The
epidermoid is a tumor- like mass. 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 acquired), and are formed by
skin cells that are deposited in the wrong place during neural
tube closure causing "ectodermal elements" to be
trapped. 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. They do grow, but at a slow rate, and if not
removed entirely, tend to grow back. The most common sites in the
brain for these tumors are the cerebellopontine angle and the
pituitary area. In surgery removal part of the capsule must often
be left in because of adhesion to cranial nerves or the brain
stem. The incidence of intracranial epidermoids is between 0.2% to
1.8% of all brain tumors. They can also be found on the brain stem
in extremely rare instances.
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 preoperative 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 epidermoid tumors have also been referred to in the
literature as epidermoid cysts, epidermoid lesions, 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.
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