Collision tumor of the frontal sinus: evidence of prior intrasinus instillation of thorotrast.

Carcinoma of the frontal sinus is relatively rare. We describe a case of two independent carcinomas, squamous cell and adenoid cystic, in the right frontal sinus region of a patient who received sinus irrigation with an unidentified, substance 30 years previously. Radioautography performed on sections of the tumor tissue revealed linear tracks of the type produced by thorium decay, strongly suggesting that the substance was thorotrast. In addition to being the first description of a "collision tumor" of the frontal sinus, the case would represent the first reported instance of frontal sinus carcinoma following intrasinus instillation of thorotrast.