Congenital microcephaly detected by prenatal ultrasound: genetic aspects and clinical significance

Fetal Neuroimaging Update

OBJECTIVES

To review the current imaging techniques available for the evaluation of the fetal brain.

FINDINGS

Ultrasound remains the initial screening modality with routine scanning typically performed at 18-20 weeks gestation. When a central nervous system (CNS) abnormality is noted by ultrasound, MRI is increasingly being used to further clarify findings. Fetal MRI has the unique ability to provide high detailed anatomical information of the entire human fetus with high contrast resolution. This technique has grown due to the development of rapid single shot image acquisition sequences, improvement of motion correction strategies and optimizing shimming techniques.

CONCLUSIONS

The assessment of fetal CNS anomalies continues to improve. Advanced MRI techniques have allowed for further delineation of CNS anomalies and have become a cornerstone in the assessment of fetal brain well-being. Those interpreting fetal studies need to be familiar with the strengths and limitations of each exam and be sensitive to the impact discussing findings can have regarding perinatal care and delivery planning. Collaboration with neurologists, neurosurgeons, geneticists, counselors, and maternal fetal specialists are key in providing the best care to the families we treat.

Second-trimester Ultrasound and Neuropathologic Findings in Congenital Zika Virus Infection

Zika virus is a mosquito-borne virus that causes congenital Zika syndrome, characterized by microcephaly and other fetal brain anomalies. This case report presents a case of Zika virus-related fetal brain anomalies including pathologic evidence of cerebral neuronal apoptosis and macrophage infiltrates and intracerebral calcification, ventriculomegaly and corpus callosum dysgenesis detected by ultrasound at 18 weeks of pregnancy.

Diagnostic approach to fetal microcephaly

Microcephaly in utero is conventionally defined as a fetal head circumference (HC) 3SD below the mean for gestational age according to Jeanty et al.'s reference range. Prediction of microcephaly at birth (micB) based on conventional prenatal biometry is associated with a high percentage of false positive diagnoses and as a result, in countries in which it is an option, termination of pregnancy may be offered in cases that would have culminated in birth of a normocephalic child. A false negative diagnosis is rarer, but may lead to the birth of a symptomatic microcephalic child. In this review we present the results of our recent studies aimed at improvement of accurate prenatal detection of microcephaly including: (1), application of two new reference ranges for fetal HC in cases with a prenatal diagnosis of microcephaly based on the conventional reference; (2) assessment whether integration of additional parameters (stricter fetal HC cut-offs, small-for-gestational age (SGA), decreased HC/abdominal circumference and HC/femur length ratios, presence of associated malformations and family history) can improve prediction; (3), estimation of the difference between Z-scores of prenatal HC and the corresponding occipitofrontal circumference (OFC) at birth in order to propose an adjustment for better prediction of the actual OFC deviation at birth; (4), assessment whether micB diagnosis can be improved by accurate detection of false positive Fmic cases whose small HC is due to an acrocephalic-like head deformation by applying a new reference range of a vertical measurement of the fetal head: foramen magnum-to-cranium distance (FCD). The conventional and new reference ranges for fetal HC, all result in considerable over-diagnosis of fetal microcephaly (ranging from 43% to 33%). The use of the new references does not significantly improve micB prediction compared with the conventional one, whilst integrating additional parameters results in a better positive predictive value (PPV), but an increase in false negatives. The degree of Fmic severity is significantly over-estimated compared to the corresponding micB. The difference between the postnatal OFC deviation from the mean and the prenatal HC ranges from -0.74 SD to -1.95 SD for various fetal HC references. Application of the reference range for vertical cranial dimensions enables exclusion of fetuses with a small HC associated with a vertical cranial deformity without missing those with actual micB. Combining the fetal HC with the developed FCD criteria raised the PPV of micB to 78%. CONCLUSIONS: Prediction of micB can be improved by integrating additional parameters and by application of the FCD criteria, however the correct diagnosis of Fmic remains challenging. An algorithm for evaluation of fetal microcephaly is provided.

