesion.

• E. multilocularis (E. alveolaris)

The second Echinococcus organism is E. multilocularis. It is similar to E. granulosus except that it grows by external budding of the germinal membrane. The budding causes progressive infiltration of surrounding tissues, giving rise to an amorphous semisolid or multiloculated cystic structure. Ninety-five percent of lesions occur in the liver. Brain involvement has been reported in 5% of cases and vertebral involvement in less than 1%. Surrounding edema and calcification in the wall are more common, helping to distinguish it from E. granulosus. In addition, peripheral enhancement is commonly seen. The differential diagnosis includes metastases, abscesses (including tuberculomas and fungal infection), and gliomas. A primary hepatic focus may help to distinguish these lesions from the others on the list.

Figure 4. 42-year-old man with headache and weakness attributed to cerebral alveolar hydatid disease. A,CT scan of head shows calcified nodular lesions surrounded by edema in right frontoparietal and left occipital regions. B, Enhanced CT scan shows nodular enhancing lesions. C1, Axial TI-weighted contiguous MR sections show heterogeneous lesions of low signal intensity.C2, Axial T2-weighted contiguous MR sections show lesions of low signal intensity. Note surrounding edema. Calcified areas produce low signal intensity and surrounding edema produces high signal intensity. D, Axial contrast-enhanced TI weighted MR image shows heterogeneous contrast enhancement.

• Management of Hydatidosis in humans

Albendazole and mebendazole are the only anthelmintics effective against cystic echinococcosis. Albendazole is the drug of choice against this disease because its degree of systemic absorption and penetration into hydatid cysts is superior to that of mebendazole. Albendazole in combination with percutaneous aspiration or PAIR therapy can lead to a reduction in cyst size, and, in one study, it improved efficacy over albendazole alone against hydatid cysts. When surgery cannot be avoided, presurgical use of albendazole in echinococcus infestations reduced risk of recurrence and/or facilitated surgery by reducing intracystic pressure.

Treatment of echinococcosis for patients weighing more than 60 kg is albendazole administered PO with meals in a dose of 400 mg twice daily for 28 days. A dose of 15 mg/kg of body weight daily in 2 divided doses (not to exceed total daily dose of 800 mg) has been suggested for patients weighing less than 60 kg. For CE, the 28-day course may be repeated after 14 days without treatment to a total of 3 treatment cycles..

References

1. Onal C, Orhan B, Metis O et al , Three unusual cases of intracranial hydatid cysts in paediatric age group. Pediatr Neurosurg 1997; 26 : 208-213.

2. Trehan V, Shah P, Yusuf J, Mukhopadhyay S, et al, Thromboembolism: A Rare Complication of Cardiac Hydatidosis. Indian Heart J 2002; 54: 199-201

3. Turgut M, Benli K, Eryilmaz M et al, Secondary multiple intracranial hydatid cysts caused by intracerebral embolism of cardiac ecchinococcosis. Neurosurgery 1997; 86:714-718

4. Kaufman LM, Villablanca P,Mafee MF, Diagnostic imaging of cystic lesions in the child’s orbit. RCNA 1998; 36:1149-1162

5. El-Nasser A, Mohammad A,Ray CJ et al,Echinococcus cyst of the orbit and substernum. AJO 1994; 118: 676-678

6. Nurchi G, Francesco F, Montaldo C et al , Multiple cerebral hydatid disease : case report with magnetic resonance imaging study. Neurosurgery 1992; 30 : 436-438.

7. Coates R, Von Sinner W, Rahm B : MR imaging of an intracranial hydatid cyst. AJNR1990; 11 : 1249-1250.

8. Kohli A, Gupta RK, Poptani H et al : In vivo proton magnetic resonance spectroscopy in a case of intracranial hydatid cyst. Neurology 1995; 45 : 562-564.

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INTRODUCTION

February 10, 2012 — Radiological pathology of Hereditary ataxias

In this topic Professor Yasser Metwally discusses the pathology and pathogenesis of Hereditary ataxias and its radiological picture.

Click here to download file in PDF format

Click here to download file in PDF format

1. Metwally, MYM: Textbook of neuroimaging, A CD-ROM publication, (Metwally, MYM editor) yassermetwally.com corporation, version 14.1 January 2013 [Click to have a look at the home page]

http://yassermetwally.com

INTRODUCTION

February 2, 2012 — The intravascular malignant lymphomatosis (IML), also known as angiotropic large cell lymphoma, represents only 3% of the non-Hodgkin lymphomas and affects middle-aged and elderly patients (median 61 years) with a cerebral manifestation in 74% of the individuals. Signs of dementia or disorientation are reported in the literature in 53% and seizures in 25% of patients (1,3). Important features in intravascular malignant lymphomatosis (IML), are the symmetrical involvement of the temporal lobes and the cingulate gyri that might be misdiagnosed as limbic encephalitis. The prognosis of IML is poor with a median survival time of only 6 months after symptom onset. Temporary remission to a maximum of a few weeks is described in patients who received corticoids or cytostatic drugs (3).

Figure 1. MRI in a case of intravascular malignant lymphomatosis revealed in T2-weighted images hyperintense lesions bilaterally in both temporal lobes, the right occipital white matter and in the region of the cingulate gyrus

The key microscopic feature of IML is the filling of lumina of small and medium-sized vessels with large atypical lymphoid cells. These cells possess predominantly round nuclei, vesicular chromatin and prominent nucleoli. Mitotic figures are common. Immunohistochemically, these cells are positive for leukocyte common antigen and usually B cell markers, but a few cases of T cell origin have been described. The blood vessels are closed and sometimes thrombosed by tumor cells leading to circulation disturbances resulting in multiple, ischemic microinfarctions as well as small parenchymal hemorrhages. Endothelial proliferation may be present (4). Migration out of the vascular spaces is rarely seen and this is likely due to the lack of surface expression of leukocyte adhesion molecule CD11a/CD18 by the tumor cells (2). Securing the diagnosis by brain biopsy is controversial, however, brain biopsy confirmed the diagnosis in 50% of individuals with brain involvement. While skin biopsy is more convenient, dermal involvement is sufficiently low to miss the diagnosis in 2/3 of all patients (3). Consequently, brain biopsy is recommended as the preferable way to establish this diagnosis.

