Fetal cerebral ventriculomegaly

INTRODUCTION — Ventriculomegaly is the term used to describe cerebral ventricular dilation unrelated to increased cerebrospinal fluid (CSF) pressure, such as dilation due to brain dysgenesis or atrophy. Hydrocephalus is the term used to describe pathologic dilation of the brain's ventricular system due to increased CSF pressure; obstruction is a common etiology. However, the two terms are sometimes used interchangeably when applied to the fetus because fetal ventricular pressure cannot be measured. Prenatally, a common convention is to use the term ventriculomegaly when the fetal ventricles are mildly enlarged and hydrocephalus when they measure >15 mm or an anatomic etiology associated with obstruction and increased CSF pressure is visualized or can be inferred.

Fetal ventriculomegaly is a relatively common finding on second trimester obstetric ultrasound examination. Isolated mild ventriculomegaly can be a normal variant associated with normal pediatric outcome. Ventriculomegaly can also be caused by a variety of disorders that result in neurologic, motor, and/or cognitive impairment; these cases are often associated with other anomalies and abnormal findings.

This topic will discuss the prenatal diagnosis and clinical significance of ventriculomegaly and options for management of affected pregnancies. Hydrocephalus in children is reviewed separately. (See "Hydrocephalus in children: Physiology, pathogenesis, and etiology" and "Hydrocephalus in children: Clinical features and diagnosis" and "Hydrocephalus in children: Management and prognosis".)

CLINICAL PRESENTATION — Assessment of the ventricles is a standard component of fetal ultrasound examination. Ventriculomegaly is often first detected during a routine second trimester fetal anatomic survey at 18 to 20 weeks of gestation but can be identified during a standard sonographic examination performed for any reason in the late second trimester or the third trimester.

In the late first or early second trimester, the sonologist may have a subjective impression of ventriculomegaly, but objective criteria for normal and abnormal ventricular measurements are not available.

PRENATAL DIAGNOSIS

Ultrasound procedure — Ultrasound is the preferred diagnostic technique for assessing ventriculomegaly.

The atrium of the lateral ventricle is the area where the body, posterior (occipital) horn, and inferior (temporal) horn converge (figure 1). Atrial diameter remains stable between 15 and 40 weeks of gestation, with reported means of 5.4 to 7.6 mm and an upper limit of normal <10 mm [1-6].

The atrium of the lateral ventricle is measured in the transventricular (axial) plane at the level of the frontal horns and cavum septi pellucidi, with the cerebral hemispheres symmetric in appearance (image 1) [7]. The calipers should be positioned on the internal margin of the medial and lateral walls of the atria, at the level of the parieto-occipital groove, perpendicular to the long axis of the lateral ventricle. Incorrect placements include middle-middle, outer-outer, and placement that is too posterior in the narrower part of the ventricle or not perpendicular to the ventricular axis. Substantial interobserver variability in interpretation can occur and is most common at ventricular diameters near 10 mm and when other CNS anomalies are detected [8,9].

In addition, the normal fetal brain is quite sonolucent and may simulate CSF, which may incorrectly lead to the diagnosis of ventriculomegaly. Therefore, careful evaluation by an experienced sonologist is important [10].

Diagnosis — Ventriculomegaly is diagnosed when the atrial diameter is ≥10 mm (irrespective of gestational age), which is 2.5 to 4 standard deviations above the mean, depending on the study [1,2,11]. It is usually classified as [7,12]:

●Mild: 10 to 12 mm

●Moderate: 13 to 15 mm

●Severe ≥16 mm. A diagnosis of severe isolated ventriculomegaly implies obstruction (hydrocephalus) (image 2). Severe ventriculomegaly may or may not be accompanied by macrocephaly (ie, head circumference greater than two standard deviations above the mean).

In addition to ventricular dilation, the choroid plexus often appears to fall toward the dependent ventricular wall (dangling choroid) [13] and takes up <50 percent of the cerebrospinal fluid (CSF) space (normally, the choroid plexus fills 50 to 100 percent of the lateral ventricle) [14-16].

Approximately 50 to 60 percent of cases of ventriculomegaly are unilateral; the remainder are bilateral [17,18]. The etiology and outcome of unilateral and bilateral ventriculomegaly are similar; therefore, counseling and management are generally the same [19].

