Aneurysmal Bone Cyst¶

Definition¶

An aneurysmal bone cyst (ABC) is an expansile, blood-filled, benign cystic bone lesion that occurs most commonly in the posterior elements of the spine in patients under 20 years of age. ABCs can be primary or arise secondarily within another tumor (giant cell tumor, osteoblastoma, chondroblastoma).

Imaging Findings¶

MRI¶

Fluid-fluid levels — The hallmark feature. Multiple cystic cavities containing blood products of different ages layer by gravity, creating horizontal interfaces best seen on axial or sagittal T2 images.
Expansile, multiloculated lesion centered on the posterior elements
Thin internal septations
Variable signal depending on the age of blood products (T1 can be bright in subacute hemorrhage)
Surrounding bone marrow edema
Septations and walls enhance; the cystic contents do not

CT¶

Expansile lytic lesion with thinned, "blown out" cortex (eggshell-thin cortical rim)
No matrix mineralization
May contain fluid-fluid levels (visible on axial CT)
Usually centered on the posterior elements but can extend into the vertebral body

Clinical Pearl

Fluid-fluid levels are the imaging hallmark of ABCs but are not specific — they can also be seen in giant cell tumors, telangiectatic osteosarcoma, simple bone cysts, and other lesions. The combination of an expansile, posterior element lesion with fluid-fluid levels in a patient under 20 is most consistent with ABC, but always consider the possibility of a secondary ABC arising within another tumor.

Management¶

Curettage with bone grafting
Selective arterial embolization (for surgically challenging locations like the sacrum)
Sclerotherapy (percutaneous injection of polidocanol or doxycycline)
Recurrence rate is 10–30% after curettage

Key Points¶

ABCs are expansile, blood-filled cystic lesions most common in the posterior elements of young patients
Fluid-fluid levels on MRI are the hallmark but not pathognomonic
Can be primary or secondary (arising within another tumor)
CT shows an expansile lytic lesion with eggshell-thin cortex
Posterior elements are more commonly involved than the vertebral body
Recurrence rate of 10–30% after curettage

References¶

Restrepo R, Zahrah D, Pelaez L, Temple HT, Murakami JW. Update on aneurysmal bone cyst: pathophysiology, histology, imaging and treatment. Pediatr Radiol. 2022;52(9):1601–1614. Available from: https://pubmed.ncbi.nlm.nih.gov/35941207/
Zileli M, Isik HS, Ogut FE, Is M, Cagli S, Calli C. Aneurysmal bone cysts of the spine. Eur Spine J. 2013;22(3):593–601. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC3585636/
Nasri E, Reith JD. Aneurysmal bone cyst: a review. J Pathol Transl Med. 2023;57(2):81–87. Available from: https://www.jpatholtm.org/journal/view.php?number=17061
Mahnken AH, Nolte-Ernsting CCA, Wildberger JE, et al. Aneurysmal bone cyst: value of MR imaging and conventional radiography. Eur Radiol. 2003;13(5):1118–1124. Available from: https://pubmed.ncbi.nlm.nih.gov/12695836/
Stevens KJ, Stevens JA. Aneurysmal Bone Cysts. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2023. Available from: https://www.ncbi.nlm.nih.gov/books/NBK546654/
Aneurysmal bone cyst. Radiopaedia.org. Available from: https://radiopaedia.org/articles/aneurysmal-bone-cyst