In conclusion, in a case of dementia, seizures and infarct-like lesions by MRI, the diagnosis of an intravascular malignant lymphomatosis should be considered.

References

1. Chapin, J.E., Davis, L.E., Kornfeld, M., Mandler R.N. (1995) Neurologic manifestations of intravascular lymphomatosis. Acta Neurol Scand 91: 494-499.

2. Jalkanen, S., Aho R., Kallajoki, M., Ekfors, T., Nortamo, P., Gahmberg, C., Duijvestijn, A., Kalimo, H. (1989) Lymphocyte homing receptors and adhesion molecules in intravascular malignant lymphomatosis. Int J Cancer 44: 777-782.

3. Teves, T.A., Gadoth, N., Blumen, S., Korczyn, A.D. (1995) Intravascular Malignant Lymphomatosis: A Cause of Subacute Dementia. Dementia 6: 286-293.

4. Warnke, R.A., Weiss, L.M., Chan, J.K.C., Cleary, M.L., Dorfmann, R.F. (1995) Atlas of Tumor Pathology, Tumors of the Lymph Nodes and Spleen. Third Series, Fascicle 14, Armed Forces Institute of Pathology, Washington.

The author: Professor Yasser Metwally

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INTRODUCTION

January 12, 2013 —  Lacunar infarcts or lacunes are small, deep cerebral infarcts involving the penetrating arteries that supply the basal ganglia, internal capsule, thalamus, and brainstem. These small arteries arise from the major cerebral arteries and include the lenticulostriate branches of the anterior and middle cerebral arteries, the thalamoperforating branches of the posterior cerebral arteries, and the paramedian branches of the basilar artery. These penetrating arteries are small end arteries (100-500 m in diameter) that are difficult to evaluate angiographically. Most of these arteries are unbranching single vessels with essentially no collateral circulation. For these anatomic reasons, deep lacunar infarcts typically are spherical in shape and range from 0.3 to 2.5 cm in diameter. The larger lacunes typically result from more proximal obstructions.

Lacunar infarcts are commonly seen in patients older than 60 years with hypertension. Because this population is also prone to chronic small vessel disease, identification of small recent lacunar infarcts superimposed on chronic disease can be difficult. Diffusion imaging is extremely helpful in acute and early subacute infarcts in this regard. Contrast enhancement is likewise extremely helpful in identifying late subacute infarcts.

The pathogenesis of lacunar infarction is as follows. Chronic hypertension causes degeneration of the tunica media (i.e., arteriosclerosis), with hyalin deposition in the artery wall that narrows the lumen. Plaque or thrombosis, called microatheroma, may subsequently occlude these vessels, particularly the larger vessels. The weakened tunica media also predisposes to the formation of microaneurysms, which can rupture, causing an intraparenchymal hematoma. A hypertensive hemorrhage or hypertensive hemorrhagic infarction has a characteristic location in the deep cerebral structures supplied by these deep penetrating arteries. Other uncommon causes of lacunar infarction include secondary arteritis caused by meningitis, microemboli, and arterial dissection.

Figure 1. Early subacute lacunar infarction involving the posterior limb of the left internal capsule. Vasogenic edema is noted (with abnormal high signal intensity) on the T2-weighted fast spin echo (A) and fluid-attenuated inversion recovery (B) scans. There is corresponding abnormal low signal intensity on the postcontrast T1-weighted scan (C). However, there is no abnormal contrast enhancement (with disruption of the blood-brain barrier yet to occur). The mean transit time (MTT) for the lesion is prolonged, as seen on a calculated MTT image (D) from a first-pass perfusion study. E, Diffusion weighted imaging and the apparent diffusion coefficient map (F) reveal the presence of cytotoxic edema, as would be anticipated in an infarct less than 1 week old.

Figure 2. Late subacute lacunar infarction involving the posterior limb of the right internal capsule. The patient is an elderly diabetic who presented with acute hemiparesis. The magnetic resonance exam was obtained 10 days after presentation, at which time the hemiparesis had resolved. Multiple high signal intensity abnormalities are noted bilaterally on the T2-weighted scan (A). The postcontrast T1-weighted scan (B) reveals punctate enhancement (arrow) in the posterior limb of the right internal capsule. This corresponds to a high signal intensity lesion on the T2-weighted scan. By identification of abnormal contrast enhancement, this subacute infarct can be differentiated from other chronic ischemic lesions, which are incidental to the patient’s current medical problems.

Lacunar infarction is often recognized by a distinctive clinical presentation. A pure motor stroke is the most common clinical syndrome, accounting for 30% to 60% of lacunar infarcts. A pure sensory stroke, combined sensorimotor stroke, ataxic hemiparesis, dysarthria (or ”clumsy hand syndrome”), and brainstem syndromes are other characteristic clinical presentations of lacunar infarction. Patients with lacunar infarction often have a gradual progression of symptoms. An antecedent TIA occurs in approximately 25% of patients with lacunar infarction.