It should be noted that some degree of asymmetry of the lateral ventricles exists in the human fetal brain, and occasionally, this can be seen prenatally [20]. By itself, asymmetry (≥2 mm difference between the two lateral ventricles) does not appear to be associated with an adverse neurodevelopmental outcome when both ventricles are <10 mm [21].

Differential diagnosis — CNS lesions that could be misdiagnosed as ventriculomegaly by an examiner inexperienced in neurosonography include holoprosencephaly, hydranencephaly, porencephaly, schizencephaly, and various cystic lesions, such as arachnoid cysts. (See "Prenatal diagnosis of CNS anomalies other than neural tube defects and ventriculomegaly" and 'Etiology' below.)

EPIDEMIOLOGY — The prevalence of mild ventriculomegaly was 1 in 675 (0.15 percent) in a general obstetric population undergoing routine prenatal sonographic examinations between 16 and 22 weeks of gestation [4]. We consider this a reasonable assessment of the prevalence, although others have reported prevalence as high as 2 percent [22].

The male-to-female sex ratio is 1.7 [23].

ETIOLOGY

●Normal variant – Isolated mild ventriculomegaly (ie, 10 to 12 mm) is usually a normal variant since postnatal evaluation and development are usually normal. Even isolated moderate ventriculomegaly has been associated with a normal postnatal evaluation in most cases [7] (see 'Counseling' below). The etiology may be related to the normal formation and absorption of cerebrospinal fluid (CSF) during fetal development.

●Large choroid plexus cysts – Large isolated choroid plexus cysts may transiently dilate the fetal cerebral ventricles. While data are available on a limited number of such cases, choroid plexus cysts are typically benign, and the mild ventriculomegaly in such cases is unlikely to be clinically significant [24]. (See "Prenatal diagnosis of CNS anomalies other than neural tube defects and ventriculomegaly", section on 'Choroid plexus cysts' and "Sonographic findings associated with fetal aneuploidy", section on 'Choroid plexus cysts'.)

●Pathologic disorders – Mild enlargement of the lateral ventricles may be the initial manifestation of an underlying pathologic process [23]. Pathologic ventriculomegaly can result from loss of cerebral tissue, obstruction to CSF flow, or excessive CSF production and is often associated with other findings on detailed neurosonography.

Pathologic etiologies include idiopathic causes, chromosomal disorders and genetic syndromes, congenital infections, intracranial hemorrhage, ischemic injury, cortical malformations, migrational abnormalities, and structural abnormalities such as aqueductal stenosis, agenesis of the corpus callosum, Dandy-Walker malformations, Chiari malformations, and neural tube defects.

In congenital aqueductal stenosis, the cerebral aqueduct is narrow or consists of several minute channels (figure 2). The narrowing may be developmental (eg, X-linked hydrocephalus with stenosis of the aqueduct of Sylvius) or due to acquired changes, such as fibrosis from infection (eg, cytomegalovirus, toxoplasmosis, Zika virus, or other viruses), intraventricular hemorrhage, or a mass. Infection can also result in isolated ventriculomegaly due to cerebral atrophy, aqueductal stenosis from ependymal fibrosis, or communicating hydrocephalus from inflammation of arachnoid granulations. Rarely, overproduction of CSF by a tumor or choroid plexus papilloma may result in ventriculomegaly. (See "Hydrocephalus in children: Physiology, pathogenesis, and etiology".)

POSTDIAGNOSTIC EVALUATION — Postdiagnostic evaluation involves:

●Determining whether additional central nervous system (CNS) or other anatomic abnormalities are present

●Diagnostic testing for the most common causes of ventriculomegaly

Comprehensive sonographic evaluation — A physician experienced in the diagnosis of fetal anomalies should perform a comprehensive sonogram to confirm the diagnosis of ventriculomegaly and determine whether other structural abnormalities are present. Associated abnormalities have been reported in 10 to 76 percent of cases [25-28]. Identification of these abnormalities helps in determining the cause of ventriculomegaly and the prognosis.

