The Fetal Face and Neck - Clinical Tree

Summary Key Points

Ear and eye anomalies often accompany abnormalities of the skull and face.
Abnormalities of fetal head size and shape may be associated with various syndromes and chromosomal anomalies.
Hypoplastic or absent nasal bone may be seen in fetuses with trisomy 21.
Cleft lip may be associated with cleft palate, and detailed description of the cleft is important to accurately counsel parents, predict postnatal outcome, and anticipate type of treatment.
Isolated cleft palate is rarely diagnosed on prenatal ultrasound and is often associated with micrognathia and a variety of syndromes.
Micrognathia is best assessed on sagittal midline views, can be associated with a variety of syndromes, and may lead to difficulties with feeding and airway management.
Fetal neck masses are uncommon, and include lymphatic malformations, teratomas, hemangiomas, and thyromegaly. Evaluation of the fetal airway in relation to the mass is critical for delivery planning.

With technical advances in gray-scale and three-dimensional (3-D) imaging, sonographic evaluation of the fetal face and neck has become a routine part of the second-trimester fetal anatomic survey. An increasing number of craniofacial anomalies are detectable in the first trimester. Abnormalities of the fetal face are particularly important because they are frequently associated with syndromes and chromosomal anomalies. This chapter reviews the embryology and normal development of the fetal face and neck and describes anomalies that can be detected sonographically.

Embryology and Development

Face

Fetal face development begins at approximately 4 weeks' gestation and rapidly progresses, with the completion of major events by 8 weeks' gestation ( Fig. 33.1 ). In this complex process, ectoderm, mesoderm, endoderm, and neural crest cells all interact to develop the classic human facial features. Ectoderm surrounds the stomodeum (primitive mouth). The paired pharyngeal arches, or branchial arches, composed of central mesenchyme with outer ectoderm and inner endoderm coverings, progress to fuse in the midline. Neural crest cells give rise to connective tissues of the face (cartilage, bone, ligaments).

Five main tissue buds (called prominences ) form the fetal face. The frontonasal prominence forms the forehead and dorsum apex of the nose. The lateral nasal prominences form the nasal ala. The medial nasal prominences form the nasal septum. Maxillary prominences form the upper cheeks and most of the upper lip. Mandibular prominences form the lower cheeks, lower lip, and chin. The maxillary and mandibular processes are derived from the first branchial arch. The remaining branchial arches go on to form the oropharynx.

During the fourth week of gestation, the frontal prominence forms at the cephalic end of the embryo. The two nasal placodes are present on the frontal prominence, and the optic discs are present posterolaterally. In the stomodeum, the buccopharyngeal membrane becomes fenestrated.

The fifth week brings development of nasal pits in the nasal placodes and differentiation of medial and lateral nasal prominences. The lens vesicles invaginate within the optic discs, and the caudal end of the medial nasal prominences begins to fuse with the maxillary prominences.

During the sixth week, six auricular hillocks (mesenchymal swellings) form and will become the pinna of the ears. Auricular pits may arise when these nodules do not fuse completely. Medial and lateral nasal prominences fuse, and the maxillary prominences begin to form the upper jaw. The nasal septum forms as the medial nasal prominences join in the midline. The edges of the optic fissures fuse, and the hyaloid vessels are present in the center of the optic stalk. These vessels will eventually form the retinal artery and vein.

By the seventh week, the tip of the nose is visible in profile, and the pinna of the ears is taking shape. The central axis of the nose and philtrum are formed as fusion of the medial nasal prominences is completed. Eyelids become prominent. By the end of the eighth week, the developing eye is up to 2 mm in diameter.

Neck

Development of the fetal neck is similarly complex, with extensive embryologic events contributing to development of vascular, neurologic, musculoskeletal, lymphatic, and endocrine systems. The laryngotracheal groove forms during the fourth week of gestation along the floor of the primitive mouth. After evagination of this groove, the laryngotracheal diverticulum forms. The distal end forms the lung bud. The endoderm of this diverticulum forms the epithelium of the larynx and trachea. The endothelium of the larynx proliferates and temporarily occludes its lumen. Recanalization occurs by the tenth gestational week, with formation of the laryngeal ventricle, vocal folds, and vestibular folds. The fourth and sixth pharyngeal arches form the surrounding cartilage and muscles.

