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Hello.

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Welcome back to Proscan MRI online.

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My name is Dr. Benjamin Laser, neuroradiologist,

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and we are going to continue our discussion

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on non-glial CNS tumors.

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This is a 27-year-old man

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who presents with progressive headaches.

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On the left sequence,

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we see a T1 sagittal weighted image

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and you can see a

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iso-intense or low signal intensity mass,

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centered within the prepontine cistern,

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which scallops the pons with dorsal displacement,

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slide to face under the 4th ventricle

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and inferior descent of the salivary tonsils.

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On the center sequence,

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we see a T2 axial image

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showing the mass as hyperintense,

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which insinuates itself within the prepontine system

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and throughout the basilar systems,

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extending into the ambient system,

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and actually,

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continuing to the cerebellopontine angle on the left,

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the mass displaces the basilar artery,

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which is right here

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and also involves the cranial nerves on the left.

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Here is the left trigeminal susternal nerve,

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which is pushed laterally.

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The cranial nerve seventh

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complex on the left is also displaced and irregular.

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The far-right panel shows

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another T1-weighted sequence

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where the mass is low signal

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on the T1-weighted sequence.

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If I show you the diffusion-weighted imaging,

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the mass has intense

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hyperintense signal on the B1000 sequence,

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consistent with restricted diffusion.

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These characteristics are most consistent

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with an epidermoid cyst in the most common location,

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prepontine cistern and cerebellopontine angle.

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Symptoms for epidermoid cyst,

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depending on the location

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and the effect on adjacent neurovascular structures,

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as I've already alluded to.

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In this case, this patient

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has involvement of the left cisternal trigeminal nerve,

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which is markedly displaced laterally,

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and also involvement of the left

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cranial nerve 7 sachet complex.

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The vascular structures of the basilar artery

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is partially encased and displaced rightward.

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Additional symptoms would include headache,

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and as you notice on the sagittal T1-weighted sequence,

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the mass has marked mass effect upon the pons

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with a scallop appearance,

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involvement of the 4th ventricle,

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which is slightly narrowed,

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and inferior descent of the cerebellar tonsils.

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These tumors have rare malignant degeneration

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into squamous carcinoma.

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Treatment of this lesion

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typically consists of microsurgical resection,

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which can be complicated by the investment

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of the local structures as I've described.

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Recurrence is common if it is incompletely removed

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and chemical meningitis is a possibility from content leakage.

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The main age at presentation for this lesion,

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epidermoid cyst,

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is about 52 years, with a male predominance.

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Differential considerations would include arachnoid cyst.

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However, these images are

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extremely characteristic for an epidermoid cyst,

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and the most important sequence to

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evaluate is the B1000 sequence

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with the hyperintense signal within the mass.

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Finally, epidermoid cysts are benign lesions

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that usually arise from ectodermal inclusions

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during neural tube closure,

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usually the 3rd to 4th week of embryogenesis.

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They are most commonly located

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intraduraly, within the basilar cisterns.

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About 40% to 50% of the time,

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they are at the cerebellopontine angle.

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About 20% of the time, they're in the 4th ventricle.

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They can be seen in the parasellar

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and middle cranial fossa,

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about 10% to 15% of the time,

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and it is extremely rare to have

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epidermoid cysts within the

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cerebral hemispheres.

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In summary, epidermoid cysts have classic

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increased signal on the B1000 sequence,

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have T2 hyperintensity,

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and are predominantly located within the basilar cisterns,

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involving adjacent neurovascular structures.