Bologna, Italy pilu@mbox.queen.it

Synonyms: Mild hydrocephalus, mild ventriculomegaly.

Definition:  mild enlargement of the lateral ventricles (atrial width 10-15 mm) in the absence of other sonographically demonstrable CNS anomalies.

Prevalence: uncertain. An atrial width of 10 mm is about 3 standard deviations above the mean.[1] The only two prospective series on low risk patients had conflicting results, spanning from 1:50 to 1:1600.[2]^,[3] The reason for such a discrepancy is not obvious. It may represent the consequence of a different technique for obtaining the measurement, or of a discrepancy in the gestational age of the fetuses examined.

Pathogenesis and pathology: Unknown. In most cases, it probably represents a normal variant. In other cases, mild enlargement of the lateral ventricles is the only obvious epiphenomenon of heterogeneous cerebral anomalies.

Diagnosis The widely accepted definition of borderline cerebral lateral ventriculomegaly is an atrial width of 10-15 mm on the transverse plane (figure 1-3).[4] Other proposed definitions include an atrial width of 10-12 mm[5] and a distance greater than 4 mm between the medial wall of the ventricle and the glomus of the choroid plexus.[6]

Figure 1: axial view of fetal cerebral borderline ventriculomegaly.

Figure 2: sagittal view of fetal cerebral borderline ventriculomegaly

Figure 3: coronal view of fetal bilateral cerebral borderline ventriculomegaly 

Differential diagnosis: Isolated borderline 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, spina bifida).  

Implications for targeted examination: The main problem in cases that are referred with borderline lateral ventricles is to exclude other neural and extra-neural malformations. We recommend careful Multiplan 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. Fetal echocardiography should also be performed. 

Implications for sonographic screening: In all standard sonographic examinations, a view of the lateral ventricles should be obtained, and at least one of the atria should be visualized and assessed. A qualitative evaluation is acceptable, and the presence of the choroid plexus filling the cavity of the atrium, being closely apposed to both the medial and lateral wall of the ventricle, is indicative of normalcy.  A quantitative approach is however favored, and a measurement less than 10 mm is considered normal between 15-40 weeks. [7] The natural history of borderline ventriculomegaly is unknown, but we expect that this finding may appear at times only in late in gestation and that a normal midtrimester exam does not exclude this condition. Borderline ventriculomegaly may be unilateral,[8] while in standard examination only one atrium is measured.

 Prognosis: Fetal borderline cerebral ventriculomegaly is a recently described and elusive entity. The available evidence suggests that this finding is most frequently without consequences. However, most of the available studies are consistent in indicating an increased risk of abnormal outcomes. A summary of these studies[9] is demonstrated in Table 1. Of 9 cases with aneuploidies, trisomy 21 was the most frequent one. It is unclear from most of the studies whether the couples had other risk factors for chromosomal aberrations. Several malformations were not detected sonographically. In particular, in 4% of cases developmental malformations of the cerebrum were found in late gestation or after birth including progressive hypertensive hydrocephalus and cystic brain lesions. Independently from the presence of aneuploidies or underlying malformations, most studies were consistent in indicating an excess of abnormal intellectual and motor development. This was predominantly of mild and moderate entity. Males were found to have borderline ventriculomegaly more frequently than females, and to have a lesser degree of abnormal outcomes (5% vs. 24%), and this is consistent with the observation that male fetuses tend to have a slightly greater atrial width than females.[10]^,[11] Abnormal outcomes were also more frequent with an atrial width greater than 11 mm (9 vs. 24%). Intrauterine remission of borderline ventriculomegaly has been documented. However, it is debated is this implies or not an amelioration of the prognosis. One shortcoming of the available studies is that they are mostly based upon measurement of one atrium, while it has been more recently demonstrated that borderline ventriculomegaly is frequently unilateral (Figure 4). It has also been proposed that the unilateral type is benign. However, in the original report of 30 cases some abnormal outcomes were reported, there was one fetus affected by trisomy 21 and one infant with seizures.[12]

