Lumbosacral plexiform neurofibroma: a rare case in an adult without neurofibromatosis type I.

Plexiform neurofibromas are an uncommon variant of neurofibromas that are described as being essentially pathognomonic of neurofibromatosis type 1 (NF1). Plexiform neurofibromas in the absence of NF1 are extremely rare. We present the case of a 38-year-old woman with a large multilobulated lumbosacral mass extending into the pelvis and proximal thigh. Histopathology of a CT-guided biopsy of the mass revealed it to be a neurofibroma. The imaging findings were consistent with a plexiform subtype. Further imaging and clinical workup showed that the patient had no other identifiable neurofibromas and did not meet criteria for the diagnosis of NF1.