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Prenatal diagnosis of CNS anomalies other than neural tube defects and ventriculomegaly

Ana Monteagudo, MD
Ilan E Timor-Tritsch, MD
Section Editors
Louise Wilkins-Haug, MD, PhD
Deborah Levine, MD
Deputy Editor
Vanessa A Barss, MD, FACOG


Malformations of the central nervous system (CNS) are among the most common types of major congenital anomalies. Ultrasound examination is an effective modality for prenatal diagnosis of these anomalies.

Prenatal sonographic diagnosis of midline CNS anomalies will be reviewed here. Prenatal diagnosis of neural tube defects and ventriculomegaly are discussed separately. (See "Ultrasound diagnosis of neural tube defects" and "Fetal cerebral ventriculomegaly".)


CNS structures typically evaluated during a basic fetal ultrasound examination include: lateral ventricles, choroid plexuses, cavum septi pellucidi, falx, thalami, cerebellum, cisterna magna, and spine (image 1 and image 2 and image 3) [1]. In addition, the head, face, and neck should be included as part of the routine CNS ultrasound examination.

A thorough understanding of the normal sonographic appearance of the CNS across gestation is crucial for accurate diagnosis because the presence or absence of a structure may be normal or abnormal depending upon the age of the fetus. Poor timing of the examination, rather than poor sensitivity, can be an important factor in failing to detect a CNS abnormality [2]. As an example, a sonogram of the fetal brain at 14 weeks of gestation cannot detect agenesis of the corpus callosum since this structure does not become sonographically apparent until 18 to 20 weeks of gestation and does not acquire its final form until 28 to 30 weeks. (See 'Disorders of the corpus callosum' below.)

Ideally, pregnancies at increased risk of fetal CNS anomalies and those with suspicious findings on a basic examination should undergo fetal neurosonography performed by clinicians with expertise in this area. Magnetic resonance imaging (MRI) is an option for further evaluation in cases of diagnostic uncertainty when additional information will influence subsequent management of the pregnancy [3].


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