Epidermoid cyst

Epidermoid cyst, was first described by an artist in a French medical school in 1807, ¹⁾ is a kind of congenital disease characterized by a stratified epithelial capsule and laminated keratin debris contents.

Key concepts

● usually arise from ectoderm trapped within or displaced into the CNS

● predilection for: cerebellopontine angle, Fourth ventricle, suprasellar region, spinal cord

● sometimes AKA cholesteatoma(not to be confused with cholesterol granuloma)

● grow at linear rate (unlike exponential rate of true neoplasms)

● imaging: CSF-like mass (hi-signal on DWMRI is the best test to differentiate)

● may produce aseptic meningitis (Mollaret’s meningitis is one form)

● treatment: surgical excision. XRT has no role

Although epidermoids and cholesteatomas are histologically identical (both arise from epithelium entrapped in an abnormal location, epidermoids are intradural, cholesteatomas are extradural), the term cholesteatoma is most often used to describe the lesion in the middle ear where the entrapped epithelium usually arises from chronic middle ear infections which lead to a retraction pocket (rarely, may instead be congenital).

Epidermoid cysts are known as embryonic or acquired ectopic aberrations of the ectoderm.

May arise from any of the following ²⁾ :

1. displaced dorsal midline ectodermal cell rests trapped during neural tube closure between gesta- tional weeks 3–5

2. multipotential embryonic cell rests

3. epithelial cell rests carried to the CPA with the developing otic vesicle

4. epidermal cells displaced into CNS, e.g. by LP – see Lumbar puncture or repeated percutaneous cranial subdural taps.

Intracranial and spinal epidermoids are benign slow-growing congenital lesions. They are predominantly intradural, extra-axial in location, with intra-axial locations (intra-parenchymal and spinal intramedullary) being rare. The most common locations of intradural epidermoids are cerebellopontine angle cistern followed by supra- and para-sellar regions, and fourth ventricle. Less common locations include inter-hemispheric fissure, sylvian fissure, lateral ventricle, intracerebral, velum interpositum cistern, superior cerebellar cistern and pineal gland. They can also be extradural, usually arising in the diploic space of the calvaria, though they are less common. Magnetic resonance imaging is the primary modality for diagnosis and knowing the extent of the lesion. In this pictorial review, we intend to illustrate their classical and unusual locations, atypical imaging findings including calcifications, rare complications like haemorrhage or spontaneous rupture ³⁾.

Epidermoid cysts within the neuraxis are rare benign neoplasms that are most commonly located in the intracranial region.

see Intracranial epidermoid cyst.

see Spinal epidermoid cyst.

see Extradural epidermoid cyst.