Posterior Fossa Arachnoid cyst MRI

MRI Brain

Seq planned are Axial FLAIR, T2, Sag T2, Axial Diffusion. 

This MRI study of Brain shows:
Wide posterior fossa with scalloping.
Posterior fossa cyst iso intense to Csf. No restricted diffusion on Dw images. Cyst non communicating with fourth ventricle. Fourth ventricle normal sized.
An associated hypoplastic left cerebellar hemisphere.

An associated Dysgenesis of posterior portion of Corpus callosum with Colpocephaly.
Cerebellar tonsils protruding down across foramen magnum_ Arnold chiari type i malformation with an associated cervical cord syrinx.

Imaging wise diagnosis : Posterior fossa Arachnoid cyst.

DDs ruled out are Dandy walker and other cerebellar malformation as Cyst non communicating with fourth ventricle. Epidermoid Cyst ruled out as no restricted diffusion on Dw images.

Operated and excisional biopsy done.

Histopathology Report

Gross appearance : The specimen consist of thin pearly white soft membranous cystic tissue. The entire tissue submitted for processing.
Microscopy : Sections shows thin undulating delicate fibro collagenous cyst wall lined by meningothelial cells, at places seen to form focal aggregates. There is no e/o cytotological atypia.

Final Diagnosis : Arachnoid cyst.