At 4 to 6 weeks' gestation, right and left jugular lymph sacs develop as diverticula of the subclavian veins. Lymphatic capillaries permeate the body and drain into these sacs. Abnormal connections between the lymphatic sacs and venous system are thought to contribute to lymphatic malformation and thickened nuchal translucency (NT) in the first trimester, as well as a thickened nuchal fold in the second trimester.

Sonography of the Normal Fetal Face

Sonographic evaluation of the fetal face is part of the routine anatomic survey in midpregnancy, but little is actually required. According to the American Institute of Ultrasound in Medicine 2013 practice guidelines, only visualization of the fetal upper lip is mandatory during an anatomic survey. Although not required, it is possible to obtain exquisite multiplanar two-dimensional (2-D), 3-D, and four-dimensional (4-D) views of the fetal face with state-of-the-art equipment. Profile and 3-D views ( Fig. 33.2A ) are helpful, especially when a true coronal view cannot be obtained because of fetal position. Sagittal 3-D volumes of the fetal face can often be obtained in these situations, and the image can then be rotated to show the upper lip and palate clearly. Coronal (see Fig. 33.2B ) and axial views of the fetal nose and lips are obligatory in screening for fetal cleft lip.

The sagittal facial profile view is acquired whenever possible and should demonstrate the presence and normal configuration of the nasal bone, lips, chin, and forehead (see Fig. 33.2C ). Three-dimensional volumes can frequently be obtained and can be helpful for characterizing abnormalities. Axial views of the orbits can be obtained to verify that both globes are present, of normal size, and at a normal distance apart (see Fig. 33.2D ). Axial images of the maxilla and alveolar ridge can be obtained to determine if a cleft primary palate is present (see Fig. 33.2E ). The palate separates the nasal cavity from the oral cavity. The secondary palate is difficult to visualize on 2-D sonography but may be evaluated with special 3-D sonographic views and is often readily visible on midline sagittal and coronal fetal magnetic resonance imaging (MRI; see Fig. 33.2F ).

Images of the fetal neck are obtained in sagittal, axial, and coronal planes to evaluate the cervical spine and airway and to assess for masses ( Fig. 33.3 ). The neck should also be evaluated for abnormal positioning, such as hyperextension, which can be present with anterior neck masses such as an enlarged thyroid or cervical teratoma. Thickening of the nuchal fold is evaluated at the second-trimester survey and is measured in the suboccipital bregmatic plane, where notable landmarks include the cavum septum pellucidum, cerebral peduncles, cerebellar hemispheres, and cisterna magna.

Abnormalities of the Head

Abnormal Size

The fetal head is typically oval in configuration, and in this case, measurements of biparietal diameter (BPD) and head circumference will give similar estimates of gestational age. If sonographic head measurements are three standard deviations (SDs) below the mean, microcephaly is diagnosed. If the measurements are greater than 3 SDs above the mean, macrocephaly is suggested. Abnormalities of head size are important. Microcephaly may be associated with abnormalities of brain development and often leads to poor neurologic outcome. Macrocephaly may have a benign cause, such as a family history of a large head, or pathologic causes such as underlying brain maldevelopment or injury or, rarely, a space-occupying lesion. If the fetal head is sufficiently large, cephalopelvic disproportion can occur at delivery, leading to failure of labor to progress and the need for cesarean delivery.

Abnormal Shape

Abnormal head shape takes many forms. An abnormally long and narrow (oblong) cranium is described as dolichocephaly and is more frequently seen in fetuses in breech position and in the setting of oligohydramnios. An abnormally round head is termed brachycephaly, which may be caused by premature fusion of the coronal sutures. A lemon-shaped skull, with indentation of the frontal bones, is often seen in association with open neural tube defects and the Chiari II malformation of the hindbrain, but it may also be seen in normal fetuses ( Fig. 33.4 ). A strawberry-shaped skull —flattening of the occiput and narrowing of the bifrontal portion of the cranium—may be seen in association with trisomy 18. A cloverleaf-shaped skull is seen with some dwarfs, especially thanatophoric dysplasia, and in some fetuses with craniosynostosis.

