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