Histology can be predictive of the clinical course of a primary aneurysmal bone cyst.

INTRODUCTION: Aneurysmal bone cyst is a benign lesion occurring in young patients which frequently recurs after treatment. Biopsy is mandatory for the diagnosis of a putative aneurysmal bone cyst as this lesion can be secondary to another underlying process including a malignant bone tumour. The histopathological features of aneurysmal bone cysts have been examined with the goal of finding relevant criteria for predicting favourable evolution or recurrence of the disease.

PATIENTS AND METHODS: Twenty-one biopsies of surgically treated aneurysmal bone cysts, from 21 patients, were analysed. Histomorphometry by two different methods (3,000- and 200-point-counting) and by two observers was performed to quantify the percentage of each tissue type in the cyst (cellular, fibrillar, osteoid). A healing index was developed by calculating a ratio of osteoid and fibrillar material divided by cellular tissue. Biopsies were also examined using two immunostains, cluster of differentiation 68 (CD68) and proliferating cell nuclear antigen (PCNA).

RESULTS: The final outcome was healing for 16 aneurysmal bone cysts (healing group) and recurrence for the five others (recurrence group), after a mean follow-up of 4.43 years. The two groups differed significantly in the proportion of their cellular content and their healing index. The ratio of CD68 negative to CD68 positive cells was also significantly different between the two groups.

CONCLUSION: Biopsy should be considered as a helpful prognostic factor for aneurysmal bone cyst.