Splenic Stromal Sarcoma in a Labrador Dog

Abstract

Background: Splenic stromal neoplasms are a heterogeneous group of tumors that shares the morphology of spindle cells, and are considered a primary mesenchymal neoplasm of the spleen. Among these neoplasms, some are as yet unclassified. Although stromal neoplasms represent 25 a 50% of dog splenic neoplasms in dogs, subtypes rarely occur alone. As these neoplasms are difficult to diagnose in the routine veterinary medical examination, the objective of this article was to report a case of splenic stromal sarcoma in a dog treated at a private veterinary hospital in Recife, Pernambuco, Brazil. Case: An 8-year-old male labrador dog was treated at a veterinary hospital for an initial clinical suspicion of gastroenteritis. Clinical examinations showed anemic ocular mucosa and a distended abdomen. Considering the animal’s condition, blood count, serum biochemistry, and abdominal ultrasonography (US) were requested. The laboratory tests revealed anemia, thrombocytopenia, leukocytosis with neutrophilia, and changes in the indices of alanine aminotransferase (ALT) and alkaline phosphatase (ALP), among other findings. Abdominal ultrasound showed hepatomegaly, diffuse splenomegaly, a neoformation in the spleen suggestive of splenic neoplasia, and mild cystic prostatic hyperplasia. The dog underwent exploratory laparotomy with splenectomy. During the procedure, a nodule was found attached to the spleen. It was removed, fixed in a 10% neutral buffered formalin solution, and sent for histopathological and immunohistochemical examinations (vimentin, S100, desmin, MyoD1, HHF35, CD31, and alpha smooth muscle actin). The histopathological diagnosis was poorly differentiated spindle cell splenic sarcoma, compatible with splenic stromal sarcoma. Immunohistochemistry showed neoplastic cells immunoreactive for vimentin and S100, and it was not reactive for other markers. Based on the immunohistochemical and morphological profile, the diagnosis of splenic stromal sarcoma was confirmed.  Discussion: Dogs affected by splenic neoplasms are generally aged between three and 17 years, and clinically present withanorexia, emesis, lethargy, weight loss, and abdomen distension, which were observed in the present case. However, a purelyclinical diagnosis is disputable, since other diseases can present the same signs. Thus, complementary exams are essential for a correct diagnosis. Laboratory changes in blood count and serum biochemistry are considered nonspecific for splenic neoplasms, with neutrophilic leukocytosis and anemia being consistent with paraneoplastic syndromes frequently diagnosed in small animals.  Microscopically, splenic stromal sarcomas are characterized by focal splenic nodules composed of cohesive polygonal to spindle-shaped cell layers. The cells usually exhibit anisokaryosis and often have large oval to round vesicular nuclei and, occasionally, multinucleated cells. They have large areas of necrosis, diffuse or nodular lymphoid aggregates, and foci of extramedullary hematopoiesis, consistent with the histopathological examination reported in the present case. The immunohistochemical analysis included evaluation of seven markers to elucidate the histogenesis of the neoplasm, with the anti-vimentin and anti-S100 markers demonstrating positive cytoplasmic immunoreactivity, revealing the mesenchymal origin of the neoplasm. Thus, the definitive diagnosis was splenic stromal sarcoma, a rare and aggressive neoplasm. Keywords: spleen, histopathology, immunohistochemistry, neoplasm.  Descritores: baço, histopatologia, imunohistoquímica, neoplasia