On MRI, lacunar infarcts appear as focal slit-like or ovoid areas of increased water content. They are high signal intensity on T2-weighted images and isointense to low signal intensity on T1-weighted images. T2 -weighted scans are more sensitive than T1 – weighted scans for detection. In acute lacunar infarction, vasogenic edema may not be present; thus, diffusion- weighted scans are important for detection. Fluid-attenuated inversion recovery (FLAIR) scans are helpful in identifying small lacunes and differentiating them from spaces containing cerebrospinal fluid (CSF). If FLAIR is not an option, then spin echo scans with intermediate T2-weighting provide similar information. On either type of scan, lacunar infarcts appear as small high-signal intensity focal lesions and can be easily distinguished from the intermediate to low signal intensity of normal surrounding brain and CSF. MRI is much more sensitive than CT in detecting lacunar infarcts. Contrast enhancement of subacute lacunar infarcts, after intravenous gadolinium chelate administration, is consistently seen on MRI. Enhancement occurs as a result of blood-brain-barrier disruption. Chronic lacunar infarcts are characterized by focal cavitation and a more pronounced decreased signal intensity on T1-weighted images than in the earlier stages of lacunar infarction. These chronic (cavitated) lacunar infarcts are isointense with CSF on all imaging sequences.

Figure 3. Early subacute thalamic infarction. A, Two round lesions, with abnormal high signal intensity corresponding to vasogenic edema, are noted medially on the T2-weighted scan. The smaller lies in the right thalamus, the larger in the left thalamus. There is subtle low signal intensity in the corresponding areas on the T1-weighted precontrast scan (B). There was no abnormal contrast enhancement (not shown). Thalamic lesions are easily missed by inexperienced film readers, leading to the recommendation that the thalamus be visually checked for abnormalities on each scan.

Figure 4. Early subacute bilateral pontine infarction. The central portion of the pons has abnormal high signal intensity on the T2- weighted scan (A) and abnormal low signal intensity on the T1-weighted scan (B). Despite the lesion being bilateral, there is some indication of a straight border along the midline. A follow-up T1-weighted scan (C) performed 6 months later demonstrates cavitation of the lesion.

Figure 5. Late subacute pontine infarction. On the precontrast T2- weighted scan (A), an area of abnormal hyperintensity is noted in the left pons, with a sharp line of demarcation along the median raphe. The lesion enhances on the postcontrast T1-weighted scan (B). As with other lacunar infarcts, pontine infarcts will consistently demonstrate contrast enhancement after gadolinium chelate administration in the late subacute time period.

Penetrating vessels from the basilar artery and adjacent segments of the posterior cerebral arteries supply the brainstem. Infarcts involving the pons are most frequently small, unilateral, and sharply marginated at the midline. This location reflects the distribution of paramedian penetrating arteries, which consist of paired branches. Bilateral pontine infarcts do occur but are less common than unilateral infarcts. Lateral pontine infarction is extremely uncommon. The predominant finding on MRI in early subacute pontine infarction is vasogenic edema. Contrast enhancement is consistently seen in late subacute pontine infarction.

Figure 6. Late subacute lacunar (basal ganglia) infarction. On adjacent T2-weighted fast spin echo sections (A and B), abnormal high signal intensity is noted in the globus pallidus and body of the caudate nucleus on the right. Enhancement of both lesions is seen on the corresponding postcontrast T1- weighted sections (C and D). The use of intravenous contrast assists in lesion recognition (conspicuity) and in dating lesions. Involvement of both the globus pallidus and caudate nucleus is not uncommon and points to involvement of the lenticulostriate arteries. These small perforating vessels arise from the superior aspect of the proximal middle cerebral artery (M1 segment) and supply the globus pallidus, putamen, and caudate nuclei.

• Pontine lacunar infarction

The pons, or metencephalon, extends from the pontomedullary junction caudally to the pontomesencephalic junction rostrally. It is subdivided into the basis pontis ventrally and the pontine tegmentum dorsally by an arbitrary coronal line drawn through the two medial lemnisci [13].

Figure 7. Brainstem perforators. Gross anatomic specimens of the anterior surfaces of the upper medulla, pons, and midbrain after opacification of the major branches with micropulverized barium. (A) Upper medulla and pons. The vertebral arteries (V) of each side join to form the basilar artery (BA) (B) at the pontomedullary junction. Paramedian perforating branches (horizontal arrow) penetrate the brainstem immediately adjacent to the BA to supply the anteromedian arterial territory. Short circumflex arteries (vertical arrow) extend a short distance laterally before entering the stem to supply the anterolateral arterial territory. Long circumflex arteries (arrowheads) arise directly from the BA or from larger traversing branches, such as the anterior inferior cerebellar artery (AICA) (A), to supply the lateral arterial territory. Note that the AICA passes between fascicles of cranial nerve (CN) 6 (6) and then extends laterally to run along the anterior surface of CN 7 (7), loop over CN 7, nearly touch CN 5 (5), and then return toward the surface of the stem along the anterior surface of CN 8 (8). (B) Upper pons and midbrain. (Click to enlarge figure)

Figure 8. Intrinsic arterial territories of the low pons. Shaded areas displayed clockwise from anterior to posterior: anteromedial (a), anterolateral (b), and lateral (c) pontine vascular territories. Numbered structures include pontocerebellar fibers (1), pontine nuclei (2), corticospinal tract (3), medial lemniscus (4), spinothalamic tract (5), lateral lemniscus (6), superior olivary nucleus (7), facial nucleus (CN 7) (8), spinal nucleus (9) and tract (9′) of the trigeminal system (receiving CN 5, 7, 9, and 10), inferior cerebellar peduncle (10), lateral vestibular nucleus (CN 8) (11), superior vestibular nucleus (CN 8) (12), medial vestibular nucleus (CN 8) (13), fibers of the facial nerve (CN 7) (14 and 14′), abducens nucleus (CN 6) (15), fibers of the abducens nucleus (CN 6) (15′), and medial longitudinal fasciculus (16). (Click to enlarge figure)

