Conventional Schwannoma

Most VSs have histopathological features of conventional schwannoma. Although frequently removed in a piecemeal fashion in multiple fragments, a well-formed fibrous pseudocapsule may be identified toward the periphery, and fascicles of the associated parent nerve may also be seen. The VS “capsule” has been shown to hold neoplastic cells, which carries implications with regard to tumor recurrence when “subcapsular dissection” is employed.s. Literatur VSs characteristically show two intermingled, histologically distinct regions, designated Antoni A and Antoni B (Fig. 4‑1 ). Antoni A regions are composed of compact arrangements of elongated cells, arranged as sheets, intersecting fascicles, and, occasionally, palisades. The cells have eosinophilic cytoplasmic processes and indistinct cell membranes.

The nuclei are spindle shaped, tapering and wavy, with uniformly distributed chromatin and inconspicuous nucleoli. The most distinctive palisaded arrangements, termed “Verocay bodies,” are composed of two parallel rows of nuclei separated by a relatively anuclear zone of eosinophilic fibrillary cytoplasmic processes (Fig. 4‑2 ). In contrast, Antoni B regions are relatively hypocellular, with a loose-textured pale-blue, myxoid stroma. The tumor cells in these regions have somewhat more ovoid to rounded nuclei and loosely knit cytoplasmic processes. These Antoni A and B regions can be present in variable relative proportions. Mitotic figures are rarely seen in conventional schwannomas.

Schwannomas are typically well vascularized, with blood vessels ranging from thick walled and hyalinized (Fig. 4‑1 , arrow) to thin walled and dilated. Episodes of prior intratumoral bleeding may result in perivascular hemosiderin deposition. Aggregates of foamy macrophages may be seen, particularly adjacent to Antoni B regions. In long-standing tumors, scattered cells may show degenerative nuclear changes (the so-called ancient change/schwannoma), with markedly enlarged and hyperchromatic nuclei that have lost chromatin texture and may occasionally show intranuclear pseudoinclusions (Fig. 4‑3 ). Foci of bland, infarct-like necrosis, hyalinization, and calcification may also be present in long-standing cases. These findings are of no prognostic significance.

Epithelioid Schwannoma

In some schwannomas, the tumor cells may show epithelioid features, with more abundant cytoplasm, identifiable cell borders, and some degree of nuclear atypia.s. Literatur These may be diagnosed as epithelioid schwannomas when such features are extensive. A recent series of 58 epithelioid schwannomas arising in various systemic sites did not identify any association with adverse outcomes, even in the presence of identifiable mitotic activity and moderate nuclear atypia.s. Literatur

Cellular Schwannoma

Another variant that may rarely be seen in this region is the cellular schwannoma.s. Literatur ^,​ s. Literatur This tumor has high cellularity, is predominantly composed of Antoni A areas, and often has readily identifiable mitotic figures. However, even with elevated mitotic activity (generally no more than 4 mitoses per 10 high-power fields), these tumors have been well established to behave akin to conventional schwannoma. The significance of recognizing this variant lies in averting misdiagnosis as a malignancy and potential overtreatment.