Test yourself answer: pain in the right hemithorax

Abstract

Objective: This case report describes a rare osteoblastoma involving the posterior aspect of the right fourth rib presenting with right-sided hemithoracic pain. CT demonstrated an expansile lytic lesion with cortical erosion, concentric periosteal reaction involving adjacent ribs, and reactive pleural effusion. MRI revealed avid contrast enhancement, extensive bone marrow and soft tissue edema, and pleural enhancement, findings that could mimic an aggressive malignant tumor. Dynamic contrast-enhanced MRI demonstrated rapid enhancement with washout in the tumor nidus, whereas the surrounding edema and pleural effusion showed gradual enhancement, consistent with the flare phenomenon rather than tumor extension. Histopathological examination following surgical resection confirmed osteoblastoma with tumor-free margins. The report emphasizes that osteoblastoma is an uncommon benign but locally aggressive bone tumor, with rib involvement being rare. Recognition of the flare phenomenon and correlation between CT and MRI findings are essential to avoid misinterpreting reactive inflammatory changes as malignant invasion. Dynamic contrast-enhanced MRI is highlighted as a valuable tool for distinguishing the tumor nidus from peritumoral inflammation, thereby improving diagnostic accuracy and guiding appropriate management.