FIG. 33.4, Variety of Abnormal Head Shapes.

Craniosynostosis

Craniosynostosis describes a heterogeneous group of disorders in which there is premature fusion of one or several of the cranial sutures. Although abnormal head shape may be diagnosed in utero, this diagnosis often does not become evident until after birth. It occurs in about 1 per 2500 births. Recent research suggests that the pathophysiology of craniosynostosis is related to abnormal molecular signaling by fibroblast growth factors, leading to premature closure of cranial sutures ( Fig. 33.5 ). About 85% of cases are isolated and about 15% syndromic. Craniosynostosis is associated with multiple syndromes, including Apert, Crouzon, Pfeiffer, Antley-Bixler, Beare-Stevenson, Fetter, and Carpenter, as well as thanatophoric dysplasia. The abnormal head shapes resulting from craniosynostosis can lead to facial abnormalities, including hypertelorism, hypotelorism, exorbitism, and midface hypoplasia. Dolichocephaly (oblong head) is the most common craniosynostosis condition and results from premature fusion of the sagittal suture. Asymmetrical heads are termed plagiocephalic.

When fetal position is favorable, it is possible to trace the sutures sonographically and to evaluate their patency using high-frequency linear array probes.

Classification of Skull Deformities Based on Sutures Involved

Dolichocephaly/scaphocephaly: sagittal suture; most common synostosis
Anterior plagiocephaly: one coronal suture
Posterior plagiocephaly: one lambdoid suture
Brachycephaly: bilateral coronal suture; second most common synostosis
Trigonocephaly: metopic suture
Oxycephaly/turricephaly: all skull sutures and sutures at base of skull
Cloverleaf (kleeblattschädel): all but squamous (squamosal) suture

Prenatal diagnosis can be difficult; fetuses can appear normal in midtrimester but show changes in late pregnancy, when normal physiologic molding can be a confounder. In at-risk cases, head shape changes have been seen as early as 12 weeks. The fused sutures can be detected as absence of the sonolucent space normally seen between skull bones. The loss of hypoechoic suture appearance lags shape changes by 4 to 16 weeks. Three-dimensional multiplanar and surface rendering are helpful. Associated anomalies can allow differentiation among types.

Additional problems can arise from the cranial deformity, including intracranial hypertension, obstructive apnea, proptosis, visual loss, dental malocclusion, and intellectual impairment. Learning disorders have been observed in 47% of school-age children.

Fetuses prenatally suspected to have craniosynostosis should undergo detailed neurologic and anatomic sonography. MRI may be helpful. Postnatally, computed tomography (CT) surface rendering helps confirm the diagnosis and is needed for surgical treatment planning. Family history and molecular analysis for FGFR and TWIST mutations can help. Multidisciplinary counseling including craniofacial and neurosurgical specialists is important because therapy can involve molding helmets and surgery.

Wormian Bones

Wormian bones are ossicles located in the sutures or fontanelles and may be associated with multiple conditions, such as pyknodysostosis, osteogenesis imperfecta, cleidocranial dysplasia, hypothyroidism, and trisomy 21. Three-dimensional views are particularly useful in the assessment of wormian bones ( Fig. 33.6 ).

Differential Diagnosis of Wormian Bones

Cleidocranial dysplasia
Congenital hypothyroidism
Hypophosphatasia
Osteogenesis imperfecta
Trisomy 21
Menkes kinky-hair syndrome
Progeria
Pyknodysostosis

Forehead Abnormalities

The forehead is best evaluated in the sagittal profile view, where the angle between the frontal and nasal bone can be assessed. Frontal bossing is abnormal prominence of the frontal bones and is a rare finding on fetal sonography. However, it has been reported in a variety of bony dysplasias and syndromes, including achondroplasia and thanatophoric dysplasia, and in syndromes with associated craniosynostosis.

Wolf-Hirschhorn (4p ⁻ ) syndrome has an abnormally sloped forehead, the “Greek warrior facies” ( Fig. 33.7 ). The forehead can also be sloped in the settings of microcephaly and encephalocele, in which the forebrain is underdeveloped ( Fig. 33.8 ).

