Ventriculomegaly
Ventriculomegaly is a brain condition that occurs when the lateral ventricles become dilated. The most common definition uses a width of the atrium of the lateral ventricle of greater than 10 mm (Cardoza, 1988). This occurs in around 1% of pregnancies (Salomon, 2007). When this measurement is between 10 and 15 mm, the ventriculomegaly may be described as mild to moderate. When the measurement is greater than 15mm, the ventriculomegaly may be classified as more severe (Breeze, 2007). Enlargement of the ventricles may occur for a number of reasons, for example due to loss of brain volume (perhaps due to infection or infarction), or due to impaired outflow or absorption of cerebrospinal fluid from the ventricles. Often, however, there is no identifiable cause. The interventricular foramen may be congenitally malformed, or may have become obstructed by infection, hemorrhage, or rarely tumor, which may impair the drainage of cerebrospinal fluid, and thus accumulation in the ventricles. This diagnosis is generally found in routine fetal anomaly scans at 1822 weeks gestation. It is one of the commonest abnormal brain findings on prenatal ultrasound, occurring in around 1-2 per 1000 pregnancies (Achiron et al, 1993). In many cases of mild ventriculomegaly, however, there is resolution of ventriculomegaly during the pregnancy.

# Associations
Ventriculomegaly is also known to be associated with other malformations such as agenesis
-f the corpus callosum, spina bifida, and heart defects. Fetuses with both isolated ventriculomegaly and with other anomalies have an increased risk of having a chromosomal abnormality, including that of Down Syndrome (Breeze, 2007; Gaglioti, 2005).
Many conditions associated with ventriculomegaly can be defined prior to birth, but the possibility remains of other anomalies (either structural, chromosomal or genetic) only being identified later in pregnancy or after birth (Breeze, 2005). Ventriculomegaly associated with abnormal findings and other structural malformations, often has an adverse prognosis, which ranges from disability (often mild) to death. However, in cases of mild isolated ventriculomegaly, there is around a 90% chance of a normal outcome (Signorelli, 2004; Gaglioti 2005).
Increasingly, fetal magnetic resonance imaging is being considered as part of the assessment of pregnancies complicated by fetal ventriculomegaly (Glenn & Barkovich, 2006), and appears to be important in the postnatal assessment of affected children (Falip, 2007)
References:
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: 8992.
Breeze AC, Dey PK, Lees CC, Hackett GA, Smith GCS, Murdoch EM. 2005. Obstetric and neonatal outcomes in apparently isolated mild fetal ventriculomegaly. J Perinat Med 33: 236240  Abstract
Breeze AC, Alexander PM, Murdoch EM, Missfelder-Lobos HH, Hackett GA, Lees CC. 2007. Obstetric and neonatal outcomes in severe fetal ventriculomegaly. Prenat Diagn. 27(2):124-9  Abstract
Cardoza JD, Goldstein RB, Filly RA. 1988. Exclusion of fetal ventriculomegaly with a single measurement: the width of the lateral ventricular atrium. Radiology 169: 711714.
Falip C, Blanc N, Maes E, Zaccaria I, Oury JF, Sebag G, Garel C. 2007. Postnatal clinical and imaging follow-up of infants with prenatal isolated mild ventriculomegaly: a series of 101 cases. Pediatr Radiol. 2007 Oct;37(10):981-9.  Abstract
Gaglioti P, Danelon D, Bontempo S, Mombro M, Cardaropoli S, Todros T. 2005. Fetal cerebral ventriculomegaly: outcome in 176 cases. Ultrasound Obstet Gynecol. Apr;25(4):372-7.
Glenn OA, Barkovich AJ. 2006. Magnetic resonance imaging of the fetal brain and spine: an increasingly important tool in prenatal diagnosis, part 1. AJNR Am J Neuroradiol. Sep;27(8):1604-11.
Signorelli M, Tiberti A, Valseriati D, Molin E, Cerri V, Groli C, Bianchi UA. 2004. Width of the fetal lateral ventricular atrium between 10 and 12 mm: a simple variation of the norm?
Ultrasound Obstet Gynecol. Jan;23(1):14-8.
Salomon, LH, Bernard JP, Ville Y. 2007. Reference ranges for fetal ventricular width: a non-normal approach . Ultrasound Obstet Gynecol (in press) Abstract