The fetal central nervous system can already be examined in the first trimester of pregnancy. Acrania, alobar holoprosencephaly, cephaloceles, and spina bifida can confidently be diagnosed at that stage and should actively be looked for in every fetus undergoing first-trimester ultrasound. For some other conditions, such as vermian anomalies and agenesis of the corpus callosum, markers have been identified, but the diagnosis can only be confirmed in the second trimester of gestation. For these conditions, data on sensitivity and more importantly specificity and false positives are lacking, and one should therefore be aware not to falsely reassure or scare expecting parents based on first-trimester findings. This review summarizes the current knowledge of first-trimester neurosonography in the normal and abnormal fetus and gives an overview of which diseases can be diagnosed.

Sonographic detection of central nervous system defects in the first trimester of pregnancy.

Most brain abnormalities are present in the first trimester, but only a few are detected so early in gestation. According to current recommendations for first-trimester ultrasound, the fetal head structures that should be visualized are limited to the cranial bones, the midline falx and the choroid-plexus-filled ventricles. Using this basic approach, almost all cases of acrania, alobar holoprosencephaly and cephalocele are detected. However, the majority of other fetal brain abnormalities remain undiagnosed until the midtrimester. Such anomalies would be potentially detectable if the sonographic study were to be extended to include additional anatomic details not currently included in existing guidelines. The aim of this review article is to describe how best to assess the normal fetal brain by first-trimester expert multiplanar neurosonography and to demonstrate the early sonographic findings that characterize some major fetal brain abnormalities. © 2020 International Society of Ultrasound in Obstetrics and Gynecology.

First-trimester fetal neurosonography: technique and diagnostic potential.

Fetal micrognathia involves abnormal or arrested development of the fetal mandible. Till recently, the prenatal diagnosis was subjective, based on the evaluation of the fetal profile and assessment of the relationship between the maxilla and the mandible. Recently objective sonographic methods have been utilized for diagnosing micrognathia such as the inferior facial angle, the jaw index, the frontal nasomental angle, the mandible width/maxilla width ratio and the mandibular length. Another useful sonographic sign, the mandibular gap in the retronasal triangle view, increases the accuracy of the diagnosis early in the first trimester. 3D sonographic views can add to the diagnosis and prenatal MRI is a useful adjunct to ultrasound in cases of limited acoustic window, maternal obesity, oligohydramnios and anterior spine position. The identification of micrognathia should prompt karyotyping and sonographic investigation for other abnormalities. The outcome of fetuses with this seemingly isolated finding is more guarded than one would intuitively believe, and the parents should be counseled accordingly. Postnatal complications including mild to severe upper airway obstruction leading to respiratory distress, feeding difficulties and mild to severe long-term developmental delay are common. One should be careful in pronouncing a fetus having ‘micrognathia’, especially on subjective evaluation, as this term implies that the fetus is abnormal with presence of significant pathology. There is no ‘gold standard’ for a definitive diagnosis of micrognathia on post-natal evaluation. Using a combination of objective sonographic markers as well as follow-up ultrasound assessments can significantly reduce the risk of a false diagnosis. Follow-up scans should be arranged, and neonatal service should be alerted in cases of ongoing pregnancies.

/pdf/focus-on-prenatal-detection-of-micrognathia-2h517c1x33.pdf

Focus on Prenatal Detection of Micrognathia

Micro- and retrognathia of mandibular origin may lead to life-threatening respiratory problems in connection with glossoptosis immediately after birth. Prenatal screening for this malformation is therefore increasingly important. Today this is accomplished by predominantly subjective standards. Objective criteria have been proposed but have not become established. We therefore made an effort to develop indices that would identify major skeletal discrepancies or micrognathia in as straightforward a fashion as possible during routine prenatal sonography. Series of fetal jaw sonograms (Toshiba Aplio MX®) were obtained in 313 women with normal pregnancies from weeks 19–29 of gestation. Upper- and lower-jaw landmarks were interactively located on screen and evaluated for reproducibility. Linear parameters representative of maxillary and mandibular length (SpA’–SpP’ and Rami–SymMe) were measured and related to femur length and gestational age. Based on these data, indices for maxillary, and mandibular length were derived and analyzed. High correlations were identified for mandibular length both with gestational age (R = 0.845; R2 = 0.713) and with femur length (correlation coefficients (R) = 0.839; coefficients of determination (R2) = 0.704). For maxillary length, the respective correlation coefficients were 0.691 (R2 = 0.477) and 0.656 (R2 = 0.430). Estimates of mandibular and maxillary length based on gestational age and femur length were obtained by regression analysis. The mean bimaxillary length ratio was 0.628 ± 0.043. Maxillary and mandibular growth can be objectively evaluated via indices. It is conceivable to develop this approach into a sensitive and reliable method of prenatal jaw screening for major skeletal anomalies and congenital malformations.

