Cholesteatoma. Poor function in the eustachian tube leads to negative pressure in the middle ear. This pulls a part of the eardrum (tympanic membrane) into the middle ear, creating a pocket or cyst that fills with old skin cells and other waste material (cholesteatoma). The cyst may get bigger and break down some of the middle ear bones. More at: http://www. Ncbi. Nlm. Nih. Gov/pubmedhealth/pmh0002045/.