This was a tough one both in seeing the abnormality and getting the actual diagnosis ( how about we go half credit for each)

The finding is the left 5th rib.. and yes, it is there. noticed the very long segment of marked lytic appearance with expansion and somewhat scalloped margins. Note the history has really nothing to do with the finding. Yes, the first thing you should think is metastatic disease (I didn’t give you an age), but how about benign conditions. And would you expect such extensions remodeling and bony involvement from a solitary bone met? Any soft tissue mass? (ok, I won’t fault you for getting the CT but make sure you have an idea on how to tell the difference - remember that a majority of bone tumors are differentiated bases on their plain film findings, not necessarily cross-section findings)

Answer: Fibrous dysplasia.

70-80% of fibrous dysplasia is monostotic AND the most common site of monostotic FD is the rib. So this is a “fairly” common rib lesion. All this things I mentioned above should tend you towards FD (especially the extensive nature with lack of any other bone involvement), but I won’t fault you for including mets as a possibility.

Blatant rip from Radiopeadia:

Radiographic features

Plain film

• ground-glass opacities
• may be completely lucent (cystic) or sclerotic
• well circumscribed lesions

Pelvis + ribs

Ribs are the most common site of monostotic fibrous dysplasia. Fibrous dysplasia is the most common cause of a benign expansile lesion of a rib (see rib lesions)

http://radiopaedia.org/articles/fibrous-dysplasia

Lots-o-info: http://www.ajronline.org/doi/full/10.2214/ajr.182.6.1821389

Kransdorf’s article from 1990 is good but pictures are very dated: http://pubs.rsna.org/doi/pdf/10.1148/radiographics.10.3.2188311

If you’re interested, neat link I found while regarding the discovery of what is believed to be fibrous dysplasia in the RIB of a Neanderthal skeleton. Kind of shows you what the bone really looks like grossly. http://www.the-scientist.com/?articles.view/articleNo/37152/title/A-Bone-Deep-Kinship/