Fetal cerebral ventricular measurement and ventriculomegaly: time for procedure standardization

In this issue of the Journal, Melchiorre et al.1 provide clear, up-to-date, evidence-based answers to the questions most commonly raised by the diagnosis of isolated mild fetal ventriculomegaly. While the issues raised by the authors are important and represent a real challenge in fetal medicine, in our experience first and foremost must be to establish whether the ventriculomegaly actually exists, which is itself a challenge in the absence of a clear and standardized method of measurement. To measure the ventricle reliably is particularly problematic when the ventricular measurement is close to the standard threshold of 10 mm, a situation that is often referred to as ‘borderline ventriculomegaly’. We share the view of Melchiorre et al. that this expression should be avoided, as it suggests the presence of a gray zone which is inappropriate in the context of a biometric parameter with a fixed cut-off value. In clinical practice, when faced with a ‘borderline’ measurement, some physicians will record it as being just below the threshold so as to be considered normal, while the vast majority, due to pessimism or prudence, tend to diagnose ventriculomegaly. As a result, in our department, a large number of fetuses referred for ventriculomegaly between 10 and 12 mm have normal ventricular measurements when we examine them (Figure 1). Difficulty in measurement may also explain the large variation in incidence of isolated mild ventriculomegaly, which, according to various studies in low-risk populations, has been found to be between 1/50 and 1/16001. The issue was recently revisited by Levine et al.2 in an interesting analysis of the frequency and causes of disagreement in diagnosis of fetal ventriculomegaly2. They showed that differences of opinion between physicians in the diagnosis of ventriculomegaly were prevalent; among four physicians, all highly experienced at high-risk obstetric ultrasound, disagreement regarding the presence of ventriculomegaly on ultrasound was encountered in 10% of 196 cases. Interestingly, in cases that were subject to disagreement, the physcians who indicated that ventriculomegaly was present consistently recorded a larger ventricular atrial diameter (mean, 10.2 mm) than did those who indicated that ventriculomegaly was absent (mean, 8.4 mm). For a given fetus, the variation in ventricular diameter among the four physicians was 0.3 mm. As suggested by Hilpert et al.3, if disagreement in 10% of cases can be encountered in an expert medical population, with a variation in ventricular diameter measurement of 0.3 mm, we might expect these values to be even higher in a less-trained medical population. The consequences of such difficulties in measurement are important since ventriculomegaly is the pivotal finding for diagnosing central nervous system (CNS) pathology, justifying invasive procedures such as fetal karyotyping and generating considerable parental anxiety regarding the postnatal outcome1,4. Even when there is a falsepositive test result on the initial routine ultrasound examination and the diagnosis is ultimately rejected, the anxiety generated does not dissipate easily. These issues regarding the measurement of the lateral ventricles and the medical and psychological consequences therefore justify revisiting the standardization of the measurement technique. The reference method of sonographic ventricular measurement was described by Cardoza et al. in 19885. The potential measurement error on sonographic evaluation was reported 2 years later by Heiserman et al.6, who found that measurement of the lateral ventricle can be subject to error due to an off-axis image plane, an angled measurement, or an improper choice of ventricular boundary, all of which tend to lead to false-positive test results6. We provide here an image-scoring method similar to the one published by Herman et al. for nuchal translucency measurement7, which can be used either as the first step in quality control or, at the very least, as an auto-evaluation tool in routine practice. Our image-scoring method builds on previously published recommendations (including the method initially described by Cardoza et al.5) and makes use of improved anatomical details provided by modern equipment, which enables clear delimitation of the atrium independently of the choroid plexus. This scoring method is based on two sets of three criteria (summarized in Table 1). The primary criteria (Criteria 1–3) provide the adequate reference image to perform atrial width measurement, while the secondary criteria (Criteria 4–5) ensure a high quality of measurement by appropriate caliper placement on an optimally magnified image. The first set of criteria evaluates the quality of: the axial plane, the anatomical level, and the site of measurement of the atrial width. Criterion 1 (Score 0–2) provides a strict axial plane. The midline structures should be equidistant from the proximal and distal calvarial margins (Criterion 1a, Score 0–1) and perpendicular to the ultrasound beam (Criterion 1b, Score 0–1). Regarding Criterion 1a, Heiserman et al.6 have demonstrated that an off-axis image plane provides