Epidermoid Facts

What exactly is this thing in Michael's head?  The following information comes from The Epidermoid Brain Tumor Community website.

The epidermoid is a tumor-like mass.  An epidermoid tumor is a benign (i.e. non-cancerous) neoplasm of 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 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 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.

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.