Micrognathia in a 13-week fetus with trisomy 18. Note receding chin 

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... noted in fetuses with trisomy 13 and 18. 35 However, from the diagnostic point of view, the detection of other evident ultrasound features in association with these aneuploidies would probably make the demonstration of ventriculomegaly in these cases very limited. Visualization of the fetal face is an integral part of first- trimester ultrasound screening for chromosomal anomalies, as the midsagittal view of the face is mandatory to obtain a reproducible image of the NT and nasal bones. 36 On the other hand, first-trimester diagnosis of orofacial malformations, such as cleft lip and palate, has been rarely reported probably because routine assessment of the face for these conditions is difficult due to the small size of the facial structures. Indeed, before 2010 only two cases of bilateral cleft lip and palate had been reported in contrast to the very large numbers of trisomy 21 detected, despite the fact that these two conditions have a similar prevalence in the general population. This can be taken as evidence that although visualization of the fetal head in the sagittal plane is extremely useful for the screening of aneuploidy, it is not the case for the detection of orofacial anomalies. We have recently described an alternative technique for the evaluation of the midface in the first trimester, i.e. the assessment of the coronal plane for the visualization of the maxilla, which displays a characteristic echogenic image that was termed the retronasal triangle. 13 This is formed by the primary palate on its base and both frontal processes of the maxilla on the sides (Fig. 11). In addition, the nasal bones can be also identified on the top of the triangle, making this view another useful technique for visualizing the nasal bones in the ultrasound screening of aneuploidy. 14,39 Midfacial hypoplasia is frequent in fetuses with trisomy 21. This is clinically evidenced by demonstrating absent or hypoplastic nasal bones. Midfacial hypoplasia is also associated with an abnormal frontomaxillary facial angle, 40,41 although this technique is difficult to implement, is more accurate if offline reformatting of three-dimensional data sets are analyzed, and requires a significant expertize to be obtained. Severe midfacial hypoplasia is also seen in fetuses with holoprosencephaly, especially when a large cleft palate is present (Fig. 12). The incidental detection of cleft lip and palate diagnosed in the first trimester has been reported. 37,38 First-trimester fetuses with bilateral cleft lip and palate present with a characteristic premaxillary protrusion as second-trimester fetuses do (Fig. 13). This finding is evident in the first trimester only if a detailed examination of the fetal profile is undertaken. However, first-trimester fetuses with a medial facial cleft present with a flat profile and, therefore, the diagnosis can be easily missed. Differentiation between these two entities is important as in the latter cases they are almost invariably associated with lethal aneuploidies. 42 Detailed examination of the fetal face is also important in first-trimester fetuses with increased NT, as the prevalence of cleft lip and palate in these cases is significantly increased in comparison to fetuses with normal NT thickness. 43 A more systematic approach for the early diagnosis of cleft lip and palate using two- and three-dimensional ultrasound has been reported by our group. 13,44 This technique relies on the assessment of the coronal plane of the face focusing on the base of the retronasal triangle for the evaluation of the primary palate. 13 First-trimester fetuses with cleft of the primary palate present with a gap at the base of the retronasal triangle (Fig. 14). However, a false- positive diagnosis of 1% have been described, which has been attributed to shadowing artifacts from the limbs over the fetal face. 44 On the other hand, fetuses with cleft of the secondary palate can be identified using the axial plane, which assessment can be greatly facilitated with the adjunct use of new three-dimensional algorithms, such as the VolumeNT and OmniView softwares. 45,46 Clefts of the secondary palate can also be demonstrated by examining the axial plane of the head at the level of the hard palate with two-dimensional ultrasound. As all clefts of the secondary palate are medial, an important clue is the identification of an abnormal hard palate on the standard midsagittal plane of the head. Micrognathia is a rare facial malformation characterized by a small, underdeveloped mandible. It represents a prominent feature in a number of chromosomal and genetic syndromes including the Robin anomaly, acrofacial dysostosis, orofacial-digital syndrome, trisomy 18 and triploidy. The prenatal diagnosis of severe micrognathia in a first-trimester fetus with Pierre-Robin syndrome has been reported. 