This chapter should be cited as follows:
de Jong-Pleij EA, Bilardo KC, Glob. libr. women's med.,
ISSN: 1756-2228; DOI 10.3843/GLOWM.419283

The Continuous Textbook of Women’s Medicine Series – Obstetrics Module

Volume 18

Ultrasound in obstetrics

Volume Editors: Professor Katia Bilardo, University of Groningen
Dr Valentina Tsibizova, PREIS International School, Firenze, Italy

Chapter

Evaluation of the Fetal Face and Neck

First published: July 2024

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FETAL FACE

INTRODUCTION

The face is probably the most frequently viewed part of the fetus and this visualization is much appreciated by parents as well as by ultrasonographers. The face speaks a universally understood emotional language (Figure 1). Ultrasonographic visualization of the fetal face (with both two- and three-dimensional ultrasound) has a positive effect on parental bonding, which is seen as a necessary element for the process of parental care.^1,2,3

The prenatal recognition of a facial anomaly will evoke several strong emotions. Prenatal diagnosis with counseling will give parents time to process these feelings. When a facial anomaly is found on ultrasound, the process of mourning for the loss of the expected ‘normal-looking’ child can start before the child is born, making psychological coping easier, enabling parents to help to accept the child at birth and improves neonatal care.^4,5,6

Facial anomalies are frequently associated with other anomalies or part of an underlying genetic condition which may profoundly influence medical care.^7,8 The finding of a facial anomaly therefore requires a thorough examination of the fetus. The face is a functionally and anatomically complex structure which poses several challenges for prenatal ultrasound. A segment-specific analysis (as detailed below) should be performed in all three orthogonal planes when an anomaly is suspected.

Facial clefts and micrognathia are the most common anomalies seen on prenatal ultrasound.

THE ULTRASONOGRAPHIC APPROACH OF THE FETAL FACE

Many countries have developed local guidelines for the routine mid-trimester scan. They usually recommend visualization of the profile, eyes and upper lip. The mid-sagittal plane (profile), the axial plane (orbits) and the anterior oblique coronal or nose-mouth plane (upper lip) are usually sufficient to visualize these structures with 2D-ultrasound (Figure 2).⁹

When facial anomalies are encountered, an attempt has to be made to perform an advanced scan and evaluate systematically the three orthogonal planes (sagittal, axial and coronal) of the face. In each plane the different segments of the face must then be assessed systematically. Knowledge of normal relationships, proportions and angles is helpful in the evaluation of the fetal face. Sometimes it can be useful to supplement a subjective assessment with objective measures of which there are numerous available in the literature. It has to be kept in mind that the face is influenced by racial differences and familial traits, especially later in pregnancy.

Three-dimensional ultrasound can sometimes be a helpful next step in the advanced examination. Three-dimensional ultrasound is especially advantageous in demonstrating curved structures and surface malformations. Three-dimensional ultrasound is also helpful in obtaining exact planes and improves accurate topographic depiction of structures.

Finally, the facial examination should be combined with other findings such as associated structural defects, minor dysmorphic markers, growth and poly- or oligohydramnios, and also with information obtained from the pregnancy history, medical illnesses, environmental exposure, family history and when necessary genetic information obtained from invasive procedures. The combination of typical facial features with additional findings and information can lead to the recognition of a known syndrome.

THE ROUTINE MID-TRIMESTER SCAN

Mid-sagittal plane (profile view)

The exact plane

In the mid-sagittal plane the profile is visible (Figure 3). This view is not only usually well recognized and appreciated by the parents, but also contains a lot of information. Abnormal profiles are seen in a large number of genetic disorders.

Finding the exact mid-sagittal plane should be the first point of attention. Evaluation of the profile in a deviating midsagittal plane can lead to diagnostic inaccuracies. For example, in a view deviating from the midsagittal plane, the most protruding part of the chin will not be visualized creating the impression of retrognathia. Also, the forehead often seems more bossing and the shape of the nose may change (Figure 4).

There are some clues that indicate that the image is in the right midsagittal position. An important clue is the vomer. The vomer is part of the nasal septum. It is a narrow, almost triangular bony structure located on the palate. If the vomer is visible in the profile view, the exact midsagittal plane is depicted (Figure 5). Also, the fastigium of the 4th ventricle is located in the exact midsagittal plane. The fastigium is the top of the triangular 4th ventricle. When the fastigium and the nasal tip are visible in the same image the exact midsagittal plane has been depicted (Figure 5). Note that the insonation angle has to be from above to image both clues clearly.

