Aneurysmal bone cyst and giant cell tumor of the foot.

From 1950 to 1994, 257 cases of benign bone tumors of the foot were treated at the Bone Tumor Center of the Rizzoli Institute. Aneurysmal bone cysts (ABC) and giant cell tumors (GCT) are rare and often they are misdiagnosed. To define the clinical and radiographic features useful for diagnosis, x-rays of 24 ABCs and 21 GCTs of the foot were reviewed. Adding our series to the cases reported in the literature, the only important clinical data that emerged was the average age of patients affected by ABC and GCT (15 and 27 years, respectively). ABCs localized in small tarsal bones were rare (6%), whereas 19% of GCTs were found in this site. The eccentric, round shape of a lytic lesion was more characteristic of GCT. An aggressive pattern of radiographic bone destruction was observed more frequently in GCT than in ABC (P = 0.01). Septation was seen in both tumors. Typical of ABC was a sharp and trabeculated margin, whereas GCT had an ill-defined edge with normal cancellous bone (P = 0.007). The growth of ABCs often expanded the cortex, while GCTs eroded, thinned, and broke the cortical bone (P = 0.001). A saucerized cortex was observed only in ABCs. A bony shelf was more characteristic of ABC than of GCT (P = 0.002). Pathologic fractures (67%) and joint involvement, evaluated by computed tomography and magnetic resonance imaging (83%), were more frequent in GCTs, whereas fluid levels were more frequently observed in ABCs (47%). The majority of the tumors were stage 2, but GCTs represented 70% of stage 3 aggressive lesions.