Prenatal visualisation of the torcular herophili by means of a Doppler technology highly sensitive for low-velocity flow in the expert assessment of the posterior fossa: a prospective study

OBJECTIVE

To evaluate the usefulness of a Doppler technology highly sensitive for low-velocity flow in the antenatal imaging of the torcular herophili (TH) in the second trimester of pregnancy.

DESIGN

Prospective study.

SETTING

Referral Fetal Medicine Unit.

POPULATION

Non-consecutive series of singleton pregnancies submitted to antenatal neurosonogram between 20 and 28 weeks of gestation.

METHODS

A midsagittal section of the fetal brain was obtained by insonating through the anterior fontanelle, then the MV-Flow™ and LumiFlow™ presets were selected to visualise the TH as the posterior confluence of the superior sagittal sinus and the straight sinus.

MAIN OUTCOME MEASURES

Evaluation of the anatomic relationship of the TH with the 'transpalatal line' joining the upper bony palate to the fetal skull.

RESULTS

A total of 99 pregnant women were recruited, including one fetus with open spina bifida, one with Dandy-Walker malformation (DWM) and two with Blake's pouch cysts. In normal fetuses, the TH appeared to lie on or just below the 'transpalatal line'. In the cases of Blake's pouch cyst, the position of the TH appeared normal if compared with controls, whereas in DWM a supra-elevated position of the TH in respect of the transpalatal line was demonstrated. Finally, in the fetus with Chiari II malformation the TH was identified below the 'transpalatal plane'.

CONCLUSIONS

Prenatal ultrasound visualisation of the TH by means of newly developed Doppler technologies characterised by high sensitivity for low-velocity flow is feasible and allows the indirect evaluation of the insertion of cerebellar tentorium in the second trimester.

TWEETABLE ABSTRACT

Prenatal imaging of the torcular herophili using a Doppler technology highly sensitive for low-velocity flow.

Utility of fetal anteroposterior to transverse cerebellar diameter ratio to exclude cerebellar hypoplasia in trisomy 18

AIM

This study was aimed to determine reference ranges for fetal cerebellar hemisphere biometry, including the transverse cerebellar diameter (TCD), anteroposterior cerebellar diameter (APCD) and APCD/TCD ratio in normal fetuses. In addition, we investigated which parameter would be useful for cerebellar hypoplasia in trisomy 18.

METHODS

This retrospective study included 340 normal singleton pregnancies and 15 cases of trisomy 18, in all of which fetal cerebellar biometry was performed between 14 and 40 weeks of gestational age (GA). The TCD, APCD and APCD/TCD ratio were assessed ultrasonographically.

RESULTS

In normal fetuses, the TCD (r_s = 0.876, P < 0.001) and APCD (r_s = 0.791, P < 0.001) were strongly correlated with GA. However, the APCD/TCD ratio was not correlated with GA (r_s = 0.058, P = 0.289), with median values of 0.52. Low TCD, APCD and APCD/TCD ratio values were detected in 53%, 100% and 100% of trisomy 18 cases, respectively. The median APCD/TCD ratio for trisomy 18 was 0.39 (range, 0.30-0.43), which was significantly lower than that of normal fetuses (P < 0.001). A cut-off APCD/TCD ratio of 0.44 served as a good predictor for trisomy 18 (sensitivity 100%, specificity 95.3% and negative predictive value 100%).

CONCLUSION

This study shows that TCD and APCD are correlated with GA, while the APCD/TCD ratio is a fixed value throughout gestation. Using the APCD/TCD ratio to assess cerebellar hypoplasia in trisomy 18 is useful because it does not require the individual evaluation of the TCD and APCD.

Fetal cerebellar disorders

The embryologic development of the cerebellum extends over a long time period, thus making it vulnerable to a broad spectrum of malformations and disruptions. Knowledge of the main steps of fetal posterior fossa development; the normal imaging patterns at different stages of embryogenesis; the large spectrum of cerebellar malformations; and their clinical presentations enables diagnosis and precise counseling of parents. Sonography is the most important imaging method for the screening of cerebellar malformations since it is noninvasive, widely available, and safe for both mother and child. The ultrasonographic approach for the evaluation of the fetal posterior fossa is based on the classic transabdominal visualization of axial planes with addition when indicated of a more comprehensive, multiplanar transvaginal or transfundal approach, including coronal and sagittal imaging planes. Fetal magnetic resonance imaging (MRI) has become an adjunct to prenatal ultrasound since the 1980s. Good-quality images have been obtained thanks to the implementation of fast and ultrafast MRI sequences. Fetal MRI has higher-contrast resolution than prenatal sonography and may contribute to the differentiation of normal from abnormal tissue. Both prenatal neurosonography and fetal MRI enable accurate prenatal diagnosis of most posterior fossa anomalies.