Cholesteatomas are not true neoplasms, but they are cystic masses lined by squamous epithelium. The desquamated epithelium and keratin degenerates, resulting in cholesterol formation and giant cell reaction. Although their histologic findings are benign, cholesteatomas can gradually enlarge, eroding and destroying the middle ear and surrounding structures. They occur as a complication of chronic otitis media. Although cholesteatomas have a squamous epithelial lining, malignant transformation does not occur. An eosinophilic granuloma of bone occasionally may be seen in the region of the skull in young children, but it is characterized by the presence of Langerhans cells. Labyrinthitis typically is caused by a viral infection and is self-limited. Otosclerosis is abnormal bone deposition in the ossicles of the middle ear that results in bone deafness in adults.