Nerve sheath myxoma: a clinicopathologic and immunohistochemical analysis of 57 morphologically distinctive, S-100 protein- and GFAP-positive, myxoid peripheral nerve sheath tumors with a predilection for the extremities and a high local recurrence rate.

This report describes the clinicopathologic findings in 57 cases of nerve sheath myxoma. Our study group included 34 males and 23 females, ranging from 8 to 72 years of age at the time of their first surgical procedure (mean, 36 years; median, 34 years). The patients typically presented with solitary, superficial, multinodular masses in the 0.5- to 2.5-cm size range. Eighty-six percent of cases occurred in the extremities, with the most common locations being the hand/fingers (n = 22), knee/pretibial region (n = 10), and ankle/foot (n = 7). Only 7 cases (12.3%) involved the trunk or head and neck region. The tumors were generally slow growing, and often, they were present for many years before surgical resection was sought. In the majority of instances, the lesions were painless. Histologically, the tumors involved the dermis and/or subcutis, and they formed distinct multinodular/multilobular masses with abundant myxoid matrix and a peripheral fibrous border. All cases had small epithelioid Schwann cells in corded, nested, and/or syncytial-like aggregates, a variable number of Schwann cells with a ring-like appearance, and scattered spindled and stellate-shaped Schwann cells. These cells often had cytoplasmic-nuclear invaginations, and they were immunoreactive for S-100 protein, glial fibrillary acidic protein, neuron specific enolase, and CD57. They were also bordered by collagen IV. Epithelial membrane antigen-positive perineurial cells were typically present in small numbers, primarily in the fibrous tissue directly adjacent to the myxoid nodules. CD34-positive intraneural fibroblasts were generally sparse. Mitotic figures were uncommon. All cases were initially managed by simple excision, and in almost all instances, tumor extended to the tissue edge. Follow-up information is available for 34 patients (follow-up range, 8 months to 28 years; median follow-up interval, 14 years 3 months). Sixteen patients (47%) had one (n = 11) or more (n = 5) local recurrence of their tumor, and 2 additional patients had findings suspicious for a recurrence. Nerve sheath myxomas are morphologically distinct peripheral nerve sheath tumors with a peak incidence in the fourth decade of life and a strong predilection for the extremities. These tumors have a relatively high local recurrence rate when managed by simple local excision. They appear to be unrelated to so-called cellular and mixed-type neurothekeomas.