Fig. 3.1
Sagittal two-dimensional ultrasound view in a 13-week fetus. The fetal profile is clearly depicted despite the small size of the fetal face; calipers denote the nasion-to-chin distance, which in this case was 12 mm
Fig. 3.2
Sagittal view of the fetal head used for first-trimester aneuploidy screening purposes to measure the nuchal translucency (NT) thickness and assess the nasal bone (NB). The facial structures that are clearly visualized at this gestational age are: 1 frontal bone, 2 prefrontal and prenasal subcutaneous tissue, 3 nasal skin, 4 tip of the nose, 5 upper lip, 6 lower lip, 7 chin, 8 palate, 9 oral cavity and tongue, 10 mandibular bone
In the coronal plane (Fig. 3.3), the two frontal bones are visualized in the upper aspect of the face, which at this gestational age appear clearly separated in the midline by the metopic suture. In a slightly more caudal view, the eyeballs can be identified as predominantly anechoic, paired structures within the orbits. Within each eyeball, the lens is seen as a small, anechoic round structure surrounded by an echogenic rim. In the midface, the maxilla is the most prominent structure, which is seen as an echogenic, triangular-shaped structure forming the “retronasal triangle” (RNT) corresponding to the alveolar ridge at the base and the frontal processes of the maxilla laterally (Fig. 3.4) [43]. At the top of the RNT, the nasal bones can be easily seen [44,45]. In the lower part of the face, the right and left mandibular bones are seen, normally displaying a gap between them (the “mandibular gap”) [46]. In between the maxilla and mandible, the mouth is seen as a predominantly anechoic, oval-shaped area. In contrast to the straightforward visualization of the echogenic alveolar ridge, the upper lip is difficult to image in the coronal plane of the face.
Fig. 3.3
Left panel, coronal view of the fetal face in the first trimester. The facial structures that are clearly visualized at this gestational age are MS metopic suture, FB frontal bone, O orbit, RNT retronasal triangle (alveolar ridge and frontal processes of the maxilla with the nasal bones on the top, see also Fig. 3.4), M mouth, MB mandibular bone, MG mandibular gap. Right panel, calipers delineating the mandibular gap
Fig. 3.4
Retronasal triangle. Left panel, drawing of the retronasal triangle. 1 frontal process of the maxilla, 2 alveolar ridge (primary palate), 3 nasal bones. Middle and right panels, coronal ultrasound view of the face in a first trimester fetus. FB frontal bones, MS metopic suture, NB nasal bones, FP frontal process of the maxilla, PP primary palate, M mandibular bone
A detailed study evaluating which fetal anatomic structures can be identified in the first trimester was undertaken in 1144 singleton pregnancies undergoing first-trimester screening ultrasound in a dedicated Fetal Medicine Center [47]. Visualization rates of the fetal face, aiming to identify the orbits, lens, and profile according to the fetal crown-rump length, were 98.3, 99.5, 99.0, and 100 % for fetuses with crown-rump lengths of 45–54, 55–64, 65–74, and 75–82 mm, respectively. The overall visualization rate of the fetal face was 99.2 % (1135 of 1144 fetuses). In another study involving 300 first-trimester pregnancies with complete pregnancy follow-up, the fetal face was seen in 95 % of cases [48]. These data suggest that properly trained sonographers can confidently visualize the fetal face and hence perform a basic examination of this area during the first-trimester ultrasound scan.
In order to define the normal first-trimester facial structure, normative data have been reported including measurement of the nasal bone [49–52], prenasal thickness [53], maxillary and mandibular bone length [54–56], premaxillary thickness [57], frontomaxillary facial angle [42], and frontal space [58, 59]. These measurements, although potentially useful for the detection of several anomalies affecting the fetal face in the first trimester, seem to have limited value for screening in the general population and should be restricted either to those cases in which an anomaly is suspected or for research purposes.