●CNS – Comprehensive examination of the CNS should include a detailed evaluation of the lateral, third, and fourth ventricles; corpus callosum; thalami; germinal matrix region; cerebellum and cerebellar vermis; and spine [29,30].

●Detailed fetal anatomic survey and biometry – Ventriculomegaly can be a feature of several infections and genetic syndromes, which may be associated with non-CNS abnormalities and/or growth restriction. Characteristic sonographic findings of fetal infection, such as intracerebral and periventricular calcifications, hepatic calcifications, hepatosplenomegaly, ascites, and polyhydramnios, increase the chance that ventriculomegaly is related to infection. (See "Sonographic findings associated with fetal aneuploidy".)

Although some experts also suggest routinely performing a fetal echocardiogram, we generally do not perform advanced cardiac imaging when the cardiopulmonary anatomy, as described in the American Institute of Ultrasound in Medicine (AIUM) guidelines, appears normal on a detailed ultrasound examination [31].

Diagnostic amniocentesis — We offer diagnostic amniocentesis to all patients ≥15 weeks of gestation. Amniotic fluid is tested for:

●Chromosomal microarray – Ventriculomegaly is associated with an increased risk for a chromosomal abnormality. In a systematic review including over 1200 fetuses with apparently isolated mild ventriculomegaly at initial presentation, 4.7 percent had an abnormal karyotype, most commonly trisomy 21 [32]. The risk of a chromosomal abnormality is higher when ventriculomegaly is severe or associated abnormalities are present.

For patients who underwent a biochemical marker or cell-free DNA screening test for fetal aneuploidy before ventriculomegaly was detected, we offer diagnostic testing even if the screening test indicated a low-risk of a common autosomal trisomy (screen-negative) because of the higher yield from diagnostic testing [7].

●Alpha-fetoprotein and acetylcholinesterase – Ventriculomegaly may be caused by open neural tube defect; amniotic fluid alpha-fetoprotein (AFAFP) and acetylcholinesterase (AChE) are elevated in these cases [33]. Testing for AFAFP and AChE is not required when an open neural tube defect is visualized on ultrasound, which is an excellent screening tool for these defects. However, the defect may be missed because it is very small, visualization is hampered by maternal or fetal factors, and/or high-resolution ultrasound is not available. If no defect is visualized in a patient with ventriculomegaly, testing is reasonable as they are relatively inexpensive tests that, when positive, support the diagnosis of an open neural tube defect as the etiology of ventriculomegaly or the presence of another associated anomaly.

●Polymerase chain reaction (PCR) for cytomegalovirus (CMV) and toxoplasmosis; RNA nucleic acid test for Zika virus in at-risk patients – Many cases of ventriculomegaly due to infectious causes will have other sonographic findings, such as intraabdominal or CNS calcifications. However, in some cases, the ventriculomegaly is the first (or only) sonographic feature; therefore, testing for selected infectious pathogens should be offered in all cases of isolated ventriculomegaly and strongly recommended if other markers suspicious for congenital infection are present [7]. The overall prevalence of infection in fetuses with ventriculomegaly is <2 percent; toxoplasmosis and CMV infection are the most common infections detected [34-36]. Sporadic cases of ventriculomegaly associated with other viruses have been reported (mumps enterovirus 71 [EV71], parainfluenza virus type 3, parvovirus B19, lymphocytic choriomeningitis virus) [37-42]. Possible exposure to Zika virus should be assessed. (See "Zika virus infection: Evaluation and management of pregnant patients", section on 'Fetal ultrasonography'.)

If the patient declines amniocentesis or microarray was performed before diagnosis of ventriculomegaly, then maternal serology can be performed to screen for an infectious etiology; however, serology is neither as sensitive nor as specific as amniotic fluid PCR. Thus, amniotic fluid PCR is the preferred method of evaluation for fetal infection. (See "Cytomegalovirus infection in pregnancy" and "Toxoplasmosis and pregnancy".)

●DNA testing for single gene disorders – Some cases of ventriculomegaly, particularly more severe cases or those with other anomalies, are associated with single gene disorders. The family medical history should be reviewed to identify any suggestion of an inherited condition in the pedigree. The L1 cell adhesion molecule (L1CAM) gene plays an important role in nervous system development, and variants in this gene are associated with a variety of X-linked neurologic syndromes, and most include hydrocephalus. However, a large number of other genes and genetic disorders are also associated with CNS anomalies, including ventriculomegaly.

