|
NORMAL MANDIBLE |
|
MICROGNATHIA /
RETROGNATHIA |
Fetuses
with mandible anomalies are at risk of acute neonatal respiratory distress
syndrome. This is a neonatal emergency since the tongue may obstruct the upper
airways and lead to suffocation
Retrognathia (recession of the chin) is assessed through the measurement
of the inferior facial angle, as defined on a mid-sagittal view
|
|
|
|
Micrognathia (mandible of insufficient size) is a malformation of the fetal face characterized by a small mandible. Micrognathia may be idiopathic but is more commonly associated with many different syndromes.
Micrognathia
refers to size, and retrognathia to position
(2).
|
|
|
|
|
|
ULTRASOUND |
- The diagnosis depends on a favorable fetal position to assess the relationship between the mandible and rest of the fetal face.
- Small mandible and receding chin.
- Lower lip of the fetus is not directly under the upper lip.
- Normal measurements for the mandible are reported.
|
|
|
|
|
Normal Coronal Plane
In the coronal plane the echogenic anterior tip of the
mandible should normally be seen in the same plane as the lips. In retrognathia the echogenic tip is not seen in this
plane. |
- The Jaw Index.
- Inferior Facial Angle – An inferior facial angle value below 49.2°
(mean - 2 standard deviations) defined retrognathism.
- The Mandibular width /Maxillary width ratio was constant between 18 and 28 gestational weeks (regression line, P = 0.8). The mean value of the MD/MX ratio in the 18-28-gestational-week interval was 1.017 (SD = 0.116). Consequently, a MD/MX ratio < 0.785 defined micrognathism
- Careful search for other abnormalities including cardiac and skeletal dysplasias.
- Evaluate the fetal ears (Treacher Collins / Goldenhar syndrome).
- High frequency of polyhydramnios (? swallowing difficulties).
- Ask for a maternal history of drug exposure.
- Ask if there is any history of familial syndromes.
- Karyotyping is recommended (chromosomal anomalies in 66% (1).
ANOMALIES ASSOCIATED WITH MICROGNATHIA |
Link to
Anomalies Associated With Micrognathia
REFERENCES |
- Nicolaides KH, Salvesen DR,
Snijders RJM et.al. Micrognathia fetal facial defects: Associated malformations
and chromosomal abnormalities. Fetal Diagn Ther 1993;8:1-9.
- Cohen
MM Jr. Robin sequences and complexes: causal heterogeneity and
pathogenic/phenotypic variability. Am J Med Gen 1999; 84:
311-5