Congenital microcephaly: A diagnostic challenge during Zika epidemics

The multiple, wide and diverse etiologies of congenital microcephaly are complex and multifactorial. Recent advances in genetic testing have improved understanding of novel genetic causes of congenital microcephaly. The recent Zika virus (ZIKV) epidemic in Latin America has highlighted the need for a better understanding of the underlying pathological mechanisms of microcephaly including both infectious and non-infectious causes. The diagnostic approach to microcephaly needs to include potential infectious and genetic etiologies, as well as environmental in-utero exposures such as alcohol, toxins, and medications. Emerging genetic alterations linked to microcephaly include abnormal mitotic microtubule spindle structure and abnormal function of centrosomes. We discuss the diagnostic challenge of congenital microcephaly in the context of understanding the links with ZIKV emergence as a new etiological factor involved in this birth defect.

[How to deal with a fetal head circumference lower than the third percentile?]

The prenatal finding of a head circumference (HC) below the 3rd percentile (p) remains, in the same way as short femur or increased nuchal translucency with normal karyotype, one the most difficult situations for the praticionner in the setting of prenatal diagnosis. Microcephaly is a gateway to possible cerebral pathologies, but the main objective is to identify serious prenatal situations. A standardized HC measurement, the use of adapted reference tools and charts, longitudinal following of cephalic biometrics in high-risk situations, and systematic central nervous system analysis can increase the diagnostic performance of ultrasound which is often disappointing for microcephaly. The early distinction between associated or isolated microcephaly makes it possible to quickly orient the prenatal management and counseling. Fetal MRI and genetic counseling are fundamental in this context, making it possible to specify at best the etiological diagnosis and to provide assistance to the neuropediatrician in the establishment of an often uncertain prognosis. The recent increase in cases of microcephaly concomitant with the epidemic of the ZIKA virus is an additional argument to improve our practices and the daily apprehension of HC<3rd p.

Microcephaly

Microcephaly is defined as a head circumference more than two standard deviations below the mean for gender and age. Congenital microcephaly is present at birth, whereas postnatal microcephaly occurs later in life. Genetic abnormalities, syndromes, metabolic disorders, teratogens, infections, prenatal, perinatal, and postnatal injuries can cause both congenital and postnatal microcephaly. Evaluation of patients with microcephaly begins with a thorough history and physical examination. In cases of worsening microcephaly or neurological signs or symptoms, neuroimaging, metabolic, or genetic testing should be strongly considered. Any further studies and workup should be directed by the presence of signs or symptoms pointing to an underlying diagnosis and are usually used as confirmatory testing for certain conditions. Neuroimaging with magnetic resonance imaging (MRI) is often the first diagnostic test in evaluating children with microcephaly. Genetic testing is becoming more common and is often the next step following neuroimaging when there is no specific evidence in the history or physical examination suggesting a diagnosis. Microcephaly is a lifelong condition with no known cure. The prognosis is usually worse for children who experienced an intrauterine infection or have a chromosomal or metabolic abnormality. Zika virus has rapidly spread since 2015, and maternal infection with this virus is associated with microcephaly and other serious brain abnormalities. Microcephaly has become much more prevalent in the news and scientific community with the recent emergence of Zika virus as a cause of congenital microcephaly.

Prediction of microcephaly at birth using three reference ranges for fetal head circumference: can we improve prenatal diagnosis?

OBJECTIVE

To evaluate the prediction of microcephaly at birth (micB) using established and two new reference ranges for fetal head circumference (HC) and to assess whether integrating additional parameters can improve prediction.

METHODS

Microcephaly in utero was defined as a fetal HC 3SD below the mean for gestational age according to Jeanty et al.'s reference range. The records of cases with fetal microcephaly (Fmic) were evaluated for medical history, imaging findings, biometry and postnatal examination/autopsy findings. Microcephaly was confirmed at birth (micB) by an occipitofrontal circumference (OFC) or a brain weight at autopsy 2SD below the mean for gestational age. The new INTERGROWTH-21(st) Project and a recent Israeli reference for fetal growth were applied for evaluation of the Fmic positive predictive value (PPV) for diagnosis of micB cases. Optimal HC cut-offs were determined for each of the new references with the aim of detecting all micB cases whilst minimizing the number of false positives found to have a normal HC at birth. We also assessed the difference between the Z-scores of the prenatal HC and the corresponding OFC at birth, the frequency of small-for-gestational age (SGA), decreased HC/abdominal circumference (AC) and HC/femur length (FL) ratios, the prevalence of associated malformations and family history.

