Aneurysmal bone cyst - sacrum

Case contributed by Dr Yasser Asiri


Swelling in the sacral region for 3 months.

Patient Data

Age: 9 years
Gender: Male

There is lytic lesion in the sacrum causing asymmetry of the sacral foramina. An overlapping fecal filled bowel loops degrade the image quality.

The differential diagnosis of a midline sacral lesion in pediatric age group would include sacrococcygeal teratoma, chordoma, Ewing sarcoma or aneurysmal bone cyst. Further assessment with cross sectional imaging is needed to narrow the list. 

The CT study shows an expansile lytic lesion involving the sacral spine, mainly the posterior elements with thinning of the overlying cortex. Multiple fluid-fluid levels can be appreciated. The lesion extends anteriorly results in significant narrowing of the spinal canal. The lesion extends anteriorly through the right S2/3 neural foramen. The presacral fat appears unremarkable. No associated soft tissue mass. 

The diagnostic possibilities might include aneurysmal bone cyst versus osteoblastoma.


The MRI study better depicts the cystic nature of the sacral lesion. The lesion is bubbly-looking with multiple septations and fluid-fluid levels. It is arising from the posterior element of the sacral spine extending from S1 to S5 with mild extension to the body of S2 and S3 through the bilateral pedicles. There is significant narrowing at the distal sacral spinal canal, however, there is no compromise on the neural foramina. Minimal septal enhancement is seen in the post contrast images.  

The MRI features are highly suggestive of aneurysmal bone cyst.

Case Discussion

This case shows an unusual location of the aneurysmal bone cyst in the sacrum, when assessed by MRI study, it demonstrates the typical imaging appearance of expansile multiseptated lesion with multiple fluid-fluid levels.

Part of the imaging work up is to do an angiogram study to assess for feeding vessels to plan for embolization. Other options of treatment include corticosteroid or alcohol injections. This patient received no interventions and was followed up by serial imaging over a period of 4 years and show significant regression of the bone cyst.

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