Surgical Excision of Perirectal Melanoma in the Horse. 3 Cases

Equine melanoma is one of the most common skin neoplasms encountered in equine practice. Surgical excision of melanocytic tumors is a viable treatment option and is considered to be locally curative. In the literature, information regarding surgical removal and long-term outcome of perirectal melanomas is limited. A total of three cases were included in this report, all presented with large perirectal melanomas, infiltrating the retroperitoneal musculature, leading to extra-luminal obstruction of the rectum. Horses were showing signs of dyschezia and tenesmus, secondary to rectal fecal impaction. Rectal palpation and transrectal ultrasonography aided in assessing the depth and size of the masses, as well as tumor invasion into the rectal wall. Tumor biopsy by fine needle aspiration was used to confirm the diagnosis. All horses underwent surgical excision of the masses to permanently alleviate clinical signs. In one horse, complete incision and reconstruction of the rectal wall was necessary in order to excise the whole tumor. Although surgery was successful in all three horses, one of them had to be euthanized 5 days after surgery, as clinical signs persisted. The aim of this report was to extensively describe the surgical approach, pre-operative considerations and postsurgical complications associated with surgical excision of perirectal melanoma in the horse.