Osteochondromyxoma; occurring in an adult at an unusual location

Osteochondromyxoma (OCHM) is an extremely rare benign, sometimes locally aggressive chondroid and osteoid matrix–producing tumour with extensive myxoid changes. It is seen in approximately 1% of patients with Carney complex (CNC) and constitutes one of its 11 diagnostic criteria. We report a case of a 36-year-old man who presented with an incidentally detected chest wall mass. Computed tomography (CT) suggested an osteochondroma. Intraoperatively, a globular, fragile lesion was identified arising from the posterior aspect of the seventh rib, and piecemeal excision was performed. Microscopically, the fragments showed a thick fibrous capsule enclosing mature bony trabeculae and hypocellular marrow spaces, with areas of fibro-myxoid stroma containing short plump to oval spindle cells with bland nuclei, with no atypia, mitoses, or necrosis. Systemic evaluation revealed no spotty skin pigmentation, breast lumps, or thyroid enlargement. Ultrasound of the thyroid and testes, echocardiogram, and adrenal imaging were unremarkable. Endocrine evaluation including serum cortisol, ACTH, and growth hormone levels was normal, excluding syndromic association. Although PRKAR1A mutation analysis, a supplementary criterion for CNC, was suggested, it was not performed. OCHM is an exceedingly rare benign bone tumour with an excellent prognosis following complete excision. Considering the patient’s age and absence of clinical or endocrine features of CNC, this case most likely represents an isolated OCHM. However, long-term multidisciplinary follow-up is essential, as patients may develop diagnostic criteria for CNC in the future.