Comprehensive testing with targeted gene panels or exome sequencing is increasingly available and may be useful in some cases (eg, positive pedigree, associated anomalies). In general, consultation with a geneticist is warranted if such testing is considered. We do not perform DNA testing with gene panels or exome sequencing in cases of isolated mild or moderate (<15 mm) ventriculomegaly because the yield of such testing is likely to be low; the yield is better in cases of isolated bilateral severe ventriculomegaly [43]. (See "Hydrocephalus in children: Physiology, pathogenesis, and etiology", section on 'X-linked hydrocephalus'.)

Role of magnetic resonance imaging — We suggest considering magnetic resonance imaging (MRI) in cases of isolated ventriculomegaly with a normal microarray and no clear etiology because the information can be helpful for parental counseling. Confirmation that mild ventriculomegaly is isolated increases the likelihood that long-term neurodevelopment will be normal, and identification of other CNS malformations makes it more likely that the fetus will have neurologic abnormalities, including developmental delay. MRI is generally not useful in cases of known aneuploidy, when the neurologic outcome is almost certainly abnormal regardless of findings on additional imaging, but may assist in determining the extent of destructive injury in fetuses with infection, hemorrhage, or ischemia, and when other sonographically evident CNS malformations are present, so that counseling can be more informed and specific.

Cortical malformations, migrational abnormalities, and other potentially significant defects, such as porencephaly, may not be evident on ultrasound examination but may be detected by MRI [44-46]. Although these abnormalities could affect patient counseling and management decisions, there is no consensus on the clinical value of routine MRI when fetal ventriculomegaly is detected on ultrasound [47,48]. The likelihood of finding another abnormality by MRI depends, in large part, on the quality of the original sonogram. In a meta-analysis that stratified by type of ultrasound assessment, MRI detected additional associated anomalies in 5 percent (95% CI 3.0-7.0) of fetuses with mild or moderate ventriculomegaly assessed by dedicated neurosonography, defined as a detailed assessment of the fetal brain according to the International Society of Ultrasound in Obstetrics and Gynecology guidelines [49], but in 16.8 percent (95% CI 8.3-27.6) of fetuses assessed by standard ultrasonography [50]. The information from MRI changed perinatal management (primarily to termination of pregnancy) in 3 percent of cases that underwent dedicated neurosonography and in 5 percent of those that underwent standard ultrasonography.

If MRI is performed, timing should consider anatomic developmental milestones as well as utility for pregnancy management. Structural malformations suspected by ultrasound may be diagnosed earlier than abnormalities of sulcation or migration, as the latter may only become evident as gestation advances.

In a series of 147 fetuses with isolated ventriculomegaly on ultrasound and normal karyotype, MRI confirmed the diagnosis in 122 (83 percent) and detected additional brain abnormalities in 25 (17 percent) [12]. In 12 cases, the severity of ventriculomegaly was reclassified up (10/12) or down (2/12); however, others have observed that the width of the ventricle may be slightly larger when measured by MRI as compared with ultrasound [51]. Additional brain abnormalities were identified in 5/90 fetuses (6 percent) with mild (10 to 12 mm) ventriculomegaly, 4/29 fetuses (14 percent) with moderate (13 to 15 mm) ventriculomegaly, and 16/28 fetuses (57 percent) with severe (≥16 mm) ventriculomegaly. Agenesis of the corpus callosum was the most common anomaly detected on MRI, but missed on ultrasound, and accounted for 11 of the 25 cases. The effects of agenesis of the corpus callosum range from subtle or mild to severe, depending on associated brain abnormalities. (See "Prenatal diagnosis of CNS anomalies other than neural tube defects and ventriculomegaly", section on 'Disorders of the corpus callosum'.)

COUNSELING — The etiology of ventriculomegaly often cannot be determined prenatally, and there is wide variation in outcome of infants with prenatally diagnosed ventriculomegaly, both of these factors make counseling challenging. The range of potential outcomes should be discussed with the family.

