A cholesteatoma is an abnormal collection of skin behind the eardrum. Often this results from chronic eustachian tube dysfunction, but more rarely may be present at birth. Though not a tumor, a cholesteatoma may cause destruction of the normal ear structures, including the eardrum, or the middle ear bones. These bones, also known as ossicles, include the malleus, incus and stapes. More rarely, cholesteatomas may cause injury to the facial nerve, disrupt the balance system, or lead to meningitis. It is important that cholesteatomas be evaluated by an otolaryngologist in a timely manner. Most often tympanomastoidectomy ear surgery is required for removal. Physicians in the Ear, Nose and Throat Associates of San Mateo practice perform these surgeries regularly. They are performed using NIM (Nerve Integrity Monitoring) to help protect of the facial nerve during surgery.