Tumoral Thrombus in Cranial Mesenteric Artery Secondary to Intestinal Leiomyosarcoma

Background: Leiomyosarcoma is a non-encapsulated tumor, belonging to the group of soft tissue sarcomas and often invasive. This histological type comprises the most aggressive solid tumors and, because they respond poorly to therapy, are considered the worst prognosis. The dissemination of metastatic cells can occur mainly hematologically to the liver, lungs and bones or by direct invasion, but metastases to blood vessels are rare and surgery is the treatment of choice in most cases. This paper aims to report a rare case of tumor thrombus in the cranial mesenteric artery secondary to an intestinal leiomyosarcoma.Case: A 9-year-old female S.R.D dog presenting inappetence, evolving to anorexia, weight loss, anemia and vomiting for approximately 15 days was referred to the Hospital of Veterinary Clinics of the Federal University of Rio Grande do Sul. Previous therapy at another clinic with three blood transfusions did not promote reversal of anemia. Ultrasonographyrevealed a nodule in the small intestine of seven cm in diameter and in the hemogram a hypochromic macrocytic anemia. Thoracic radiography did not reveal metastases. After a new blood transfusion, the patient was referred to an exploratory laparotomy, where the nodule was identified in the small intestine, which was cyanotic and two nodules in the cranialmesenteric artery, partially obstructing the local blood flow. Resection and intestinal anastomosis were performed from the final portion of the duodenum to the cecum, with ligation of the mesenteric artery and the nodules were sent for histopathological analysis. The animal presented a gradual improvement of the condition, with the introduction of liquidfeeding on the second postoperative day. After these days, he presented hypochromic macrocytic anemia, with presence of Howell-Jolly corpuscle, spherocytes and icteric plasma, compatible with hemolytic anemia. Treatment with prednisone was started, with a worsening of the condition. The patient had generalized jaundice and died five days after surgery. Theanimal was referred to the necropsy in which it showed abdominal fluid of slightly reddish color, adherence of viscera (intestine, stomach and omentum). In the surgical area (enterectomy) there was purulent secretion on the points, the large intestine presented ecchymosis and petechiae on the mucosa. Histological examinations of the nodule and thrombus revealed malignant mesenchymal neoplasia formed by spindle cells with elongated nuclei, abundant