If the etiology of ventriculomegaly has been determined (eg, trisomy 21, congenital cytomegalovirus) or associated malformations are identified, parents can be given more specific information than in cases where counseling is only based on ventricular width. Pregnancy termination is an option and should be offered. In those patients who elect to terminate, evaluation of the abortus to confirm or determine the etiology is warranted, as identifying a cause can be helpful in determining recurrence risk in future pregnancies.

Most children with isolated mild and even moderate ventriculomegaly will have a normal outcome [19,32,52]. In the past an atrial diameter of 10 to 15 mm was considered mild (image 3) and >15 mm was considered severe and these classification criteria were used as the basis for many outcome studies. In a 2014 meta-analysis including 652 cases of isolated ventriculomegaly between 10 and 15 mm with postnatal follow‐up, the overall prevalence of developmental delay was 7.9 percent (95% CI 4.7-11.1 percent) at a median age of 30 months, which is similar to the background rate [32]. However, parents should understand that it is not possible to determine with certainty prenatally that mild ventriculomegaly is truly isolated [7]. The same meta-analysis reported that postnatal imaging found previously undiagnosed abnormalities (false negatives) in 7.4 percent (95% CI 3.1-11.8 percent) of cases, and some of these abnormalities were prognostically important [32]. Parents should also understand that reported rates of developmental delay vary because they are related, at least in part, to the thoroughness of the neurodevelopmental evaluation, length of follow-up, and inclusion or exclusion of fetuses with additional anomalies.

Neurologic, motor, and cognitive impairment are more likely with more severe ventriculomegaly. For example, when ventriculomegaly is severe, a meta-analysis reported a survival rate of 88 percent, and only 42 percent of these children had normal neurodevelopment [53]; by comparison, survival in mild to moderate apparently isolated ventriculomegaly is 97 to 98 percent, and over 90 percent of these children have normal neurodevelopment [25,27,32].

Neurodevelopmental outcome is also worse when associated anomalies are present (either central nervous system [CNS] or non-CNS); prognosis depends on the specific anomaly. Persistence or progression is an additional poor prognostic finding because it suggests underlying neurodevelopmental pathology [25,54,55]. (See 'Sonographic follow-up and prognostic findings' below.)

PRENATAL CARE — Few data are available to support a specific management plan in those patients who continue their pregnancies. Our management is based on findings in observational studies, expert opinion, and our clinical experience.

Sonographic follow-up and prognostic findings — We perform at least one additional detailed ultrasound examination between 28 and 34 weeks of gestation to reevaluate for CNS and non-CNS abnormalities; determine regression, persistence, or progression of dilation; and measure head circumference to identify macrocephaly, which is rare.

Follow-up ultrasounds have detected fetal abnormalities not detected on the initial scan in 13 percent of cases [23].

Early isolated mild ventriculomegaly may resolve by the third trimester; persistence or progression has been associated with a less favorable prognosis [23,56]. Among 106 live born infants followed in one series, ventriculomegaly increased in utero in 19 (18 percent), remained unchanged in 37 (35 percent), and improved or disappeared in 50 (47 percent) [23]. Normal outcomes were observed in 46 of the 50 fetuses (92 percent) in whom ventriculomegaly improved versus 13 of the 37 fetuses (35 percent) with stable ventriculomegaly and 4 of the 19 fetuses (21 percent) with worsening ventriculomegaly. Overall, in utero progression was associated with an adverse outcome in 44 percent of cases, while only 7 percent of the no progression group had an adverse outcome.

If ventriculomegaly is progressive, consultation with a pediatric neurosurgeon may be useful. Although uncommon, some neonates require surgical intervention, such as ventriculoperitoneal shunting.

Role of in utero shunting — Fetal ventriculoamniotic shunting is an investigational procedure first performed in the 1980s. A series including 44 fetuses reported a procedure-related death rate of 10 percent, a perinatal mortality rate of 17 percent, and moderate-to-severe handicaps in 66 percent of the survivors [57]. The expert consensus at that time was that these results did not represent an improvement in outcome over expectant management, which led to a de facto moratorium on such procedures [58]. Subsequently, some investigators have questioned whether improvements in prenatal diagnosis might allow better selection of those fetuses most likely to benefit from in utero shunting. At present, however, such procedures are investigational.