Figure 9. Intrinsic arterial territories of the midpons. Shaded areas displayed clockwise from anterior to posterior: anteromedial (a), anterolateral (b), and lateral (c) pontine vascular territories. Numbered structures include pontocerebellar fibers (1), pontine nuclei (2), corticospinal tract (3), medial lemniscus (4), spinothalamic tract (5), lateral lemniscus (6), motor trigeminal nucleus (CN 5) (7), principal sensory trigeminal nucleus (CN 5) (8), mesencephalic trigeminal nucleus (CN 5) (9), fibers of the motor root of CN 5 (10), fibers of the sensory root of CN 5 (11), superior vestibular nucleus (CN 8) (12), superior cerebellar peduncle (13), and medial longitudinal fasciculus (14). (Click to enlarge figure)

Figure 10. Intrinsic arterial territories of the upper pons. Shaded areas displayed clockwise from anterior to posterior: anteromedial (a), anterolateral (b), lateral (c), and posterior (d) pontine vascular territories. Numbered structures include pontocerebellar fibers (1), pontine nuclei (2), corticospinal tract (3), medial lemniscus (4), spinothalamic tract (5), lateral lemniscus (6), superior cerebellar peduncle (7), mesencephalic trigeminal nucleus (CN 5) (8), locus ceruleus (nucleus coeruleus) (9), and medial longitudinal fasciculus (10). (Click to enlarge figure)

Figure 11. Vascularization of the basis pontis and pontine tegmentum. (Click to enlarge figure)

Anatomy of pontine structures

The arterial territories of the pons are considered in four zones: a large anteromedial, smaller anterolateral, large to extremely large lateral, and (in the rostral pons only) a small dorsal arterial zone [13]. From ventral to dorsal, the pons comprises the following:

Figure 12. Intrinsic arterial territories of the pons (multiple levels). (Note that the diagram is oriented with ventral to the bottom). The usual external arterial supply to each zone is given as a list of vessels in the lower right corner. (Click to enlarge figure)

anteromedial pontine structures

The anteromedial pontine structures include the medial pontine nuclei and pontocerebellar fibers, medial portions of the corticospinal tracts intermixed with corticopontocerebellar and corticobulbar fibers, medial portions of the medial lemnisci, fibers of the facial nerve (CN 7), small medial wedges of the abducens nuclei (CN 6) and some emerging sixth nerve fascicles, the paramedian pontine reticular formation (PPRF; horizontal gaze center), and the MLF.

Anterolateral pontine structures

The anterolateral pontine structures include the lateral pontine nuclei and pontocerebellar fibers, lateral portions of the corticospinal tracts intermixed with corticopontocerebellar and corticobulbar fibers, sixth nerve fascicles (lower pons), and small midlateral portions of the medial lemnisci (variable). Depending on the specific caudorostral level along the axis of the pons, the anterolateral zone may terminate ventral to the medial lemnisci or extend into the medial lemnisci. It typically does not extend further dorsally into the pontine tegmentum. The anterolateral zones do not extend far enough laterally to involve the spinothalamic tracts [13].

Lateral pontine structures

The lateral pontine structures are comprised of two separate pontine regions (the upper and lower). In the large lateral zone of the low to midpons, lateral pontine infarctions include the lateral pontine nuclei and pontocerebellar fibers, rostral portions of the inferior cerebellar peduncles (low pons only), middle cerebellar peduncles (low and mid pons), lateral portions of the medial lemnisci and lateral spinothalamic tracts, lateral lemnisci, facial nuclei and fascicles, the trigeminal complex (including the spinal nuclei and tracts, motor nuclei and fascicles, and principal sensory nuclei and fascicles of CN 5), the vestibular complex (including the medial, superior, and lateral vestibular nuclei), and most of the abducens nuclei and their fascicles. At these levels, the fascicles of CN 7 arise from the laterally situated facial nuclei and course dorsomedially to the medial aspects of the abducens nuclei (CN 6). The facial fibers then recurve ventrolaterally around the rostral poles of the abducens nuclei to course ventrolaterally to their exits at the supraolivary fossettes. In the smaller lateral zone of the upper pons, lateral pontine structures include the lateral pontine nuclei and pontocerebellar fibers, lateral portions of the medial lemnisci and lateral spinothalamic tracts, lateral lemnisci, and a ventral portion of the superior cerebellar peduncle (uppermost pons only).

Dorsal pontine structures

The dorsal pontine structures are present in the upper pons only. No separate dorsal zones are found in the low to midpontine levels. Dorsal pontine structures include portions of the lateral lemnisci, portions of the superior cerebellar peduncles, the loci cerulei, and the mesencephalic nuclei of CN 5. The precise structures in each arterial territory vary from the low to high pons, so structures that extend along the length of the pons may exist in different vascular compartments at different pontine levels.

• Blood supply to the pons

The blood supply to the pons derives primarily from the uppermost VAs, the BA, and the AICA and SCA branches of the BA:

Anteromedial pontine arterial zone

The anteromedial zone is supplied by anteromedial pontine perforators arising from the BA and entering (1) the foramen cecum at the midline pontomedullary junction inferiorly, (2) along the median sulcus of the pons in the middle, and (3) at the interpeduncular fossa superiorly.  [13]. These perforators follow different courses for the basis pontis and the pontine tegmentum. The perforators for the basis pontis pass directly posteriorly from the BA into the basis pontis. The perforators for the tegmentum arise in three major groups: (1) perforators for the inferior tegmentum pass from the BA into the foramen cecum at the pontomedullary junction and then ascend to supply the inferior pontine tegmentum; (2) perforators for the midtegmentum arise from the BA and pass directly posteriorly through the basis pontis to supply the midpontine tegmentum; and (3) perforators for the superior tegmentum arise from the interpeduncular branches of the BA, enter the stem via the interpeduncular fossa, and then descend to supply the superior pontine tegmentum.