The corpus callosum is often mentioned as a marker for the exact mid-sagittal plane. However, because the corpus callosum has a certain width it is possible to image the corpus callosum even without seeing a profile at all (Figure 6). The corpus callosum is therefore not a very strong marker for the exact mid-sagittal plane.

There are also (and maybe even more important) clues that indicate the image is not in the exact midsagittal plane. Examples are the metopic suture, the frontal processes of the maxilla, a nostril, or the body of the mandible (Figure 7). If any of these structures are seen, the plane is not exactly midsagittal.

The segmental analysis of the profile

It is recommended to evaluate the profile systematically segment by segment. The segments that have to be evaluated are:

• Forehead;
• Nasofrontal area;
• Nose;
• Philtrum;
• Maxilla;
• Palate;
• Tongue;
• Mandible/chin.

Forehead

At the time of the mid-trimester scan the frontal bone has to be visible in the profile view (Figure 3). If the frontal bone is not depicted on the mid-sagittal view, a pathologically wide metopic suture should be suspected. This widening can be caused by severe hydrocephaly, some craniosynostosis syndromes or a delayed closure of the metopic suture which can be associated with facial defects (Figure 8).^10,11

The most common deviations to look for are bossing forehead and sloping forehead. A bossing forehead is a prominent, protruding forehead (Figure 9a) and is often associated with serious conditions like craniosynostose syndromes or skeletal anomalies. If there is an inclination of the forehead (the forehead slants back) (Figure 9b), this is called a sloping forehead. A sloping forehead is often associated with microcephaly as a result of severe brain anomalies like lissencephaly. Microcephaly can also be the result of brain infections and is seen in some syndromes like Neu Laxova syndrome or Nager syndrome.

Both bossing and sloping foreheads are very subtle in the first trimester of pregnancy, but become increasingly evident during pregnancy.

An objective tool that can be helpful in the evaluation of the forehead is the profile line (Figure 10).¹² The profile line is defined as the line that passes through the anterior borders of the mandible and nasion. The nasion is the most anterior point at the junction between the frontal bone and the nasal bone. In the second trimester, the forehead of almost all fetuses is straight and the profile line is aligned with the lower part of the frontal bone (Figure 10a). In the third trimester, however, the forehead changes to a more curved shape in about 25% of cases. In these fetuses the profile line continues slightly behind the frontal bone Figure 10b).

If the profile line passes exaggerated behind the frontal bone, especially more than 4 mm, one should be aware of a bossing forehead (Figure 11a). If the profile line passes in front of the frontal bone it is very likely that the fetus has a sloping forehead (Figure 11b).

Nasofrontal area

There is overwhelming evidence that absent or hypoplastic nasal bones and increased prenasal thickness are markers for trisomy 21, and also for some other syndromes. Several measurement techniques for nasal bone length (NBL) and prenasal thickness (PT) have been described in literature.¹³ For NBL measurement only the length of the white ossified part of the nasal bone is used, while taking care not to include the frontal bone in the measurement. For prenasal thickness (PT), the shortest distance between the nasion and the frontal skin is measured. In case of a gap between the frontal bone and the nasal bone, the landmark nasion is set at the point of intersection of two lines drawn tangentially to the nasal bone and to the lower part of the frontal bone.

In normal fetuses the nasal bone is usually 2/3 of the prenasal thickness. This ratio is stable throughout pregnancy and therefore an easy tool if there is any doubt about whether or not a chromosome abnormality is present.¹⁴ A suspicious PT/NBL ratio is a ratio larger than 0.8. Measurements of nasal bone length and prenasal thickness are shown in Figure 12.

Also, the naso-frontal angle (NFA) can be evaluated in the nasofrontal area. The NFA is the angle between the nasal and frontal bones. In normal fetuses the 50th centile of this angle is 117° and does not change during the second and third trimester. The 10th and 90th centiles are 105° and 129°, respectively.¹⁵ The NFA is enlarged in fetuses with a sloping forehead (Figure 13) or a flat nose (Figure 14). The NFA is small in fetuses with a bossing forehead (Figure 15).

