title: Frontal lobe shortening in second-trimester fetuses with trisomy 21: usefulness as a US marker.
abstract: OBJECTIVE
  To determine whether the frontal lobe is disproportionately smaller than normal in second-trimester fetuses with Down syndrome by using prenatal ultrasonographic (US) measurements of the frontothalamic distance (FTD).
  
  
  METHODS
  The FTD, measured from the inner table of the frontal bone to the posterior margin of the thalamus, was measured in 43 fetuses (mean gestational age, 17.2 weeks +/- 1.3 [standard deviation]; range, 15.0-20.4 weeks) with chromosomally proved trisomy 21 and in 160 chromosomally normal fetuses (mean gestational age, 17.1 weeks +/- 1.5; range, 14.5-22.5 weeks). Other cranial biometric ratios also were calculated.
  
  
  RESULTS
  The FTD was best predicted from the estimated gestational age (EGA) in the euploid population with the quadratic equation FTD = -0.0120 x EGA2 + 0.6917 x EGA - 5.2349 (R2 = .731) or from the biparietal diameter (BPD) with the linear equation FTD = 0.6837 x BPD + 0.5525 (R2 = .731). If an observed-to-expected ratio of 0.84 is used as a cutoff sign to screen for trisomy 21, a sensitivity of 16%, specificity of 97%, odds ratio of 6.03 (95% confidence interval, 1.81, 20.1), and relative risk of 5.98 are achieved.
  
  
  CONCLUSIONS
  The frontal lobe is statistically significantly smaller in fetuses with trisomy 21. US measurement of the FTD may prove to be a useful adjunctive screening tool if used with other markers for Down syndrome.
authors.affiliation: Department of Radiology, University of Washington Medical Center, Seattle, WA 98195-7115, USA.
authors.forename: T C
authors.initials: TC
authors.lastname: Winter
authors.forename: J A
authors.initials: JA
authors.lastname: Reichman
authors.forename: J A
authors.initials: JA
authors.lastname: Luna
authors.forename: E Y
authors.initials: EY
authors.lastname: Cheng
authors.forename: A M
authors.initials: AM
authors.lastname: Doll
authors.forename: C A
authors.initials: CA
authors.lastname: Komarniski
authors.forename: H V
authors.initials: HV
authors.lastname: Nghiem
authors.forename: U P
authors.initials: UP
authors.lastname: Schmiedl
authors.forename: L E
authors.initials: LE
authors.lastname: Shields
authors.forename: S B
authors.initials: SB
authors.lastname: Uhrich
mesh_terms: D004314:Down Syndrome / Q000000981:diagnostic imaging* / Q000196:embryology; D005260:Female; D005625:Frontal Lobe / Q000000981:diagnostic imaging* / Q000196:embryology; D005865:Gestational Age; D006801:Humans; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D012372:ROC Curve; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal