Abstract

Schwannomas are common benign cutaneous tumors, of which several variants are known to exist. Some subtypes of schwannomas can pose diagnostic challenges. Neuroblastoma-like schwannomas (NLS) are among the rare variants. In this report, we contribute an additional case of neuroblastoma-like schwannoma with INI1 loss by immunohistochemistry. A 38-year-old man presented with a long-standing asymptomatic lesion of approximately 4-5 years, that slowly grew over time and became pigmented. He had no clinical history of neurofibromatosis, evidence of café au lait macules, lisch nodules, or axillary freckling. Dermatologic examination revealed a 3.0 cm rubbery, mobile nodule with overlying hyperpigmentation and effacement of skin markings in the right upper flank. Histologic examination revealed a well-circumscribed neoplasm composed of large collagenous rosettes, surrounded by small monomorphic round cells with hyperchromatic nuclei. No significant cytologic atypia or necrosis was detected. The cells were diffusely positive for S100, had a low proliferative index, and demonstrated INI1 loss by immunohistochemistry. This was consistent with NLS. The patient has had no recurrence or metastasis one year following the diagnosis. The recognition of the microscopic features and immunohistochemical phenotype of NLS is important in order to make an accurate diagnosis of this rare subtype of schwannoma, and to distinguish this entity from the other histologic mimics.