The NFA is also enlarged in cases with a flat nose as seen for example in Binder Syndrome (maxillonasal dysplasia). Some examples of fetuses with a flat nose are shown in Figure 14. Note that the profile line was normal in these fetuses indicating that the enlarged NFA is not the result of a sloping forehead.

The NFA is small in cases with a bossing forehead. Theoretically it is possible that the NFA is small due to a large nose. It is however extremely unlikely that this occurs before birth, unless in rare cases with an encephalocele or a tumor. Some examples of fetuses with frontal bossing are shown in Figure 15.

Nose

The nose has a tremendous impact on the visual impression and overall facial harmony. The nose is part of the respiratory system. A newborn needs a good nasal passage to be able to drink well after birth.

Some nose anomalies are easily recognizable like arhinia (Figure 16). Arhinia is a rare condition characterized by the congenital absence of the external nose, nasal cavities, cribriform plate, olfactory bulbs and tracts. Arhinia can be encountered as an isolated anomaly, but often coexists with holoprosencephaly and other facial anomalies.

Another clear anomaly of the nose is proboscis (Figure 17). A proboscis is a development disorder of the nasal placodes characterized by a blind-ended, rudimentary tube-like nasal structure, commonly located in the midface between or above the eyes. A proboscis is typically associated with holoprosencephaly and other severe facial anomalies like cyclopia.

In many syndromes the nose has a specific feature. A normal nose is prenatally small, delicate and upturned (Figures 2, 3a, 4a and 12a). Abnormal small or flat noses can be seen in several syndromes in contrast to large noses that are extremely rare prenatally. Care has to be taken to image the exact midsagittal plane when assessing the nose. Some examples of flat noses are shown in Figure 14 and some examples of generally small noses are shown in Figure 18. A depressed nasal bridge is shown in a fetus with thanatophoric dysplasia in Figure 15d. In a depressed nasal bridge the bony part at the top of the nose has not developed as much as it should have and is known to be associated with for example skeletal dysplasias.

Philtrum

Abnormal philtrum lengths are part of many genetic conditions. Long philtra are more common than short philtra (Figures 20 and 21). Studies that generated nomograms of philtrum length are available.^16,17 In normal fetuses the philtrum is, subjectively, about as long as the nasal protrusion (Figure 19).

When the philtrum is long it is often bulging (has a convex aspect) (Figure 20).

Maxilla

The main abnormality affecting the maxilla in the profile view is bilateral cleft lip and palate, causing protrusion of the premaxilla and prolabium (Figure 22). The premaxilla and prolabium are the central triangular parts of the palate and lip between the two clefts. They move forwards because the pressure of the tongue is not counteracted by the musculus orbicularis oris.¹⁸ Figure 22 shows that the premaxilla/prolabium complex seems to fuse with the nose, because the columella is usually short in these fetuses.

Another anomaly affecting the maxilla is hypoplasia of the maxilla creating a flat profile. In several syndromes like Binder syndrome and skeletal dysplasias, and also in about 17% of trisomy 21 cases the maxilla is hypoplastic (Figure 24).¹⁹

The position of the jaws can be objectivated by the maxilla-nasion-mandible angle (MNM angle) (Figure 22).²⁰ The MNM angle is defined as the angle between the intersection of the lines maxilla-nasion and mandible-nasion. The jaw landmarks are defined as the middle points at the anterior borders of the maxilla and mandible. Care has to be taken to image the exact midsagittal plane. The 50th centile of the MNM angle is 13.5° and does not change during the second and third trimester of pregnancy. The 5th and 95th centile are 10° and 17°, respectively. The MNM angle is increased in most fetuses with a facial cleft and also in fetuses with micrognathia (Figure 23). The MNM angle is decreased in fetuses with a flat profile (Figure 24).

Palate

The prenatal diagnosis of a cleft palate is challenging, but when the head is tilted backwards and the mouth is slightly open, the hard and soft palate can be visualized. In this situation the shadow of the maxillary alveolar ridge falls above the palate (Figure 25).

When the fetus is swallowing, the movements of the tongue are very helpful in identifying the palate (Video 1).

If the fetus is swallowing or making breathing movements, adding color can be very helpful.

Figure 26 and Video 2 show amniotic fluid passing along an intact palate in a fetus making breathing movements. If there is a cleft palate, bidirectional flow of amniotic fluid over the palate may become evident as the mouth and nose cavities are connected through the cleft (Figure 27).

