A rare rib lesion due to parosteal osteosarcoma: a case repo
A 23-year-old woman presented at an out-patient clinic with a 9-month history of a painless swelling on the right posterolateral side of her chest wall.

She did not recall any trauma that may be associated with this condition neither did she have a history of genetic disease or cancer. A physical examination revealed a hard, painless mass at the posteroinferior and lateral thoracic region.

On a plain chest radiograph, an area of calcified opacity was observed at the ninth rib, with no destruction of the underlying bone. Computed tomography (CT) demonstrated a mass of 6 cm × 5 cm × 2.5 cm in size arising from the ninth rib. Whole-body scintigraphy and CT did not show any skip or lung metastases. After these examinations, an incisional biopsy was performed.

Histopathologic examination revealed fibroblastic and osteoblastic cells with mild nuclear atypia and pleomorphism which was consistent with parosteal OS.

Osteosarcomas (OSs) are the most frequent primary malignant bone tumor in which neoplastic cells produce osteoids and they usually develop in an intramedullary location. Group OSs which originate from the outer surface of the cortex are known as surface OSs. Parosteal OSs are the most common type of surface OSs and comprise approximately 4% of all OSs. Parosteal OSs develop from the outer fibrous layer of the periosteum and are generally seen around the knee and proximal humerus.

Learning Points:
- Masses which develop on the surface of the rib bones are rare.
- The case reported here is a very rarely seen parosteal osteosarcoma of the rib that was treated with wide resection and chest wall reconstruction.
- Correct diagnosis of parosteal osteosarcoma is challenging. Although rare, in the differential diagnosis of lesions located on the ribs, parosteal osteosarcoma should be considered and a systematic diagnostic approach should be taken.

Source: Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6343249/pdf/13256_2018_Article_1958.pdf
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