Posterior Palatine Line: A Marker for Cleft Secondary Hard Palate

Keywords

2D ultrasound - cleft lip - cleft palate - posterior palatine bone - pterygoid process - secondary hard palate - secondary palate

Introduction

The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) and most professional societies have recommended three planes for fetal face evaluation: midsagittal view for facial profile, coronal view of the nose and lips, and axial view of the orbits.

Evaluation of the palate is not a routine component of the midtrimester anomalies scan at 19 to 23 weeks. The incidence of cleft lip (CL) with or without palate or isolated palate defect is 1 in 500 to 1 in 1,000 births[1] and can be isolated or a part of a syndrome. CL and cleft of the alveolar ridge are easy to diagnose, but involvement of the secondary palate (SP) with CL or in isolation is challenging to diagnose. Prenatal detection is very low, although many signs have been described by various authors using 2D and 3D ultrasound. Wilhelm and Borgers[2] suggested the “equal sign” to evaluate a normal soft palate. The “absent superimposed line” sign to evaluate SP by Lakshmy et al[3] is a very useful sign to detect midline SP defect between 12 and 20 weeks. Fuchs et al[4] suggested a 2D axial view of the hard palate (HP) to detect SP involvement. We used this 2D axial view to evaluate our midtrimester fetuses.

Methods

We prospectively evaluated 1,450 midtrimester fetuses ranging from 18 to 26 weeks, between December 2023 and June 2024. All midtrimester fetuses with or without anomalies were included. We included three views as suggested by the ISUOG 20 + 2 planes approach to evaluate the fetal face. These are the midsagittal section of the face (profile view), a coronal view of the nose and lips, and an axial view of the orbits. We added a 2D axial view of the posterior HP in all the fetuses as recommended by Fuchs et al.[4]

All images were acquired by the Expert 22 and Voluson E 10 machine (GE, Austria). This view is obtained when the fetal spine is posterior and the face is facing toward the transducer. With the face facing toward the transducer (profile view), the transducer is rotated 90 degrees to visualize both eyes. From this axial view, the transducer is tilted to view the alveolar ridge and further adjusted to view the posterior transverse echogenic plate of the palatine bone and two pterygoid processes as they look connected to the lateral edges of the transverse plate ([Figs. 1] and [2]). Complete visualization of the horizontal plate of the palatine bone without any interruption is a normal posterior palate and considered an “intact posterior palatine line.” This view is best obtained when both the orbits are facing toward the transducer ([Fig. 1A]).

Fig. 1 (A) 2D ultrasound image of axial orbital view as an initial view and (B) tilting the probe in the same view to get view of the premaxilla (y). (C) Fine manipulation to view the horizontal plate of the palatine bone (arrow) with median pterygoid processes (x). (D) Defect in the horizontal plate of the palatine bone (arrow) suggests secondary hard palate defect.

Fig. 2 (A) Graphic and (B) 2D ultrasound demonstration of the normal posterior palatine line (arrow) with both median pterygoid processes (x). (C) 2D and (D) 3D images of case 3 show a cleft SHP (arrow) with vomer bone (v) and bilateral CL and premaxillary protrusion (y). (E) 2D and (F) postnatal images of case 4 show a normal SHP (arrow) with a bilateral cleft lip and a premaxillary protrusion (y). Note the normal SHP in (F). (G) 2D and (H) postnatal images of case 5 show a cleft SHP (arrow), a bilateral CL (y), and vomer bone (v). CL, cleft lip; SHP, secondary hard palate.

