Background: Hemangiosarcoma (HSA) is a malignant tumor of vascular endothelial origin. Primary neoplasms are extremely rare in the third eyelid of dogs. Neoplasia affecting ocular surface has been associated with increased exposure to solar radiation. Treatment reported for dogs with conjunctival neoplasia is surgical excision. Definitive diagnosis is confirmed in the histophatological examination. In this report, we describe a case of HSA of the third eyelid in a dog that was successfully treated with surgical excision. Case: A 5-year-old female Boxer dog was referred to the Ophthalmology Section of the Veterinary Clinics Hospital of the Federal University of Rio Grande do Sul (UFRGS), presenting a red mass in the third eyelid of the right eye. Physical examination it was normal except for the ocular disease. The dog had signs of ocular discomfort an epiphora. On ophthalmic examination a fixed, raised, red mass approximately 4 to 5 mm in diameter was identified on the anterior surface of the third eyelid in the right eye. Under general anesthesia, and using an operating microscope the mass was excised with a gross margin and submitted for histopathological analysis. Microscopic examination revealed a lesion composed of neoplastic mesenchymal cells forming irregular channels containing blood. These plump cells showed moderate anisocytosis and anisokaryosis with a low mitotic index. The postoperative treatment involved the administration of systemic carprofen 4 mg/kg, daily for 5 days. In addition, topical broad-spectrum antibiotic containing tobramycin 0.3%, and a non-steroidal anti-inflammatory solution of sodium diclofenac 0.1%, administered six times a day for two weeks. The surgical wound was left to heal by second intention. After surgery, the dog had no signs of ocular discomfort. No complications or recurrence of the lesion have been noted after two years of follow-up. Discussion: Excessive exposure to ultraviolet radiation has been implicated as a risk factor for development of the ocular surface tumors in dogs. In this case, the outdoor housing of the dog in a sunny area resulted in a high exposure to solar radiation. In dogs these tumors usually present as small, red, raised lesions of the conjunctiva, most commonly on the leading margin of the third eyelid. In the present case, the ophthalmic examination revealed a small red mass protruding from the anterior surface of the conjunctiva of the third eyelid. Definitive diagnosis is made after histopathologic examination. Possible differential diagnoses for the nictitans mass in dogs include squamous cell carcinoma, melanomas, adenocarcinomas, mastocytomas, papillomas, hemangiomas, angiokeratomas, histiocytomas, and lymphosarcoma. The diagnosis of hemangiosarcoma in this dog was confirmed through the histopathology of the mass after surgical excision. This case was similar to previously reported HSA in dogs in terms of their histopahtological characteristics. There is little information about the success of the treatment of HSA only by surgical removal as compared with surgical excision associated with adjacent therapies. In this study, the surgical removal of the mass with a margin of safety was the treatment of choice. The surgical wound was left to heal by second intention. After surgery, the dog had no signs of ocular discomfort. Postoperatively, antibiotic eye drops, and a non-steroidal anti-inflammatory were administered. The surgical wound healed well postoperatively. Periodic evaluations were realized and there are no signs of recurrence after two years. HSA should be considered as differential diagnosis in dogs with any third eyelid mass. In the present case, surgical excision was effective for the treatment of HSA in third eyelid of a dog.