Prenatal indices for mandibular retrognathia/micrognathia

Fetal micrognathia in the first trimester: An ominous finding even after a normal array.

Objective
To describe the sonographic features of fetal cephalocele diagnosed at the time of first-trimester ultrasound screening for aneuploidy.

Methods
This was a retrospective review of cases of cephalocele diagnosed in the first trimester at four fetal medicine referral centers. Once diagnosis was suspected, a transvaginal ultrasound examination was offered to improve depiction of the cranial defect and enhance examination of fetal anatomy, with special attention given to the location, size and content of defects. To assure consistency in diagnosis, representative pictures and videoclip sequences of the cranial defect were obtained and reviewed by at least two authors. Cases were classified and compared with the assessment made at diagnosis.

Results
Of the 35 affected fetuses identified, 33 were of a singleton pregnancy and two were of twin pregnancies in which the other fetus was unaffected. The lesion was classified as a cranial meningocele in 13 (37%) cases and as an encephalocele in 22 (63%). The bone defect was occipital in 27 (77%), frontal in three (9%), parietal in three (9%) and non-classifiable in two (6%). Twelve (34%) were considered as small in size, 11 (31%) as medium and 12 (34%) as large. There were no reported cases of aneuploidy; however, four (11%) cases were associated with Meckel–Gruber syndrome, two (6%) with a disruptive syndrome and one (3%) with skeletal dysplasia. Eight (23%) pregnancies were lost to follow-up. Parents opted for termination of pregnancy in 21 of the 27 remaining cases and, of the six ongoing pregnancies, four patients miscarried or the fetus died in utero during the second trimester, one liveborn infant died shortly after delivery and one underwent neonatal surgery for an isolated cranial meningocele and is currently doing well.

Conclusions
First-trimester sonographic diagnosis of cephalocele is accomplished easily with a detailed examination of the skull contour at the time of routine assessment of the axial and sagittal views of the head for measurement of the biparietal diameter and nuchal translucency, respectively. However, the sonographic features are highly variable. A significant proportion of cases are associated with genetic or disruptive syndromes. Prenatal diagnosis of cephalocele in the first trimester was associated with a high rate of termination of pregnancy and early intrauterine fetal demise. Only one fetus in this series survived and is neurologically intact; therefore, the prognosis of this condition remains poor. Copyright © 2014 ISUOG. Published by John Wiley & Sons Ltd.

Sonographic spectrum of first-trimester fetal cephalocele: review of 35 cases

Objective

To describe a new ultrasound technique that may be useful for the diagnosis of micrognathia in the first trimester of pregnancy.



Methods

The retronasal triangle (RNT) view is a technique that captures the coronal plane of the face in which the primary palate and the frontal processes of the maxilla are visualized simultaneously. Normal first-trimester fetuses display a characteristic gap between the right and left body of the mandible in this view (the ‘mandibular gap’). The presence or absence of this gap was evaluated and measured prospectively during real-time scanning (n = 154) and retrospectively by analyzing three-dimensional (3D) datasets (n = 50) in normal first-trimester fetuses undergoing screening for aneuploidy at 11–13 weeks' gestation. 3D datasets from 12 fetuses with suspected micrognathia were also collected and examined retrospectively for the same features.



Results

The mandibular gap was identified in all 204 normal fetuses and increased linearly with increasing crown–rump length (y = 0.033x + 0.435; R2 = 0.316), with no statistically significant differences between measurements obtained by two-dimensional ultrasound and 3D offline analysis. Among fetuses with suspected micrognathia, three 3D datasets were excluded from analysis because of poor image quality in one and the diagnosis of a normal chin in two. In the remaining nine fetuses, the mandibular gap was absent and was replaced by a bony structure representing the receding chin in seven (77.8%) cases and was not visualized due to severe retrognathia in the remaining two (22.2%) cases. All fetuses with micrognathia had associated anomalies, including seven with aneuploidy and two with skeletal dysplasia.



Conclusions

The RNT view may be a helpful technique for detecting micrognathia in the first trimester. The absence of the mandibular gap or failure to identify the mandible in this view is highly suggestive of micrognathia and should prompt a targeted ultrasound scan to assess for other anomalies. Further research is needed to determine the false-positive and false-negative rates of this technique. Copyright © 2012 ISUOG. Published by John Wiley & Sons, Ltd.

https://obgyn.onlinelibrary.wiley.com/doi/pdf/10.1002/uog.10121

Absent mandibular gap in the retronasal triangle view: a clue to the diagnosis of micrognathia in the first trimester

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Sonographic spectrum of first-trimester fetal cephalocele: review of 35 cases

Absent mandibular gap in the retronasal triangle view: a clue to the diagnosis of micrognathia in the first trimester