Differential Diagnosis of Frontal Bossing

Achondroplasia
Acromegaly
Basal cell nevus
Cleidocranial dysostosis
Congenital syphilis
Crouzon syndrome
Fetal trimethadione
Pfeiffer syndrome
Russell-Silver syndrome
Thanatophoric dysplasia

FIG. 33.7, Sloped Forehead in Fetus With Wolf-Hirschhorn Syndrome and Cleft Palate.

FIG. 33.8, Sloped Forehead in Fetus With Posterior Encephalocele.

Encephaloceles

An encephalocele or cephalocele is an abnormal protrusion of the brain and/or meninges through a defect in the skull and is considered a form of spinal dysraphism. In the United States and Western Europe, the occiput is the most common location for encephaloceles. Frontoethmoidal encephaloceles are more often found in Southeast Asia. Many encephaloceles are diagnosed during fetal sonography; they appear as abnormal defects in the calvaria with herniation of brain tissue or meninges. Fetal MRI is excellent for evaluating contents of the encephalocele and in assessing the appearance of the intracranial brain parenchyma. Frontal encephaloceles can be seen during sonographic evaluation of the fetal face and are often associated with hypertelorism and midline facial clefting (see Chapter 34 ).

Orbit Abnormalities

Sonographic evaluation of the fetal orbits is best obtained in axial or coronal views, in which one can confirm the presence of both orbits, evaluating their sizes and shapes and the distance between them. The sagittal view may help to evaluate abnormal anterior displacement of the globes ( proptosis or exorbitism ). The orbits should be symmetrical in size and the outer and inner interorbital distances within a normal range. Detailed nomograms are available for reference ( Table 33.1 ).

TABLE 33.1

Normal Orbital Diameters in the Fetus

With permission from Trout T, Budorick NE, Pretorius DH, McGahan JP. Significance of orbital measurements in the fetus. J Ultrasound Med. 1994;13(12):937-943.

Gestational Age (wk)	INNER DIAMETERS (mm)			OUTER DIAMETERS (mm)
Gestational Age (wk)	5th Percentile	50th Percentile	95th Percentile	5th Percentile	50th Percentile	95th Percentile
13	4	7	10	12	16	20
14	5	8	11	14	18	22
15	5	8	11	17	21	25
16	6	9	12	19	23	27
17	7	10	13	21	25	29
18	8	11	14	24	27	31
19	8	11	14	26	30	34
20	9	12	15	28	32	36
21	10	13	16	30	34	38
22	10	13	16	32	36	40
23	11	14	17	33	37	41
24	12	14	17	35	39	43
25	12	15	18	37	41	45
26	13	16	19	39	43	47
27	13	16	19	40	44	48
28	14	17	20	42	46	50
29	14	17	20	43	47	51
30	15	18	21	45	49	52
31	15	18	21	46	50	54
32	16	19	22	47	51	55
33	17	20	23	48	52	56
34	17	20	23	49	53	57
35	18	21	24	50	54	58

Table generated from raw data using two separate quadratic regression models:

Outer diameter = −2.17 + 3.36(Age) − 0.03 (Age ² )

R ² = 0.96, p < .001

Inner diameter = −4.14 + 0.94(Age) − 0.007 (Age ² )

R ² = 0.84; p < .001

Hypotelorism

Hypotelorism is defined as an abnormally small distance between the orbits and is often associated with other anomalies ( Fig. 33.9 ). Holoprosencephaly ( Fig. 33.10 ) can be associated with cyclopia (single midline eye with failed development of nose with or without a proboscis [ Fig. 33.11 ]); ethmocephaly (hypotelorism with failed development of nose and a proboscis); or cebocephaly (hypotelorism and poorly developed nose with a single nostril).

Conditions Associated With Hypotelorism

Abnormalities of the brain
- Holoprosencephaly
- Microcephaly
Chromosomal abnormalities
- Trisomies 13, 18, and 21
- Chromosome 5p deletion
Head shape abnormalities
- Trigonocephaly
Syndromes
- Langer-Giedion syndrome
- Oculodentodigital dysplasia
- Nasal maxillary dysostosis (Binder syndrome)
- Myotonic dystrophy
- Meckel-Gruber syndrome
- Williams syndrome

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