Pathologic quiz case: An incidental gastric mass in a 71-year-old man who presented with pancreatic pseudocyst

Archives of Pathology & Laboratory Medicine, Dec 2002 by Bhattacharya, Baishali, Jakate, Shriram

A 70-year-old white man of Russian descent with history of pancreatitis, which had ultimately developed into a pancreatic pseudocyst, was transferred to Rush-Presbyterian-St Luke's Medical Center from another hospital. The patient underwent an endoscopy for an episode of hematemesis. Esophagogastroduodenoscopy demonstrated moderate erosive esophagitis and duodenitis as the possible sources of bleeding. An incidental submucosal mass was also found in the stomach; there was no ulceration or bleeding from this mass. Endoscopic ultrasonography demonstrated findings consistent with known pancreatic pseudocyst and confirmed the presence of a 2.5-- cm, diffusely homogenous, and hyperechoic submucosal mass in the gastric antrum. The mass seemed to be surrounded by muscularis propria and was suggestive of a gastric lipoma. The patient underwent an exploratory laparotomy, resection of the gastric mass, pyloroplasty, truncal vagotomy, and cyst duodenostomy. The patient's postoperative course was uneventful, and he was discharged after 10 days.

The surgical specimen consisted of a 3 x 3 x 2.6-cm segment of gastric antrum. The mucosa was grossly unremarkable. On bisecting the specimen, a well-defined, hemorrhagic, round mass measuring 2 x 2 X 1.5 cm was present in the submucosa and muscularis propria. Histologically, the tumor was surrounded by a fibrous pseudocapsule (Figure 1) and consisted of variably sized arborizing vessels lined by flattened endothelial cells surrounded by sheets of tumor cells. Individual tumor cells were small to intermediate with uniform round nuclei, coarse chromatin, and eosinophilic, nongranular cytoplasm (Figure 2). Mitosis and necrosis were absent. Immunostains for vimentin, alpha-smooth muscle actin, and muscle-specific antigen (Figure 3) were positive. Cytokeratins 8/18 and AE1/3, S100 protein, chromogranin, and synaptophysin were negative. A lymph node along the greater curvature showed reactive change and no tumor. What is your diagnosis?

Pathologic Diagnosis: Gastric Glomus Tumor

The intimate tumor cells-vessel wall relationship, remarkably uniform round nuclei, cytoplasmic eosinophilia, and gastric antral location and immunophenotype are characteristic of glomus tumor.

Although glomus tumor occurs commonly in the skin, extracutaneous glomus tumors, especially those arising in the viscera, are rare.1 Glomus tumors usually occur in the gastric antrum of adults, and there is no sex predilection.2,3 Just like those seen in the skin, this tumor is derived from the specialized cells of the glomus apparatus, a peculiar arteriovenous shunt concerned with local readjustment of the vascular flow in response to certain mediators. Frequently, the mucosa overlying the tumor ulcerates, leading to bleeding, which is a common initial symptom.1 Glomus tumors can also be incidental findings during clinical evaluation or abdominal operation.2 Most are small, with an average size of 2 to 2.5 cm.2,3

Glomus tumors are intramural nodules situated mainly in the muscularis propria that can become collagenized at the margins, forming a pseudocapsule.2,3 The basic histologic pattern consists of blood vessels and characteristic glomus cells. Glomus tumors are highly vascular with dilated, irregularly shaped, thin-walled vessels. The vessels are lined by endothelium, which in turn is surrounded by nests, strands, or sheets of glomus cells. Glomus cells are uniform and round, with central dark nuclei containing coarse chromatin and pale, eosinophilic, amphophilic, or clear cytoplasm. Three microscopic types of glomus tumors have been recognized: solid, angiomatous, and myxoid. Ultrastructural studies and immunohistochemical analysis have shown that glomus tumors are identical to smooth muscle cells.1,3 Glomus tumor, hemangiopericytoma, leiomyoblastoma, and leiomyoma all fall into the broad category of smooth muscle tumors.1

Gastric glomus tumors behave in a benign fashion. A case of malignant gastric glomus tumor with metastases to the liver, lymph nodes, and peritoneum has been reported; the patient, however, lived for more than 15 years following the surgical resection.4 Another case of gastric glomangioma included a massive tumor of the greater curvature of the stomach that weighed 12 kg. The patient made an uneventful recovery and died 21 years later of causes unrelated to the tumor.5 It is believed that the malignant or massive forms may most probably represent epithelioid leiomyosarcoma or epithelioid leiomyoma rather than glomus tumors.3

The main differential diagnosis of gastric glomus tumor includes carcinoid and malignant lymphoma. Differentiation from carcinoid and lymphoma may be specially difficult at frozen section. The histologic feature that sets a glomus tumor apart is the arrangement of glomus cells in complete and incomplete lobules along the vascular channels, giving an organoid appearance. This pattern is distinguished from carcinoids because vascular channels are not a feature of carcinoids.1 In glomus tumors, immunostains for smooth muscle markers, such as smooth muscle actin and muscle-specific antigen, are positive, and leukocyte common antigen and neuroendocrine markers, such as synaptophysin and chromogranin, are negative, differentiating glomus tumors from carcinoid and lymphoma, respectively.