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Diagnosis: Aneurysmal Bone Cyst
Findings:Lucent lesion in the acetabulum demonstrates fluid fluid levels on MRI
Diff Dx:Differential considerations are based on the age of the patient. In addition to aneurysmal bone cyst, lucent pelvic masses in a young patient may represent Ewing sarcoma or Langerhan Cell Histiocytosis (Eosinophilic granuloma). In an older patient, metastatic disease and myeloma may have a similar appearance. Fluid fluid level is a non-specific finding that likely represents a blood filled space. These can be seen in secondary aneurysmal bone cysts related to certain osteosarcomas and other lesions.