Anterolateral pontine arterial zone

The anterolateral zone is supplied by anterolateral pontine perforators arising directly from the BA.

Lateral pontine arterial zone

The lateral zone is supplied by lateral pontine perforators that arise directly from the BA, from the AICA, or from the SCA. The inferior lateral pontine artery arises directly from the BA to supply the middle cerebellar peduncle. The superior lateral pontine artery arises directly from the BA to penetrate the lateral pons in the region of the entrance or exit zone of CN 5. Lateral pontine branches of the AICA and SCA may similarly irrigate the lateral zone.

Dorsal pontine arterial zone

Where present rostrally, the dorsal zone is supplied by posterior pontine perforators that arise from the SCA to supply the superior cerebellar peduncles.

External to the brainstem, the AICAs also supply the fibers of CN 6 in the prepontine cistern, the fibers of CN 7 and 8 in the cerebellopontine angles, and the petrous surfaces of the cerebellum. Internal auditory artery branches of the BA or AICA often supply the fibers of CN 7 and 8 within the porus acusticus. Occlusion of the internal auditory artery may cause ipsilateral hearing loss.

• Function of the pontine structures

The functions of the pons are usually considered in terms of their intrinsic arterial territories.

Anteromedial pontine structure

The medial corticobulbar tracts contain motor fibers that cross in the upper pons to reach the bulbar nuclei to assist in movements of the eyes, face, pharynx, and tongue. Just lateral to these, the corticospinal tracts contain motor fibers for the upper extremities en route to the spinal cord. The corticopontocerebellar tracts receive fibers from the motor cortex and send fibers to the cerebellar nuclei via the middle cerebellar peduncles to assist with motor control. The medial portions of the medial lemnisci convey ascending fibers for vibration, proprioception, and deep sensation from the contralateral upper extremities. The fascicles of the facial nerve provide motor innervation to the ipsilateral face. The abducens nuclei and fascicles provide motor innervation to the lateral recti. The PPRF lies adjacent to the abducens nucleus and assists in horizontal gaze in the ipsilateral direction. At the lower pontine level, the MLF contain predominantly vestibulocervical spinal cord fibers to coordinate gaze with head motion, whereas at the upper pontine level, the MLF contain predominantly fibers that extend between CN nuclei 3 and 6 to coordinate horizontal gaze.

Anterolateral pontine structure

The lateral corticopontine nuclei connect extrapyramidal fibers from the cortex with the contralateral cerebellum to assist in motor control. Lateral portions of the corticospinal tracts contain predominantly motor fibers traveling to the contralateral lower extremity. Sixth nerve fascicles innervate the ipsilateral lateral rectus muscle to provide ipsilateral monocular abduction. Lateral portions of the medial lemnisci provide contralateral vibration and position sense, especially for the lower extremities.

Lateral pontine structure

The lateral pontine nuclei and pontocerebellar fibers make up a small portion of the lateral territory. The rostral portions of the inferior cerebellar peduncles in the lower pons convey inflow tracts to the cerebellum to assist in motor control. The middle cerebellar peduncles in the midpons carry corticopontine fibers from the pons to the cerebellum to assist in control of movement. Lateral portions of the medial lemnisci receive contralateral fibers concerned with joint position sense and vibratory sense from the contralateral upper and lower extremities. The spinothalamic tracts carry pain and temperature sensation from the contralateral body and extremities, excluding the face. The lateral lemnisci carry multisynaptic auditory input from the cochlear nuclei to the inferior colliculi. The facial nuclei and fascicles provide motor innervation to the ipsilateral facial muscles. The spinal nuclei and tracts of CN 5 carry pain and temperature sensation from the ipsilateral face. The motor nucleus of CN 5 provides innervation to the ipsilateral muscles of mastication (temporalis, masseter, medial and lateral pterygoid, tensor veli palatini, and tensor tympani muscles). The principal sensory nucleus of CN 5 receives ipsilateral light touch sensation from the face and subserves the corneal reflex. The pontine vestibular complex (medial, superior, and lateral vestibular nuclei) assists in maintaining equilibrium. The abducens nuclei and their fascicles innervate the lateral rectus for ipsilateral gaze. The facial fibers provide ipsilateral motor innervation to the facial muscles.

Dorsal pontine structure

The lateral lemnisci convey auditory fibers from the contralateral trapezoid body to the inferior colliculus. Portions of the superior cerebellar peduncles represent outflow tracts from the cerebellum to assist in motor control. The mesencephalic nuclei of CN 5 receive proprioceptive information from the muscles of mastication.

• Infarction of the pons

Epidemiology of pontine infarcts

Isolated pontine infarcts make up 3% of all ischemic strokes and 12% of posterior circulation strokes [6]. Most pontine strokes result from hemodynamic effects of BA stenoses or occlusions or from atherosclerotic lesions that occlude the origins of small perforating arteries to the brainstem. Emboli account for fewer than 10% of ischemic strokes of the pons because emboli usually travel beyond the pons to lodge at the top of the BA. Dissections rarely cause ischemic pontine infarcts. Risk factors for pontine stroke include hypertension (73%), hypercholesterolemia (32%), diabetes mellitus (30%), and smoking (21%) [6]. Pontine infarctions affect men (53%) slightly more frequently than women (47%) [6].

