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Lumbar spine anatomy in women sustaining unintentional dural puncture during labor epidural placement: a descriptive study using magnetic resonance imaging and ultrasound
Abstract Number: F-16
Abstract Type: Original Research
Introduction: Unintentional dural puncture is one of the most frequent complications of the epidural technique. One previous study suggested that atypical sonoanatomy of the ligamentum flavum-dura mater unit may be a risk factor for this complication, however this study lacked confirmation by MRI(1). The objective of this study was to describe the sonoanatomy of the lumbar spine, as assessed by both MRI and ultrasound, in women sustaining unintentional dural puncture during epidural catheter placement for labor analgesia.
Methods: We approached women who sustained a recognized unintentional dural puncture during labor epidural placement. Those agreeing to participate had detailed documentation of the technical aspects of the epidural placement, including: pre-procedural ultrasound assessment or palpation, number of attempts, overall difficulty of placement, level of placement and operator experience. An MRI of the lumbar spine was performed in the immediate postpartum period to investigate for any spinal abnormalities, particularly those of the ligamentum flavum and dura mater. Additionally, all women had their lumbar spine scanned with ultrasound in both the transverse and longitudinal paramedian oblique views. Ultrasound images of the ligamentum flavum-dura mater unit in the transverse view were classified as typical, atypical or inconclusive. An atypical image was defined as that depicting all elements of the interspace, except for the ligamentun flavum-dura mater unit(1). All MRI images were reviewed by a neuroradiologist, who was blinded to the ultrasound images and to the level at which the unintentional dural puncture occurred.
Results: We included 10 women in the study. Half these punctures occurred despite experienced practitioners and no woman had an extremely low or high body mass index. The depth to loss of resistance was between 4 to 6 cm in all cases, 9 were at L3/4 and 1 at L2/3 level. Two women suffered two dural punctures each. Seven of the ten women developed postdural puncture headache and went on to have an epidural blood patch. Ultrasound imaging in the longitudinal paramedian oblique view produced typical images in all patients. However in the transverse view 7 of 10 women showed atypical or inconclusive scans, the atypical images being at either L4/5 or L5/S1 interspace. The MRI results for all women revealed no anatomical abnormalities, with the exception of 1 woman who had a ligamentum flavum gap left of midline at the L2/3 level (away from the puncture site).
Discussion: Our results suggest that unintentional dural punctures occur in likely anatomically normal women. Furthermore, the transverse ultrasound views may fail to demonstrate typical ligamentum flavum-dura mater unit at the lower lumbar levels despite its confirmed presence on MRI.
References: 1) Reg Anesth Pain Med 2008; 33: 266–270