Arteriovenous fistula in the orbit of a calf.

An Ayrshire calf with a protruding left eye and a fluctuant swelling dorsal to the orbit was examined. A diagnosis of arteriovenous fistula was made based on the findings of pulsation, a palpable thrill and a machinery-like bruit on auscultation over the swelling. Arteriography failed to outline the full extent of the fistula. The calf was euthanized and the fistula dissected. An enlarged superficial temporal artery communicated with a branch of the maxillary vein by way of a tortuous mass of vessels. The frontal bone was eroded by this plexus.