Answer: Iatrogenically-induced changes

Histology: The specimen was obtained by surgical evacuation of the maxillary sinus. It is comprised almost exclusively of mature fat. There is focal fat necrosis, but now other pathologic alterations. The fat is lined by respiratory epithelium.

Discussion: Patients with chronic sinus disease resulting from compromised natural drainage of the frontal sinus are sometimes treated with frontal sinus obliteration. The material of choice for obliteration is freshly removed abdominal fat. The subsequent histologic picture undergoes evolution over time. Initially the graft undergoes necrosis, but over time the necrotic fat is absorbed and replaced by vital fat. True adipose neoplasms of the sinonasal tract are exceedingly rare, and the possibility of iatrogenic obliteration of the sinus by an autologous fat graft should be considered when mature fat is encountered in the frontal sinus. This diagnosis can generally be confirmed by probing into the clinical history.