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The aim of this study is to clarify the details of distribution patterns of spinal epidural fluid and to establish it as measure of spontaneous intracranial hypotension (SIH) syndrome diagnosis. Magnetic resonance imaging findings of the spine were analyzed in 37 patients, 24 women and 13 men (mean age 46.3 years), with SIH. Detection rate, thickness and patterns of the fluid collection were evaluated at every vertebral level. Follow-up spinal MRI findings were also analyzed for changes in epidural fluid collection and association with clinical symptoms. The MR images of the cervical spine were obtained in 30 patients, the thoracic spine in 36, and the lumbar spine in 17 patients. Epidural fluid collection was detected totally in 36 patients (97%) and was predominantly found at the mid-thoracic vertebrae. The fluid tended to locate dorsal to the dural sac at the thoracic spine and ventral at the cervical and lumbar spine. Patients with shorter duration of illness tended to have thicker fluid in the thoracic spine. In follow-up MRI, the findings of epidural fluid collection has disappeared in 32/36 cases within 3 months after treatment. Although residual fluid collection was found at the thoracic level in 4 cases, clinical symptoms were improved in all patients. This study suggested that the mid-thoracic spine should be chosen as the target of MRI in screening of SIH, and enlarged dorsal epidural space is strongly indicative of SIH.