Distal lateral ventricular atrium: Reevaluation of normal range

PURPOSE: To reassess the mean size of the lateral cerebral ventricular atrium in the fetus. MATERIALS AND METHODS: Measurements were obtained from axial ultrasound (US) images of 500 fetuses by using the standard criteria, and they were reviewed for consistency. Eleven fetuses had ventricular atrial measurements of 10 mm or more, and they were also followed up. Postnatal evaluation consisted of US examinations of the head in three patients and clinical examination of all 11 patients. RESULTS: The mean size of the ventricular atrium was 6.6 mm with a standard deviation (SD) of 1.4 mm. However, the mean plus 2.5 SD would yield an upper normal limit of 10.1 mm. Findings at the postnatal examinations of the 11 fetuses with isolated lateral ventriculomegaly (three with measurements of 13 mm or less and eight with measurements at 10 mm) were normal. CONCLUSION: Use of 10 mm (mean from this study plus 2.5 SD) as the upper limit of normal for the ventricular atrial measurement should be continued. Measurements of 10 mm or above should prompt a careful search for associated fetal abnormalities and consideration of amniocentesis.