Delayed radiation necrosis of brainstem related to fast neutron beam irradiation: case report and literature review.

A 42-year-old man developed necrosis of the brainstem 10 months following fast neutron irradiation of a recurrent adenocystic carcinoma of the right submandibular salivary gland. The neoplasm had been diagnosed 15 years earlier. Neck dissection and several local excisions failed to control local extension, so that 7000 rad 4.8 MeV x-rays were administered. The right mandible and part of the tongue and palate were resected for recurrence and chemotherapy and transfer factor were given. Because of cranial neuropathy and erosion of the skull base, fast neutron radiation (2.080 rads) was administered five and one-half years after the x-ray therapy, but to a nonoverlapping field. Ten months later, rapidly progressive symptoms and signs of multiple cranial nerve palsies on the right side and left hemihypesthesia and hemiplegia appeared. Clinical manifestations of brainstem necrosis lasted 4 months. Postmortem examination demonstrated radionecrosis of pons and upper medulla, predominantly on the right side. This case illustrates the efficacy of neutron radiation in eradicating local carcinoma and also the serious complications of this therapeutic modality.