We present the case of a 27-year-old man who had a soft-tissue lumbar spine mass causing back, abdominal, and groin pain. Imaging showed the lesion filling the right neural foramen, invading the anterior L2 vertebral body and both pedicles, and protruding into the central canal, causing compression of the thecal sac. The final pathologic diagnosis was a malignant peripheral nerve sheath tumor, with histologic evidence of a precursor neurofibroma. The patient did not have an underlying diagnosis of neurofibromatosis.