Malignant Peripheral Nerve Sheath Tumor Arising Within Lumbar Spinal Plexiform Neurofibroma.

A 41-year-old woman presented with a 16-year history of lumbar pain and right leg paresthesia. Twenty-four years previously, she had been diagnosed with neurofibromatosis type 1 syndrome. Magnetic resonance imaging showed a heterogeneous mass extending through widened lumbar neural foramina to the psoas muscles bilaterally, with a dumbbell-like appearance. Biopsy led to the diagnosis of a malignant peripheral nerve sheath tumor, an uncommon soft tissue sarcoma of neural origin that may occur in the context of neurofibromatosis type 1 syndrome. Given the aggressive behavior of these tumors, prompt and accurate diagnosis is critical to improve patient outcomes.