Results

We were able to visualize the posterior palatine region in 1,448 of 1,450 and not in 2 cases due to high body mass index and unfavorable fetal position. We were able to visualize satisfactorily the posterior palatine region in 1,448 cases. We found facial cleft in 12 cases as shown in [Table 1]. Discontinuity in the horizontal plate was found in nine cases and categorized as “cleft in the posterior palatine line.” Two cases had isolated cleft secondary hard palate (SHP) without CL as the posterior palatine line was open ([Fig. 3A, 3B]). Three cases of CL were without a cleft of the SHP as the posterior palatine line was intact ([Figs. 2E, 2F]; [Figs. 3C, 3D, 3G, 3H]). We tried to examine the vomer in the same axial view to see if it was visible through the palatine defect from anterior to posterior. In some cases of CL and palate (CLP) and SP defect, the vomer was visible through the defect ([Table 1;] [Fig. 2C]). We found two cases of median CLP with a severe holoprosencephaly and absent nose (arrhinia) and typically we noted the absence of the vomer because the nose was absent ([Fig. 3E, 3F]). Of the nine cases of a cleft in the posterior palatine line, the defect was confirmed in seven cases postnatally or after termination. Two cases were lost to follow up. In the three cases of CL with an intact posterior palatine line, there was no defect in the SHP as confirmed in two cases postnatally. We followed the majority of normal cases using the medical records and telephone based questionnaires with an intact palatine line for normal HP. Of the 1,450 cases, we were able to follow up 1,123 normal cases and 9 abnormal cases. We were not able to follow up in 313 normal and 3 abnormal cases ([Table 1]) in our cohort. None of the normal cases had an HP defect postnatally. We did not evaluate for soft palate defect.

Table 1 Description of 12 cases of facial cleft including CL, cleft PP (premaxilla), and SHP

Sl. no.	GA (wk)	Posterior palatine line defect	Cleft SP	Cleft lip	Cleft PP (premaxilla)	Vomer seen	Associated findings	Outcome	Postnatal F/U
1	20	Yes	Yes	B/L	B/L protrusion	Yes	TOF, microtia	Termination	Yes
2	20	Yes	Yes	U//L	U/L	No	No	Termination	Yes
3	22	Yes	Yes	B/L	B/L	Yes	No	Termination	No
4	28	No	No	B/L	B/L	Partial	Cerebellar hypoplasia, VSD	PROM PTVD	Yes
5	24	Yes	Yes	B/L	B/L	Yes	No	PTVD	Yes
6	28	No	No	U/L	No	No	No	FTND	Yes
7	24	Yes	Yes	U/L	U/L	No	No	PTVD	Yes
8	20	Yes	Yes	Median	Yes	Absent	Holoprosencephaly, arrhinia	Termination	No
9	20	No	No	U/L	U/L	No	No	Termination	Yes
10	18	Yes	Yes	No	No	Yes Posterior	Skeletal dysplasia, micrognathia	Lost to F/U	No
11	18	Yes	Yes	No	No	No	Cerebellar hypoplasia	Termination	Yes
12	22	Yes	Yes	Median	Yes	Absent	Holoprosencephaly, arrhinia	Termination	Yes

Abbreviations: B/L, bilateral; CL, cleft lip; FTND, full term normal delivery; F/U, follow up; GA, gestational age; PP, primary palate; PROM, premature rupture of membrane; PTVD, preterm vaginal delivery; SHP, secondary hard palate; TOF, tetralogy of Fallot; U/L, unilateral.

Fig. 3 (A) 2D and (B) post abortus images of case 11 show an isolated cleft SHP (arrow) with intact lip and PP. (C) 2D and (D) post abortus images of case 9 show a normal SHP (arrow) and an isolated UCL (x). (E) 2D and (F) 3D images of case 12 show a cleft SHP (arrow) and a median CL (o). (G) 2D and (H) 3D images of case 6 show a normal SHP (arrow) and a UCL (x). CL, cleft lip; PP, primary palate; SHP, secondary hard palate; UCL, unilateral cleft lip.

In these 12 cases, we advised chromosomal microarray and next generation sequencing, but this was refused by relatives because of the cost factor. 2D ultrasound findings of cleft, associated findings, and outcome are illustrated in [Table 1]. [Figs. 2] and [3] illustrate normal and abnormal cases.

