Peripheral nerve sheath tumors in Neurofibromatosis Type 2: Surgical and histopathologic features

Management of peripheral nerve sheath tumors (PNST) in Neurofibromatosis Type 2 (NF2) is complicated by frequent involvement of major peripheral nerves and concern that these tumors may be plexiform and/or involve multiple fascicles. Hybrid histologic features of both schwannoma and neurofibroma have been described in NF2-associated tumors, although the incidence of this phenotype in PNSTs is unknown. We sought to define the outcomes of surgery for tumors involving major peripheral nerves in NF2 and identify the rate of hybrid histology in PNSTs.

Functional outcomes of surgery for patients with tumors on major (named) peripheral nerves were recorded. Histopathologic analyses were performed on all available excised tumors.

Nineteen operations were performed in 12 patients with NF2, for resection of 28 PNSTs. Among 11 tumors involving major peripheral nerves, 10 involved nerves related to motor function. Presenting symptoms in this group included pain (9) and weakness (4). Median tumor diameter was 3.4 cm (range:2.2-10.3 cm). Gross-total resection was achieved in 10 cases. Motor function was stable/improved in 10 cases but diminished after one case involving a small motor fascicle. All tumors involved a single fascicle. Histopathologic analyses of 21 available specimens revealed 19 pure schwannomas. In two cases (10 %) hybrid features of both schwannoma and neurofibroma were identified, with mast cells within regions consistent with neurofibroma.

PNSTs can be resected safely in NF2, even if they involve major peripheral nerves. A small proportion (10 %) of these tumors harbor hybrid histologic features, which may explain reports of plexiform or multi-fascicular tumors in NF2.