Prenatal ultrasonography of the fetal system often reveals widening of the ventricular system. Severe ventricular widening (hydrocephalus) is often combined with neurological developmental abnormalities and has a poor prognosis, with little difficulty in clinical consultation. Clinical prognostic assessment and counseling for mild ventricular widening that is combined with other structural abnormalities or chromosomal abnormalities depends on the combined abnormality. In contrast, prenatal counseling for isolated presence of critical ventricular widening is difficult because critical ventricular widening can be the only ultrasound manifestation of some occult brain developmental anomalies or can be an intracranial image of a normal fetus, and therefore the prognosis may vary significantly from case to case. In this paper, we give a brief description of critical lateral ventricular widening, which has a high prenatal incidence, and expect to provide useful information for prenatal consultation. 1. Definition The fetal lateral ventricular width is measured as the width of the body of the lateral ventricle via the lateral ventricular choroid on a transverse cranial section of the fetal lateral ventricle. Regarding the criteria for critical lateral ventricular dilatation, most of the study data use the reference range proposed by Cardoza et al. in 1988, that is, fetal lateral ventricular width <10 mm throughout pregnancy is defined as normal, >15 mm is defined as hydrocephalus, and 10-15 mm is defined as critical lateral ventricular widening or mild lateral ventricular widening, see Figure 2. With the accumulation of follow-up case data, some studies in recent years have found that that in cases traditionally defined as critical lateral ventricular widening, fetuses with lateral ventricular width >12 mm have a higher probability of combining other malformations and a low probability of combining aneuploidy (excluding cases combining other malformations), while fetuses with simple lateral ventricular widening of 10-12 mm have a relatively good prognosis for neurological development. Because of the inconsistent prognostic regression using 12 mm as the boundary, it has been proposed to define lateral ventricular width of 10-12 mm as mild lateral ventricular widening and 12-15 mm as moderate lateral ventricular widening. 2. Epidemiological data The incidence of critical lateral ventricular widening in newborns born in the literature ranges from 0.3‰ to 1.5‰, and the incidence in high-risk groups is about 20 times higher than that in low-risk groups. The incidence of antenatal fetal critical lateral ventricular widening reported in the literature is about 0.5%, 10%-71% have combined abnormalities (structural abnormalities, chromosomal abnormalities, intrauterine infections), among which 33%-61% have combined structural abnormalities, 3%-9% have combined chromosomal abnormalities, 5% have combined congenital infections, and the incidence of fetal simple critical lateral ventricular widening is 0.07%-1%. The incidence of simple critical lateral ventricular widening is 0.07-1%. The abnormalities associated with critical lateral ventricular widening are not a disease, but a complication of abnormal development of brain structures. Lateral ventricular widening alone is often a diagnosis of exclusion, and can only be considered when other related abnormalities are excluded. Possible anomalies that can cause or complicate lateral ventricular widening are listed below. 3.1 Central nervous system anomalies Intracranial anomalies that can lead to critical widening of the intracranial ventricular system include agenesis or absence of the corpus callosum, early changes in obstructive hydrocephalus, ChiariII malformation, and Dandy-Walker malformation. For severe intracranial anomalies, they are easily detected and diagnosed during midtrimester systematic ultrasonography, but for those with mild lesions or insignificant morphologic changes, the diagnosis of ventricular widening is often given only. 7.4% to 12.5% of intracranial anomalies often present with significant structural abnormalities suggestive of a diagnosis on dynamic monitoring. When ventricular widening is detected, the recommended interval for ultrasound monitoring is 2 to 3 weeks; the interval is too short to detect changes. A detailed neurological examination at 30 to 34 weeks is recommended for the purpose of monitoring the extent of lateral ventricular widening and for the detection of intracranial anomalies that are not evident in midtrimester. Magnetic resonance imaging may be recommended for simple critical lateral ventricular widening detected by prenatal ultrasound, which may increase the diagnostic information of combined intracranial anomalies in 6-10% of cases. 