Benign Nerve Sheath Tumors




Schwannoma (Neurilemmoma) and Neurofibroma


CLINICAL SUMMARY


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.


DIAGNOSTIC FEATURES


















History


  • 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

Location


  • Schwannomas more commonly intermuscular, in the lower extremity



  • Neurofibromas have a more diffuse distribution

MRI


  • Fusiform shape with rim of surrounding fat



  • Entering and exiting nerve fiber



  • Deep lesions are more distinctive




IMAGING




























  • 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 ).


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