Presentation
Incidental finding on prior trauma CT.
Patient Data
Expansile lucent lesion within the neck of the left 10th rib with thin sclerotic margin and narrow zone of transition. Cortex is thinned and deficient in places. No soft-tissue mass outside the bone. No chondroid, osteoid or ground glass matrix. Major differential based on CT appearance would include fibrous dysplasia, enchondroma and aneurysmal bone cyst. Metastasis unlikely in absence of any history of malignancy.
MRI shows the lesion to be centrally low signal on T1 and T2, with peripheral high T2 signal and surrounding mild edema within the marrow of the rib head and posterior rib. The lesion demonstrates low grade predominantly peripheral enhancement. No obvious extra-osseous component. No cystic component of fluid-fluid levels. The appearance in most in keeping with fibrous dysplasia.
Case Discussion
Fibrous dysplasia is relatively common in the ribs. In this case, the CT has a differential diagnosis between fibrous dysplasia, enchondroma, ABC and less likely metastasis. The low T2 signal on MRI of this lesion strongly favors fibrous dysplasia over the other differentials.
The mnemonic FAME can be used to remember the differential for a lucent expansile rib lesion.
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