Fetal Face and Neck

Embryology Of The Fetal Face

During the fourth and fifth weeks, the embryo has characteristic external features of the head and neck area in the form of a series of branchial arches, pouches, grooves, and membranes. Their development and evolution require a very precise and complex process with defined and orderly expectations throughout the fetal stage of formation. These structures, referred to as the branchial apparatus , bear a resemblance to gills and necessitate all three primary embryonic tissues of the endoderm, mesoderm, and ectoderm working together in sequence to avoid potential disfiguring and devastating facial malformations. The broad spectrum of congenital facial anomalies ranges from cosmetic indiscretions such as cleft lips to potentially life-threatening malformations such as arrhinia and obstructive oropharyngeal teratomas and their sequelae.

There are six branchial arches, but only the first four are visible externally ( Fig. 59.1A ). Neural crest cells migrate into the branchial arches and proliferate, resulting in swelling that demarcates each arch. The neural crest cells develop the skeletal features of the face, and the mesoderm of each arch develops the musculature of the face and neck. The arches are separated by branchial grooves, and each is composed of a core of mesenchymal cells and tissues derived from intraembryonic mesoderm covered by ectoderm. The mesenchyme forms the cartilage, bone, muscle, and blood vessels.

The fusion of five facial prominences must occur to form the lips and nose: frontonasal prominence, a pair of maxillary prominences, and a pair of mandibular prominences. Aberrant anatomical variations affecting the face may occur due to defects involving any of the branchial arches. The first branchial arch develops into the maxillary and mandibular arches, forming the jaw, zygomatic bone, ear, and temporal bone (see Fig. 59.1B ). The maxillary prominences arise and grow cranially just inferior to the eyes, and the mandibular prominence grows inferiorly, forming the mandible and squamous components of the temporal bones. The second branchial arch contributes to the hyoid bone. The severity and magnitude of congenital abnormalities of the first and second branchial arches will depend on the extent of the insult, with timing playing a crucial component of its scope, often relating to hypoplasia or even aplasia of these anatomical variations.

Development of the Lips

The complex formation of the facial lips is composed of multiple prominences growing steadily together, with the correct timing being essential to completing the process correctly. The maxillary prominences grow medially between the fifth and eighth weeks, with this growth compressing the medial nasal prominences together towards the midline. The two medial nasal prominences and the two maxillary prominences lateral to them fuse together to form the upper lip ( Fig. 59.2 ). The medial nasal prominences form the medial aspect of the lip, which is the origin of the labial component of the lip, the upper incisor teeth, and the anterior aspect of the primary palate. The lateral nasal prominences form the alae of the nose. The maxillary prominences and lateral nasal prominences are separated by the nasolacrimal groove, where the nasolacrimal duct and lacrimal sac reside. The mandibular prominences merge at the end of the fourth to fifth week and form the lower lip and jaw, chin, and mandible.

Development of the Nose

The nose is formed in three parts. The nasal pits are formed as the surface ectoderm thickens into the nasal placodes on each side of the frontal nasal prominence; these placodes then invaginate on either side ( Fig. 59.3 ). The bridge of the nose originates from the frontal prominence, the two medial nasal prominences form the crest and tip of the nose, and the lateral nasal prominences form the sides, or alae. The maxillary prominences then fuse with the nasal prominences and soon after fuse in the midline to form a continuous central structure.

Development of the Mouth

The primitive mouth is an indentation on the surface of the ectoderm (referred to as the stomodeum ) (see Fig. 59.2 ). Until 24 to 26 days of gestation, the stomodeum is separated from the pharynx by a membrane that ruptures to place the primitive gut in communication with the amniotic cavity. At approximately the same time, five prominences are identified: the frontal nasal prominence, forming the upper boundary of the stomodeum; the paired maxillary prominences of the first branchial arch, forming the lateral boundaries of the stomodeum; and the paired mandibular prominences, forming the caudal boundary. As these prominences fuse together in the midline, the mouth continues to be separated from the nasal cavity by the palate ( Fig. 59.4 ).

Development of the Palate

The palate forms the roof of the mouth and the floor of the nasal cavity and is divided into the hard palate, located more anteriorly, and the soft palate, which is located more posteriorly. The primary palate begins forming early in the sixth week, with the wedge-shaped mass created by the emergence of the medial nasal prominences between the developing maxillae. As the nose forms, the fusion of the medial nasal prominence with its contralateral counterpart creates the primary palate (becomes the anterior one-third of the definitive palate). The primary palate forms the anterior and midline aspect of the maxilla, which represents a small part of the adult hard palate ( Fig. 59.5 ).

