Purpose or Case Report: Background:
Conventional medullary osteosarcoma is a malignant bone-forming tumor characterized by the production of osteoid matrix by malignant mesenchymal cells. Although it is the most common primary malignant bone tumor in children, primary osteosarcoma of the spine is exceptionally rare, accounting for less than 5% of pediatric osteosarcomas. Symptoms are frequently nonspecific, and early radiographic clues may be subtle. Due to its rarity and nonspecific presentation, spinal osteosarcomas are often diagnosed late, typically after structural destruction or neurologic compromise has occurred.

Case Report:
A 12-year-old female presented with two months of progressive low back pain and an unintentional 15-pound weight loss. She denied weakness, sensory loss, or bowel/bladder dysfunction. Lumbar spine radiographs revealed a lucency of the left L2 pedicle, producing a “winking owl sign.” Follow-up CT demonstrated a lytic, destructive lesion with asymmetric enlargement of the left psoas and paraspinal musculature. Additionally, CT was useful in demonstrating the presence of osseous matrix within the primary tumor. MRI revealed an expansile, enhancing lesion centered in the left posterior elements of L2, with paraspinal soft-tissue extension and circumferential epidural involvement causing moderate to severe canal stenosis. Biopsy confirmed the diagnosis of conventional medullary osteosarcoma. The patient remained neurologically intact and was referred for multidisciplinary oncologic management.
Methods & Materials:
Results:
Conclusions: This case represents a rare primary spinal osteosarcoma in a pediatric patient, presenting with the classic winking owl sign and aggressive cross-sectional imaging features. Multimodality imaging accurately defined the local and distant extent of disease, guiding surgical and oncologic treatment. Recognition of this radiographic sign and correlation with advanced imaging are essential for early diagnosis of spinal osseous malignancy, which carries significant implications for prognosis and treatment strategy.