Atypical villonodular synovitis in a horse.

The research presents a case of a 4-year-old horse diagnosed with severe cartilage damage. The horse was treated with different medications and a large villonodular lesion was removed surgically. Histological examination of the mass revealed granulation tissue covered with keratinized epithelium, which researchers believe developed due to the implantation of epithelial cells into a reactive villonodular lesion.

Case Presentation and Diagnosis

• The horse in question presented with left forelimb lameness.
• The initial diagnosis was severe cartilage damage due to a history of infectious arthritis in the left metacarpophalangeal joint.
• An arthroscopic evaluation showed the presence of a presumed large villonodular lesion.

Treatment and Outcome

• To address this health issue, a surgical procedure was undertaken to remove the mass.
• Post-surgery, the horse was treated with procaine penicillin G, trimethoprim-sulfamethoxazole, phenylbutazone, and polysulfated glycosaminoglycans. These medications worked as antibiotics and anti-inflammatory drugs to prevent infection and manage pain after the operation.
• The horse was able to return to racing after treatment, indicating a successful recovery.

Histologic Examination

• The mass removed from the horse was later examined under a microscope.
• The histologic examination found a bed of granulation tissue, which is new connective tissue and microscopic blood vessels that form on the surfaces of a wound during the healing process, covered with keratinized epithelium, a tough protective layer.

Hypothesis

• The researchers suggest that the lesion may have developed as a secondary condition following the implantation of epithelial cells into a reactive villonodular lesion.
• This hypothesis, if proven, could provide valuable insight into the progression of such conditions in horses and potentially inform treatment strategies.