The use of 3D ultrasound in the evaluation of the fetal anatomy has been an important contribution to clinical practice. In the particular case of first-trimester fetuses, this technique can provide detailed, high-definition views of the fetal facial anatomy in all possible angles, especially when high-quality volume datasets are obtained with transvaginal probes and analyzed offline. Display of the three orthogonal planes or, alternatively, multiple parallel views using multiplanar mode facilitates the identification of all the facial structures, particularly the frontal bones, orbits, primary and secondary palates, and mandible. Surface-rendering mode is another extremely useful technique to display the upper lip and metopic suture to rule out facial malformations. Surface-rendering views can also be enhanced with the use of HDLive™ technology, which allows lightening and shadowing of certain areas of the anatomy to generate more realistic images of the fetal face [60].
3.3 Retronasal Triangle View
Due to its potential utility in determining the normal facial anatomy in the first trimester, the RNT is discussed separately in this section. The RNT corresponds to the triangular-shaped, echogenic lines seen in the coronal plane of the midface that represents the maxillary bone (Figs. 3.3 and 3.4). The maxilla is formed by the alveolar ridge (the anterior part of the primary palate situated in the caudal aspect of the midface) and two bony prolongations, the frontal processes of the maxilla, which join in the midline superiorly at the level of the nasal bones below the metopic suture. In the first trimester, the coronal view of the maxilla displays an echogenic triangle that can be easily visualized just posterior to the nose, hence the term “retronasal triangle” used to describe this landmark [43]. First-trimester ultrasound screening studies have demonstrated that the visualization rate of the RNT during the scan is very high, ranging from 98 to 100 % [43, 61, 62].
There are two techniques to visualize the RNT with transabdominal ultrasound. The first is to identify the midsagittal plane of the fetal head to image the fetal profile. Then, the transducer is rotated 90° and a sweep to the lower part of the face is performed until the RNT is visualized. The other technique is to first visualize the axial view of the fetal brain at the level of the choroid plexuses (“butterfly” sign) [63] and then to sweep the transducer downward in the same angle until the midface is identified. Once the RNT is visualized, a short sweep should be done to assess the nasal bones and the primary palate. The latter technique is the one recommended by the authors because it has the advantage of being able to evaluate more structures, therefore improving the early detection of other anomalies. Indeed, in this sweep, it is possible to visualize both eyes, including the orbits, eyeballs, and lenses just above the RNT. At the top of the triangle, one or both nasal bones can be easily identified, which can be an alternative technique for the assessment of the nasal bone in the first-trimester screening of aneuploidy [44, 45]. In a more inferior plane, the mandibular bones can also be identified, and this view can be used for the screening of micrognathia by assessing the “mandibular gap,” which corresponds to the separation between the two mandibular bones posterior to the chin [46]. In addition, we have noted that by extending the sweep caudally, it is also feasible to identify the clavicles and the upper extremities, which can also be helpful for confirming the presence of the clavicles and the two hands to rule our upper limb reduction defects (unpublished observations).
3.4 3D Ultrasound Evaluation of the Fetal Face in the First Trimester
3D ultrasound is an important tool for the evaluation of the fetal face in the first trimester. Using both multiplanar and surface-rendering modes, almost all anatomical structures of the fetal face can be identified and examined using offline analysis of the acquired 3D volume datasets. As the acquired 3D volume can be reformatted in any given angle and depth, any desired plane can be obtained. This possibility has enormous advantages over the 2D ultrasound technique, as the 3D volume can be stored and analyzed offline as many times as required without loss of resolution. In addition, 3D datasets can also be sent for remote specialist consultation. Nevertheless, although 3D ultrasound has been extensively used to examine the face in normal and abnormal second- or third-trimester fetuses, its use in the first trimester has intrinsic limitations because the soft tissue at this gestational age is more difficult to delineate and the skeletal bony structures are still hypomineralized. In addition, 3D acquisition should be obtained at optimal planes, with high-resolution equipment and, ideally, using the transvaginal approach. Additional sources of suboptimal imaging are technical factors such as early gestational age, poor fetal position, and maternal habitus or previous abdominal surgery if the transabdominal route is used. If possible, the transvaginal route should be offered to the patient and attempted every time high-quality 3D datasets are required, especially in cases of suspected fetal anomalies.
