Pediatric Non-vestibular Schwannoma.

While the clinicopathologic features of pediatric vestibular schwannomas, often in the context of neurofibromatosis type 2 (NF2), have been well studied, there is less data regarding the characteristics of pediatric non-vestibular schwannomas (NVS). Additionally, the rate of loss of SMARCB1/INI1 expression in this population has not been systematically evaluated. Our institutional archives were searched for cases of NVS arising in patients 18 years or younger. Clinicopathologic features including SMARCB1/INI1 status were assessed for each case. Twenty-three NVS from 9 males and 13 females (age range, 2 months to 18 years) were identified, and sites included paraspinal (n = 10), head and neck (n = 6), extremities (n = 4), trunk (n = 1), mediastinum (n = 1), and retroperitoneum (n = 1); 22 cases were Antoni A predominant with 6 cases comprising solely Antoni A tissue. The mitotic rate of the tumors ranged from 0 to 10/10 high-power fields (HPFs), and 3 tumors had mitotic rates of ≥4 mitoses/10 HPFs. Two tumors showed plexiform architecture. No NVS showed diffuse atypia, calcifications, microcystic/reticular architecture, epithelioid morphology, pseudoglandular change, neuroblastoma-like features, or necrosis. All tumors tested (23/23) showed retained nuclear expression of SMARCB1/INI1. Follow-up was available in 21 patients (range 1 week to 194 months), and 5 tumors recurred. Pediatric NVS have a relatively homogeneous appearance with a predominance of Antoni A areas. Pathologists should be aware that schwannomas in this age group may be cellular with mitotic rates of ≥4/10 HPFs to avoid misclassification as a spindle cell sarcoma.