Kumral and colleagues [6] divided pontine ischemic lesions into five possible syndromes: anteromedial pontine infarcts constitute 58% of pontine strokes, followed by the anterolateral pontine infarcts (17%), tegmental infarcts (10%), bilateral infarcts (11%), and multiple pontine infarcts (4%). Lateral pontine infarcts are uncommon (1 of 150 cases [0.7%]) [6]. These clinical groupings do not correspond directly with the vascular territories delineated by Duvernoy [13].

Anteromedial pontine infarcts

Anteromedial pontine infarcts cause dysfunction of the anteromedial structures injured: hemiplegia or hemiparesis from the corticospinal tracts; contralateral ataxia or pathologic laughter [22] from the corticopontine tracts; dysarthria, dysphagia, or contralateral facial palsy from the corticobulbar tracts; rare contralateral loss of proprioception from the medial lemnisci; ipsilateral facial palsy from the nuclei or fibers of CN 7; ipsilateral sixth nerve palsy from the fascicles of CN 6; and paresis of ipsilateral horizontal gaze from the PPRF or the nucleus of CN 6. Injury of the MLF leads to internuclear ophthalmoplegia (INO) with disconjugate lateral gaze. The ipsilateral eye is unable to adduct as it attempts to look to the contralateral side, whereas the contralateral eye abducts normally but shows horizontal nystagmus as it gazes to the contralateral side. The INO seen with pontine infarcts characteristically spares convergence. Pure motor strokes that involve the face, the arm, and the leg equally are the most common presentation of anteromedial pontine infarcts. By the somatotopic organization of motor fibers within the corticospinal tracts, however, extremely medial pontine infarcts may cause pure motor plegias of the arm and face out of proportion to leg weakness [23]. Because the corticospinal, corticopontine, and corticobulbar tracts lie together in the ventral pons, paresis or paraplegia may occur in conjunction with ataxia as part of the ataxic-hemiparesis syndrome or in conjunction with dysarthria as part of the clumsy-hand dysarthria syndrome. Pure sensory strokes and combined sensory-motor strokes are other possible presentations of the anteromedial syndrome. It must be noted that lacunar strokes of the internal capsule may cause the same clinical findings as pontine strokes, including pure motor stroke, ataxic hemiparesis, sensorimotor stroke, and clumsy-hand dysarthria, because the internal capsule is the one other site at which all these fibers converge [24].

Figure 13. Anteromedial pontine stroke. A 93-year-old-woman with dysarthria and right hemiparesis. Axial T2 (A) and diffusion-weighted (B) images. The narrow band of increased signal in the midpons reaching to the median raphe indicates an anteromedial medullary infarction. (Click to enlarge figure)

Table 1. Pontine stroke syndromes (Click to download in PDF format)

Anterolateral pontine infarcts

Anterolateral pontine infarcts cause dysfunction of the anterolateral structures injured, including plegia or paresis from the corticospinal tracts, ataxia or pathologic laughter from the corticopontine tracts, and vibration or proprioceptive loss from the medial lemnisci. Because the anterolateral zone of the pons contains the lateral portions of the same structures found in the anteromedial zone, the major clinical features of anterolateral pontine infarcts are similar to those of anteromedial pontine infarcts. Therefore, anterolateral infarcts may also present with pure motor stroke, ataxic hemiparesis, hypesthetic ataxic hemiparesis, clumsy-hand dysarthria, or sensorimotor stroke. Pontine infarctions may also involve the anteromedial and anterolateral zones in continuity. At times, however, subtle features may suggest that a pontine infarct is purely anterolateral. Because the lateral zones of the corticospinal tracts contain predominantly motor fibers to the lower extremities and the lateral zones of the medial lemnisci contain predominantly sensory fibers from the lower extremities, more severe weakness and loss of position sense in the lower extremities could theoretically signify anterolateral involvement. Further, because the anterolateral zones contain the spinothalamic tracts, loss of pain and temperature sensation from the contralateral trunk and extremities may also signify anterolateral zone infarction. Rare extension of the infarct into the tegmentum might present as conjugate gaze paralysis, vertigo, skew deviation, or INO.

Figure 14. Anterolateral pontine stroke. A 65-year-old-man with new right hemiparesis. Axial T2 (A) and diffusion-weighted (B) images. The paramedian band of increased signal in the midpons not reaching to the median raphe or the lateral pial surface indicates an anterolateral medullary infarction. (Click to enlarge figure)

Lateral pontine infarcts

Lateral pontine infarcts in the large lateral pontine zone of the low to midpons cause dysfunction of the lateral pontine structures injured, including ataxia from the inferior cerebellar peduncles, pontocerebellar fibers, and middle cerebellar peduncles; loss of pain and temperature sensation in the contralateral upper and lower extremities and trunk from the lateral spinothalamic tracts; tinnitus, reduced auditory acuity on either side, and abnormal sound lateralization from the lateral lemnisci [27–29]; ipsilateral motor deficits of the face from the facial nuclei and fascicles; loss of facial sensation, paresis of the ipsilateral muscles of mastication, and loss of the ipsilateral corneal reflex from the trigeminal complex; vertigo, nausea, and vomiting from the vestibular complex; and lateral rectus palsy from the abducens nuclei.

Figure 15. Lateral pontine stroke. An 85-year-old-woman with slurred speech and weakness of the left face, arm, and leg. Axial fluid-attenuated inversion recovery (A) and diffusion-weighted (B) images. The posterolateral band of increased signal in the midpons with concurrent anterolateral cerebellar involvement indicates a lateral pontine infarction in association with an anterior inferior cerebellar artery infarction. (Click to enlarge figure)

Infarctions in the smaller lateral pontine zone of the rostral pons cause dysfunction of the lateral pontine structures injured, including ataxia from the pontocerebellar fibers, the middle cerebellar peduncles, and the superior cerebellar peduncles; loss of pain and temperature sensation in the contralateral upper and lower extremities and trunk from the lateral spinothalamic tracts; reduced auditory acuity and sound localization from the lateral lemniscus; and ipsilateral loss of jaw movement and facial sensation from the motor and sensory nuclei and fascicles of the trigeminal complex. These infarcts lie rostral to the nuclei and fascicles of CN 6, 7, and 8, so the patients do not display palsies of those cranial nerves.

