Review Question - QID 219539

This 24-year-old male presents with low back pain and an MRI demonstrating an L3 vertebral body cystic mass with fluid-fluid levels and a biopsy exhibiting an increase in ubiquitin-specific protease-6 (USP6) transcription. This presentation is diagnostic for aneurysmal bone cyst.

Aneurysmal bone cysts (ABC) are benign, non-neoplastic bone lesions that most commonly occur in long bones, namely the femur or tibia, but more uncommonly in the axial skeleton. Diagnosis can often be narrowed based on plain films and MRI imaging alone, but a biopsy is required to make the diagnosis. Genomic sequencing can also be performed, often revealing upregulation of the USP6 promotor. Its presence can be diagnostic for primary ABCs, as it is a key differentiator from the similarly-appearing telangiectatic osteosarcoma. Not all ABCs exhibit USP6 upregulation, however, as only 70% demonstrate this characteristic.

Galant et al. report on two cases of lytic, cystic lesions (16-year-old male, 13-year-old female) where genomic sequencing (karyotyping, Fluorescence in situ hybridization [FISH]) identified chromosomal discrepancies that aided in the identification of malignant degeneration in a suspected ABC following histological analysis. Ultimately, the authors highlight the importance of performing a biopsy in ABC-appearing lesions as well as genomic analysis to identify chromosomal aberrations that may portend risk for malignant degeneration in patients.

Tsagozis and Brosjö provide a review of the current strategies for the treatment of ABCs, noting historically, these lesions underwent en bloc excisions, but recent treatment paradigms have shifted to more limited, percutaneous methods, including intralesional debridement with an adjuvant, sclerotherapy with polidocanol injections, and radiotherapy. The authors note high success rates, with greater than 90% cure rates regardless of modality, but find curettage with high-speed burr and adjuvants, as well as sclerotherapy with polidocanol injections the most suitable treatments due to their low incidence of side effects.

Figure A is an AP radiograph of the lumbar spine showing cystic formation with widening of the L3 vertebral body. Figures B & C are sagittal and axial MRI imaging demonstrating the cystic nature of the lesion with fluid-fluid levels.

Incorrect answers:
Answer 2: While they can be found in the axial spine, giant cell tumors would not express USP6 upregulation.
Answer 3: Non-ossifying fibromas would exhibit a better-demarcated lesion on plain films and lack fluid-fluid levels on MRI.
Answer 4: Unicameral bone cysts are found less commonly in the axial spine and do not demonstrate fluid-fluid levels.
Answer 5: Though telangiectatic osteosarcoma exhibits findings very similar to ABCs, the entity does not express USP6 upregulation.