Abstract

Osteoblastoma is a rare osteogenic tumor, accounting for approximately 1% of all primary bone neoplasms. It most commonly arises in the vertebral column, whereas involvement of the ribs is exceedingly uncommon. We report the case of a 41-year-old female who presented with left-sided flank and lower back pain. Plain radiography demonstrated an area of increased radiodensity with superimposition over the posterior arc of the left ninth rib. Subsequent computed tomography revealed a relatively well-demarcated, heterogeneously hyperdense lesion involving the left 9th ribs, measuring 4.1 × 3.9 cm, with compression of adjacent soft tissues and associated thickening of the left pleura. The patient underwent surgical curettage of the lesion. Gross examination showed multiple brownish-red tissue fragments with a firm, bone-like consistency, measuring approximately 4 cm in aggregate. Histopathological evaluation demonstrated interconnecting trabeculae of immature woven bone rimmed by osteoblasts. The osteoblasts were polygonal, with oval to flattened nuclei, finely dispersed chromatin, mild nuclear uniformity, and inconspicuous nucleoli, set within a richly vascularized stroma. No mitotic figures, atypical mitoses, or tumor necrosis were identified. This report highlights a rare osteogenic tumor occurring in an older patient at an unusual anatomical site, which may pose diagnostic challenges by mimicking both benign and malignant bone lesions in routine clinical and pathological practice.