Plexiform Cellular Schwannoma in Infancy and Childhood: A Clinicopathological Study of Seven Cases of an Underrecognized Nerve Sheath Tumor with a Tendency Toward Local Recurrence.

Plexiform cellular schwannoma (PCS) is very rare, and it is not completely understood. We present our experience with 7 additional cases of PCS in infancy and childhood to further characterize its distinctive clinicopathological features. There were 5 females and 2 males with a mean age of 28 months (ranging, 2 months to 8 years). The involved sites included the left forearm (n = 2), sacrococcygeal region (n = 2), retroperitoneum (n = 1), thoracic spinal canal and thoracic cavity (n = 1), and neck (n = 1). Tumor sizes ranged from 3 to 13 cm in maximum diameter (mean, 7.1 cm). Histologically, all tumors consisted of abundant spindle cells arranged in a multinodular or plexiform growth pattern, possessing elongated, hyperchromatic nuclei and pale eosinophilic cytoplasm with indistinct cell margins. Mitotic figures were easily identified, with a mean count of 4 per 10 consecutive high power fields (HPF). Immunohistochemically, all tumors were strongly and diffusely positive for S100 protein, SOX10 and H3K27me3. The Ki-67 index ranged from 5% to 30% (mean, 15%). Follow-up (available in 6 cases) revealed that 5 patients experienced local recurrence and were treated by re-excision. There was no evidence of recurrence and metastasis in 3 patients, and the other 2 were alive with the disease. In conclusion, PCS is an uncommon nerve sheath tumor predominantly occurring in infants and children, featuring a plexiform or multinodular growth pattern and exhibiting a tendency toward local recurrence. PCS is easily mistaken as malignant peripheral nerve sheath tumor (MPNST) due to its locally aggressive behaviors and worrisome features, including hypercellularity, hyperchromatism and high proliferative activity. Increased awareness of its potential occurrence and greater familiarity with its characteristic features are helpful for both clinicians and pathologists to avoid misdiagnosis and unnecessary overtreatment.