Case 1

A 25-year-old woman (gravida 1) with non-consanguineous marriage in 18 weeks of gestational age with no personal or familial medical history was referred to our clinic for an anomaly scan. The combined screening in the first trimester (including NT, PAPP-A, Free B-hCG) was normal in her obstetric history. Two-dimensional sonography was performed using a Philips Affiniti 50 Ultrasound Machine (PHILIPS Company, Andover, USA) with a 4.5-MHz convex probe. In our assessment, at 17 weeks of gestational age, we noticed bilateral symmetric cystic masses measuring 6 × 7 mm, possibly originating from the occipital region of the fetus skull (upper part).
Figure 1a shows the transthalamic plane, which is the fetal head’s transverse plane for measuring the head circumference and biparietal diameter. The skull’s shape, integrity, size, and bone density may be assessed when the head’s size is measured. As Figure 1a highlights, there is no skull defect in the parietal or frontal region, showing a completely normal transthalamic view of the fetus.
Figure 1b illustrates the transcerebellar plane, assessing posterior fossa (cerebellum, cisterna magna, cavum septum pellucidum, and falx). In this plane, also, there is no evidence of skull defect. Figure 1c highlights the transventricular plane, which is used for measuring the size of the lateral ventricle.
We did not see any evidence of bony skull defect or any protruding lesion in the 3 basic planes, but we incidentally noticed a bony defect in the parasagittal and transorbital view, after which we performed a transvaginal scan to have a better view of the fetus. We noticed the defect in the fetal head’s parieto-occipital region, which could easily be missed in a basic sonographic examination (Figure 2).
 

Case 2

A 34-year-old woman (gravida 2, abortion 1) was admitted to our clinic for a prenatal visit and performing a detailed anomaly scan at 22 weeks from her last menstrual period. She did not report any history of a genetic condition or congenital anomaly. Two-dimensional sonography using Mindray DC80 (Mindray, Shenzhen, China) with a 3.5-MHz convex probe revealed a single live fetus; placenta and amniotic fluid volume were normal. On ultrasonographic examination, 2 symmetric cystic structures were measured approximately 8 × 6.5 mm; they were protruded through the posterior and upper part of the skull.  In the standard axial fetal brain planes, we did not see any defect or pathologic finding (Figure 3); however, there was a small bony defect in the parasagittal view on transvaginal sonography (Figure 4). Posterior fossa and lateral ventricles were within normal limits, and there was no sign of neural tube defect. Overall, no other anomaly was found in the detailed anomaly scan.
Also, we did not see any pathologic finding in these standard axial fetal brain planes for the second patient.

CNS anomalies are known as one of the most prevalent malformations detected by antenatal sonography. Nowadays, prenatal detection of anencephaly using ultrasound is possible in almost 100% of cases. The diagnosis of encephalocele is usually made during the second trimester of pregnancy, around the 20th week (4). However, in some cases, the findings may be subtle, whereas, in others, the anomaly may be progressive and manifest only in late gestation or after birth.
Further, ultrasound frequently demonstrates normal anatomic variations difficult to differentiate from true malformations. Fetal cephalocele is suspected when a paracranial mass is seen on sonography (Figure 4). The diagnosis of encephalocele is typically straightforward, as the presence of brain tissue inside the sac is striking on ultrasound images. Anatomical location is used for defining cephaloceles (e.g., parietal, frontal, frontoethmoidal, occipital, etc.). Occipital cephalocele is more common in the United States and Europe, while frontal cephalocele is more common in Asia (5).
Due to the outstanding role of ultrasound in clinical decision-making and its operator-dependent nature, it is vital to develop guidelines to define minimum performance standards for this modality in different obstetric ultrasound areas. The brain anomaly scan is among the most important assessments in anomaly scan. Three axial planes are included in the CNS malformations’ standard screening protocol (transthalamic, transcerebellar, and transventricular). International guidelines have defined the anatomical landmarks and methodology of these planes (5-7). The skull’s shape, integrity, size, and bone density may be assessed when the head’s size is measured.
In this study, 3 basic axial views of the fetal head were completely normal with no calvarial bony defect in both cases. Because we doubted the defect in other planes, we performed transvaginal sonography. In transvaginal sonography, we noticed 2 symmetric cystic masses from the occiput, which could easily be missed in axial planes. Therefore, normal assessment of 3 routine axial planes cannot exclude some major, lethal, or morbid fetal neurological problems as encephalocele.
According to the latest guidelines, scanning the 3 axial planes is not sufficient for fetal brain morphology’s basic ultrasonographic evaluation. Currently, the neurosonographic examination (8-10), i.e., evaluating the axial, coronal, and sagittal planes of the brain, is performed only for high-risk patients or for those who have brain anomaly in anomaly scan.
However, it is necessary to add other planes such as sagittal and coronal planes to 3 routine planes for better detection of CNS anomalies. It results in early anomaly detection, particularly in the first trimester and early second trimester. Consequently, it is helpful to decide on termination, plan interventions, and manage pregnancy.
Some CNS anomalies may be associated with more morbidity. Early detection would help parents make the right decision. If the parents decide to terminate the pregnancy, they have enough time for a legal abortion. This is for the reason that legal abortion in Iran is permitted under 19 weeks; one of our patients who was diagnosed at 22 weeks got an illegal abortion.
The limitation of this study is that our patients had outpatient abortions, and missed fetuses were not examined. Postmortem examination and simple radiographic studies are important to evaluate associated malformations and confirm the prenatal findings (6). These are straightforward, inexpensive, and effective methods.

For better detection of CNS anomalies, it is necessary to add other views such as sagittal view to three routine planes. It leads to early detection of anomalies especially in first and early second trimester. Consequently, it helps in deciding for termination, planning interventions and further management.
 

For better detection of CNS anomalies, it is necessary to add other views such as sagittal view to three routine planes. It leads to early detection of anomalies especially in first and early second trimester. Consequently, it helps in deciding for termination, planning interventions and further management.

 

The authors have no conflicts of interest.