47 However, the diagnosis in less severe cases relies on subjective criteria by examining the fetal profile to identify the receding chin (Fig. 15). An alternative technique is the examination of the fetal face using the retronasal triangle view. In this view, normal fetuses display a gap between the two mandibular bones, the so-called mandibular gap, whereas fetuses with micrognathia devoid this gap or the mandible cannot be identified at this level (Fig. 16). 48 Holoprosencephaly is often associated with severe facial anomalies, such as hypotelorism and medial facial clefts. 23 In severe cases, the orbits can be fused and a trunk-like structure called proboscis is visualized in the upper face. The first-trimester ultrasound diagnosis of cyclopia and proboscis is easy in cases in which HPE has been previously detected (Fig. 8). 23,49 The fetal neck, particularly its posterior aspect, is the main focus of attention when measuring the NT thickness. 2 NT, the collection of fluid behind the fetal neck has been discussed in great detail in the prenatal literature and is currently the topic of thousand of papers. There is a massive body of evidence demonstrating that the NT is the best single ultrasound marker for several conditions, mainly chromosomal and structural defects. The Fetal Medicine Foundation has issued the guidelines for the correct measurement of the NT thickness and provides both educational as well as audit material for the registered operators, which are widely available to the reader. 2,36 Neck anomalies amenable for prenatal diagnosis include cystic hygroma, lymphangioma, teratoma, hemangioma and branchial cyst. Among them, only two conditions are relevant in the first trimester, i.e. cystic hygroma and distended jugular lymphatic sacs, as none of the other conditions have been reported in the first trimester. Cystic hygroma colli is a benign lymphatic lesion that is due to failure of the lymphatic system to communicate with the venous system in the neck. It usually presents as multiloculated, fluid-filled cavities in the posterior aspect of the cervical region. 50 Most if not all cases of cystic hygroma, present with a significant increase in the NT thickness (Fig. 17). The posterior ligament of the neck is easily identified in the axial plane in most cases. Associated findings frequently include features of fetal hydrops, such as severe subcutaneous edema and pleural effusion. Chromosomal abnormalities, such as Turner syndrome and trisomy 21, are frequently the underlying cause. 51 Therefore, prenatal karyotyping in these cases is indicated. Intrauterine lethality is high, although survivors can have a relatively normal life if alternative connections between the lymphatic and circulatory system take place in the midtrimester. 51 Among these cases, second-trimester examination usually shows nuchal fold and cardiac outflow tract anomalies. A horseshoe kidney is also a frequent associated second- trimester finding. For screening purposes, it is important to note that differentiation between increased NT and cystic hygroma is not relevant as only the thickness is an independent predictor of aneuploidy. 52 In contrast to cystic hygroma colli, distended jugular lymphatic sacs have only recently received some attention in the literature. 53 In the first trimester, they present as local, ovoid echolucent mass in the lateral aspect of the fetal neck (Fig. 18). 54 This condition is thought to be due to mesenchymal edema and abnormal lymphangiogenesis at the level of the neck and it is closely related to the development of the nuchal edema leading to increased NT. Indeed, transvaginal ultrasound examination of the neck in first-trimester fetuses demonstrated the presence of distended jugular lymphatic sacs in 85% of the fetuses with increased NT and in only 1.5% of the fetuses with normal NT. 54 However, careful examination of the data shows that the two fetuses considered to have normal NT in the latter group had indeed NT over the 95th percentile. Due to the clear association between distended jugular lymphatic sacs, increased NT thickness, and chromosomal abnormalities, prenatal karyotyping in these cases is indicated. 55 Recognition of the normal first-trimester ultrasound anatomy of the brain, face and neck could improve the early detection of congenital abnormalities affecting these important segments of the body. Confirmation of normal ultrasound features can be reassuring for the parent-to-be whereas the detection of any abnormality of this area should prompt additional studies, including chromosomal analysis, follow-up scans and genetic ...