When there is a unilateral cleft lip and palate, the nasal septum may deviate to the non-cleft side giving the septum an abnormal round aspect in the profile view (Figure 28). This deviation is caused by the musculus orbicularis oris, which pulls harder on the unaffected side.

The equal sign (two hyperechoic lines with a hypoechoic intermediate space) described by Wilhelm is an important marker for an intact uvula (Figure 29).²¹ The two white lines are the outer lining of the uvula surrounded by amniotic fluid, which is normally present in the pharynx. The equal sign can be made visible in all three orthogonal planes. An intact uvula is proof for an intact secondary palate (hard and soft). If the uvula cannot be visualized in its typical presentation (equal sign), there should be a suspicion of a cleft palate.

Tongue

In the normal resting state the tongue is usually between the frontal parts of the alveolar ridges and close to the hard and soft palate (Figure 30). A tongue between the jaws is a normal feature in prenatal life and should not be mistaken for macroglossia. The tongue moves a lot prenatally, which is very helpful in recognizing the tongue during ultrasound examination.

When the tongue is outside the mouth for a longer time, especially when the fetus is at rest or swallowing, there should be a suspicion for macroglossia. Macroglossia is uncommon and frequently associated with specific genetic conditions like Beckwith-Wiedemann syndrome. The tongue may protrude due to increased size and also due to hypotonia as seen in fetuses with trisomy 21. Tumors arising from the tongue like lymphangiomas, hemangiomas or cysts can also produce macroglossia. Macroglossia caused by storage diseases usually presents later in life. A large oral tumor like epignathus (oropharyngeal teratoma) or epulis (benign gingival tumor usually from the maxillary alveolar mucosa) may resemble macroglossia. Polyhydramnios may develop because of impaired swallowing due to obstruction of the mouth. A postpartum emergency due to airway obstruction may occur.

Aglossia or microglossia, such as seen in Moebius syndrome are extremely rare and almost always associated with other striking facial anomalies.

Glossoptosis is a tongue that is farther back in the mouth than it should be. This position can block the airway after birth making intervention of an otolaryngologist of vital importance. Polyhydramnios often develops because the fetus has problems swallowing amniotic fluid. Glossoptosis is typically associated with micrognathia (Figure 32).

Mandible/chin

The main anomaly to look for when evaluating the mandible is micrognathia which refers to a hypoplastic mandible. The anteroposterior axis is mostly affected, which explains the retrognathic position in the profile view (Figures 23c, 32 and 33).

Micrognathia is often associated with an underlying genetic condition. The search for associated anomalies is paramount when micrognathia is diagnosed. Micrognathia may interfere postnatally with breathing and feeding. Neonatal morbidity is high usually due to associated anomalies.²²

Agnathia or otocephaly is a severe and lethal form of mandibular maldevelopment. Otocephaly is extremely rare and characterized by the absence of the mandible, microstomia and ears fused together just below the chin (synotia). Otocephaly is often associated with holoprosencephaly.²³

The diagnosis micrognathia is usually made in the profile view where the retracted and small mandible is the most striking feature. It is of vital importance to define precisely the exact midsagittal plane when evaluating the position of the mandible. In severe cases a hanging upper lip (and often a hanging lower lip) may be visible (Figure 33).

Objective tools can be helpful in ambiguous cases or in supporting the diagnosis. The inferior facial (IF) angle was the first published tool applicable in the profile view. Thereafter, the fronto-naso-mental (FNM) angle and the maxilla-nasion-mandible (MNM) angle (Figure 34) were published.^24,25,26 The angles are shown in Figure 34 with their cut-off levels. Below (IF angle, FNM angle) or above (MNM angle), these values a suspicion of micrognathia should arise.

Skin tags can be found on the chin (Figure 35), although preauricular skin tags are more common. These fleshy tumors of the chin are benign and have not been reported in association with congenital syndromes.²⁷

Axial orbital plane

Normal image

In the axial plane at the level of the eyes both of the hypoechoic eyeballs are easy to recognize. It is generally known that in normal fetuses the distance between the orbits is the same as the diameter of one orbit (Figure 36). Between the orbits the nasal bones are visible as a small symmetrical pyramid. The lenses are visible as clear round structures in the front of the eye socket (Figure 36). Normal values are established for the distance between the inner and outer orbits as well as for the size of the orbits throughout gestation.²⁸ The interorbital distance (inner to inner) is the most sensitive tool to detect pathological variations. Also, for the distance between the center of the lenses normal values are available.²⁹

Abnormal orbital position

When the interorbital diameter is decreased, this is called hypotelorism (the orbits are too close to each other). When the interocular diameter is increased this is called hypertelorism (the orbits are too far away from each other) (Figure 37). The eyeballs can also protrude which is called exophthalmos.

Hypotelorism is usually a midline migration defect and almost always associated with holoprosencephaly. The orbits can even completely fuse which is called synophthalmia or cyclopia (Figure 17).

Hypertelorism is frequently associated with genetic syndromes like Greig’s syndrome, frontonasal dysplasia or craniosynostosis.

Exophthalmos or proptosis is protrusion of the eyeballs. This is prenatally mainly seen in cases with craniosynostosis syndromes like Apert and Crouzon syndrome. In these cases the premature closure of the skull bones affects the shape of the face and produces shallow orbits causing ocular protrusion. Microcephaly or holoprosencephaly are sometimes accompanied by exophthalmos.

Abnormal orbital size

In microphthalmia there is a decrease in the size of the eyeball (Figure 38).

In anophthalmia there is absence of the eyeball, optic nerve and chiasma. Both microphthalmia and anophthalmia can be unilateral (Figure 39) or bilateral, although real anophthalmia is usually bilateral. The clinical distinction between real anophthalmia and severe microphthalmia is difficult. Pathological examination is usually necessary to confirm the total absence of ocular structures in case of anophthalmia. Real anophthalmia is often accompanied by severe malformations of the forebrain and then usually a lethal condition. Microphthalmia and anophthalmia both have genetic and non-genetic causes.

Cataract

Cataract is a cloudy or opaque area in the (normally crystal clear) lens of the eye or in the surrounding membranes of the lens (Figure 40). Cataract can be unilateral, bilateral or asymmetric (one eye is more affected than the other eye). The ultrasound image of cataract is variable and includes a homogenous opacity, thick hyperechogenic borders or irregular clusters of hyperechogenic spots. Sometimes cataracts develop later in pregnancy. The forms presenting with total opacification are sight-threatening conditions. Early surgery, within the first months of life, is critical for a good visual prognosis and prevents visual impairment and blindness.

Bilateral cataract is usually syndromic, whereas unilateral forms are usually related to infections (e.g. rubella, measles, toxoplasmosis, CMV); however, many cases are idiopathic. Other possible causes are metabolic disturbances, diabetes and drug-induced reactions (e.g. coumarine).

Dacryocystocele

A dacryocystocele is an expansion of the lacrimal sac due to delayed canalization of the distal end of the nasolacrimal duct. Dacryocystocele is visible as a cyst between the nose and the lower part of the orbit (Figure 41). A dacryocystocele is rarely larger than 10 mm and usually visible in the second half of pregnancy. Most cystoceles are unilateral, but bilateral cystoceles have been described. Canalization of the nasolacrimal pathway solves the problem, which may occur spontaneously before birth. A dacryocystocele may be the result of facial anomalies in some syndromes, but is usually an isolated finding.

Persistent vasculature

The hyaloid artery is a transient fetal vessel that supplies nutrients to the developing lens and disintegrates when the lens matures. This artery is visible as a continuous thin echogenic line between the posterior wall of the orbit and the posterior border of the lens (Figure 42). Regression of this artery starts between 18 and 29 weeks’ gestation and is a normal process. Abnormal or insufficient regression result in an irregular hyperechogenic line often with a broad attachment at the posterior wall of the orbit (Figure 43) called persistent hyperplastic primary vitreous (PHPV). PHPV is often accompanied by cataract and microphtalmos and causes serious vision problems.

Arhinia

In cases with arhinia (absent nose), the pyramid formed by the nasal bones is missing in the axial plane (Figure 44).³⁰

Miscellaneous

Tumors of the fetal face like hemangiomas, lymphangiomas or teratomas are rare and are challenging due to their heterogeneous features. Although tumors are described at 16–17 weeks, most facial tumors are identified in the second half of pregnancy.

A few tumors can occur typically next to the nose and are visible in the axial orbital view. A nasal glioma is a rare benign tumor composed of heterotopic neuroglia tissue often located just next to the nasal bones (Figure 45).³¹ Also, a frontal encephalocele (herniation of intracranial content through a skull base defect) can be located on the nasal dorsum.