3.2 Chromosomal abnormalities Critical bilateral lateral ventricular widening is a soft ultrasound indicator of fetal chromosomal abnormalities. The prevalence of combined chromosomal abnormalities in fetuses with antenatal findings of critical lateral ventricular widening is approximately 5%. The incidence of chromosomal abnormalities is about 7.9% in cases of critical lateral ventricular widening combined with other abnormalities and 3.0% in those without combined abnormalities. According to VandenHof et al, the incidence of mild lateral ventricular widening was 0.15% in haploid fetuses and 1.4% in trisomy 21 children, with a likelihood ratio of 9. This study suggests that antenatal detection of critical lateral ventricular widening can be used as an indication for invasive chromosomal testing. The author concluded that among 158 cases of fetuses with trisomy 21 diagnosed prenatally at the First Hospital of Sun Yat-sen University, 21 cases (13.29%) showed critical lateral ventricular widening, but the vast majority of them were combined with other ultrasound soft indicators. The posterior occipital cortex is thickened, and the long bones are slightly short. The more information on combined malformations provided by prenatal ultrasound, the easier it is to determine the corresponding genetic syndromes. For example, ultrasound findings of wide lateral ventricles, short limb malformations, small thorax and cloverleaf head shape may suggest the detection of specific genetic loci for lethal dwarf type II to clarify the diagnosis; if the fetus has homozygous If the fetus has immune thrombocytopenia syndrome, intracranial hemorrhage and widening of the lateral ventricles will occur in about 10% to 30% of cases. Therefore, when there is a critical widening of the lateral ventricle combined with intracranial hemorrhage, anti-platelet antibody testing can be done to exclude alloimmune thrombocytopenia syndrome. 3.4 Intrauterine infection Mild lateral ventricular widening is associated with toxoplasmosis and cytomegalovirus infection in about 1.5% of fetuses, and in about 18% of fetuses with confirmed cytomegalovirus infection, there is a combination of mild lateral ventricular widening. Antenatal ultrasound findings of mild widening of the lateral ventricles require careful search for signs associated with intrauterine infection, such as subventricular vesicles, periventricular calcification, enhanced intestinal echogenicity, ascites, and calcified foci in the liver. Prenatal MRI may reveal some signs of brain parenchymal abnormalities due to intrauterine infection. For fetuses with antenatal ultrasound suggesting critical lateral ventricular widening, maternal blood or amniotic fluid should be performed to check intrauterine infection items. 4. prognosis 4.1 Prognosis associated with combined other anomalies In fetuses with combined other anomalies, the prognosis depends on the type and severity of the combined anomalies, and the prognosis is relatively good in children without combined anomalies. the Meta-analysis by Pagani et al. showed that when the fetus was first detected by antenatal ultrasound with simple critical widening of the lateral ventricle (without combined other intracranial and extracranial anomalies), the results of postnatal examination were followed up. Chromosomal abnormalities were found in 4.7% (57/1213) and in 33.5% (387/1156) of the chromosomally normal cases combined with other abnormalities. Therefore, in cases where simple lateral ventricular widening is found prenatally, it is still important to note that about 1/3 of cases have a combination of other anomalies. 4.2 Prognosis and regression of lateral ventricular widening One study showed that in fetuses with mild lateral ventricular widening, progressive ventricular widening occurred prenatally in 15.7% of cases, lateral ventricular improvement occurred in 34% of cases, and lateral ventricular width remained constant in 55.7% of cases. This suggests that the regression of postnatal lateral ventricular widening is related to the neurological developmental status, and therefore there is a need for continuous postnatal monitoring of cases of prenatally detected lateral ventricular widening. 4.3 Prognosis of neurological development in fetuses with isolated lateral ventricular widening Data from follow-up of neurological development in children with simple lateral ventricular widening (years 3 to 151 months, mean time 27.7 months) suggest that the incidence of neurodevelopmental delay is 7.9% (67/652), compared with 2% to 3% in the normal population. Neurodevelopmental abnormalities include ADHD, attention deficit, learning disabilities, autism, and schizophrenia. Gaglioti et al. found that there was a difference in postnatal neurological development between simple mild lateral ventricular widening (10-12 mm) and moderate lateral ventricular widening (12.1-14.9 mm), with 96% of the former having a good prognosis and 76% of the latter having a good prognosis, and there was also a difference in the probability of combining other structural abnormalities between the two. The incidence of combined anomalies in the former was 41%, while that in the latter was 76%. In case of prenatal detection of bilateral lateral ventricular widening, the fetus should first be carefully scanned for cranial and global structures to determine whether the widening is simple. Fetal chromosomal examination should be recommended in cases of combined structural abnormalities or soft ultrasound indicators. Since 7.4% to 12.8% of combined abnormalities cannot be detected at the first examination, parents should be informed during the prenatal consultation that other abnormalities may occur during later monitoring. Most of the combined abnormalities such as chromosomal abnormalities, intrauterine infections, and other structural abnormalities can be ruled out by prenatal testing, but in some cases, combined abnormalities are found during ongoing follow-up after birth. Pregnant women should be informed that the chance of neurological delay is about 7.9% for a child with definite simple lateral ventricular tegmental widening.