Dorsolateral pontine infarcts

Dorsolateral pontine infarcts (at the same rostral level) cause dysfunction of the dorsolateral pontine structures, including reduced auditory acuity and sound localization from the lateral lemniscus or cochlear nucleus, ataxia from the superior cerebellar peduncles, theoretic parkinsonian symptoms from the loci cerulei, and decreased ipsilateral jaw jerk from the mesencephalic nuclei of CN 5. One small case series indicates that these lesions may manifest as sensorimotor or pure motor infarctions and often involve the leg more than the arm or face [30]. (See Table 1).

Three named but rare syndromes arise from infarcts in the (dorso)lateral arterial distribution (see Table 1):

1. Marie-Foix syndrome is a lateral pontine syndrome characterized by ipsilateral ataxia (from the middle cerebellar peduncle), contralateral hemiparesis (from the corticospinal tracts), and contralateral hypesthesia to pain and temperature (from the spinothalamic tract).

2. Foville syndrome is a dorsal caudal pontine infarct involving the PPRF, the nucleus and fascicles of CN 7, and the corticospinal tract; it is characterized by ipsilateral horizontal gaze paresis, ipsilateral peripheral facial palsy, and contralateral hemiparesis.

3. Raymond-Cestan-Chenais syndrome is a rostral dorsal pontine infarct characterized by ataxia (from the cerebellum), contralateral loss of facial and body sensation (from the medial lemniscus and spinothalamic tracts), and contralateral hemiparesis (from the corticospinal tracts).

Tegmental pontine infarcts

Tegemental pontine infarcts are characterized by predominant localization of the infarct to the dorsal (tegmental) portion of the pons. Clinically, tegmental infarcts exhibit prominent cranial nerve deficits and ataxia that are out of proportion to the motor findings. The overall picture may resemble other pontine syndromes but with more frequent diplopia, skew deviation of the eyes, abducens (CN 6) palsy, and vertigo.

Bilateral pontine infarcts

Bilateral pontine infarcts of the ventral pons disrupt the corticospinal, corticopontine, and corticobulbar fibers on both sides; the fascicles of the abducens nerve on both sides; the PPRF on both sides; and the reticular formation. These lesions typically present as acute or subacute onset of quadriplegia, aphonia, bilateral facial paralysis, and horizontal gaze paresis. Involvement of the reticular formation reduces consciousness initially, but consciousness returns later. Variable injury to the spinothalamic tracts may cause loss of pain and temperature sensation in the body and extremities (but not the face), or not. In severe cases, affected patients may be left with vertical gaze movements as their sole remaining motor function (“locked-in syndrome”). Overall outcome of vertebrobasilar steno-occlusion has traditionally been poor, with a mortality of 50% to 90% [31], although more recent data suggest the potential for good outcome in 71% of cases, residual severe disability in 23%, and death in 2.3% [32]. Those with locked-in syndrome, however, rarely have a meaningful recovery [33].

Hemipontine syndrome usually results from pontine hemorrhage but may be seen with ischemic pontine stroke secondary to occlusion of the BA or multiple BA branches [34]. The major manifestations include ipsilateral gaze paresis, ipsilateral facial weakness, contralateral hemiparesis, contralateral hemisensory loss of the face and extremities, contralateral ataxia, and dysarthria.

• Brain stem lacunar infarction

In the elderly population with arteriosclerotic disease, lateral medullary infarction (Wallenberg’s syndrome) is not uncommonly encountered. This lesion is not clearly seen on CT. It is important for the radiologist to be familiar with the MRI appearance of this lesion and for the medulla to be included in the routine search pattern. Otherwise, a lateral medullary infarct may go unrecognized. Clinical presentation includes long-tract signs (contralateral loss of pain and temperature sensation, ipsilateral ataxia, and Horner’s syndrome) and involvement of cranial nerves V, VIII, IX, and X. Acute respiratory and cardiovascular complications can occur. In addition to the more common presentation resulting from thrombotic occlusion, lateral medullary infarction has also been reported after chiropractic neck manipulation. The latter occurs as a result of dissection of the vertebral artery near the atlantoaxial joint. The arteries supplying the lateral medulla typically arise from the distal vertebral artery but can originate from the PICA. Thus, lateral medullary infarction can accompany PICA infarction. Medial medullary infarction is less common than lateral medullary infarction. The clinical presentation of medial medullary infarction is that of contralateral hemiparesis, sparing the face.

Figure 16. Lateral medullary infarction (early subacute). Abnormal hyperintensity is noted on the T2- weighted scan in the right lateral medulla (A). The T1-weighted scan (B) is grossly normal.

References

1. Brown RD, Whisnant JP, Sicks JD, et al.. Stroke incidence, prevalence, and survival: secular trends in Rochester, Minnesota, through 1989. Stroke. 1996;27(3):373–380.

2. Broderick J, Brott T, Kothari R, et al.. The Greater Cincinnati/Northern Kentucky Stroke Study: preliminary first-ever and total incidence rates of stroke among blacks. Stroke. 1998;29(2):415–421.

3. Morris D, Schroeder E. Stroke epidemiology. Available at:http://www.uic.edu/com/ferne/pdf/strokeepi0501.

4. Turney TM, Garraway WM, Whisnant JP. The natural history of hemispheric and brainstem infarction in Rochester, Minnesota. Stroke. 1984;15(5):790–794.