The differential diagnosis further includes nasal dermoid, nasal teratoma or a super numerous proboscis.

Anterior oblique coronal plane (nose-mouth view)

Normal nose-mouth view

Recognition of the upper lip and mouth is best achieved using a slight oblique coronal plane touching the tip of the nose and upper lip (Figures 2c and 46).

The nose with the nostrils, upper lip, mouth and chin should appear symmetrical.

Normal nostrils are prenatally wide open round or oval (Figure 47).

This plane is mainly used to detect a cleft lip or confirm an intact upper lip. An intact upper lip is an indication for an intact alveolar ridge of the maxilla. A (unilateral or bilateral) cleft of the lip, however, can be associated with a cleft in the alveolar ridge as well as with an intact alveolar ridge. To assess the palate other planes are necessary (see section on palate).

It is advisable to turn the transducer a little more oblique (away from the nasal tip) to image the vermillion border (Cupid’s bow) to detect incomplete clefts (Figure 48). Incomplete clefts can take on a variety of appearances. An incomplete cleft does not involve the complete thickness of the lip but only involves the lower part of the lip (sometimes only a very small gap or cleft in the vermillion) and does not extend to the ipsilateral nostril.

Abnormalities visible in the nose-mouth view

The anterior oblique coronal plane is mainly used to detect clefts. However, rare anomalies such as a single nostril, a bifid nose, macroglossia or a cyst protruding through the mouth can be encountered (Figure 49).

Cleft lips, with or without a cleft palate, are the most common facial abnormalities. Clefts can be unilateral, bilateral (symmetrical or asymmetrical) or incomplete. Clefts can be isolated or associated with other abnormalities, therefore a thorough examination of the entire fetus is of vital importance when a cleft is encountered.

In case of a cleft lip a vertical hypoechoic region can be seen through the fetal upper lip located under a nostril. Much variation exists in the severity and extent of the cleft (Figure 50). There are isolated microforms that are very easily missed on ultrasound examination and on the other end of the spectrum there are large clefts associated with a cleft palate. Clefts, especially large clefts, can produce distortion of the anatomy in the nose-mouth region. In bilateral clefts the protrusion of the nose (length of collumela) is usually reduced (Figure 22). Due to the cleft in the musculus orbicularis oris, the nostrils are stretched and changed from a round to a more flattened shape. These changes together with the protrusion of the premaxilla/prolabium complex make the anterior nose-mouth view in cases with a bilateral cleft often very deviating (Figure 51).

In cases with a unilateral cleft the nostril on the cleft side can also be stretched making the nostrils asymmetric, even when the cleft is incomplete (Figure 52). The nose can even deviate because the musculus orbicularis oris pulls harder on the non-cleft side (Figure 50b).

Atypical facial clefts are very rare. They can be found in a wide range of patterns over the face and are classified by Tessier anatomical classification.³² The most common atypical clefts are midline clefts, which are usually associated with other serious anomalies like holoprosencephaly. In extremely rare cases, clefts are acquired like in the amniotic band syndrome resulting in a variable spectrum of unusual facial clefts.

A multidisciplinary approach is usually needed postnatally for all types of clefts to ensure the best functional, esthetic and psychological result.

FETAL NECK

Tumors

Introduction

Neck tumors pose a challenge because they have rather similar heterogenous features, can have irregular extensions into adjacent tissue and are often large. Most common tumors in the fetal neck region are teratomas, hemangiomas, lymphangiomas and, although more rare, branchial cleft cysts. Thymic cysts as well as tumors of the submandibular glands and cervical myelomeningoceles are extremely rare but have to be taken into account.

Magnetic resonance imaging (MRI) may help in assessing the extent of the tumor.

Large cervical tumors can cause hyperextension of the neck with compression of the airways, swallowing problems resulting in polyhydramnios, abnormal fetal position and premature delivery. When the tumor is very large, postpartum ventilation difficulties, prematurity and bleeding are causes of neonatal emergencies. It may be necessary to manage fetuses with large neck masses through cesarean section with the ex utero intrapartum treatment (EXIT) procedure to secure the airway.

