Neurofibroma

Neurofibroma is a benign lesion of unknown origin that may occur in peripheral nerve, soft tissue, skin or bone. It occurs as a solitary lesion more commonly than as a multiple lesion or in neurofibromatosis (NF-1 or von Recklinghausen's disease). NF-1 is characterized by neurofibromas, acoustic nerve schwannomas, Lisch nodules and cafe-au-lait spots. Neurofibromas that occur as part of von Recklinghausen's disease are generally larger than solitary lesions and have a 4% chance of malignant transformation.l Solitary lesions most commonly present from age 20 to 30 and often arise as a superficial painless mass in the dermis. Neurofibromas may form in the brachial plexus, lumbrosacral plexus, peripheral nerve or spinal nerve.

On plain x-ray, if the neurofibroma involves the bone it may appear as an intraosseous lytic lesion. The lesion visible on plain film may be a neurofibroma that has worked into the bone by pressure erosion or it may be a non-ossifying fibroma that is associated with NF-1. On ultrasound, a neurofibroma is a well-defined hypoechoic mass. On CT scan, a neurofibroma is a hypodense, well-defined mass. On a T2 weighted MRI the lesion is bright and may have a central low density which gives a "target" appearance. The lesion appears hyperintense on T1 weighted MRI. The term "dumbbell" lesion is used to describe a neurofibroma that is enlarging the intervertebral foramen.

On gross appearance, a neurofibroma is a firm, gray-white mass with no capsule. They vary in size from a few millimeters to four to five centimeters.

Microscopically, neurofibromas are made of interlacing bundles of elongated cells. These cells are bland and disorderly with intracellular collagen strands. Neurofibromas have variable S-100 expression and nerve fibers should be present. There are two types of neurofibromas: solitary and plexiform. Solitary neurofibromas are well delineated and firm lesions that are white and shiny in appearance. Plexiform neurofibromas are multifocal myxoid lesions that are often described as a "bag of worms". Plexiform neurofibromas are diagnostic of von Recklinghausen's disease.

Patients with NF-1 should perform regular self-exams to detect tumors early. Close follow up of these patients is necessary due to the high rate of malignant transformation. Treatment, if necessary, is surgical excision.

References
^l Beggs, I, Pictorial Review: Imaging of Peripheral Nerve Tumors, Clinical Radiology, 52:8-17,1997.

Bulloughs, Peter, Orthopaedic Pathologv (third edition), Times Mirror International Publishers Limited, London, 1997.

Cotran, Robbins and Kumar, Robbins Pathologic Basis for Disease, W.B. Saunders, Co., 1994.

Huvos, Andrew, Bone Tumors:Diagnosis. Treatment and Prognosis, W.B. Saunders, Co., 1991.

Adapted, with permission from bonetumor.com By Henry DeGroot III, M.D.