Tarsal Villonodular Tenosynovitis (Giant Cell Tumor Of Tendon Sheath) In A Dog

A 12-year-old female mixed-breed dog presented with lameness, pain. and an enlarged, non-ulcerated, nodular mass in the region proximal to the tarsal joint of the right pelvic limb. Surgical excision was performed, revealing a 6.5 cm mass adherent to the deep flexor tendon and adjacent tissues. The cut section had cysts filled with blackened clotted material. which exuded reddish semusfluid. Microscopically, the cysts were filled with red blood cells and were either denuded or covered by synoviocytes. In addition, the mass was characterized by marked ,fibrovascular connective tissue associated with siderophages and multinucleated giant cells. These findings were consistent with those of pigmented villonodular tenosynovitis, a rare condition affecting several animal species and humans.