Figure 4: coronal view of fetal unilateral cerebral borderline ventriculomegaly

Obstetrical management: A search for associated congenital anomalies including echocardiography is indicated. Limited data exist with regard to the association with chromosomal aberrations. However, the available studies report aneuploidies in 4% of cases, mostly trisomy 21. We believe therefore that at present it would be prudent to offer a procedure for fetal karyotyping. A workup for a congenital infection associated with hydrocephalus (i.e., toxoplasmosis, cytomegalovirus, and rubella) is also commonly recommended, although thus far an association has not been demonstrated. Infants with isolated borderline cerebral ventriculomegaly are at increased risk for developmental delay. It has been suggested that this finding could represent an indication for early childhood intervention, as special educational programs maximize the developmental potential.[13] However, counseling these couples is a major undertaking. It has been our experience that the communication that the infant has even a slightly increased risk of cerebral damage or low intellect causes major distress to most couples. We expect that at least some patients will request termination of pregnancy. This will raise a difficult ethical dilemma, as most cases of isolated borderline cerebral ventriculomegaly result in the birth of healthy infants. In continuing pregnancies, borderline cerebral ventriculomegaly is not an indication to modify standard obstetric care. We believe that serial scans should be performed, as in a handful of cases, ventriculomegaly and macrocrania may develop.

Reference

[1] Cardoza JD, Goldstein RB, Filly RA (1988): Exclusion of fetal ventriculomegaly with a single measurement: the width of the lateral ventricular atrium. Radiology 169:711-4.

[2] Alagappan R, Browning PD, Laorr A, McGahan JP (1994): Distal lateral ventricular atrium: reevaluation of normal range. Radiology 193:405-8

[3] Achiron R, Schimmel M, Achiron A, Mashiach S (1993): Fetal mild idiopathic lateral ventriculomegaly: is there a correlation with fetal trisomy? Ultrasound Obstet Gynecol 3:89-92

[4] Goldstein RB, La Pidus AS, Filly RA, Cardoza J (1990): Mild lateral cerebral ventricular dilatation in utero: clinical significance and prognosis. Radiology 176:237-42.

[5] Bromley B, Frigoletto Jr FD, Benacerraf BR (1991): Mild fetal lateral cerebral ventriculomegaly: clinical course and outcome. Am J Obstet Gynecol  164:863-7

[6] Mahony BS, Nyberg DA, Hirsch JH, Petty CN, Hendricks SK, Mack LA (1988): Mild idiopathic lateral cerebral ventricular dilatation in utero: sonographic evaluation. Radiology 169:715-21

[7] Filly RA, Goldstein RB, Callen PW (1991): Fetal ventricle: importance in routine obstetric sonography. Radiology 181:1-7.

[8] Lipitz A, Malinger G, Meizner I, Zalel Y, Achiron R (1998): Outcome of fetuses with isolated borderline unilateral ventriculomegaly diagnosed at mid-gestation. Ultrasound Obstet Gynecol 12:23-6.

[9] Pilu G, Falco P, Gabrielli S, Perolo A, Sandri F, Bovicelli L: The clinical significance of fetal isolated cerebral borderline ventriculomegaly: report of 31 cases and review of the literature. Ultrasound Obstet Gynecol (in press)

[10] Patel MD, Goldstein RB, Tung S, Filly RA (1995): Fetal cerebral ventricular atrium: difference in size according to sex. Radiology 194:713-5.

[11] Nadel AS, Benacerraf BR (1995): Lateral ventricular atrium: larger in male than female fetuses. Int J Gynecol Obstet 51:123-6.

[12] Lipitz A, Malinger G, Meizner I, Zalel Y, Achiron R (1998): Outcome of fetuses with isolated borderline unilateral ventriculomegaly diagnosed at mid-gestation. Ultrasound Obstet Gynecol 12:23-6.

[13] Bloom SL, Bloom DD, Dellanebbia C, Martin LB, Lucas MJ, Twickler DM (1997): The developmental outcome of children with antenatal mild isolated ventriculomegaly. Obstet Gynecol 90:93-7