title: Prenatal evaluation of the position of the fetal conus medullaris.
abstract: OBJECTIVE
  To determine the position of the fetal conus medullaris during pregnancy in relation to the last vertebral body and to examine its use in detecting skin-covered spinal dysraphism.
  
  
  METHODS
  This was a retrospective study involving 300 consecutive ultrasound examinations between 15 weeks of gestation and term. Two operators independently assessed images of the spine to determine whether the conus medullaris and the last vertebral body could be visualized in a single image in a midsagittal plane. The distance between these two landmarks (the conus distance) was measured twice by both operators who were not aware of any previous measurements. Intra- and interobserver variability was assessed by 95% limits of agreement. Linear regression analysis was used to determine the relevant contributors to the conus distance and a normal range was computed based on the best-fit model. The normal results were compared with five cases of prenatally detected skin-covered spinal dysraphism.
  
  
  RESULTS
  In 84.7% of the 300 cases, both operators were able to visualize the conus medullaris and the last vertebral body. Ninety-five percent limits of agreement for the intraobserver variability in measurement of conus distance were ± 1.9 mm. For the interobserver variability, they were - 3.7 and 2.5 mm. We found a linear relationship between conus distance and gestational age, biparietal diameter and abdominal circumference. The strongest relationship was observed for femur length (conus distance = - 8.2 + femur length (mm)). In the five abnormal cases, conus distance was well below the 5(th) percentile.
  
  
  CONCLUSIONS
  Determination of conus distance allows for an objective and feasible assessment of the conus medullaris position. This parameter promises to be useful in the prenatal detection of skin-covered spinal dysraphism.
authors.affiliation: Department of Obstetrics and Gynaecology, University of Tuebingen, Tuebingen, Germany. mhoopmann@gmx.de
authors.forename: M
authors.initials: M
authors.lastname: Hoopmann
authors.forename: H
authors.initials: H
authors.lastname: Abele
authors.forename: B
authors.initials: B
authors.lastname: Yazdi
authors.forename: M U
authors.initials: MU
authors.lastname: Schuhmann
authors.forename: K O
authors.initials: KO
authors.lastname: Kagan
mesh_terms: D000293:Adolescent; D000328:Adult; D042241:Early Diagnosis; D005260:Female; D005865:Gestational Age; D006801:Humans; D016014:Linear Models; D008159:Lumbar Vertebrae / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000196:embryology; D015588:Observer Variation; D011247:Pregnancy; D012016:Reference Values; D012189:Retrospective Studies; D013116:Spinal Cord / Q000000981:diagnostic imaging* / Q000196:embryology; D016135:Spinal Dysraphism / Q000000981:diagnostic imaging* / Q000196:embryology; D016216:Ultrasonography, Prenatal; D055815:Young Adult