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.
In general, there are several ways to acquire this type tumor:
1. By skin cells that are deposited in the wrong place during neural tube closure causing “ectodermal elements” to be trapped.
2. Skin cell penetration, such as a fall, infection, or puncture such as a spinal tap.
3 Radiation exposure.
The epidermoid tumor (cyst) consists of an outer covering (the capsule part of it) and an inner mixture of dead 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 usually 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, can grow back. The most common sites in the brain for these tumors are the cerebellopontine angle and the pituitary area. In surgery, removal of 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 approximately 1% of all brain tumors. They can also be found in the brain stem (intrinsic) in extremely rare instances. (Journal of Neurosurgery/2006/Vol. 104/ No. 4/ pages 285-289).
In a 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.
Benign brain tumors are usually defined as a group of similar cells that do not follow normal cell division and growth patterns and develop into a mass of cells that microscopically do not have the characteristic appearance of a cancer. Most benign brain tumors are found by CT or MRI brain scans. These tumors usually grow slowly, do not invade surrounding tissues or spread to other organs, and often have a border or edge that can be seen on CT scans. These tumors rarely develop into metastatic (cancerous or spreading) tumors. Most benign brain tumors can be removed; the benign tumors usually do not reoccur after removal. The exact causes of benign brain tumors are not known, but investigators have suggested that family history, radiation exposure or exposure to chemicals (for example, vinyl chloride, formaldehyde) may be risk factors.