5. Bogousslavsky J, Van Melle G, Regli F. The Lausanne Stroke Registry: analysis of 1,000 consecutive patients with first stroke. Stroke. 1988;19(9):1083–1092.

6. Kumral E, Bayulkem G, Evyapan D. Clinical spectrum of pontine infarction. Clinical-MRI correlations. J Neurol. 2002;249(12):1659–1670.

7. Kumral E, Bayulkem G, Akyol A, et al.. Mesencephalic and associated posterior circulation infarcts. Stroke. 2002;33(9):2224–2231.

8. Martin PJ, Chang HM, Wityk R, et al.. Midbrain infarction: associations and aetiologies in the New England Medical Center Posterior Circulation Registry. J Neurol Neurosurg Psychiatry. 1998;64(3):392–395.

9. Bogousslavsky J, Regli F, Maeder P, et al.. The etiology of posterior circulation infarcts: a prospective study using magnetic resonance imaging and magnetic resonance angiography. Neurology. 1993;43(8):1528–1533.

10. Caplan LR, Wityk RJ, Glass TA, et al.. New England Medical Center Posterior Circulation registry. Ann Neurol. 2004;56(3):389–398.

11. Kameda W, Kawanami T, Kurita K, et al.. Lateral and medial medullary infarction: a comparative analysis of 214 patients. Stroke. 2004;35(3):694–699.

12. Bassetti C, Bogousslavsky J, Barth A, et al.. Isolated infarcts of the pons. Neurology. 1996;46(1):165–175.

13. Duvernoy HM. The human brain stem and cerebellum surface, structure, vascularization and three-dimensional sectional anatomy with MRI. Wien (NY): Springer-Verlag; 1995;.

14. Haines DE. Neuroanatomy: An atlas of structures, sections, and systems. 6th edition. Baltimore: Lippincott Williams & Wilkins; 2004;.

15. Brazis PW, Masdeu JC, Biller J. Localization in clinical neurology. 4th edition. Philadelphia: Lippincott Williams & Wilkins; 2001;.

16. Carpenter MB. Core text of neuroanatomy. 4th edition. Baltimore: William & Wilkins; 1996;.

17. Kim JS. Pure lateral medullary infarction: clinical-radiological correlation of 130 acute, consecutive patients. Brain. 2003;126(Pt 8):1864–1872.

18. Bogousslavsky J, Khurana R, Deruaz JP, et al.. Respiratory failure and unilateral caudal brainstem infarction. Ann Neurol. 1990;28(5):668–673.

19. Brazis PW. Ocular motor abnormalities in Wallenberg’s lateral medullary syndrome. Mayo Clin Proc. 1992;67(4):365–368.

20. Sacco RL, Freddo L, Bello JA, et al.. Wallenberg’s lateral medullary syndrome. Clinical-magnetic resonance imaging correlations. Arch Neurol. 1993;50(6):609–614.

21. Mossuto-Agatiello L, Kniahynicki C. The hemimedullary syndrome: case report and review of the literature. J Neurol. 1990;237(3):208–212.

22. Parvizi J, Anderson SW, Martin CO, et al.. Pathological laughter and crying: a link to the cerebellum. Brain. 2001;124(Pt 9):1708–1719.

23. Kataoka S, Hori A, Shirakawa T, et al.. Paramedian pontine infarction. Neurological/topographical correlation. Stroke. 1997;28(4):809–815.

24. Fisher CM. Lacunar strokes and infarcts: a review. Neurology. 1982;32(8):871–876.

25. Shintani S, Tsuruoka S, Shiigai T. Pure sensory stroke caused by a pontine infarct. Clinical, radiological, and physiological features in four patients. Stroke. 1994;25(7):1512–1515.

26. Shintani S, Tsuruoka S, Shiigai T. Pure sensory stroke caused by a cerebral hemorrhage: clinical-radiologic correlations in seven patients. AJNR Am J Neuroradiol. 2000;21(3):515–520.

27. Furst M, Aharonson V, Levine RA, et al.. Sound lateralization and interaural discrimination. Effects of brainstem infarcts and multiple sclerosis lesions. Hear Res. 2000;143(1–2):29–42.

28. Cho TH, Fischer C, Nighoghossian N, et al.. Auditory and electrophysiological patterns of a unilateral lesion of the lateral lemniscus. Audiol Neurootol. 2005;10(3):153–158.

29. Sato K, Nitta E. A case of ipsilateral ageusia, sensorineural hearing loss and facial sensorimotor disturbance due to pontine lesion [in Japanese]. Rinsho Shinkeigaku. 2000;40(5):487–489.

30. Kataoka S, Miaki M, Saiki M, et al.. Rostral lateral pontine infarction: neurological/topographical correlations. Neurology. 2003;61(1):114–117.

31. Devuyst G, Bogousslavsky J, Meuli R, et al.. Stroke or transient ischemic attacks with basilar artery stenosis or occlusion: clinical patterns and outcome. Arch Neurol. 2002;59(4):567–573.

32. Voetsch B, DeWitt LD, Pessin MS, et al.. Basilar artery occlusive disease in the New England Medical Center Posterior Circulation Registry. Arch Neurol. 2004;61(4):496–504.

33. Mellado P, Sandoval P, Tevah J, et al.. [Intra-arterial thrombolysis in basilar artery thrombosis. Recovery of two patients with locked-in syndrome]. Rev Med Chil. 2004;132(3):357–360[in Spanish].

34. Kushner MJ, Bressman SB. The clinical manifestations of pontine hemorrhage. Neurology. 1985;35(5):637–643.