A rare case of gastroduodenal junction Kaposiform hemangioendothelioma in a cat: pathological findings and follow-up.

Kaposiform hemangioendothelioma (KHE) is a rare vascular neoplasm predominantly affecting pediatric human patients and has rarely been reported in veterinary medicine. We described the clinicopathological features of an uncommon gastroduodenal junction KHE in a 2-year-old male cat presented with a history of intermittent vomiting, acutely worsening over 48 h. Imaging and endoscopic evaluation revealed complete pyloric obstruction caused by an infiltrative mass with enlarged regional lymph nodes, which were surgically excised and examined histologically and immunohistochemically. Specimens were routinely processed and stained using Hematoxylin and Eosin and Masson's Trichrome. Immunohistochemical analysis was made using an extended panel of endothelial markers, including Erythroblastosis Transformation-Specific Regulated Gene (ERG) and caveolin-1 (Cav-1), which, to the authors' knowledge, have not previously been applied in feline vascular tumors, in addition to von Willebrand Factor (vWF) and α-smooth muscle actin (α-SMA). Histologically, the gastroduodenal junction exhibited transmural infiltration by a poorly delimited mass composed of spindle cells organized in short fascicles with slit-like vascular lumina, and a swirling growth pattern conferring a glomeruloid morphology. Neoplastic endothelial cells demonstrated immunoreactivity for von Willebrand factor, ERG and Cav-1 and were surrounded by α-SMA positive cells, supporting the diagnosis of KHE. Gastric lymph nodes displayed marked sclerosis and lymphoid atrophy. The cat showed no recurrence or metastasis one year after surgery. To our knowledge, this is the first reported case of a gastroduodenal KHE in animals. This report highlights the value of expanded immunohistochemical panels in differentiating KHE from other vascular lesions and suggests a possible paraneoplastic fibrotic response within regional lymph nodes.