Case report: primary aneurysmal bone cyst of the epiphysis

Abstract

Aneurysmal bone cysts are benign active or aggressive bone tumors that commonly arise in the long bones, especially the femur, tibia, and humerus and the posterior elements of the spine. Aneurysmal bone cysts affect all age groups but are more common before skeletal maturity (first two decades of life). They usually involve the metaphysis or metadiaphyseal region of long bones. Although juxtaphyseal lesions abutting the growth plate and extending into the epiphysis have been described, there is no report of an aneurysmal bone cyst entirely and primarily located in the epiphysis. We report on a 3-year-old boy who presented with an entirely contained aneurysmal bone cyst to the proximal tibial epiphysis. We discuss the clinical presentation, diagnosis, including imaging and pathology, and treatment. A review of the pertinent literature also is presented.

Fig. 1A–G

(A) Anteroposterior and (B) lateral radiographs of the knee show a well-defined, eccentric, radiolucent lesion confined in the proximal tibial epiphysis. (C) Coronal and (D) sagittal CT scans show the extent of primary involvement and close proximity to the articular cartilage and growth plate. (E) Axial, (F) sagittal, and (G) coronal T2-weighted MR images show characteristic fluid-fluid levels caused by the different densities of the cyst fluid attributable to the setting of red blood cells, preservation of the physis, and articular surface.

Fig. 2A–B

(A) The initial biopsy specimen shows predominantly solid areas with a few cyst walls (upper left) and abundant blood and fibrin (lower right) (Stain, hematoxylin and eosin; original magnification, ×2). (B) A higher-power view of the tumor shows the bland spindle cell background and evenly distributed multinucleated giant cells. There are areas of hemorrhage in the tumor with hemosiderin pigment accumulation (middle of picture) (Stain, hematoxylin and eosin; original magnification, 20×).

Fig. 3A–E

Followup images show recurrence of the ABC. (A) Anteroposterior and (B) lateral radiographs show resorption of the bone graft and recurrence of the lytic lesion. (C) Axial, (D) sagittal, and (E) coronal T2-weighted MR images confirm a recurrent lesion without any evidence of articular cartilage or growth plate arrest.

Fig. 4A–B

(A) The resection specimen shows even more classic features of an ABC with variably sized cyst spaces, which are lined by lesional cells instead of vascular endothelium. In the walls of the cysts is a bland spindle cell proliferation with uniformly scattered multinucleated giant cells, immature bone and cartilage, hemorrhage, and hemosiderin deposition (Stain, hematoxylin and eosin; original magnification, ×4). (B) A higher-power view of the lesion shows bland spindle cells and scattered multinucleated cells (Stain, hematoxylin and eosin; original magnification, ×10).

Fig. 5A–B

(A) Anteroposterior and (B) lateral radiographs obtained at the 1-year followup show resolution of the lesion with no signs of residual cysts or recurrence. Clinically, the patient was pain free, had full ROM, and had returned to activity without limitations.