Diagnostic imaging studies from three patients with the same
condition are shown. What is the most likely diagnosis?
An aneurysmal bone cyst is an expansile lesion containing
thin-walled, blood-filled cystic cavities. In this disorder, large
vascular channels are associated with slender-to-plump cells with
hemosiderin granules and surrounding giant cells. Aneurysmal bone
cysts are generally regarded as non-neoplastic in nature; trauma
appears to be important in their pathogenesis. They may exist as a
primary abnormality of bone, or as a secondary phenomenon,
superimposed on a pre-existing osseous lesion. The nature of the
underlying bone disorder is quite variable; examples of aneurysmal
bone cysts superimposed on chondroblastomas, giant cell tumors, and
osteoblastomas have been recorded.
Aneurysmal bone cysts are usually seen in the first, second, or
third decades of life, affecting men and women with equal
frequency. They may arise in almost any bone, although most reports
indicate their predilection for the spine, innominate bones, and
metaphyses of long tubular bones (femur, humerus, tibia, fibula).
Small tubular bones in the hands and feet (figure 1), and
additional flat or irregular bones such as the scapula, clavicle,
ribs, calcaneus (figures 2A and 2B), mandible, maxilla, and
calvarium also may be affected.
Radiographically, in the appendicular skeleton, an eccentric
osteolytic and expansile lesion which displaces and obscures the
cortex may be evident (figure 3). Horizontally-oriented trabeculae
may extend into the adjacent soft tissue. Additionally, a shell of
bone may surround the lesion, though at early stages the shell can
be absent and the aggressive appearance may simulate that of a
malignant process. In the spine, the posterior elements are
generally affected, and an expansile lucent lesion is seen.
Extension into, or primary involvement of a vertebral body can also
be found in some cases.
This series of diagnostic challenges is prepared by David J.
Sartoris, MD, Profesor, Department of Radiology, University of
California School of Medicine, San Diego, CA