Melanotic Schwannoma, a Deceptive Misnomer for a Tumor With Relative Aggressive Behavior: A Series of 7 Cranial and Spinal Cases

Abstract

The authors present in this article a series of 7 intracranial/spinal cases of melanotic schwannomas that highlight the aggressive nature of these tumors. The series comprises 2 males and 5 females, age range 19 to 50 years, with spinal/paraspinal location in 4/7 (57%), and intracranial (along the trigeminal nerve) location in 3/7 (43%). There was no association with Carney’s complex. All the cases showed similar histology of epithelioid to spindled cytomorphology with vesicular nuclei (including prominent nucleoli) and conspicuous intracytoplasmic melanin pigment. Mitotic activity was seen in 3/7 cases (43%), 2 of which showed atypical forms. Immunohistochemically, all the cases were positive for S100 protein, HMB-45, melan-A and p16 protein; while negative for PDL1. Ki-67 labeling index was >5% in cases with mitotic activity. Two cases were asymptomatic (after 2.5 and 5 years postsurgery), 2 cases (one was mitotically active, while the other had no mitosis) had recurrence 6 months and 3.5 years after initial surgery, respectively, probably suggesting that mitosis alone may not be a robust predictor of biological behavior. These patients were treated with various adjuvant modalities and were alive for 4 years and 3 years of post-therapy period, respectively. Three patients were offered adjuvant radiotherapy, based on presence of aggressive histological features or significant residual tumor. One showed good clinical response. This series highlights the variability of clinical behavior of these neoplasms belying a deceptively bland nomenclature and also highlights the lack of correlation between histological features and biological behavior.