Micrognathia

Anne Kennedy, MD

DIFFERENTIAL DIAGNOSIS

Common

Technical
Idiopathic
Oligohydramnios
Trisomy 18

Less Common

Amniotic Band Syndrome

Rare but Important

Pierre Robin Syndrome
Diabetic Embryopathy
Treacher Collins Syndrome
Cornelia de Lange Syndrome
Otocephaly
Other Syndromes/Conditions

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Is micrognathia real or technical due to incorrect scan plane?
- Reproducible finding if real
Use 3D ultrasound if available
- Helpful to assess additional dysmorphic features (e.g., ear malposition, ear malformation, eye orientation)
- Volume acquisition increases likelihood that true midline sagittal view of profile is being analyzed
- Surface rendering → way to qualitatively evaluate chin from different perspectives
  - Help parents understand appearance and consulting services plan treatment
Mandibular measurements
- Plethora of measurement described with some nomograms available, most are technically challenging & not widely used
  - Jaw index
  - Mandibular area
  - Inferior facial angle, mandibular angle
  - Mandible width/maxilla width ratio

Helpful Clues for Common Diagnoses

Technical
- Incorrect scan plane
Idiopathic
- No other abnormalities identified
- May be familial; look at both parents
Oligohydramnios
- Part of Potter sequence
  - Beaked nose, redundant skin, low set ears, club feet
Trisomy 18
- Facial features include micrognathia and clefting
- Usually associated with growth restriction and multiple anomalies
  - Omphalocele, congential heart disease, abnormal finger positioning, arthrogryposis/radial ray malformation, central nervous system anomalies, congenital diaphragmatic hernia

Helpful Clues for Less Common Diagnoses

Amniotic Band Syndrome
- Random constriction/amputation defects; “slash” defects
- Careful search for bands mandatory as no significant recurrence risk
  - Linear echoes in amniotic fluid
  - Extend from fetal parts to uterine wall
  - Fetus appears tethered or in fixed position
- Occasionally, inspection of placenta after delivery may be only way to confirm diagnosis

Helpful Clues for Rare Diagnoses

Pierre Robin Syndrome
- Micrognathia often severe
- U-shaped palatal cleft hard to see sonographically as lip intact but may be evident on MR
- Glossoptosis (posterior displacement of tongue), also easier to see on MR
Diabetic Embryopathy
- Caudal regression sequence ± extremity malformations
- Brain malformations including holoprosencephaly
- Congenital heart disease, especially transposition and double outlet right ventricle
- Long standing diabetes → IUGR, oligohydramnios
- Gastrointestinal malformations (e.g., anorectal atresia)
- Genitourinary malformations (e.g., renal agnesis)
Treacher Collins Syndrome
- Genetic disorder characterized by craniofacial deformities
- Down sloping palpebral fissures
- Malar hypoplasia
- Microtia
Cornelia de Lange Syndrome
- Typical facies: Prominent upper lip, crescent-shaped mouth, micrognathia, fine arched eyebrows, long eyelashes
- Upper extremity limb reduction defects
- Congenital diaphragmatic hernia, occasionally bilateral
- Intrauterine growth restriction (IUGR)
Otocephaly
- Extremely rare but lethal anomaly
  - Microstomia
  - Aglossia or oroglossal hypoplasia
  - Agnathia or mandibular hypoplasia
  - Synotia: Low set medially rotated ears
- Fetus cannot swallow → marked polyhydramnios
Other Syndromes/Conditions
- Online Mendelian Inheritance in Man (OMIM) database includes 211 genetic conditions featuring micrognathia
- Many other multiple anomaly complexes without unifying diagnosis also feature micrognathia
- Micrognathia is rarely isolated
- Presence mandates careful search for other anomalies and consideration of of formal fetal echocardiography
  - 22q11 deletion associated with micrognathia and conotruncal malformations
- Families should be evaluated by clinical genetics service
Important to recognize autosomal recessive conditions as 25% recurrence risk
- Neu-Laxová syndrome
  - Lethal syndrome with IUGR
  - Microcephaly
  - Exophthalmos, absent eyelids
- Nager syndrome
  - Severe micrognathia and malar hypoplasia
  - Spectrum of radial ray malformations
  - 28% survival reported
  - Some dispute as to nature of inheritance, some cases appear dominant

Other Essential Information

Micrognathia may be associated with skeletal dysplasia
- Assess bone density
- Measure long bone lengths
- Look at vertebral contours
- Use 3D ultrasound
If associated with ear anomalies may also be associated with renal malformations
- Neonatal renal ultrasound worthwhile
Other potential complications
- Polyhydramnios → increased risk of preterm labor
- Respiratory distress ± feeding difficulties and typically requires one or more surgical procedures for repair
- Increased risk of genetic/syndromic condition

Image Gallery

Sagittal ultrasound shows possible micrognathia

in the second trimester. No other abnormal findings. Because fetal position precluded a better profile view, follow-up was suggested.

Sagittal transabdominal ultrasound in the same fetus as previous image, shows normal profile in the third trimester. The apparent micrognathia was due to incorrect scan plane.

(Left) Clinical photograph shows typical Potter syndrome facies with low set ears

and flattened nose

. Also note micrognathia

. (Right) Transabdominal ultrasound is extremely compromised by maternal obesity and oligohydramnios. The lack of fluid causes compression of the fetus resulting in the “squashed” appearance seen in Potter syndrome, which was due to renal agenesis in this case.

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