Background

Intraspinal meningeal "drop" metastases are a recognised complication of several CNS tumours, and MRI of the spine with contrast plays an important role in the correct staging of these tumours. Flow artefacts visible on MRI of the spine are well described and commonly seen on T2 weighted images as regions of signal reduction within the CSF.

Objective

We describe a new type of CSF flow artefact which is most visible on T1 weighted images with fat suppression; a protocol commonly used for staging of tumours at risk for drop metastases. We also describe the process where the artefact was identified, the quality process to prevent diagnostic errors, MRI experiments and subsequent changes to the protocol to mitigate the artefacts.

Methods

We retrospectively reviewed the imaging of two cases of young adult patients with posterior fossa tumours, where the radiological reports of the staging study indicated drop metastases, but where MDT review and subsequent repeat imaging confirmed that these were artefactual. MRI parameters were compared between equipment which generated this type of artefact and that which did not. Experiments with protocol modification were performed to confirm the source of the artefact.

Results

The artefacts were related to the use of low refocusing angle sequences combined with the use of SPAIR fat suppression. Increasing refocusing angle and using chemical shift fat suppression substantially reduced the artefact visibility.

Conclusions

A previously unreported type of CSF flow artefact has been identified which has the potential for significant errors in diagnosis. Caution is needed when making parameter changes for reasons of speed optimisation or SAR, or for image quality problems related to choice of fat suppression method.