46 Korean J Pain Vol. 24, No. 1, 2011 recovery room. To find out the causes of the epidural an- esthesia failure, iohexol 5 ml was injected through the epi- dural catheter and radiographic images were taken (Fig. 2). However, since the accurate position of the catheter was not found, cervical and thoracic computed tomography (CT) was performed after ensuring the patient that the hospital would cover the cost of the CT and receiving agreement from the patient and caregiver. CT findings revealed that the catheter had entered between T1 and T2 but failed to penetrate into the ligamentum flavum, proceeded along the T2 right lamina, and was eventually positioned within the erecter spinae muscle after converting the direction back- wards (Fig. 3). DISCUSSION Anesthesiologists sometimes experience a situation where epidural anesthesia fails even when the loss of re- sistance and hanging drop methods have been successful and the catheter has been inserted without any particular difficulty [12]. Rissanen [13] and Sharrock [14] reported that pseudo loss of resistance or false positive loss of resistance may appear when the Tuohy needle is advanced to a region where a cavity has been formed due to degeneration of the interspinous ligament. Gupta et al. [15] reported pseudo positive loss of resistance due to subcutaneous emphysema generated after chest damage. Lirk et al. [16] reported that embryologically generated fissures from the lack of midline fusion of ligamentum flavum were found in the cervical spine region about 51-74% and thoracic vertebra region about 2-21%, respectively, and the mean area of fissures was 1.0 ± 0.3 mm. They also mentioned that the un- certain loss of resistance that takes place by such a fis- sure can probably cause dural puncture or spinal cord damage. To solve this problem, Kil et al. [2] measured the depth of the epidural space by means of ultrasonic waves before operation children and infants aged seven or less, applied the drip infusion method for epidural puncture and re- Fig. 3. Epidural catheter inserted between T1 and T2 spinous process in the spine CT axial (A, B), sagittal (C) and 3D (D-F) views. Instead of crossing ligamentum flavum, epidural catheter navigated T2 right vertebral lamina and turned to the erector spinae muscle.