Intraneural glomus tumor of "uncertain malignant potential" and with BRAF mutation in the median nerve - an unusual case.

A glomus tumor of uncertain malignant potential is defined as a glomus tumor with some, but not all, criteria for malignancy and without a known metastasis. Here, we present a rare example presenting in the median nerve in a 40-year-old woman with a long history of severely impaired left median nerve function. A large panel of immunohistochemical stains excluded other diagnoses, and the designation of a "uncertain malignant potential" was based on the high proliferative activity, the tumor size and location, and the lack of WHO malignancy criteria such as marked nuclear atypia, necrosis, or atypical mitoses. A BRAF mutation was found in the tumor. Although extremely rare, both benign and malignant glomus tumors may present in large peripheral nerves and should therefore be considered in the differential diagnosis.