HISTORY: 16 year old basketball player presenting with low back pain for 1 year, worsening for 1 month, with night pain for 1 week. No acute injury. Pain at low back and sacrum, worse with flexion. Denies radicular symptoms in lower extremities, bowel/bladder incontinence, gait instability, saddle anesthesia. Recently developed fatigue, anorexia, and urinary hesitancy - requires bladder pressure for voiding. ED eval with neg x-rays; PCP eval with urgent referral to Ortho clinic. PHYSICAL EXAMINATION: Neuro: CN II-XII grossly intact. Normal muscle bulk/tone, slightly guarded gait. MSK: Lumbar spine/Sacrum/Coccyx. Inspection: No ecchymosis or deformity. Palpation: TTP at L2-L5 spinous processes, sacrum, coccyx. No TTP at SI joints, iliac crests, thoracic spine. ROM: 40 deg flexion with pain, 20 deg extension, 20 deg lat bending, 20 deg lat rotation. Neurovascular: Distally NVI, brisk pulses, 2 sec cap refill, sensation intact. 2+ DTRs bilateral patellar and Achilles tendons. No clonus. Special maneuvers: Neg Hyperextension test in prone, Neg SLR test. Neg Slump test. Neg FABER test. Hip ROM full, pain free. Anal sphincter tone normal, perineum sensation intact per PCP. DIFFERENTIAL DIAGNOSIS: 1. Spondylolysis/Spondylolisthesis 2. Syringomyelia 3. Ewing Sarcoma/Osteosarcoma TEST AND RESULTS: XR Sacrum/Coccyx: No visible fracture or malalignment. No significant abnormality in visualized portion of the lumbar spine. Soft tissues radiographically normal. MRI Pelvis: Intradural mass extending at S2-S4 level (measures 1.3 x 2.9 x 5.5 cm), likely impinging cauda equine roots at these levels. Mass causes scalloping of posterior aspects of S3-S4 vertebral bodies. Mass heterogeneous on T1/T2 with peripheral enhancement, but no definite centralenhancement. No definite extension through sacral ala. May represent filum terminale (myxopapillary) ependymoma. Meningioma or nerve sheath tumors less likely, given lack of central enhancement. FINAL WORKING DIAGNOSIS: Ewing Sarcoma TREATMENT AND OUTCOMES: 1. Admission to Neurosurgery. Sacral laminectomy/resection of intradural extramedullary spine tumor 2. Radiation therapy complete (5 mos) 3. Chemotherapy complete (10 mos) 4. Pediatric Urology: urinary hesitancy resolved 5. Surveillance q 3 months with serial imaging 6. Return to activity as tolerated