This 14-year-old girl presented with a dorso-lumbar mass. Upon MRI evaluation of the spine, a multilocular extradural right paravertebral mass with multiple fluid-fluid levels was demonstrated. Appearances were suggestive of an aneurysmal bone cyst. The lesion was biopsied and results are shown below.

Histopathology report:

Gross exam: Specimen is received and fixed in formalin, labeled with the patient's name and consists of cystic hemorrhagic mass measuring 6.5 x 6 x 2 cm. Representative sections are submitted in 4 cassettes.

Microscopic exam: Sections reveal cystic spaces containing blood with no apparent endothelial lining surrounded by solid cellular areas composed of plump fibroblasts, osteoclasts-like multinucleated giant cells, and focal osteoid trabeculae. Focal aggregates of hemosiderin-laden macrophages are seen. No malignancy noted.

Diagnosis: Consistent with aneurysmal bone cyst.