Microcystic/Reticular Schwannoma of the Mandible First Case Report and Review of the Literature

Schwannoma comprises a group of nerve sheath tumors. Morphologic variants of schwannoma have no distinct relationship to clinical behavior, but unawareness of rare variants may lead to diagnostic pitfall and risk of mistreatment. Microcystic/reticular schwannoma is a recently described rare variant of schwannoma. We report a case of a 61-year-old female with a 5.0 cm × 3.5 cm × 3.0 cm mass in the right mandible, which has never been reported to date. Light microscopic evaluation showed that the mass was circumscribed with focal infiltration. Arranged in a prominent microcystic and reticular growth pattern, tumor cells were spindle-shaped with eosinophilic cytoplasm. No evidence of cytologic atypia, mitosis, or necrosis was observed. The stroma of the tumor mainly contained myxoid material with local infiltration of hyalinized collagen. Tumor cells showed diffuse and strong nuclear and cytoplasmic immunoreactivity for S100 protein. Tumor cells were also positive for CD34, CD99, and NSE, but negative for CK, EMA, CK5/6, P63, Calponin, CD10, SMA, Desmin, GFAP, NF, Syn, and CgA. The proliferation marker MIB-1 showed <1% nuclear reaction. Furthermore, we reviewed the clinical and pathological features of 24 previously reported cases of microcystic/reticular schwannoma. Unlike classic schwannoma, the reticular variant showed striking microcystic and reticular architecture microscopically. Recognition of these distinct entities is essential in avoiding misdiagnosis. Unlike classic schwannoma with a complete capsule, some masses were reported to lack encapsulation or contain focal infiltration. Further follow-up of tentative or identified cases is necessary to better understand this schwannoma.