Background: A subdural space may form if neuroepithelial cells break up due to pressure exerted by mechanical forces, air, or fluid injection, creating fissures within the interface. Here, we report two cases of subdural extra-arachnoid injections during epidural blood patch (EBP). Case presentation: Both patients were middle-aged women diagnosed with spontaneous cerebrospinal fluid leakage as observed on computed tomography (CT) myelography. During EBP, we observed an oval-shaped contrast accumulation caudal to the puncture site. The procedure was completed with less than 10 ml of autologous blood injection, as each patient complained of headache or lower limb pain at that point. Post-EBP CT revealed that the injection had entered the subdural extra-arachnoid space. Conclusion: Epidural space adhesion likely occurred during the healing process, increasing the injection pressure that caused the injected fluid to flow into the subdural extra-arachnoid space from the dural collapse. Both patients showed improvement following a small volume of blood injection.