Survey of chronic sinusitis-induced skull anomalies in desert bighorn sheep

Bone anomalies were found in 20% of 630 skulls from desert bighorn sheep (Ovis canadensis) representing populations of california bighorn (O canadensis californiana), lower California bighorn (O canadensis cremnobates), Mexican bighorn (O canadensis mexicana), and Nelson bighorn (O canadensis nelsoni) that are native to Arizona, California, Nevada, New Mexico, and Utah. The anomalies were extremely diverse, ranging from osteonecrosis within the matrix of the paranasal sinuses to extensive lysis of the frontal bone, horn core, and sheath. In rams, the necrosis most often occurred in the mid- to posterior region of the cornual sinus and resulted in blistering of the sheath and sometimes a breaking away of the horn. In ewe skulls, the anomalies were generally at the base of the cornual sinus or within the frontal sinus. Osteonecrosis in the ewe skulls had generally invaded the region of the orbit or penetrated the cribriform plate. The skull lesions were most often observed in desert bighorn rams greater than or equal to 5 years old. The age of ewes could not be accurately determined. The skull anomalies were believed to result from pyogenic osteomyelitis.