Reply.

Abstract

We thank Drs Lachmann and Brückmann for their comments regarding measurement of the palatomaxillary diameter (PMD) in our recent paper. Having analyzed their comments, we would like to make the following clarifications. Our study objective was to present the superimposed-line sign and to compare it with known potential markers in the midsagittal view which raise suspicion of palatine cleft1. In the Methods section of their original paper on PMD2, they state: ‘Therefore, we wanted to find a measurable correlate of the reduced ossified maxillary area at 20–22 weeks using the midsagittal view for measurement of nuchal translucency.’. As per the concluding remarks in their Abstract, ‘In the midsagittal view of the fetal head, face, and brain at 11–13 weeks, the majority of fetuses with isolated CLP [cleft lip and palate] have a measurable abnormality, the PMD.’2. This would have the reader measure the maxillary line in the same midsagittal view as that used for measurement of nuchal translucency. Hence, we did likewise, while at the same time attempting to make clear that it is possible that shortening of the maxillary line might be visible not in the midsagittal view but in a sagittal view slightly off the midline (figure 4 in our original paper1). The figure legend in our original paper clearly states that part (b) is a parasagittal image showing shortening of PMD, with the defect indicated. In the Abstract Results section of the original PMD paper2, they said: ‘Firstly, 5 out of 6 referred pregnancies with isolated CLP were detected prospectively using the midsagittal view’. This could falsely reassure the operator that both PMD and the maxillary gap can be seen in the midsagittal view. Our purpose in measuring the PMD in the midsagittal view was only to highlight that there will be no obvious shortening of the maxillary line in the midsagittal view in a substantial number of cases, as the vomer mimics the maxillary line. In the Discussion section of their original PMD paper2, they say: ‘Our suggested combined approach to detect or exclude high-risk pregnancies for CLP would imply maxillary gap sign and measurement of PMD assessed in mid-/parasagittal views at the same time of nuchal translucency evaluation and coronal cross-sections as described by Sepulveda et al.’. Our primary intention was to draw the attention of the reader to the appearance of the maxillary line in midsagittal and parasagittal views, as they described in their original paper. Though, in most affected cases, the maxillary gap and maxillary length are abnormal in the midsagittal view, in a few cases, when the cleft in the secondary palate is small and confined to the posterior part of the palate, these signs may not be evident in the midsagittal view. The midline echo seen in secondary palatine clefts is actually a reflection of the nasal septum and vomer, as has been observed previously3. The scientific basis behind the observation of Drs Lachmann and Brückmann in measuring the PMD correlates with ours, as, when one scrolls from left to right through sagittal sections to measure the shortest hyperechogenic distance, one tends to lose the reflection of the vomer in the midline, and shortening can be identified. It is clear that the shortest distance, which, by definition, is required for measurement of PMD, is not always obvious in the midsagittal section. It would perhaps have been preferable to say in the conclusion of their original PMD paper that ‘the midsagittal view for measurement of nuchal translucency shows high reproducibility regarding abnormal views for maxillary gap sign, and, in sagittal views of the fetal head, face and brain at 11–13 weeks, the majority of fetuses with isolated CLP have a measurable abnormality, the PMD’. Their having used ‘midsagittal view’ rather than ‘sagittal views’ could mislead readers to attempt to measure the palatomaxillary distance in that view only. Regarding the comment of Drs Lachmann and Brückmann that, in one of our figures (figure S6), we presented only ‘one cross-section, thereby preventing assessment of PMD’, we would like to emphasize that the purpose of our study was to highlight the appearance of the vomeromaxillary junction in normal cases and in cases with secondary palatine cleft; the study was not intended to validate PMD. In the original PMD paper itself, abnormal PMD was observed only in cases of isolated cleft palate and was not evaluated in unilateral or bilateral CLP; hence, we have not evaluated PMD in all types of CLP in our cases. We believe that our images satisfy our primary intention, which was to evaluate the superimposed-line sign and confirm the defect in multiplanar imaging. The line diagram in figure 2a of their Correspondence shows that the PMD (red line) ends with the posterior border of the visible palate in secondary palatine clefts. However, the confounding appearance of the vomer in the midsagittal view has not been accounted for. We have modified the image to do so herein (Figure 1), in which the posterior border of the palate is indicated by the red asterisk and our white line indicates the nasal septum and vomer. Note the red line of the PMD ends at the asterisk. We would like to emphasize that the figures used by Drs Lachmann and Brückmann from our original paper still create confusion, as the authors themselves measured PMD at two different anatomical locations in two cases of complete bilateral CLP (Figure 2). In Figure 2a (figure S9b of their figure 1), the red line does not correspond to the PMD shown in their line diagram, whereas, in Figure 2b (figure 5b of their figure 1), they have measured the true anatomical correlate correctly. We have modified Figure 2a to show the corresponding anatomical landmark (yellow line) in Figure 3. To illustrate this point, in Figure 3, which is a case of bilateral CLP involving the secondary palate, the posterior border of the palate stops with the premaxillary portion itself, and the palate beyond the premaxillary portion is absent. We have indicated the posterior border of the palate () in the line diagram and in our ultrasound image (Figure 3). The yellow line that we have added to our ultrasound images (Figure 3) is the true anatomical correlate of the red line shown in the line diagram. The red line that they placed in our ultrasound image is not the true anatomical correlate of the corresponding line in their line diagram. Figure 3 illustrates the discrepancy between the two anatomical regions (yellow line and red line). A clear understanding of the vomeromaxillary junction will avoid measurement of the vomer and nasal septum as the palate. The maxillary length measured in the midsagittal view in our paper1 was mentioned only to make it clear to the reader that there might not be a measurable abnormality in the midsagittal view and that one might need to look at parasagittal sections slightly off the midline in order to identify this shortening. We hope that we have addressed their points and would be very happy to clarify any further queries on this topic.