27-year-old female presents for evaluation of the right thigh mass. There is a large mass within the proximal thigh posteriorly that appears to arise from the sciatic nerve. It measures approximately 7 cm x 5.5 cm in the transaxial dimension and 8.5 cm in the cranial caudal dimension (measured approximately 6.5 cm x 5 cm x 8.2 cm on previous study). It is situated between the distal fibers of the gluteus maximus muscle and the hamstring musculature and extends posteriorly to just beneath the skin surface.It is isointense to skeletal muscle on isolated T1 images, heterogeneous on fat suppressed T2 images with components that are both isointense and hypointense to skeletal muscle, and there is diffuse heterogeneous enhancement following contrast administration. Small foci of signal void along the posterior margin of the mass suggest prior intervention (presumably a surgical biopsy). Additional smaller cutaneous and subcutaneous lesions in the thigh are noted. Similar to those seen on the prior study. The remainder of the musculature of the thigh appears normal and the bones appear normal. Small cutaneous neurofibromas are seen on the left thigh on the large field-of-view images.
Slight enlargement of peripheral nerve sheath tumor arising from the sciatic nerve as described above. While it is impossible to exclude a malignant peripheral nerve sheath tumor, the relatively slow growth as well as the similar signal characteristics to the prior study argue against malignant transformation.