Antepartum fetal monitoring — Antepartum fetal testing (eg, nonstress test, biophysical profile) has no proven benefit in pregnancies with isolated fetal ventriculomegaly in the absence of other fetal findings (eg, growth restriction, oligohydramnios) or pregnancy complications that have been associated with an increased risk for fetal demise.

Timing of delivery — We base delivery timing on standard obstetric indications. Some authors have suggested planned preterm delivery of fetuses with progressive severe ventriculomegaly because, theoretically, those with severe ventriculomegaly due to increased intracranial pressure may benefit from early postnatal shunting [59]. However, there is no evidence that expectant prenatal management is harmful, whereas the risks of preterm birth are well established. (See "Hydrocephalus in children: Management and prognosis".)

If preterm birth is being considered to improve postnatal outcome, this decision should be in consultation with neonatal and pediatric neurology/neurosurgery physicians.

Delivery route — Most fetuses with ventriculomegaly have a normal head circumference (HC); cesarean birth in these cases is performed for standard obstetric indications.

Special case: Hydrocephalus with severe macrocephaly

●For fetuses with hydrocephalus and macrocephaly, planned cesarean birth is indicated when dystocia due to cephalic enlargement is likely during labor, but the appropriate HC threshold is unclear. We believe cesarean birth should be considered when the HC exceeds 40 cm, as this is an extremely large head (in the United States the 50^th percentile at term is approximately 35 cm and the 97^th percentile is approximately 38 cm).

In an unselected obstetric population, 544 patients had fetal HC ≥35 cm (mean 35.45 cm) and most of these patients gave birth vaginally; however, their rate of unplanned cesarean was significantly increased compared with HC <35 cm (32 versus 17 percent, OR 2.49, 95% CI 2.04-3.03) [60].

In a series of fetuses with severe ventriculomegaly and macrocephaly (HC >95^th percentile for gestational age), the rates of vaginal and cesarean birth were 14 and 86 percent, respectively, at a median gestational age of 37+4 weeks [61]. (Note: The 95^th percentile for HC at 37+4 weeks is approximately 35 cm).

One group suggests consideration of planned cesarean birth when HC is >95^th percentile at term, given higher risks of unplanned cesarean, forceps- or vacuum-assisted vaginal birth, and obstetric anal sphincter injury [62].

●Cephalocentesis, which almost always results in fetal death, is rarely used to decompress the head, allow vaginal birth, and avoid maternal morbidity from cesarean birth. We suggest its use in cases in which the neurologic prognosis is so dismal (eg, trisomy 13 or 18 or lethal coexistent anomalies) that, if the fetus does not succumb from the procedure, the outcome will not be substantially changed. From an ethical standpoint, the physician's beneficence-based obligation to the pregnant patient allows them to avoid the increased risks of cesarean birth in cases in which such management would be of little benefit to the fetus [5].

Cephalocentesis is performed by making an incision at the base of the skull with a sharp instrument (eg, curved Mayo scissors), inserting a cannula, and then applying suction internally to collapse the calvarium [63].

RECURRENCE RISK AND COUNSELING FOR FUTURE PREGNANCIES

●Recurrence risk

•For cases of mild isolated ventriculomegaly in which the infant appears to be normal in appearance and behavior at birth and no associated abnormalities were identified prenatally, obtaining a neonatal ultrasound to assess the brain is reasonable. Further work-up (eg, imaging, genetic studies) is not indicated. In cases of isolated ventriculomegaly in which a precise cause is not determined, the recurrence risk is in the range of 4 percent, similar to that of other multifactorial disorders [6].  

For cases of moderate ventriculomegaly, the chance of additional findings on imaging is somewhat higher. Beginning with a neonatal ultrasound may be adequate if the newborn is otherwise normal in appearance and behavior and there are no additional concerns. In other cases, a neurology evaluation and/or additional imaging with magnetic resonance imaging may be appropriate [64].

•For cases of severe ventriculomegaly, a thorough newborn evaluation should be performed to confirm the diagnosis and determine the etiology, which informs recurrence risk. (See "Hydrocephalus in children: Physiology, pathogenesis, and etiology", section on 'Congenital' and "Hydrocephalus in children: Clinical features and diagnosis", section on 'Evaluation'.) The most common inherited form of hydrocephalus is X-linked recessive.

