Epidermoid cyst

Incidence

They account for less than 1% of all intracranial tumors.

Origin

Epidermoid cysts result from abnormal inclusion of epithelial elements during closure of the neural tube, in the third to fifth week of embryonic life.

Macroscopic appearance and general characteristics

Epidermoid cysts were described as "the most beautiful tumors of the body" by Dandy. They have a shining "mother of pearl" appearance with presence of a conglomerate of multiple thin walled cysts. They are located in the subarachnoid space where they grow around the neurovascular structures. The most common sites of occurrence are the skull and the basal subarachnoid spaces, most frequently the cerebellopontine angle cistern. The occurrence in the fourth ventricle is extremely rare and can be mimicked by flow phenomena. The tumor is benign.

Microscopic appearance (image 2)

- The cysts are lined by a thin layer of keratin-producing squamous epithelial cells.

- The content of the lesion is keratin, resulted from desquamation of the cyst wall.

Imaging features (see case reports)

- CT

Epidermoid tumors appear as hypodense multilobulated masses, that can resemble arachnoid cysts. Calcification is rare.

- MRI

On MRI, epidermoid cysts have the same characteristics as CSF, presenting with long T1 and long T2. The tumor surrounds the neurovascular structures of the CSF spaces (image 3).

Differential diagnosis

The main differential diagnosis is arachnoid cyst. Differential diagnosis can be made with Steady-State Free Precession Images or diffusion weighted MR.

Case reports

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Epidermoid cyst
Epidermoid cyst, giant

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