Giant Solitary Osteochondroma of the D4 Spinous Process in an Adolescent Managed by Multilevel En Bloc Posterior Element Resection: A Case Report

Osteochondroma is the most common benign bone tumor; however, a solitary osteochondroma of a thoracic spinous process is rare, and a giant lesion in an adolescent can resemble an aggressive posterior spinal tumor.We report the case of a 17-year-old boy who presented with a four-month history of a painless, slowly enlarging swelling in the middle of the upper back.Examination showed a hard, fixed, nontender mass at the D4 level, with splaying of the transverse process and no neurological deficit.Computed tomography (CT) of the thorax showed an irregular bony outgrowth measuring 3.8 × 5.6 × 4.9 cm and arising from the D4 spinous process, with no lung or mediastinal disease.Magnetic resonance imaging (MRI) showed a bony mass measuring 4.0 × 5.9 × 5.4 cm and arising from the D4 posterior elements, with a thin cartilage cap and no extension into the spinal canal.Surgery was performed through a posterior midline approach with the patient in the prone position.A 6 × 7 cm exostosis at the D3-D4 interspinous region was removed in one piece, together with part of the D2 spinous process and the entire D3 and D4 spinous processes.Both laminae and the facet joints were left intact, and no implant was needed.The specimen weighed 97 g and measured 6.8 × 7.5 × 6.0 cm.Histopathology confirmed a benign osteochondroma with a cartilage cap measuring approximately 1.5 cm on gross bisection and 0.8 cm on microscopy, with orderly endochondral ossification, a cancellous core, and no atypia.Recovery was uneventful (Clavien-Dindo grade 0); the drain was removed on the sixth day after surgery, and the patient was discharged home in good condition.Multilevel en bloc resection of the posterior elements achieved complete excision without instability or nerve injury.Measuring the cartilage cap on the cut specimen during surgery is a simple and useful step that guides the pathologist in assessing the possibility of malignant change.