Teratomas³³

Teratomas are germ cell tumors that contain several different types of tissue, such as bone, muscle and hair. The cervical region is the most common site for fetal teratomas after the sacrococcygeal region. Teratomas are located anterior or anterolateral to the neck. Teratomas can grow rapidly in the second half of pregnancy. When growing inwards hyperextension of the neck with compression of the airways can produce polyhydramnios, abnormal fetal position and postpartum ventilation difficulties. Teratomas usually have a mixed solid and cystic appearance. The cyst can be very irregular in shape as well as in size. This tumor is often very vascular and small calcifications are common but not absolutely pathognomonic for teratomas.

Hemangiomas³⁴

Hemangiomas are vascular tumors. Their appearance varies from cystic to solid or mixed. Hyperechogenic (calcifications) or hypoechogenic (degeneration) areas are possible but less common. Suggestive for hemangiomas are visible vessels with high peak velocity. Many hemangiomas occur in the head and neck region. Some are small and resolve spontaneously postnatally. Highly vascular fetal tumors can lead to intrauterine demise as a result of high-output heart failure because of vascular steal syndrome. These highly vascular tumors can also be complicated by platelet trapping with severe consumption coagulopathy.

Lymphangiomas³⁵

Lymphangiomas are congenital malformations of the lymphatic vessels. The sonographic appearance is often multilocular with uni-or multiseptated cystic areas of variable sizes (Figure 53).

Lymphatic malformations can occur anywhere, but most commonly occur in the neck or the axillary region. They tend to increase prenatally and can infiltrate into the mediastinum or superficially to the face.

Although lymphangiomas generally have a good prognosis, they might have a poor prognosis when the onset is early, hydrops develops or the tumor is very large.

Branchial cleft cysts^36,37

Although branchial cleft cysts are a common causes of cervical tumors in children, prenatal diagnosis is still rare. A branchial cleft cyst usually arises during embryogenesis if a portion of the cleft fails to involute completely. This entrapped remnant becomes an epithelium-lined usually ultrasonic cyst located in the lateral aspect of the neck.

Thyroid

When assessing the fetal thyroid the main focus is on detecting an increased thyroid size, which may be the first sign of thyroid dysfunction. Especially fetuses of mothers with positive antithyroid receptor antibodies and users of antithyroid drugs, are at high risk of developing thyroid dysfunction and goiter (large thyroid gland). The evaluation of the thyroid dimensions is mostly based on a subjective impression. Head extension is present in cases with large goiters. Nomograms of the fetal thyroid are available (Figure 54).^38,39

Untreated hyperthyroidism may cause growth restriction, fetal neck hyperextension (with malpresentation during delivery), polyhydramnios, heart rhythm disorder, hydrops, swallowing problems, neonatal tracheal obstruction, and even fetal death.

The most common tumor of the thyroid is the teratoma (Figure 55). They typically present as a large mass with solid and cystic lesions and often contain small echogenic reflections, which indicate calcifications. Although the histological characteristics are usually benign, mortality is high due to tracheal compression causing neonatal respiratory distress after birth.

Nuchal fold

The nuchal fold is a skin fold seen at the back of the neck during the routine second trimester scan. The nuchal fold is measured in the axial plane as the distance from the outer edge of the occipital bone to the outer edge of the skin in the midline (Figure 56). It should not be confused with nuchal translucency, which is measured in the first trimester. Nuchal fold thickness ≤6 mm is normal. An increased nuchal fold thickness is a soft marker and is associated with aneuploidy, especially trisomy 21 but also multiple fetal anomalies. Other common associations include Turner syndrome, Noonan syndrome and cardiac defects. The predominant reason to assess the nuchal fold is that it is a soft marker for aneuploidy. A thickened nuchal fold may normalize toward the third trimester, however, the risk of aneuploidy will not reduce.

Hygroma colli

Hygroma colli is an anomaly of the lymphatic system characterized by a multiseptated, thin-walled cystic mass within the soft tissue, seen in axial or longitudinal views, usually involving the anterior part of the neck. Hygroma colli is frequently associated with aneuploidy and consequently with a wide variety of fetal anomalies. The most common aneuploidic association is Turner syndrome. In addition, non-aneuploidic anomalies have to be take into account like congenital cardiac anomalies. The mortality rate is high when associated with hydrops. Spontaneous remission may occur in utero in a tiny proportion of cases but this does not exclude aneuploidy. The differential diagnosis includes a meningocele, an encephalocele or a teratoma.

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