There are two 3D algorithms that can be used to examine the fetal face in the first trimester. The first is the multiplanar mode, which is extremely useful to examine simultaneously all three orthogonal planes or obtain any desired view of the facial structures (Fig. 3.5). This is the technique of choice to obtain the exact sagittal, coronal, or axial plane if needed for analysis. In addition, it provides a useful tool for avoiding misinterpretation or artifacts in the early evaluation of the fetal face. Several technological modifications of the multiplanar mode have been developed, including the OmniView™ software, which displays up to three simultaneous views in any plane (Fig. 3.6), and the ObliqueView™ software, which displays either a single orthogonal plane or multiple parallel planes of different thickness by drawing a line in any plane of the screen (Figs. 3.7 and 3.8). Visualization of the fetal palate using a commercially available algorithm (Volume NT™), which automatically obtains the true midsagittal plane of the fetal head, has proven to be extremely useful in the first trimester [64]. When the sagittal plane is obtained and combined with the ObliqueView™ utility, the axial view of the secondary palate can be easily obtained since the palate at this gestational age is flat and void of acoustic shadowing. The technique consists of obtaining a midsagittal view of the face by sweeping the mechanical 3D probe for a side-to-side acquisition. The 3D volume is then displayed in the ObliqueView™ mode and a line is drawn through the palate. The orthogonal plane showing the palate is immediately displayed in the dual screen (Fig. 3.9). The advantage of this technique is its simplicity; however, it requires the dedicated software for analysis.
Fig. 3.5
Three-dimensional multiplanar views of the orofacial structures in the first trimester show the three orthogonal planes (left, sagittal plane; middle, axial plane; right, coronal plane). Navigation through the volume allows the simultaneous visualization of different structures of the fetal face in the three planes. The dots represent the intersection of all three orthogonal planes
Fig. 3.6
OmniView™ software. Using a reference plane (in this case, the sagital plane), the operator can manually draw up to three observational lines, which generates the corresponding orthogonal planes that are simultaneously displayed in the other panels
Fig. 3.7
ObliqueView™ software. Upper panel, simultaneous visualization of the orthogonal view is obtained by drawing a line through the reference plane. Lower panel, a thick slide can be used to enhance the visualization of the bony structures of the face
Fig. 3.8
ObliqueView™ software. Simultaneous multiparallel orthogonal views are generated by drawing a line in the reference plane
Fig. 3.9
Application of the VolumeNTTM algorithm, which automatically displays the midsagittal plane of the head, in conjuction with the ObliqueViewTM software generates the axial plane to assess the secondary palate in the first trimester. Note that at this gestational age, the palate is flat and there is no acoustic shadowing from surrounding bony structures
The second algorithm is surface-rendering 3D ultrasound, which can provide high-definition views of the entire surface of the face (Fig. 3.10). This can also be enhanced with the use of HDLive™ algorithm, which can offer improved, vivid views of the facial structures in the first trimester (Fig. 3.11). With the adjunct use of the “magic cut” tool, more realistic views of the face in both the coronal and sagittal planes can also be obtained.
