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 ).




Fig. 68.1


Two-dimensional image of a fetal profile in a case of retrognathia in the third trimester. There is a receding chin with a normal size.



Fig. 68.2


Two-dimensional image of a fetal profile in a case of micrognathia. There is marked hypoplasia of the mandible that also displaces it.


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

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Jul 7, 2019 | Posted by in OBSTETRICS & GYNAECOLOGY IMAGING | Comments Off on Micrognathia and Retrognathia
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