1. How to image the fetal corpus callosum
Aly Youssef, Tullio Ghi, Gianluigi Pilu

2. How to: image the fetal corpus callosum
Indication: ultrasonographic evaluation of the fetal corpus callosum
When? The ideal gestational age is ≥ 20 weeks
Machine settings: routine obstetric scan
Ideal fetal lie: lying on the back or on one side; the transabdominal approach is facilitated by a breech or transverse lie; the transvaginal approach provides excellent resolution but requires a cephalic lie

3. Figure S1
Three dimensional sonograms of the fetal skull at midgestation (a,b) demonstrate the wide acoustic windows provided by the frontal or metopic suture (1), bregmatic fontanelle (2) and sagittal suture (3). By aligning the acoustic beam with such window excellent resolution of cerebral structures including the corpus callosum is possible (c). The window runs along the entire calvarial convexity and the corpus callosum can be imaged by either an anterior, superior or posterior approach (arrows).

4. Figure S2 a b c
The fetal profile to median plane approach. Obtain an axial view of the fetal orbits, aligning both orbits at the same horizontal level (a). Rotate the transducer by 90°, thus obtaining a median profile (b). Angulate the transducer in order to use the acoustic window of the anterior fontanel and the frontal suture thus demonstrating the corpus callosum (highlighted in yellow) (c).

5. Figure S3 a b
The coronal to median plane approach. Obtain a coronal section of the anterior horns of the lateral ventricles and the cavum septi pellucidi (arrow) so that the latter is oriented strictly vertical (a). Rotate the transducer 90° obtaining a midline brain section, visualizing the corpus callosum (highlighted in yellow) (b).

6. Figure S4
Color Doppler demonstration of the cerebral circulation in the median view: the pericallosal artery (arrows) highlights the corpus callosum; (a) normal fetus at 20 weeks’ gestation, (b) normal fetus at 16 weeks’ gestation; at this time it is usually difficult to image the small and thin corpus callosum, which can however be inferred by the Doppler signal of the pericallosal artery; (c) partial agenesis of the corpus callosum at 22 weeks’ gestation; the Doppler signals confirms the presence of the corpus callosum that was difficult to assess precisely with two-dimensional ultrasound

7. Figure S5
A comparison of 3D and 2D median views obtained in the same fetus. The ‘start’ image for the 3D examination corresponds to an axial section, parallel to the skull base and crossing the cavum septi pellucidi (a). The acquired volume is then displayed in multiplanar mode and the intersection of the planes aligned with the midline echo (a,b), to demonstrate in the sagittal plane a median view of the brain (c). The corresponding 2D image is demonstrated in (d) (3v, third ventricle).
Reproduced with permission from Pilu G, Segata M, Ghi T, Carletti A, Perolo A, Santini D, Bonasoni P, Tani G, Rizzo N. Diagnosis of midline anomalies of the fetal brain with the three-dimensional median view. Ultrasound Obstet Gynecol 2006; 27:

8. Figure S6
Images (a) and (b) were obtained from one ultrasound volume of unusually high quality: in (b), the reconstructed median plane allows to recognize the corpus callosum as an anechoic stripe with a thin echogenic contour that separates it from the underlying cavum septi pellucidi. More frequently, the two structures are not clearly separated and they generated one single anechoic comma shaped image on top of the 3rd ventricle (b,c). In both cases, the thick superior echogenic contour is formed by the lower portion of the midline echo.
Reproduced with permission from Pilu G, Ghi T, Carletti A, Segata M, Perolo A, Rizzo N. Three-dimensional ultrasound examination of the fetal central nervous system. Ultrasound Obstet Gynecol 2007; 30: