Abstract
We present a case of a surface aneurysmal bone cyst in a 19-year-old boy. Plain radiograph showed an osteolytic lesion with sclerotic margin and interrupted lamellar periosteal reaction at the posterolateral aspect of the diaphysis of the left proximal femur. MRI confirmed a bony lesion containing a fluid-fluid level (FFL) on T2-WI. Bone marrow oedema was seen within the femoral diaphysis and the soft tissue changes adjacent to the femoral cortex were enhancing. Because of the aggressive appearance on imaging, the patient underwent a biopsy and the final diagnosis of a subperiosteal aneurysmal bone cyst (ABC) was made. The patient was treated with curettage of the lesion.
Highlights
Plain radiograph showed an osteolytic lesion with sclerotic margin (Fig. A, black arrow) and interrupted lamellar periosteal reaction (Fig. A, white arrow) at the posterolateral aspect of the diaphysis of the left proximal femur
Surface aneurysmal bone cyst (ABC) may have irregular margins and are often associated with periosteal reaction mimicking an aggressive lesion on plain radiographs
Extent of fluid-fluid levels may be helpful in differentiating ABC from a malignant lesion causing FFL
Summary
Plain radiograph showed an osteolytic lesion with sclerotic margin (Fig. A, black arrow) and interrupted lamellar periosteal reaction (Fig. A, white arrow) at the posterolateral aspect of the diaphysis of the left proximal femur. Magnetic resonance imaging (MRI) was performed for further characterization of the lesion. T2 weighted images (WI) showed a cortical bone defect and an interrupted shell-like periosteal reaction (Fig. B, white arrow) containing a fluid-fluid level (FFL) (Fig. B, black arrow) at the posterior aspect of the left proximal femur shaft. Contrast-enhanced T1-WI showed a multi-cystic appearance with contrast-enhancing cyst walls (Fig. C, black arrow).
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