Secondary aneurysmal bone cyst following chondroblastoma of the patella

Abstract

Aneurysmal bone cyst (ABC) is a rare benign cystic lesion of the bone that composes 1-2% of the entire bone tumors. Some are idiopathic, and some occur secondary to other tumors such as giant cell tumor and chondroblastoma. In this article, we report the clinical, radiographic, and histological findings of a secondary ABC following chondroblastoma of the patella with a review of the literature.

Keywords: chondroblastoma; patella; secondary aneurysmal bone cyst.

Figure 1.

Radiograph of the left knee depicting (A) anteroposterior, (B) lateral and (C) skyline view. There is a 1.7×2.4 cm radiolucent area in the medial patella. On MRI, patella lesion is hypointense on T1WI (D) and hyperintense on T2WI (E). Gadolinium-contrast shows a diffusely enhanced lesion in the medial patella (F).

Figure 2.

A) Under the microscope, the tumor was a giant cell lesion with fragmented bones and fibrosis, hemosiderin deposits and mild infiltration of chronic inflammatory cells (H&E stain); B) Monocytes of the lesion was short spindle-shaped and slightly positive with S-100 staining.

Figure 3.

Radiograph at 9 months follow-up. A) Anteroposterior, B) lateral and C) skyline views of the knee. The artificial bone graft is seen in the cavity and no evidence of recurrence or arthritic change is present.