title: Sonographic Evaluation of Fetal Conus Medullaris and Filum Terminale.
abstract: BACKGROUND
  Sonographic evaluation of the fetal conus medullaris (CM) level is not reproducible. The objectives of this study were to determine the normal position of the fetal CM during pregnancy as well as the normal intradural filum terminale (FT) length and to evaluate their use in detecting tethered cord.
  
  
  METHODS
  This is a prospective evaluation of normal singleton pregnancies examined by sonography from 17 weeks of gestation to term. Each sonographer had to identify the top of the first sacral vertebra (S1) to measure the distance between it and the conus extremity (CM-S1 distance). The intradural FT distance was measured with 5- to 8-MHz probes.
  
  
  RESULTS
  194 consecutive pregnant women were included. The CM and intradural FT were demonstrated clearly in 164 (84%) cases. The mean CM-S1 distance was 20.6 mm (range 0.5-42). The mean intradural FT distance was 27.9 mm (range 6.6-49.3). Linear regression analysis showed a significant association between both those distances and gestational age (p < 0.05). In cases of tethered cord, the mean CM-S1 distance and the mean intradural FT distance were both below the 5th percentile.
  
  
  CONCLUSIONS
  Prenatal evaluation of the CM and the intradural FT is feasible and reproducible and seems useful in detecting tethered cord.
authors.affiliation: Department of Obstetrics, Gynecology and Reproductive Medicine, Hospital Antoine Béclère, AP-HP, Université Paris Sud, Paris, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Mottet
authors.forename: Julien
authors.initials: J
authors.lastname: Saada
authors.forename: Jacques
authors.initials: J
authors.lastname: Jani
authors.forename: Alain
authors.initials: A
authors.lastname: Martin
authors.forename: Didier
authors.initials: D
authors.lastname: Riethmuller
authors.forename: Michel
authors.initials: M
authors.lastname: Zerah
authors.forename: Alexandra
authors.initials: A
authors.lastname: Benachi
mesh_terms: D000328:Adult; D001699:Biometry; D002420:Cauda Equina / Q000000981:diagnostic imaging*; D005260:Female; D047109:Fetal Development; D005865:Gestational Age; D006801:Humans; D011247:Pregnancy; D012016:Reference Values; D013116:Spinal Cord / Q000000981:diagnostic imaging*; D013131:Spine / Q000000981:diagnostic imaging; D016216:Ultrasonography, Prenatal / Q000379:methods*