Gastric schwannoma: a clinicopathologic study of 51 cases and critical review of the literature

Abstract

Schwannoma is a rare gastrointestinal mesenchymal tumor, as the vast majority of gastric mesenchymal tumors are gastrointestinal stromal tumors. In this study, we analyzed clinicopathologically 51 gastric schwannomas. These tumors predominantly occurred in older adults with a marked female predominance (40 women and 11 men; median and mean ages, 60 and 58 years). They variably presented with gastric discomfort, bleeding, or rarely gastric outlet obstruction; and many were incidental findings during other medical procedures. The tumors ranged from 1 to 10.5 cm (median, 4.5 cm). The typical histologic features included spindle cells usually with microtrabecular architecture and focal nuclear atypia, and peritumoral lymphoid cuff, whereas features of soft tissue schwannomas, such as encapsulation, nuclear palisading, vascular hyalinization, and dilatation, were absent or infrequent. Median mitotic count was 2/50 high-power fields, with the highest count being 13/50 high-power fields. No malignant variants were recognized, and long-term follow-up did not reveal recurrences or metastases. Immunohistochemically, all examined tumors were S100 protein positive and most were also GFAP positive, whereas CD34 and NF68 were encountered rarely and all tumors were negative for HMB45, KIT, DOG1/Ano 1, smooth muscle actin, desmin, and synaptophysin. None of the 9 tumors studied contained gastrointestinal stromal tumor-specific KIT or PDGFRA mutations. Fluorescence in situ hybridization studies revealed multiple signals with BCR probe (chromosome 22) and centromeric probes for chromosomes 2 and 18 suggesting polyploidy. These findings indicate that gastric schwannoma is a distinctive form of peripheral nerve sheath tumor that in many ways differs from soft tissue schwannoma. It should be distinguished from gastrointestinal stromal tumor and other mesenchymal tumors of the gastrointestinal tract, such as the S100 protein-positive gastrointestinal clear cell sarcoma and metastatic melanoma.

Fig. 1

Age and sex distribution of 51 gastric schwannomas.

Fig 2

Gross appearance of two gastric schwannomas. The upper panel shows and endophytic, sessile polypoid tumor with a whitish to pale tan surface of sectioning of an unfixed specimen. The lower panel contains a portion of a fixed tumor with a yellowish surface on sectioning. Mucosa is seen on top left.

Fig. 3

Low magnification features of gastric schwannoma. A, B. Peripheral lymphoid cuff with occasional germinal centers. C. Lymphoid infiltration entrapped smooth muscle elements within the tumor. D. Tumor involves muscularis propria in an infiltrative manner.

Fig. 4

Histologic details of gastric schwannoma. A. Tumor cells show a microtrabecular architecture with interspersed fibromyxoid matrix. B. An example with a more solid to fascicular pattern. C. Focal nuclear palisading. D. Moderate nuclear atypia was often focally present.

Fig 5

Immunohistochemically typical features include positivity for S100 protein and GFAP. Both markers highlight a microtrabecular pattern. Tumor cells are negative for CD34 and SMA; the positive cells represent non-tumor elements: fibroblasts/endothelial cells and smooth muscle cells/pericytes, respectively.

Fig. 6

Both the BCR locus-specific probe and the chromosome 2 centromeric probe reveal multiple gene copies in large cells representing the neoplastic cells of gastric schwannoma.