●Future pregnancy – We recommend detailed ultrasound examination at 18 to 20 weeks of gestation in a future pregnancy to look for recurrence. Importantly, it has been noted that in some cases ventriculomegaly may develop late in gestation or after birth, so a normal mid-trimester ultrasound does not definitively rule out this diagnosis. For example, mid-trimester sonography will not detect all fetuses with X-linked hydrocephalus [65]. For some diagnoses, such as polymicrogyria, fetal magnetic resonance imaging is appropriate, as it may detect these relatively subtle brain abnormalities not diagnosable by sonographic examination. (See "Hydrocephalus in children: Physiology, pathogenesis, and etiology".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Prenatal genetic screening and diagnosis".)

SUMMARY AND RECOMMENDATIONS

●Diagnosis – In the second or third trimester of pregnancy, the diagnosis of fetal ventriculomegaly is based upon ventricular dilation: mild 10 to 12 mm, moderate 13 to 15 mm, or severe >15 mm. The diagnosis of hydrocephalus is reserved for those cases where obstruction is visualized or can be inferred. (See 'Diagnosis' above.)

●Postdiagnostic evaluation – We suggest the following diagnostic evaluation when fetal ventriculomegaly is detected (see 'Postdiagnostic evaluation' above):

•Comprehensive sonogram – A comprehensive fetal sonogram to look for associated anomalies is required. (See 'Comprehensive sonographic evaluation' above.)

•Diagnostic amniocentesis (see 'Diagnostic amniocentesis' above)

-Microarray – We offer amniocentesis for chromosomal microarray to all patients. Measurement of alpha-fetoprotein and acetylcholinesterase may be helpful in some cases, but is not required if an open neural tube defect can confidently be excluded by ultrasound.

-Genomic testing – Comprehensive testing with targeted gene panels or exome sequencing may be useful in some cases (eg, positive family history of ventriculomegaly, associated anomalies). Consultation with a geneticist is warranted if such testing is being considered. We do not perform this testing in cases of isolated mild or moderate (<15 mm) ventriculomegaly because the yield is likely to be low.

-Testing for infection – We offer testing for selected infectious pathogens (cytomegalovirus and toxoplasmosis) in all cases of isolated ventriculomegaly and strongly recommend it if other markers suspicious for congenital infection are present. If amniocentesis is not performed, maternal serology is an alternative. Testing for Zika virus or other infections may be considered if risk factors or specific exposures are present.

•Role of MRI – We consider performing fetal magnetic resonance imaging (MRI) in cases of isolated ventriculomegaly on ultrasound in which the etiology is unexplained and additional information might impact counseling and management decisions. MRI is less useful in cases of known aneuploidy, but may assist in determining the extent of destructive injury in fetuses with infection, hemorrhage, or ischemia, and when other sonographically evident CNS malformations are present, so that counseling can be more informed and specific. (See 'Role of magnetic resonance imaging' above.)

•Follow-up third-trimester ultrasound – We perform a follow-up ultrasound examination at 28 to 34 weeks to assess progression or regression. (See 'Sonographic follow-up and prognostic findings' above.)

●Prognosis – Risk factors for an abnormal outcome include increasing severity of ventriculomegaly, progression of ventriculomegaly, and presence of other anomalies. Most children with isolated mild ventriculomegaly have a normal outcome. Most children with isolated moderate ventriculomegaly also have a favorable prognosis, but the risk of neurodevelopmental disabilities is increased. (See 'Counseling' above and 'Sonographic follow-up and prognostic findings' above.)

●Timing and route of delivery – Timing of delivery should be based on standard obstetric indications. Ventriculomegaly is not an indication for planned preterm birth. (See 'Timing of delivery' above.)

Fetuses with a normal head circumference may undergo vaginal birth, with cesarean birth reserved for the usual obstetric indications. (See 'Special case: Hydrocephalus with severe macrocephaly' above.)

●Recurrence risk – Recurrence risk ranges from 4 to 50 percent, depending upon the cause. (See 'Recurrence risk and counseling for future pregnancies' above.)