"Solid" variant of aneurysmal bone cyst (extragnathic giant cell reparative granuloma) in the axial skeleton and long bones. A study of its morphologic spectrum and distinction from allied giant cell lesions.

BACKGROUND: Giant cell reparative granuloma is generally considered to be a benign tumor-like bone lesion. Its involvement of axial skeleton and long bones is rare.
METHODS: Seven cases of extragnathic giant cell reparative granuloma (GCRG), which arose in the axial skeleton and long bones, were analyzed clinicopathologically and compared with allied lesions consisting of 31 cases of aneurysmal bone cyst (ABC) and 83 cases of giant cell tumor of bone (GCT).
RESULTS: These occurred in patients ranging in age from 8-36 years; two were in the vertebrae; two, in the clavicles; one, in a rib; one, in the humerus; and one in the tibia. None of the patients with GCRG had a recurrence despite incomplete resection. Its skeletal distribution and average associated patient age were similar to those of ABC. Histologically, they were characterized by florid fibroblastic proliferation with osteoclast-like giant cell-rich areas, stromal hemorrhage, and newly formed bone or osteoid trabeculae. The histologic features could be found around either the characteristic aneurysmal cysts or sinuses, although they were lacking any large blood-filled spaces.
CONCLUSIONS: The overlapping clinical and histologic features between GCRG and ABC and their similar biologic behavior represent related responses to an intraosseous hemorrhage. The authors prefer to use the term "solid variant of aneurysmal bone cyst" to describe this lesion.