Dural fistula visualized by intradural reflux of epidural blood patch − potential role of atlantoaxial hypermobility in intracranial hypotension

• Intrathecal reflux during EBP enabled direct visualization of a C1/2 dural defect. • A rare atlantoaxial dural fistula was precisely localized by post-procedural CT. • Repetitive cervical mechanical stress may induce focal dural detachment. • Upper cervical spine may be an underrecognized site of CSF leakage. Intracranial hypotension can occur at any age and commonly presents with orthostatic headache. Dural rupture is a major underlying cause; however, its precise pathophysiological mechanisms remain incompletely understood. Although cerebrospinal fluid (CSF) leakage may be detected by imaging, direct identification of the responsible fistula is often difficult. In particular, the relationship between mechanical stress and the morphology or extent of dural disruption has not been fully elucidated. The aim of this report is to present a rare case in which intrathecal reflux during an epidural blood patch allowed direct visualization of a cervical dural defect, providing insight into possible mechanisms of dural sac disruption in intracranial hypotension. A 56-year-old woman presented with progressive orthostatic headache. Brain MRI demonstrated bilateral chronic subdural hematomas, and lumbar puncture revealed an unmeasurably low CSF pressure, leading to a diagnosis of intracranial hypotension. She had no history of trauma but reported habitual prolonged smartphone use in the prone position with cervical hyperextension. CT myelography suggested CSF leakage at the C1/2 level. A targeted epidural blood patch (EBP) was performed at C1/2 using autologous blood mixed with 10% iopamidol. Post-procedural CT revealed continuous contrast passage across the dura beneath the left posterior arch of C1, indicating intrathecal reflux through a focal dural fistula. Although the first EBP provided only partial symptomatic relief, the radiological findings strongly suggested a large dural defect at the same level. A second targeted EBP was therefore performed at C1/2, resulting in complete symptom resolution. Follow-up imaging confirmed spontaneous resolution of the chronic subdural hematomas. This case suggests that repetitive or excessive cervical mechanical stress may induce focal detachment at the dural–osseous interface, resulting in dural fistula formation and intracranial hypotension. Direct visualization of intrathecal contrast reflux during EBP allowed precise localization of a rare atlantoaxial dural fistula. These findings provide insight into a potential cervical pathomechanism of intracranial hypotension and may help refine diagnostic and therapeutic strategies.