5/17/2009 case 2

The image above is the follow up examination. The original image demonstrated a pathologic fracture within a lytic lesion. If you look closely, there is a splinter of cortical bone at the bottom of this image which was obtained with the patient upright and represents the "fallen fragment" sign. This sign is consistent with a cystic structure i.e. a simple bone cyst. This is the most common location for a simple bone cyst and 20% of SBC's have the "fallen fragment" sign.

SBC

• originally defined in 1910
• fluid filled cyst commonly in the metaphysis of long bones
• benign
• idiopathic - possibly venous obstruction and blockage of interstitial fluid drainage in an area of rapidly growing/remodeling cancellous bone
• cyst contains serous fluid and maybe blood products
• May have septa especially after fracture.
• wall - mesothelial cells and sometimes multinucleated giant cells
• M:F; 2:1; usually in the first or second decade of life
• usually single - if multiple tend to be older and male
• Humers and femur are most common (esp proximally) ; less common - tib, fib, radius, ulna
• older patients (esp >20) - calcaneus and iliac bone and other flat bones
• Asymmetric unless fx
• X-ray - well defined (geographic), lytic lesion with narrow zone of transition, intramedullary and usually abut the physis. thin sclerotic wall
• May cause thinning and expansion of the bone and can be multiloculated.
• Fallen fragment sign - pathognomonic
• Tx - curretage, bone grafting, steroid injections, cryotherapy, nailing

reference: emedicine.com and http://radiology.rsnajnls.org/cgi/reprint/209/3/884-b?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=fallen+fragment+sign&andorexactfulltext=and&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT