HSS Ultrasound of the Month Case 79

Clinical History 3 year-old-girl with a painless lump at the anterior right chest.

Initial work-up included a chest x-ray which revealed no abnormality.

The patient was subsequently referred for an ultrasound (US) to assess for a rib lesion.

Ultrasound of the Month – Case 79

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Ultrasound of the Month – Case 79

Diagnosis: Right Rib Osteochondroma Discussion Osteochondroma is the most common benign tumor of bone.

Common sites of involvement are the long bones in the lower and upper extremity, favoring the metaphysis. Much less commonly, they can be seen in the hands and feet, the pelvis, and the scapula. Spine and rib involvement is rare.

The hallmark of this lesion on imaging is cortical and medullary continuity with the parent bone. The overlying hyaline cartilage cap is well visualized and accurately measured using US, appearing hypoechoic (dark).

Osteochondromas are usually asymptomatic, presenting as a painless, hard and slow-growing lump. After skeletal maturity, these lesions cease to grow.

Although uncommon, complications related to this lesion are largely due to mass effect on adjacent structures, e.g. nerve or vascular impingement, bursal formation.

The risk of malignant transformation of solitary osteochondroma is approximately 1%. A thickened cartilage cap > 2 cm is strongly suspicious for malignancy.

Ultrasound of the Month – Case 79

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