Melorheostosis of a rib

Case contributed by Dr Domenico Nicoletti

Presentation

Incidental finding in an asymptomatic adult patient.

Patient Data

Age: 45 years
Gender: Female
X-ray

Posteroanterior chest radiograph shows irregular flowing hyperostosis along the first left rib.

CT

Sclerotic lesion arising from the lateral aspect of a first left rib, extending along its external cortex, with a "dripping candle wax" appearance.

To rule out malignancy or processes other than melorheostosis, a rib biopsy was performed.

Histology                                                                                                                

Abundance of osteoid and increased angiogenesis with numerous osteoclasts. Intramembranous ossification with the increase in the activity of the immature osteoblasts, and an irregular diameter of the Haversian canals with an irregular lamellar pattern in the trabecular area. Diagnosis: melorheostosis.

Case Discussion

Melorheostosis is uncommon in the axial skeleton and is very rare in the ribs. Diagnosis is made radiographically with a "dripping candle wax” appearance with dense hyperostosis that flows along the cortex of the bone. When occurring in an atypical anatomical location, melorheostosis may be misinterpreted as an aggressive lesion. Typical "dripping candle wax" sign and absence of aggressive features, such as cortical disruption and/or a soft tissue component, should make imaging-based confident diagnosis of melorheostosis possible even outside the appendicular skeleton. The subtlest forms of melorheostosis present more difficulties in differential diagnosis, raising possibility of a periosteal osteosarcoma or myositis ossificans.

Radiographer: TSRM Fabio Imola

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