Fig. 3.10
Representative ultrasound views of the fetal face in the first trimester using different ultrasound techniques. Upper panel: left, transabdominal ultrasound; right, transvaginal ultrasound. Lower panel: left and middle, three-dimensional surface-rendered views of the face in the frontal and lateral views; right, fetal face reformatted with the HDLive™ software
Fig. 3.11
Additional ultrasound images using the HDLive™ software obtained transvaginally from a 13-week fetus show realistic views of the fetal face in the first trimester
3.5 First-Trimester 2D/3D Ultrasound in Selected Facial Malformations
3.5.1 Cleft Lip and Palate
CLP is a relatively frequent and clinically significant congenital malformation and a prominent feature of both chromosomal abnormalities (particularly trisomy 13 and trisomy 18) and other genetic and nongenetic craniofacial syndromes. Therefore, special effort should be made to examine properly the facial structures even in the first trimester. Indeed, examination of the fetal face should be an integral part of the workup of first-trimester fetuses with ultrasound suspicion of chromosomal abnormalities and also in chromosomally normal fetuses with increased NT thickness, as the latter group seems to have a higher incidence of CLP than fetuses with normal NT thickness, probably due to a higher prevalence of underlying nonchromosomal genetic conditions [65]. Nevertheless, the vast majority of fetuses with an isolated CLP present with normal NT thickness; therefore, efforts to visualize the fetal face during the first-trimester ultrasound scan should be made irrespective of the NT thickness.
The diagnosis of CLP in the first trimester, however, is difficult because of the small size of the facial structures, scant subcutaneous tissue present in the premaxillary area, and difficulties in detecting orofacial clefts using the sagittal view of the head [43]. Indeed, a recent review of the literature involving more than 45,000 euploid fetuses undergoing routine first-trimester ultrasound screening in a dedicated Fetal Medicine Center demonstrated that the diagnosis of CLP was only made in less than 5 % of cases [66]. This low detection rate highlights the difficulty in diagnosing CLP during the routine first-trimester scan if a focused examination of the fetal face using high-resolution ultrasound equipment and proper scanning technique are not performed. Moreover, a review of the English literature until 2009 [43, 47], when the RNT view was described, revealed only a few cases of CLP diagnosed in the first trimester in euploid fetuses. In the only two reported cases with detailed ultrasound information available, the condition was severe and involved bilateral CLP with prominent premaxillary protrusion, one of which was diagnosed with transvaginal ultrasound [28] and the other with the adjunct use of 3D ultrasound [68]. This observation is further confirmed by a systematic review of the literature on the efficacy of first-trimester ultrasound scan to detect fetal malformations. The overall first-trimester detection rate for facial abnormalities, including both chromosomally normal and abnormal fetuses, was only 34 % [69].
The discordance between the detection rates of trisomy 21 and CLP in the first trimester (>80 % versus <5 %, respectively) led us to speculate that the most significant limitation to the detection of CLP was the plane of examination employed. Indeed, although the ultrasound technique used for aneuploidy screening, namely, assessment of the NT thickness, nasal bone, and frontomaxillary facial angle in the sagittal plane, is good at detecting trisomy 21, this view is poor at identifying CLP. Occasionally, 2D ultrasound visualization of the fetal profile can detect the characteristic premaxillary protrusion of bilateral CLP (Fig. 3.12); however, even this feature has not been emphasized during routine first-trimester sonographic screening. This limitation led our group to investigate an alternative technique for the detection of CLP in the first trimester, which was based on the visualization of the RNT in the coronal plane of the face [43]. This plane is similar to the one used in the second trimester to visualize the upper lip and nostrils [9, 70] and was brought to our attention by the report of the “premaxillary triangle” view suggested by Suresh et al. [71] for the screening of CLP in the second trimester. In their description, the focus is placed on the soft tissue of the upper lip and the echogenic alveolar ridge in a single coronal view. However, since the upper lip is minimally developed in the first trimester, we chose to depict only the maxilla that forms the base of the RNT. In this view, the presence of a cleft of the primary palate is demonstrated by unilateral, bilateral, or central discontinuity at the level of the alveolar ridge, which is the base of the RNT (Fig. 3.12) [43].
