title: Sonoanatomy of the lumbar spine of pregnant women at term.
abstract: OBJECTIVE
  Spinal ultrasound offers valuable information to facilitate the placement of lumbar neuraxial anesthesia. Lumbar spine sonograms are unique, and aspects may appear atypical at times, particularly the ligamentum flavum (LF). The objective of this study was to describe the sonoanatomy of the lumbar spine and to determine the frequency of atypical images of the LF in pregnant women at term.
  
  
  METHODS
  Using a 2-5 MHz curvilinear transducer, we imaged all the lumbar interspaces in the left and right paramedian longitudinal and transverse planes. The images were categorized as typical, atypical or inconclusive. The primary outcome was the presence of an atypical image of the LF in the transverse plane. The distance from the skin to the epidural space, and the dural sac width, were also measured.
  
  
  RESULTS
  One hundred subjects were studied. All the images in the longitudinal planes were conclusive and typical, whereas the number of inconclusive images in the transverse plane increased from L1-L2 to L5-S1 (1, 0, 4, 9, and 34, respectively). The incidence of atypical LF images in the transverse plane was 2.0% at L1-L2, 1.0% at L2-L3, 3.1% at L3-L4, 19.8% at L4-L5, and 28.8% at L5-S1.
  
  
  CONCLUSIONS
  The paramedian longitudinal sonograms of the lumbar spine are of superior quality to those obtained in the transverse plane. When using the transverse approach, a high incidence of inconclusive sonograms should be expected in the lower segments. The incidence of atypical LF images, especially in the upper lumbar segments, warrants further investigation because it can have implications for the epidural technique.
authors.affiliation: Department of Anesthesia and Pain Management, Mount Sinai Hospital, University of Toronto, Ontario, Canada.
authors.forename: Bruno C R
authors.initials: BC
authors.lastname: Borges
authors.forename: Paul
authors.initials: P
authors.lastname: Wieczorek
authors.forename: Paul
authors.initials: P
authors.lastname: Wieczoreck
authors.forename: Mrinalini
authors.initials: M
authors.lastname: Balki
authors.forename: Jose C A
authors.initials: JC
authors.lastname: Carvalho
mesh_terms: D000328:Adult; D005260:Female; D005865:Gestational Age; D006801:Humans; D017843:Ligamentum Flavum / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D008159:Lumbar Vertebrae / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D008875:Middle Aged; D011247:Pregnancy; D011263:Pregnancy Trimester, Third; D016896:Treatment Outcome; D014463:Ultrasonography / Q000379:methods; D055815:Young Adult