Presentation
Painful swelling of the left forearm.
Patient Data
Large expansile eccentric ovoid bony lytic lesion (frontal, oblique) at the junction middle-distal third of the ulnar diaphysis of subperiosteal location with smooth margins, multiple internal bony septa as well as thinning with irregularity of the adjacent cortex.
Well-circumscribed multiseptated ovoid mass with multiple fluid-fluid levels within. No internal flow is seen on the color Doppler.
Multiloculated expansile subperiosteal cystic mass composed of numerous thin-walled cystic cavities containing fluid-fluid levels (blood products) with enhanced internal septa. It communicates with the medullary cavity through a cortical breach.
Case Discussion
The radiographic, ultrasound, and MRI features in an adolescent are highly suggestive of aneurysmal bone cyst (ABC).
The subperiosteal location of ABCs is rarely described in the literature 1,2. They more commonly affect the diaphysis of the long bones (as in this case) compared to classic ABCs that often affect the intramedullary region of the metaphysis 1.
The main differential includes both lesions with intrinsic fluid-fluid levels (please see fluid-fluid level containing bone lesions) and those from which an aneurysmal bone cyst may arise (chondroblastoma, fibrous dysplasia, giant cell tumor, and osteosarcoma especially telangiectatic osteosarcoma).
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