Micrognathia and Retrognathia

Abstract

Both retrognathia and micrognathia are facial deformations related to the development or position of the fetal mandible. The former is characterized by an abnormal position in relation to the maxilla and the latter refers to a mandibular hypoplasia and is frequently associated to different genetic syndromes. Due to this association, it is advisable to offer a study of the fetal karyotype and an echocardiogram when fetal micrognathia is detected.

Both abnormalities can be detected by ultrasound. The evaluation of the inferior facial angle (IFA), measured in a sagittal view, is useful to identify micrognathia and make the differential diagnosis with retrognathia. The jaw index, the mandibular/maxillar width, and the mandibular ratio measured in the axial view are particularly useful to assess the severity of the micrognathia. Fetal magnetic resonance imaging (MRI) can be helpful to assess the severity of fetal micrognathia evaluating a potential obstruction of the airway.

In those cases in which there is a suspicion of an obstruction in the upper airway, polyhydramnios can be associated and an ex utero intrapartum treatment (EXIT) delivery is indicated.

Keywords

micrognathia, retrognathia, fetal mandible

Introduction

The fetal mandible is a common site for defects caused by numerous genetic conditions and adverse environmental factors. When an anomaly in the fetal mandible is detected on ultrasound (US), the clinician should look for other anomalies in the fetal anatomy because such associations are frequent.

Disease

Definition

Retrognathia refers to a facial malformation characterized by abnormal development of the mandible with an abnormal position in relation to the maxilla ( Fig. 68.1 ). Micrognathia refers to a facial malformation characterized by mandibular hypoplasia causing a small receding chin ( Fig. 68.2 ).

Prevalence and Epidemiology

Fetal micrognathia has an incidence of 1 : 1000 births. It is always accompanied by retrognathia, although fetal retrognathia can be present without micrognathia.

Etiology and Pathophysiology

The etiology of mandibular hypoplasia is unclear. It may be the result of a positional malformation, intrinsic growth abnormalities, or a connective tissue disorder. Attempts have been made to explain why fetal micrognathia is associated with different syndromes. The harmonious development of different anatomic structures in the mandible and the overall growth of the mandible are regulated by several factors, such as the prenatal activity of the masticatory muscles, the growth of the tongue, the inferior alveolar nerve and its branches, and the development and migration of the teeth. Because normal development of the fetal mandible is a multifactorial process, the maldevelopment of the masticatory muscles or nerves may lead to a hypoplastic mandible. Also, the failure of mandibular formation displaces the tongue upward, which prevents the lateral palatine shelves from medial migration and midline fusion, and explains the high association of micrognathia with cleft palate.

The normal development of the mandible can be disrupted by genetic or environmental factors (chromosomal and nonchromosomal syndromes) or environmental ones ( Table 68.1 ). Some neuromuscular conditions in which a fixed contracture of the temporomandibular joint prevents the opening of the mouth are associated with micrognathia secondary to impaired development of the mandible.

