Failed spinal anaesthesia: cause identified by MRI.

PURPOSE: To determine the cause of failed spinal anaesthesia, magnetic resonance images of the lumbar spine were examined.

CLINICAL FUTURES: A 28-yr-old woman, scheduled for closure of a rectal fistula under spinal anaesthesia, hyperbaric tetracaine 12.5 mg injected into the subarachnoid space at L3-4 repeatedly resulted in restricted sacral spread. Magnetic resonance imaging showed that the cylindrical dimension of the lumbar spinal canal was wider than in normal subjects, suggesting a larger volume of CSF within the dural sac below the termination of the cord. The summit of the lumbar convexity was located at L3, which was more cephalad than the L3-4 puncture site.

CONCLUSION

The uncommon anatomical characteristics of the lumbar spinal canal identified by magnetic resonance imaging were considered to be the reason for the restricted sacral spread observed repeatedly in this patient.