Schwannomas and neurofibromas are slow-growing, benign nerve sheath tumors that arise either eccentrically from peripheral myelin-producing cells or centrally from intraneural support cells, respectively. When located in deep tissues, they often have a distinctive MRI appearance. Small, asymptomatic lesions can be observed. Excision of symptomatic tumors is easier for schwannomas, due to their eccentric origin.
Broad age range, majority present in the third to fifth decades
Often incidental finding
Once discovered, demonstrate slow growth
Larger lesions may produce mild, intermittent pain, sometimes for years
Schwannomas more commonly intermuscular, in the lower extremity
Neurofibromas have a more diffuse distribution
Fusiform shape with rim of surrounding fat
Entering and exiting nerve fiber
Deep lesions are more distinctive
Schwannomas (neurilemmomas) often have a distinctive appearance on imaging, as seen on these thigh ( left ) and ankle ( right ) T1 MRI images.
Imaging characteristics include intermuscular location, small amount of surrounding fat, ovoid shape, and, when in large nerves, tubular structures entering and exiting the mass eccentrically.
T2 MRI of a thigh schwannoma shows high signal, reflecting the high water content of the myxoid tissue ( left ).
Benign nerve sheath tumors enhance to a variable degree with gadolinium administration ( arrow ), as seen on this axial thigh image ( right ).