Abstract
An 8-year-old male Rottweiler was presented for recurrent episodes of dysphagia and vomiting with chronic weight loss. Radiography revealed a mediastinal mass in the heart base region. Necropsy revealed a firm, white mediastinal mass extending along the distal esophagus, through the diaphragm, to the gastric cardia, leftward to the convex visceral aspect of the fundus, and rightward along the lesser curvature of the stomach to the pyloric antrum. The gastric lymph node was enlarged and the omentum contained several nodules. Histologically, deep fundic mucosa contained pleomorphic, vacuolated cells with intracytoplasmic mucin, which was hyaluronidase resistant. Neoplastic cells were cytokeratin positive and vimentin negative. Transmural invasion was evidenced by the presence of cytokeratin-positive cells between smooth muscle bundles of the gastric wall. The mediastinal mass was composed of clusters of neoplastic cells in a stroma of dense and loose connective tissue. Neoplastic cells were also within blood and lymphatic vessels, tracheobronchial and gastric lymph nodes, and around peripheral nerves. This carcinoma most likely arose from the gastric fundus and extended to the cardia, from where it advanced proximally to the mediastinum as well as further rightward along the lesser curvature, demonstrating an anatomic continuity suggestive of a direct invasion. Metastasis, evidenced by the presence of lymphatic, blood, and perineural tumor emboli, also occurred.