Mild Ventriculomegaly

Mild hydrocephalus, borderline ventriculomegaly

A measurement of the atrial width of cerebral lateral ventricles of 10-15 mm.; others suggest a further subdivision into measurements of 10-12 mm (mild ventriculomegaly) and 13-15 mm (moderate ventriculomegaly). The enlargement in unilateral in about 60% of cases, and bilateral in the remaining 40%.

Controversial; in the largest prospective prenatal study thus far available the prevalence was 1% of all fetuses in the second an third trimester of pregnancy.⁷

There is predominance of males (roughly 75% of cases).²

In most fetuses, mild ventriculomegaly is a normal a variant. In other cases, mild enlargement of the lateral ventricles may be the only obvious epiphenomenon of heterogeneous cerebral anomalies.

Isolated mild ventriculomegaly should be differentiated from more complex abnormalities of the fetal brain that have frequently a different prognosis (e.g. agenesis of the corpus callosum, cortical malformations. etc). Multiplanar brain imaging possibly by the transvaginal route is recommended. Several reports suggest that MR may be a useful adjunct to sonography, particularly in late gestation.^{2, 8-10}

The main problem in cases that are referred with mild dilatation of the lateral ventricles is to exclude other neural and extra-neural malformations. We recommend careful multiplanar examination of the fetal brain, performed if possible with a high resolution vaginal probe, and a detailed evaluation of the spine. Both lateral ventricles should be visualized and assessed as this condition can be unilateral. A detailed evaluation of entire fetal anatomy, including fetal echocardiography should also be performed. The use of magnetic resonance has also been advocated^{2, 8-10} although the yield of anomalies detected over a well performed sonographic examination is limited.

Assessment of the size of the lateral ventricles is an essential component of the evaluation of fetal anatomy in second and third trimester sonographic examinations. Different approaches have been proposed but measurement of the width of the atrium, or posterior horn is favoured by many. Congenital ventriculomegaly may develop late in gestation, and a normal midtrimester exam does not exclude this condition.

In most cases, mild ventriculomegaly is a normal variant without consequences. However, most of the available studies are consistent in indicating an increased risk of abnormal outcomes. The likelihood of trisomy 21 is 9 fold increased over the general population.² Despite careful antenatal assessment, anomalies will be present at birth in about 13% of cases.² Most of these anomalies are mild and of little consequence, but developmental malformations of the cerebrum including progressive hypertensive hydrocephalus, cystic brain lesions and abnormal cortical development have been documented in up to 4% of cases.² The problem of abnormal neuro-developmental in infants with prenatal diagnosis of mild ventriculomegaly has been the object of many studies. The limitations of the available experience have been discussed in a recent review.² Assessment of neurodevelopmental outcome is not easy, and the results depend upon the time and type of follow-up. The available studies are heteregenous, but overall the rate of neurologic abnormalities is in the range of 11%, and it is unclear whether this is increased or not over the general population.^{2, 14} Motor development is more affected than cognitive and adaptive behaviour.¹⁴ The prognostic factors for abnormal development include: the size of the ventricles (atrial width 13-15 mm and 10-12 mm and are associated with abnormal development in 17.7% and 7.8 % of cases respectively, with a relative risk of 2.276, and a 95% confidence interval of 1.233–4.202; p = 0.015)^{2, 14} the association with other abnormalities undetected at the time of the first diagnosis (about 13% of cases)² and progression of the ventricular dilatation (about 16% of cases).² There is the impression that females, that are less frequently affected by mild ventriculomegaly than males, have a higher probability of abnormal development but thus far the difference has not been found to be statistically significant.² Unilateral and bilateral enlargement have similar outcomes.^{2, 6}

Mild lateral cerebral ventriculomegaly is frequently associated with neural and extra neural anomalies and therefore a careful evaluation of the fetal anatomy should be carried out using expert ultrasound examination and, if possible, transvaginal neurosonography. Where available, fetal MRI is also indicated although there is no consensus on the optimal time for this examination. The likelihood ratio for trisomy 21 is about 9 and invasive testing for chromosomal analysis should be offered. Maternal serum cytomegalovirus and Toxoplasma studies should be considered. Follow-up sonograms and/or MRI in the third trimester should be considered.²

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