Diagnostic ultrasound ( PDFDrive )

1232 PART IV Obstetric and Fetal Sonography
A
B
F
F
C
D
FIG. 35.16 Lumbar Meningocele, 34 Weeks’ Gestation. (A) Posterior transaxial sonogram demonstrates a luid-illed sac (short arrows) along
the fetal back. There is a small defect in the neural arch (long arrow). (B) Posterior longitudinal sonogram shows the wall of the meningocele (short
arrows) and the focal spina biida defect in the posterior neural arch (long arrow). (C) Posterior longitudinal and (D) posterior transaxial sonograms
demonstrate abnormally posterior thoracic spinal cord (arrows) in the nondependent portion of the spinal canal. Cerebrospinal luid (F) is between
the anterior aspect of the spinal cord and the anterior wall of the spinal canal.
spina biida, although only 30% to 40% of fetuses with enlarged
ventricles actually have spina biida. On ultrasound, the Chiari II
malformation manifests as obliteration of the cisterna magna. 73,74
he compression of the cerebellum changes its shape, giving
the banana sign. 71,75 In two diferent series, obliteration of the
cisterna magna was noted in 22 of 23 cases with spina biida
at 16 to 27 weeks’ gestation 74 and in 18 of 20 cases at 24 weeks
and earlier. 74
Concave deformity of the fetal frontal bones in the second
trimester is called the lemon sign. 76 Various authors have shown
that 85% of fetuses with spina biida before 24 weeks’ gestation
have the lemon sign. 72,77-79 In practice, the lemon sign can be