C1-C2 false localizing sign, sometimes referred to merely as C1-C2 sign, is seen on spinal imaging and can lead to the mislocalization of a CSF leak in individuals with intracranial hypotension.
There are numerous reports of fluid at this location that have been interpreted as the actual site of leak 4,5 and, in some instances, treated locally with targetted epidural blood patches of fibrin glue 6. Whether any of these cases represented true localized leaks at this location is unclear.
Pathophysiology
When a CSF leak occurs in the epidural space, due to patient recumbency and the lack of other easy avenues of egress from the spinal canal, fluid tracks and accumulates posteriorly at the C1-C2 level. This is presumably due to limited and loose posterior ligamentous structures at this level, required to allow the rotational mobility of the spine at this level 1.
Radiographic features
The C1-C2 sign can be seen in any modality that is able to visualize fluid in the epidural and paraspinal soft tissues. Thus, it is encountered in all types of myelography (CT, MRI, fluoroscopic and nuclear medicine) as well as routine MRI of the spine.
It appears as pooling of fluid posterior to the C1-C2 posterior elements.
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