Ultrasound Examination of Fetal CNS Clinical Practice Guidelines (ISUOG, 2021)

International Society of Ultrasound in Obstetrics and Gynecology (ISUOG)

These are some of the highlights of the guidelines without analysis or commentary. For more information, go directly to the guidelines by clicking the link in the reference.

April 30, 2021

The guidelines by the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) describe sonographic screening evaluation of the fetal brain as part of the midtrimester anomaly screening examination and elaborate on the indications for detailed evaluation of the fetal CNS by targeted fetal neurosonography. They were published as part 1 and part 2 in Ultrasound in Obstetrics and Gynecology. The recommendations include the following[1,2]:

Those who are doing screening for CNS abnormalities should be familiar with the normal appearance of the central nervous system at different gestational ages. Transabdominal sonography is the technique of choice for screening fetal CNS in low-risk pregnancies at the midtrimester scan and should include the fetal head and spine.

In the transventricular plane, the aspect of the atrium distal to the transducer and the presence of the cavum septi pellucidi (CSP) should be evaluated. In the transcerebellar plane, the presence and shape of the cerebellum and the presence of the CSF in the cisterna magna should be evaluated. When possible, obtain a longitudinal section of the fetal spine to screen for open and closed spinal dysraphism.

Measure atrial width and transverse cerebellar diameter for CNS malformations. For general biometry purposes, biparietal diameter (BPD) and head circumference are usually also measured because they may identify proliferation abnormalities such as microcephaly or macrocephaly.

Perform targeted fetal neurosonography if there is suspicion of a brain or spinal abnormality during obstetric ultrasound. Fetal brain MRI should be indicated only by the findings of the expert who performed the targeted neurosonographic exam, not on the basis of suspicion of a brain abnormality at screening ultrasound.

The transvaginal approach is preferred for high-resolution targeted neurosonography. The transabdominal approach can be used when the transvaginal approach is not feasible because of situations such as breech presentation or twin pregnancy. When a transvaginal approach is not feasible, use high-resolution linear or microconvex transducers because they provide higher resolution than conventional convex probes.

The midsagittal or median plane is the reference plane to assess major midline organs and anomalies and should be approached via the anterior or posterior fontanelle or the sagittal nonossified suture by gentle manipulation of the fetal head using the free hand.

Check that all 4 components of the corpus callosum are visible and sonographically normal.

3D ultrasound is recommended in targeted neurosonography. Fetal brain MRI is considered complementary to neurosonography. When necessary, it can replace neurosonography as the second-line evaluation if the operator has sufficient training in fetal brain MRI.

For more information, please see Targeted Obstetric Ultrasound.

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