The intermaxillary segment also contributes to the labial component of the philtrum and the upper four incisors. The maxillary prominences expand medially to give rise to the palatal shelves, which continue to advance medially, fusing superior to the tongue. Simultaneously, the developing mandible expands to increase the size of the oral cavity; this allows the tongue to drop out of the way of the growing palatal shelves. The palatal shelves then fuse with each other in the horizontal plane and the nasal septum in the vertical plane, forming the secondary palate. The face and palate complete midline fusion between the sixth and twelfth weeks of gestation.

Sonographic Evaluation Of The Fetal Face

Given the often-fearful reaction that fetal anomalies in general and especially facial anomalies can carry due to their negative social and psychological impacts, sonographic facial evaluation must be closely scrutinized. Evaluations should be routinely included in all fetal anatomic surveillance studies and with increased analysis when there is a family history of craniofacial malformation or when another congenital anomaly is discovered due to the close association of facial abnormalities with coexisting fetal malformations. Typically, the sonographic evaluation consists of utilizing all three orthogonal imaging planes (sagittal, axial, and coronal), as each provides a unique perspective of the three dimensions of organs; however, with the advent of three- and four-dimensional imaging, specific information beyond these planes can often be obtained ( Fig. 59.6 ).

Facial anomalies are heterogeneous and can occur as isolated defects or as part of a larger setting (with global anomalies), as a condition, or as part of a larger syndrome (e.g., orbital fusion and a proboscis suggest alobar holoprosencephaly). Often a fetus with congenital facial deformations discovered prenatally will require a multidisciplinary team approach consisting of obstetricians, geneticists, sonographers, pediatricians, radiologists, surgeons, and specific specialty domains. As sonography has become the imaging gold standard in prenatal screening and plays a crucial role in the evaluation and with serial assessments, imaging results necessitate a high level of accuracy to provide precise and correct information regarding diagnosis and potential prognosis to the parents ( Box 59.1 ). The use of three-dimensional ultrasound (3DUS) and four-dimensional ultrasound (4DUS) reconstruction has been shown in recent years to be a useful adjunct to conventional two-dimensional (2D) or bidirectional screening assessment of the fetal face.

Worldwide, craniofacial anomalies are a concern for infant mortality and pediatric morbidity. A family history of craniofacial malformations may prompt a targeted sonographic study along with specific genetic testing in an attempt to identify associated risk factors. When available, a geneticist should complete a thorough history, often of three-generation pedigrees, in an attempt to better understand how the craniofacial malformation happened and determine the risk for future pregnancies and generations. In addition, this exercise should better determine if identified anomalies are isolated or part of a larger genetic syndrome.

Abnormalities Of The Face And Neck

Dysmorphology, or the study of human congenital malformations and syndromes, divides congenital anomalies into three classifications of alterations that occur to typical morphology. A malformation sequence , or the process of poor formation of tissue, allows for a chain reaction of defects to occur as normal tissue is not a foundation. A deformation sequence gives way to normal tissue development; however, external factors contribute to secondary distortion or deformation. These may occur in a variety of ways, and their scope of effect may be slight to profound, affecting normal tissue growth with exacerbated anatomical variations. Finally, a disruption sequence occurs when embryogenesis is disrupted by tissue breakdown or injury from a possible broad spectrum of opportunities, including infectious, mechanical, vascular, or metabolic origin. To complicate the comprehension of congenital anomalies, a fetal anomaly can often only be explained by the combination of sequential defects happening in utero.

Craniofacial malformations constitute a spectrum of anomalies, including clefting of the face, lip, and palates; craniosynostosis ; nasal deviations; tongue sizes and masses; mandibular variations that affect the chin; microtia or ear irregularities; orbital architecture disparities; and many other well-described craniofacial pathologies. Because orofacial anomalies can be isolated events or inclusive of a larger setting of a more severe syndrome, recurrence rates vary. Knowing as much information as possible will better allow the family to understand how future pregnancies may be affected and allow for the current pregnancy to be accurately monitored for possible progression of anomalies and their effects ( Boxes 59.2 and 59.3 ).