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Sacral cyst

Case contributed by Dr Bruno Di Muzio


Cystic lesion in sacral spinal canal with severe compression of S3, S4 and S5 nerve roots.

Patient Data

Age: 39
Gender: Female

MRI Lumbar spine


TECHNIQUE: T1 and T2 fat-saturated post-contrast sagittal and axial sequences of the lumbar and sacral spine.

FINDINGS: There are five lumbar type vertebral bodies. Alignment of the lumbar spine is roughly anatomical. There are disc desiccation and height loss throughout. No significant marrow lesion.Shallow annular bulges are seen along with mild facet degenerative changes, but there is no neural compression identified. There is a fluid signal injury seen in the sacral canal without distinct solid component and an enhancing component. This measures up to 47 x 21 mm in transaxial diameter. It displaces the caudal nerve roots anteriorly. It is associated with extensive bony deficiency at the posterior sacrum, and there is a remodeling of the posterior wall of the sacral body.There is no extension into the foramina.

CONCLUSION: Long-standing cystic lesion without solid component.

CT sacrum (non-contrast)


A non-contrast CT of the sacrum was obtained as planning for a CT-guided cyst aspiration.

The cyst seen on MRI, interpreted as being a Tarlov cyst within the canal appears instead to be located within the posterior sacrum, mostly surrounded by bone. No access to the cyst is possible posteriorly percutaneously without passing through bone, and although it is still conceivable that this communicates with the theca, if that were to be the case passing a bone biopsy needle into it may be inadvisable. The anterolateral margins of the cyst, also ossified/calcified, severely compress the S3-S4 and S5 nerve roots, and as such it is likely to be involved in the patient's presentation.

Case Discussion

MACROSCOPIC DESCRIPTION: "Cyst wall": A flattened piece of glistening pale grey tissue

MICROSCOPIC DESCRIPTION: Sections show fragments of fibrous tissue which show focal calcification and also some osseous tissue at the edge of some of the pieces. On one aspect, the fibrous tissue is lined by a bland monolayer of flattened cells consistent with synovium. There are occasional chronic inflammatory cells within the fibrous tissue, but there is no acute inflammation. There is no evidence of malignancy.

DIAGNOSIS: Cyst wall: Consistent with synovial cyst.


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