Lumbar Extradural Extraskeletal Ewing Sarcoma with Psoas Denervation: A Case Report

BACKGROUND Paravertebral extraskeletal Ewing sarcoma located in the extradural region is uncommon. Muscle denervation can be caused by nerve injury, destruction of the neuromuscular junctions, and aging-related loss of motor neurons. Psoas denervation caused by spinal extraskeletal Ewing sarcoma is extremely rare. CASE REPORT A 38-year-old Chinese man presented to our hospital with back pain lasting for 1 month. He presented thoracolumbar mobility limitations. Magnetic resonance imaging revealed a well-defined margin extradural soft tissue mass involving the intervertebral foramen and paravertebral region at level L1-L2. The mass measured approximately 31×47×42 mm and demonstrated heterogeneous signal intensity on T1-weighted imaging and hyperintensity on STIR images. Imaging showed psoas compression, with diffuse homogeneous edema. On post-contrast images, the mass showed heterogeneous enhancement, and the edematous psoas showed homogeneous enhancement. Pathological examination of the biopsy specimen revealed clusters of atypical small blue round cells with hyperchromatic nuclei, scant cytoplasm, and frequent mitotic figures. Immunohistochemical analysis of tumor cells demonstrated strong membranous positivity for CD99 and nuclear positivity for NKX2.2. The final diagnosis was extraskeletal Ewing sarcoma. Chest computed tomography revealed multiple nodal metastases. The patient underwent chemotherapy for 4 cycles, and the tumor showed no response to treatment. The patient refused further chemotherapy and took only oral analgesic. He died 12 months after presenting to our hospital. CONCLUSIONS Extraskeletal Ewing sarcoma is a rare subtype in the Ewing sarcoma family of tumors. Spinal extradural extraskeletal Ewing sarcoma is uncommon, and masses compressing the lumbar plexus and causing psoas denervation is extremely rare.