Superficial plexiform schwannoma of the skin and subcutis: Clinicopathological study of 48 cases

To study the clinicopathological characteristics of a large cohort of cutaneous plexiform schwannoma. A total of 48 cases of plexiform schwannoma were collected. Clinical and pathological features including age, location, location within the dermis, histology, immunohistochemical features, treatment and clinical follow-up were collected by reviewing glass slides or abstracted from the medical record. The patients were 22 women and 26 men aged 6-84 years (mean: 43). The tumours arose in the extremities in 17 patients, trunk in 17, head and neck in 12, and buttock in 2. The tumours were all superficially located and confined to the dermis, subcutis, or both and measured from 0.3 to 6.0 cm (mean: 2.0 cm). The tumours were all well-circumscribed and showed a multinodular, plexiform pattern of growth. Histologically they showed features of Antoni type A in 30 cases, Antoni type B in 3, and a combination of type A and type B in 15. Immunohistochemical stains in all cases were positive for S100 and SOX10 and showed peripheral condensation of EMA and CD34 positive perineurial cells. The Ki-67 index was low in all cases (1%-2%). Seven patients (12.5%) had type 2 neurofibromatosis (NF2). All patients were treated by complete surgical excision. Clinical follow-up from 13 months to 5 years was available in 16 patients; there was no evidence of recurrence or metastases. Plexiform schwannomas arising in the skin and subcutis are indolent. A subset shows an association with neurofibromatosis type 2.