The premaxillary triangle: clue to the diagnosis of cleft lip and palate

The prenatal detection rate of cleft lip and palate is low, especially in low-risk patients who undergo targeted sonography. The reason is that evaluating surface anatomy is relatively difficult and requires operator expertise. Our purpose was to describe a technique to improve the diagnostic accuracy of facial clefts (lip and palate) and to assess the feasibility of including this technique as part of standard protocol during targeted imaging.

A prospective study was done during 2000 through 2002 to evaluate the accuracy of the "premaxillary triangle (PMT) sign": a new sign to diagnose unilateral cleft lip and palate in women referred for prenatal sonography at our center. Patients with only isolated unilateral cleft lip and palate and cleft lip were included in this study. Before this, all examiners were trained to image the PMT. The images were reviewed by a senior consultant. It was later decided to include this sign as part of the protocol of targeted sonography done between 18 and 22 weeks in our institution. However, depending on the fetal position, the PMT was documented even in patients referred for the first time in late second and third trimesters.

Twenty-nine cases of isolated facial clefts were diagnosed during the study period, of which 2 had unilateral cleft lip and 27 had unilateral cleft lip and palate. The PMT sign was absent in all cases of unilateral cleft lip and palate but was present in 2 cases of isolated cleft lip without cleft palate.

The PMT sign can be easily incorporated into targeted sonography at 18 to 22 weeks' gestation. Its inclusion would help in increasing the detection rate of unilateral cleft lip and palate. It may also be potentially used for differentiating between isolated cleft lip and cleft lip and palate, which helps in better prenatal counseling.