Presentation
Left-arm mass felt for a few months, not increasing in size with occasional pain
Patient Data
Left anterolateral mid-arm irregular bony mass lesion seen broad-based on the outer cortex of mid humeral diaphysis with no line of cleavage. The lesion is seen projecting within the deltoid muscle. No definite continuation with the humerus medullary cavity. No evidence of osseous or soft tissue aggressive changes. It elicits typical fatty signal in all pulse sequences (high signal in T1 T2 and suppressed in STIR).
CT study shows a well-marginated wide-based bony growth on the outer cortex of mid humeral diaphysis, projecting into the soft tissues, appear well-formed bone with medullary cavity and outer cortex however, there is no evidence of continuation with the humeral medullary cavity. No associated aggressive or destructive changes.
Case Discussion
Bizarre parosteal osteochondromatous proliferations, also known as Nora lesions, are benign exophytic osteochondral lesions that have an appearance similar to an osteochondroma and are typically seen in the hands and feet. This case is atypically showing this lesion involving the humerus
On imaging, Nora lesions are shown to be continuous with the underlying cortex, but usually without continuation of the medulla, however, radiographic features alone cannot reliably diagnose the lesion. Differential diagnosis includes myositis ossificans and bone surface osteogenic or chondrogenic tumors.
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