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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. In this study, we describe the anatomy of the lumbar spine, assessed by magnetic resonance imaging (MRI) and ultrasound, in women sustaining unintentional dural puncture during epidural catheter placement for labor analgesia.We approached women who sustained a recognized unintentional dural puncture. Following consent, technical aspects of the epidural catheter placement were documented. Postpartum MRI of the lumbar spine and bedside spinal ultrasound were performed. Ultrasound images of the ligamentum flavum/dura mater unit in the transverse view were classified as typical, atypical, or inconclusive. Magnetic resonance imaging images were reviewed by a neuroradiologist, who was blinded to the level of the puncture.We included 10 women with unintentional dural punctures in the study. In 5 of the 10 women, these dural punctures occurred despite epidural catheter insertion by experienced practitioners. These women had a mean body mass index of 28.5 kg/m2 (range, 24–38 kg/m2). Two women suffered dural punctures twice. Ultrasound imaging in the paramedian view produced typical images in all patients. In the transverse view, 7 of 10 women showed atypical or inconclusive images, with atypical images seen at either L4/5 or L5/S1. Magnetic resonance imaging results revealed no anatomical abnormalities, with the exception of 1 woman who showed a ligamentum flavum gap away from the puncture site.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 by MRI.