We have experienced 30 cases of intracranial hypotension in the last three years. Spinal MRI was performed in all cases, and 27 patients demonstrated epidural fluid collection(EFC). Of these 30 patients, 6 were treated conservatively with bed rest and hydration, and 24 were treated with epidural blood patch(EBP). Twenty-two patients were cured, 4 were improved significantly, and 4 were improved partially. We examined spinal MR images of 22 patients after 3 months of treatment. The EFC wasn't visible in 11 cases;however, residual EFC was found in the 11 remaining cases. The patients without EFC were cured. Of the 11 patients with residual EFC, 4 patients were cured, 4 were improved significantly, and 3 showed partial improvement. Furthermore, in subsequent spinal MRI of 7 patients, EFC wasn't visible in 2 patients;however the patients continued to experience moderate orthostatic headache. Therefore, while EFC is closely associated with spinal CSF leakage, the presence of CSF leakage doesn't necessitate the observation of EFC by current MRI. In post-treatment spinal MRI, we sometimes observed residual EFC in the ventro-lateral area of the spinal dural sac, especially in the thoracic region;hence, we speculated that CSF leakage may occur in the ventro-lateral aspect of spinal dural sac in many cases of intracranial hypotension. Moreover, in these cases, subsequent treatment with EBP cannot assure the delivery of autologous blood to the residual EFC. Therefore, we considered that the residual EFC in the ventro-lateral epidural space is often separated from its dorsal part.