Isolated lesions induced by radiation therapy may be seen in the external ear canal and, less commonly, in the middle ear. Borsanyi (3) described necrosis of the skin of the external ear canal in approximately 10% of 100 patients who received radiation therapy for nasopharyngeal carcinoma and other tumors in the head and neck. In a study of 29 patients with osteoradionecrosis, Ramsden et al. (2) found that the most common manifestation of osteoradionecrosis of the temporal bone was necrosis of tympanic bone of the floor or anterior wall of the external auditory canal. Osteoradionecrosis of the ossicles has also been described (4, 5, 6).

Hearing loss, which may be severe to profound, may occur months or years after radiation therapy to the temporal bone (7,8). The incidence of sensorineural loss may reach 36% of patients who have received a full course of radiation (7), and in some cases vestibular damage has also been described. The effect of radiation on the membranous labyrinth as studied in an animal model (9) includes delayed degeneration of sensory and supporting cells in the organ of Corti and loss of auditory neurons. In this animal model of radiation labyrinthitis, a linear relationship between radiation dose and the percent of missing outer hair cells and supporting cells was found. In addition, significant loss of myelinated nerve fibers was seen in areas unassociated with hair cell loss, suggesting that degenerative neuropathy may be an additional and primary effect.

More diffuse osteoradionecrosis of the temporal bone may occur, resulting in intracranial complications (2). Although this diffuse form is most common in individuals with radiation therapy directed primarily at lesions within the temporal bone (2), diffuse and progressive osteoradionecrosis may occur in cases in which the temporal bone was not the primary focus of radiation (10,11). The incidence of diffuse osteoradionecrosis increases with radiation dose. Cole (12) found clinical evidence of osteoradionecrosis in 19% of 21 patients treated with radiation therapy for glomus jugulare tumors. In a series of 20 patients treated with surgery and postoperative radiation therapy (13), osteoradionecrosis was described in 25%. Wang and Doppke (14) reported that osteoradionecrosis may be minimized by limiting the radiation dose to 2,000 rets (nominal standard dose equivalent to 7,400 rads in 37 fractions at a rate of 5 fractions per week). Nadol and Schuknecht (10) described an incidence of osteoradionecrosis of 42% in cases of squamous cell carcinoma of the temporal bone that were treated with surgery resulting in an open mastoid cavity, followed by full-course radiation therapy, whereas in another group of patients receiving an average dose of 4,610 rads, no osteoradionecrosis occurred despite an open cavity technique, suggesting both a positive correlation with radiation dosage and the possibility of a threshold phenomenon.