Fig. 3.12
Left panel, two-dimensional ultrasound shows premaxillary protrusion in the sagittal view of the face in a first-trimester fetus with bilateral cleft lip and palate (arrow). Chromosomal analysis was reported as normal. Right panel, coronal view shows an abnormal retronasal triangle. Note the bilateral gaps in the alveolus (arrows)
The recent advent of 3D ultrasound technology has allowed closer examination of the fetal anatomic structures even in the first trimester. The evaluation and diagnosis of an orofacial cleft with 3D ultrasound in the first trimester was first reported by Ghi et al. in 2009 [68]. In this case, the authors detect a premaxillary protrusion at the time of a routine scan and further evaluation with 3D surface-rendering ultrasound clearly depicted a bilateral CLP. Since then, 3D ultrasound has played an increasingly important role in the prenatal examination of the fetal face including the detection and confirmation of CLP (Fig. 3.13). The technique for the systematic analysis of 3D volume datasets of the fetal face obtained from first-trimester fetuses undergoing ultrasound screening for aneuploidy was reported by our group (Fig. 3.14) [72]. 3D volume datasets from 240 first-trimester fetuses, including seven cases with CLP, were assessed offline by two independent operators. Coronal views at the level of the RNT were evaluated for possible clefts of the primary palate and axial views were evaluated for possible clefts of the secondary palate (Fig. 3.15). Overall, all fetuses with clefts affecting the primary palate and 86 % of those affecting the secondary palate were detected with a satisfactory false-positive rate [72].A more sophisticated technique for evaluating the primary and secondary palates using 3D ultrasound involves the use of OmniView™ algorithm, which allows the examination of multiple parallel views to visualize the primary and secondary palates. In a screening study of 100 low-risk and 50 high-risk fetuses, the RNT view was imaged to assess the primary palate and the axial view to assess the secondary palate [61]. The two fetuses affected with CLP in this cohort were correctly identified using this technique and none of the fetuses with normal lip and palate displayed an abnormality on this 3D ultrasound examination. The utility of the HDLive™ technique in fetuses with CLP remains to be determined; however, based on several cases in which it has been used, it seems to be promising (Fig. 3.16) [73].
Fig. 3.13
Three-dimensional ultrasound in a first-trimester fetus with premaxillary protrusion. The nuchal translucency thickness was increased and chromosomal analysis revealed trisomy 13
Fig. 3.14
Technique for three-dimensional ultrasound evaluation of the fetal face in the first trimester. Upper panel shows the initial plane for acquisition. The sagittal plane is seen in a, the axial plane in b, and the coronal plane in c. Lower panel shows the three orthogonal views after rotation in plane a. The reference dot is on the primary palate and the palate is horizontal. The retronasal triangle is displayed in plane b and the secondary palate in plane c
Fig. 3.15
Representative views of the fetal face in the three orthogonal planes and the surface-rendered images in seven first-trimester fetuses with cleft lip and palate as determined by three-dimensional ultrasound. The numbers indicate the case and a, b, and c indicate the sagittal, coronal, and axial planes. In d, the surface-rendered view is shown
Fig. 3.16
Three-dimensional ultrasound performed with the HDLive™ technique in a first-trimester fetus with unilateral cleft lip (arrows) (Courtesy of Prof. F. da Silva Costa, Melbourne)
Recently, another technique to detect clefts of the secondary palate was reported [74]. It is based on the identification of the “maxillary gap,” which is displayed in the sagittal view of the head. In this plane, the primary and secondary palates form a continuous thick and straight echogenic line. In fetuses with clefts of the secondary palate, this line is interrupted, yielding a gap (Fig. 3.17). The advantage of this technique is its simplicity, as it can be performed with 2D ultrasound and uses the same view as the one for NT assessment. However, the diagnosis should ideally be confirmed with 3D ultrasound technology. The axial view can also be used to assess the secondary palate for possible clefting. In this plane, the tongue can prevent visualization of the cleft, so it is advised to wait until the fetus swallows and fills the gap with amniotic fluid to enhance identification of the cleft (Fig. 3.18).
