The horse had a firm mass beneath the skin over his left temple (seen here) and a small melanoma on the right side of his sheath that had remained unchanged over the past two years. | Photo: Courtesy Dr. Harry Werner

By Harry Werner, VMD, WEVA board member

History—A 14-year-old gray Thoroughbred gelding had performed successfully as his current owner’s children’s hunter for two years. He had always ridden well and behaved normally. Recently, however, he began displaying episodes of headshaking and unprovoked panic while on the crossties but returned to normal when moved to a quiet stall.

Physical Examination—The horse had a firm mass beneath the skin over his left temple and a small melanoma (a type of skin cancer) on the right side of his sheath; both had remained unchanged over the past two years. The veterinarian did not identify any dental or mouth abnormalities on an oral exam, so the owners elected to pursue diagnostic imaging.

Diagnostic Imaging—The veterinarian did not identify any pathology (disease or damage) on skull radiography, but thermographic imaging revealed an increased surface temperature over the horse’s left temple and face. An endoscopic examination of his pharynx and guttural pouches revealed that melanoma had metastasized to the left guttural pouch. The veterinarian referred the horse for an MRI exam, which showed that the melanoma had invaded his left middle ear  through the bony vault containing the brain (the calvarium) and into the brain’s left temporal lobe