PMC9639397_01
Schematic anteroposterior radiograph representation depicts position of the needle and catheter within the epidural space, using a caudal approach. The target level for the needle's tip position is lower than S3 foramen. The needle is passed into the sacral hiatus from below and posteriorly but is not advanced above the S3 level to avoid inadvertent thecal sac puncture. The catheter is passed into the ventral epidural space and its tip is located at S1 segment.
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A 16 gauge Coude epidural needle was inserted through the sacral hiatus and an epidural catheter was advanced to S3 level, with gentle deviation of the catheter tip towards the left side (Figure 1). After confirming the optimal position of the catheter through anteroposterior (AP) and lateral imaging, 8 mL contrast medium (Omnipaque 240) was injected which showed good patency of L5 and S1 neuroforamina on both sides. 
Schematic representation of lateral view shows the orientation and position of the catheter tip relative to spinal segment. Tip of the catheter is placed into the ventral epidural space.
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At first an epidurography was performed, while the catheter was still in the secure position of the last day, with its tip located at left L4 level (Figure 2). A total volume of 7 mL contrast medium (Omnipaque 240) was injected without manipulating the catheter.
(A) Anteroposterior contrast-fluorogram shows a ground-glass dispersal of contrast material, extends craniocaudally, and remains across the two pedicles of the same level. It does not extend beyond the transpedicular line at each observed spinal segment. (B) Lateral radiograph after contrast injection via the epidural catheter reveals a linear and lengthy extension along the lumbar vertebral column within the subarachnoid space. Note that a significant amount of contrast material extends cephalad up to L1-L2 level owing to a long contrast dispersal.
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The imaging showed a spread of contrast in the subarachnoid space, indicating a puncture of the dura mater by catheter (Figure 3).