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Congenital lesions resulting from incomplete separation of neural and cutaneous ectoderm at time of closure of neural tube.

Lined by single layer of stratified squamous epithelium

Cyst contains desquamated epithelium.

Often incidental finding

Symptomatic lesions most often detected in 3rd to 4th decades.

No sex predilection.

Primary differential consideration is arachnoid cyst.

Epidermoids demonstrate restricted diffusion, also slightly hyperintense to CSF on proton density images (arachnoid cysts follow CSF signal on all sequences, no restricted diffusion)

Epidermoid: surrounds adjacent blood vessels rather than displacing blood vessels.