Epidermoid Facts

An epidermoid tumor is a benign (i.e., non-cancerous) neoplasm of the brain. It is also found in other parts of the body, but we are interested only with the ones located in the brain. It is congenital (there is literature suggesting that some may rarely be aquired), and are formed by skin cells that are in the wrong place during fetal development. It consists of an outer covering (the capsule part of it) and an inner mixture of skin cells, and fatty acids. The capsule is about the thickness of wet tissue paper, and the inside contents are the consistency of cottage cheese. These tumors are slow growing, and generally are diagnosed in the middle twenties to the late fifties. The incidence of intracranial epidermoids is between 0.2% to 1.8% of all brain tumors. They usually occur in the cerebropontine angle (CPA) or parasellar region. They can also be found on the brain stem in extremely rare instances. Only 9 cases of brainstem epidermoids have been reported thus far (Neurosurgical Review, 1996, 19:3,179-81).

Epidermoid tumors are classified as benign. They do grow, but at a slow rate, and if not removed entirely, tend to grow back. Sometimes part of the capsule must be left in because of adhesion to cranial nerves or the brain stem. In a recent study of 54 patients operated on for epidermoids of the brain and followed for a thirteen year period, the authors derived the following statistics: Fifty-seven percent of the tumors were completely removed. A higher total removal rate was achieved in patients with tumors confined to the primary location. Three percent died in the perioperative period. Approximately half of the patients presented with transient mild focal deficit impairments resulting from manipulation of the nervous structure over a wide area. There was a higher rate of surgical complications with fourth ventricle and mesencephalic extended CPA tumors. The mean follow-up period was 8.6 years. Thirty percent of the patients with subtotal removal experienced symptomatic recurrences after 8.1 years, whereas all patients with total removal were still asymptomatic. The recurrence-free survival rate was 95% at 13 years for patients with total removal compared with 65% for patients with subtotal removal (Neurosurgery, 1998 Feb, 42:2, 242-51).

These cysts have also been referred to in the literature as intercranial cholesteatoma, pearly tumor, or tumour perlee (French). Cholesteatomas are an older name and now considered a misnomer. They are also found in the ear, some being congenital, and some acquired.