Radiotherapy of a recurrent ossifying fibroma in the paranasal sinuses of a horse.

A 7-year-old female Thoroughbred was admitted with a history of labored breathing, stridor, and exercise intolerance. Examination revealed a mass in the left paranasal sinuses that was determined to be an ossifying fibroma. Initial treatment consisted of surgical removal of the mass alone; however, the mass recurred 9 months after surgery. The mass was again removed, and adjunctive radiotherapy consisting of 3,000 cGy of cobalt radiation was administered. This time, the tumor did not recur for > 6 years. A third surgery was performed to remove the mass, and adjunctive radiotherapy consisting of 4,000 cGy of photon beam radiation from a linear accelerator was administered. The mass did not recur during the subsequent 3 years. Ossifying fibromas are uncommon tumors that frequently recur if incompletely excised. Results in this horse suggest that adjunctive radiotherapy may delay or prevent tumor recurrence in affected horses.