Surgical management of a progressive iris melanocytoma in a Mustang.

Case Description: A 7-year-old gray Mustang gelding weighing 454 kg was presented for evaluation of a brown mass within the left eye (OS) of 1 year's duration with recent enlargement.

Clinical Findings: A nonpainful, 8 mm diameter, brown, vascularized mass was identified in the anterior chamber of the OS. Ocular B-scan ultrasound confirmed iris involvement and corneal endothelial contact. Histopathology confirmed the presumptive diagnosis of a uveal melanocytic neoplasm, and revealed 1-3 mitotic figures per high power (400x) field.

Treatment And Outcome: The mass was removed via sector iridectomy without complications, but without complete margins. Three cutaneous melanocytomas noted 1.5 months postoperatively were completely excised. No tumor regrowth was noted 15 months postoperatively, supporting a diagnosis of melanocytoma for the iridal mass.

Clinical Relevance: Sector iridectomy is a reasonable treatment option for uncomplicated iridal melanocytomas in horses. Mitotic index and presence of cutaneous melanocytic neoplasms may be irrelevant to the prognosis of equine iridal melanocytic neoplasms.