Objective: The incidence of abnormal chromosomes in fetuses with mild lateral ventriculomegaly as an isolated prenatal ultrasound finding is not well established, and the rate of progression to more severe ventriculomegaly is uncertain. We wished to better define both the incidence of karyotypic abnormalities and the in utero course of fetuses with isolated mild ventriculomegaly.
Subjects and methods: From July 1992 to September 1994, all cases of mild ventriculomegaly at our institution were reviewed (N = 94). Forty-six were isolated. Of these, 25 had genetic evaluation, and 37 had serial ultrasound examination. We evaluated the frequencies of karyotype abnormality and in utero progression for atrial measurements of 11-15 mm.
Results: In fetuses with atria 11-15 mm, three of the 25 karyotypes were abnormal (47 XXY and two 47 + 21, giving an incidence of 12% (95% CI 4.2-30.1%). Of the 37 with serial scans, five resolved in utero, 11 remained unchanged, and 20 progressed (one beyond 15 mm).
Conclusion: Isolated mild ventriculomegaly is associated with a significantly increased incidence of chromosomal abnormalities. Therefore, these patients should be offered genetic testing. When mild and isolated, some fetuses will show in utero resolution of the ventriculomegaly. Progression to more severe degrees of hydrocephalus is uncommon.