Epidermoid

Findings:
An extraaxial mass in present in the region of the right quadrigeminal plate cistern/ velum interpositum. This mass exhibits hyperintensity on PDWI, slight hyperintensity compared with CSF on T1WI, and does not enhance. The mass compresses and displaces the colliculi anteriorly and compresses the cerebral aqueduct, causing hydrocephalus.

Differential Diagnosis:
epidermoid, arachnoid cyst

Discussion:
distinguishing feature= internal architecture and hyper to CSF on PD and T1.
   -ectodermal inclusion at neural tube closure
   -1% of intracranial tumors, much more common than intracranial dermoids
   -40-50yr presentation, M=F
   -rare Ca++ and enhancement- possible fat density on CT
   -CPA, parasellar, p fossa
   -clinical: CN palsy
   -CSF signal/attenuation +/- rim enhancement +/- hyper T1
 
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