WATCH : Drainage of Infected Epidermal Cyst Lobule of Ear

Intracranial epidermoid cysts are relatively common congenital lesions which account for about 1% of all intracranial tumours. They result from inclusion of ectodermal elements during neural tube closure, and typically present in middle age due to mass effect on adjacent structures. Their content, derived from desquamated epithelial cells, mimics CSF on CT and MRI, with the exception of DWI which demonstrates restricted diffusion. Management is surgical and prognosis is good.
Epidemiology
Although predominantly congenital, epidermoid cysts are usually very slow growing and as such take many years to present. Typically patients are between 20 and 40 years of age 6. There may be increased prevalence in males, although this is not found in all series 5-6.
Epidermoid cysts account for approximately 1% of all intracranial tumours 2,8.
An uncommon association exists with anorectal anomalies, sacral anomalies and presacral mass, and is known as the Currarino triad 5.
Pathology
Epidermoid cysts may be congenital (most common, arising from ectodermal inclusion during neural tube closure 8) or acquired (post surgical or post traumatic implantation). Pathologically, intracranial epidermoid cysts are identical to the petrous apex and middle ear congenital cholesteatomas. They differ from dermoid cysts which have both epidermal and skin appendages such as hair and sebaceous cysts and mature teratomas which have all three layers.
They have a thin capsule which is made of a thin layer of squamous epithelium, which macroscopically is white and pearly, and may be smooth, lobulated, or nodular. Internal cystic components are often filled with desquamated epithelial keratin and cholesterol crystals; grossly appearing as a creamy, waxy material. It should be noted that some authors contest that epidermoid cysts are along a spectrum which includes cystic (adamantinomatous) craniopharyngiomas, which have some histological similarities 7. Cholesterol and keratin components account for their distinct imaging characteristics 2.