Unilateral posterior vertebral arch osteocartilaginous exostosis causing chronic thoracic compressive myelopathy (non-DISH): a case report

Background: Solitary spinal osteochondroma is an uncommon benign bone tumor, and symptomatic thoracic lesions causing compressive myelopathy are exceptionally rare. Owing to the indolent growth and nonspecific clinical presentation of these tumors, diagnosis is frequently delayed, increasing the risk of irreversible spinal cord injury. Case presentation: A 46-year-old man presented with progressive thoracic myelopathy characterized by gait disturbance, bilateral lower-extremity spasticity, and weakness that had evolved over approximately 20 years. Computed tomography (CT) demonstrated a large unilateral osseous lesion arising from the posterior vertebral arch at the Th1–Th2 level, producing severe dorsal spinal canal stenosis with an approximately 57% reduction in sagittal canal diameter. Magnetic resonance imaging (MRI) could not be performed because of retained metallic orthopedic hardware. Differential diagnosis included ossification of the ligamentum flavum, ossification of the posterior longitudinal ligament, diffuse idiopathic skeletal hyperostosis, congenital spinal canal stenosis, and primary osseous tumors. The patient underwent neuronavigation-assisted posterior decompression with Th1–Th2 laminectomy and en bloc microsurgical excision of the lesion. Histopathological examination demonstrated mature trabecular bone covered by a hyaline cartilage cap, confirming osteochondroma without evidence of malignant transformation. Postoperative CT confirmed complete decompression of the spinal canal. Neurological status remained unchanged in the early postoperative period, with persistent spastic paraparesis, likely reflecting irreversible spinal cord injury secondary to prolonged compression. Conclusion: Solitary thoracic osteochondroma should be considered in the differential diagnosis of chronic progressive thoracic myelopathy, even in the absence of hereditary skeletal disorders or prior trauma. CT plays a pivotal role in diagnosis when MRI is unavailable. Complete surgical excision provides definitive decompression and excellent local control; however, neurological recovery is strongly influenced by the duration of preoperative spinal cord compression, underscoring the importance of early recognition and timely surgical intervention.