TABLE 68.1

ASSOCIATED CLINICAL FINDINGS IN FETAL MICROGNATHIA

Syndrome	Predominant Features	Inheritance	Prenatal Diagnosis
Acrofacial dysostosis	Preaxial limb deficiencies, CHD, CNS anomalies	AD	Yes
Treacher-Collins	Hypoplasia of facial bones, ear anomalies, cleft palate	AD	Yes
Rodriguez type	Preaxial limb deficiencies, CHD	AR	Yes
Nager type	Microcephaly, preauricular tags, CHD, preaxial limb defects	Sporadic	Yes
Miller (Genee-Widemann) type or POADS (postaxial)	Syndactyly, thumb hypoplasia, absence of fifth digit	AR	—
Branchiooculofacial syndrome	Microcephaly, ear anomalies, hypertelorism, microphthalmia, renal anomalies, polydactyly, vermian agenesis	AD	Yes
Cerebrocostomandibular syndrome	Microthorax, CHD, small thorax, abnormal ribs, renal ectopia, polyhydramnios	AD-AR	Yes
Mandibuloacral dysplasia	Joint contractures, wide cranial sutures	AD	—
Oral-facial-digital I syndrome	Facial asymmetry, bifid tongue, polycystic kidney, syndactyly, CNS anomalies	X-linked dominant	Yes
Oral-facial-digital II syndrome or Mohr syndrome	Hypertelorism, polydactyly, porencephaly	AR	Yes
Oral-mandibular-limb hypogenesis spectrum	Acral hypoplasia, syndactyly	Sporadic	—
Otopalatodigital syndrome type II	Hypertelorism, omphalocele	X-linked dominant	—
Robin sequence	Glossoptosis, cleft palate		Yes
SKELETAL AND NEUROMUSCULAR DISEASES FREQUENTLY ASSOCIATED WITH MICROGNATHIA
Achondrogenesis types IA and IB	Severe micromelia, short ribs	AR	Yes
Amyoplasia congenita disruptive sequence	Diffuse joint contractures, gastroschisis, polyhydramnios	Sporadic	Yes
Atelosteogenesis type I	Frontal bossing, midface hypoplasia, small thorax, 11 ribs, rhizomelia, talipes, encephalocele, polyhydramnios	Sporadic	Yes
Camptomelic dysplasia	Large anterior fontanelle, hypertelorism, CHD, small thorax, sex reversal in males, hydronephrosis, bowing of tibiae and less so of femora	AD	Yes
Cerebrooculofacioskeletal syndrome	Microcephaly, microphthalmia, CHD anomalies, contractures	AR	Yes
Chondrodysplasia punctata, X-linked dominant type	Microcephaly, rhizomelia	X-linked dominant	Yes
Diastrophic dysplasia	Hitchhiker thumbs, scoliosis, short limbs	AR	Yes
Langer mesomelic dysplasia	Mesomelia	AR	Yes
Multiple pterygium syndrome	Pterygia of neck, axillae, antecubital region, popliteal region	AR	Yes
Neu-Laxova syndrome	Microcephaly, exophthalmos, CNS anomalies, joint contractures, syndactyly, subcutaneous edema	AR	Yes
Pena-Shokeir phenotype (fetal akinesia deformation sequence)	Diffuse joint contractures, cystic hygroma, microstomia	AR	Yes
CHROMOSOMAL SYNDROMES FREQUENTLY ASSOCIATED WITH MICROGNATHIA
Cat-eye syndrome	Preauricular tags, TAPVR, renal agenesis	AD inv dup (22)q11	Yes
Deletion 3p syndrome	Microcephaly, malformed ears, polydactyly in hands	Del 3p	—
Deletion 4p syndrome (Wolf-Hirschhorn)	Hypertelorism, preauricular tags, CHD, polydactyly, talipes, CNS anomalies	Isolated 4p16.3	Yes
Deletion 5p syndrome (cri du chat)	Microcephaly, hypertelorism, CHD	5p15.2	Yes
Deletion 9p syndrome	Trigonocephaly, abnormal ears, hypertelorism, CHD	AD, isolated	—
Deletion 11q syndrome	Trigonocephaly, microcephaly, joint contractures		—
Deletion 13q syndrome	Microcephaly, CHD, small or absent thumbs	Isolated	—
Deletion 22q 11.2 syndrome	Conotruncal CHD, thymus aplasia	AD	Yes
Monosomy X (Turner) syndrome	Left-sided CHD, cystic hygroma	Sporadic	Yes
Pallister-Killian syndrome	Thin upper lip, CDH, CHD, CNS anomalies, rhizomelia	Sporadic	Yes
Triploidy syndrome	IUGR, hypotonia, hypertelorism, syndactyly, CHD, CNS anomalies	Sporadic, 69,XYY	Yes
Trisomy 8 mosaic syndrome	Hypertelorism, joint contractures	Sporadic	Yes
Trisomy 9 mosaic syndrome	Joint contractures, CHD	Sporadic	Yes
Trisomy 13 syndrome	IUGR, microcephaly, microphthalmia, cleft palate, CNS anomalies, CHD, renal anomalies, polydactyly	Sporadic	Yes
Trisomy 18 syndrome	Clenched hands, CHD, omphalocele, renal anomalies, CHD anomalies	Sporadic	Yes