Discussion

CLP and isolated cleft palate (CP) are two different entities. While the prenatal diagnosis of CL and CLP is quite easy using conventional 2D and 3D sonography, CP/SP is more difficult to identify, especially if it is an isolated anomaly. CLP always starts at the lip and proceeds to different extents in the dorsal direction (alveolus, HP, soft palate). SP defects always start at the uvula (uvula bifida as the mildest form) and proceed along the midline in the anterior direction, affecting either only the soft palate or both the soft palate and the HP. The embryology of palate formation is important to understand facial clefts.[5] In the sixth week, the palatine processes of the maxilla grow medially to fuse in the midline. Fusion proceeds in a posterior direction from the incisive foramina.

Search for isolated SP is not recommended due to lack of a standardized and reproducible technique. According to the ISUOG 20-plane approach, three views are recommended for the fetal face. By a midsagittal view, the cleft upper lip and premaxillary protrusion can be detected. Lakshmy et al[3] suggested the “absent superimposed line sign” for SP defect in this view. A coronal view of the nose and lips can be abnormal in a unilateral or a bilateral CL. The third view is an axial view for orbit assessment.

Because the palate is a dome shaped structure, the entire palate cannot be visualized by 2D. Also, shadowing from the maxilla complicates sonographic assessment. 3D evaluation of the palate requires the neck in an extension position with fluid in the oral cavity. As the SP closes from anterior to posterior, visualization of the normal uvula as described by Wilhelm and Borgers[2] implies an intact palate. The “absent superimposed line” sign suggested by Lakshmy et al[3] is a very useful sign to evaluate a midline SP defect in early pregnancy between 12 and 20 weeks, where absence of the lower line instead of the normal two echogenic lines formed by the vomer and SP is suggestive of an SP defect. The retronasal triangle as suggested by Sepulveda et al[6] can identify clefts of the premaxilla in the first trimester but not cleft of the SP. Suresh et al[7] suggested evaluation of the premaxillary triangle to detect CLP in midtrimester fetuses. The maxillary gap sign suggested by Chaoui et al[8] is a useful marker to identify a CL with a primary palate at 11 to 13 weeks. The “flipped face” view as described by Platt et al[9] and the “reverse face” view as described by Campbell et al[10] require adequate 3D volume to view the SP. Fuchs et al[4] described the 2D axial transverse view of the fetal face to detect a cleft SP, that is, disruption of the horizontal plate of the palatine bone of the SP. We incorporated this view. The posterior edge of the HP with two medial pterygoid processes forms an incomplete box; the pterygoid processes of a sphenoid bone form the two lateral edges of the horizontal plate and these are used as a landmark for proper view. The anterior axial view of both orbits to measure the inter orbital diameter is the initial view. Alternatively, after the profile view of the face, the transducer is rotated 90 degrees. The transducer is then tilted to view the premaxilla (alveolar ridge with tooth buds) followed by fine manipulation to view the horizontal plate of the palatine bone and the pterygoid processes ([Figs. 1] and [2]). Fuchs et al[11] described a 3D method to detect a CP without a CL. They described disruption of the horizontal plate in the axial 3D view as a cleft SP and described four different types of cleft SP. We used a 2D axial view as previously described by the same group and we did not classify them. Type 1 defect is similar to a cleft of the uvula, which is a minor cleft of the horizontal plate and seems difficult to detect.

The advantage of this view is that it is easy to acquire after practice, reliable, less time consuming, and has a very low false positive rate. This method can image, from anteriorly, the nose and lips, the premaxilla (primary palate) to the posterior bony edge of the HP, and the nasal spine.

Incorporating the coronal view of the nose and lips as recommended by the in the ISUOG, and axial view of the “posterior palate line” to detect CL and cleft SHP should be considered during anomalies evaluation. If a CL is detected, involvement of the premaxilla should be assessed by an axial view of the premaxilla.

Our study has some limitations. The number of both normal and abnormal cases is low and different types of cleft SP were not classified.

Conclusion

This method of ultrasound enables the visualization of the SHP. If the line is intact, the SHP is normal. A cleft in the line is indicative of an SHP defect. Visualization of the posterior palatine line in routine anomaly scan might enhance the detection rate of an isolated cleft of the SP. This method is easy to perform in optimal conditions. Further research is required to assess the false positive and false negative rates of this sign.

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