“Flow void sign”: flow artefact on T2-weighted MRI can be an indicator of dural defect location in ventral type 1 spinal CSF leaks

ABSTRACT Patients with spontaneous intracranial hypotension caused by type 1 dural defects typically have an epidural fluid collection on MRI, but the location of the defect is not usually readily identifiable on standard MRI sequences and can be at any point along the length of the collection. The most common location for type 1 leaks is ventral and as such are most commonly associated with ventral predominant epidural fluid. Dynamic myelography (either digital subtraction myelography or dynamic CT myelography) is currently the standard of care to localise the defect. We describe an imaging sign on T2-weighted images caused by CSF-flow egress at the site of the defect that may permit accurate prediction of the site of the CSF leak non-invasively. Importantly, this sign was only observed on 2D T2-weighted and STIR images and not on 3D acquisitions, which notably suppress artefact. This has implications for optimal MRI spine protocol construction. This sign can be used to limit myelographic range, reduce radiation dose and may increase diagnostic confidence to dural defect location. ABBREVIATIONS: dCTM = Dynamic CT Myelography; DSM = Digital Subtraction Myelography; SIH = Spontaneous Intracranial Hypotension.