RESULTS

Forty-two fetuses were diagnosed as having Fmic according to the Jeanty reference, but micB was confirmed in only 24 (PPV, 57.1%). The optimal INTERGROWTH and Israeli reference HC cut-offs for micB diagnosis were mean - 3SD and mean - 2.3SD, resulting in a statistically non-significant improvement in PPV to 61.5% and 66.7%, respectively. The presence of a family history of microcephaly, SGA, associated malformations and application of stricter HC cut-offs resulted in a higher PPV of micB, although not statistically significant and with a concurrent increase in the number of false-negative results. The deviation of the HC from the mean, by all references, was significantly larger compared with the actual deviation of the OFC at birth, with mean differences between the corresponding Z-scores of -1.15, -1.95 and -0.74 for the Jeanty, INTERGROWTH and Israeli references, respectively.

CONCLUSIONS

The evaluated reference ranges all result in considerable over-diagnosis of fetal microcephaly. The use of the two new HC reference ranges did not significantly improve micB prediction compared with that of Jeanty et al., whilst use of additional characteristics and stricter HC cut-offs could improve the PPV with an increase in false negatives. The postnatal OFC deviates significantly less from the mean compared with the prenatal HC, and we propose that adjustment for this would enable better prediction of the actual OFC deviation at birth. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

Application of a novel prenatal vertical cranial biometric measurement can improve accuracy of microcephaly diagnosis in utero

OBJECTIVE

To construct a reference range for a new vertical measurement of the fetal head and to assess whether its combination with fetal head circumference (HC) can prevent the misdiagnosis of microcephaly in fetuses with an acrocephalic-like head deformation.

METHODS

A new vertical cranial biometric measurement was defined: the foramen magnum-to-cranium distance (FCD), measured between the foramen magnum and the upper inner cranial border along the posterior wall of the brainstem. The measurement was performed in a precise mid-sagittal plane using a three-dimensional multiplanar display of a sagittally acquired sonographic volume of the fetal head. The normal reference range was developed by measuring 396 healthy fetuses of low-risk singleton pregnancies between 15 and 40 gestational weeks. This reference was applied to 25 fetuses with microcephaly diagnosed prenatally (Fmic) based on HC ≥ 3 SD below the mean for gestational age. We determined an optimal FCD cut-off for combination with HC to detect all cases found with microcephaly at birth (micB), while excluding the fetuses with normal head circumference at birth (NHCB), who were described postnatally as having an acrocephalic-like cranial deformation.

RESULTS

In the healthy singleton fetuses, FCD increased with gestational age, with a quadratic equation providing an optimal fit to the data (adjusted R(2) = 0.934). The measurement could be assessed in 95.2% of cases. Of the 25 cases diagnosed with Fmic prenatally, on the basis of HC alone, 14 were micB and 11 were NHCB. We observed FCD below the mean - 2SD for gestational age in all 14 micB cases, but in only four of the 11 NHCB cases (P < 0.003). An acrocephalic-like cranial deformation was described at birth in five of the seven NHCB cases with normal FCD. The mean ± SD FCD Z-score of the micB cases was significantly lower (P < 0.001) than that of the false-positive ones: -3.85 ± 0.96 SD and -1.59 ± 1.45 SD, respectively. Based on HC measurement alone, the positive predictive value (PPV) was 56%. Combination of the HC and FCD criteria raised the PPV to 78%, decreasing the number of false positives from 11 to four, without missing any of the 14 micB cases.

CONCLUSIONS

Fetal vertical cranial biometric assessment in the mid-sagittal plane is feasible and correlates well with gestational age. In our series, a vertical cranial deformation was a frequent cause of a false Fmic diagnosis made on the basis of HC alone. Combination of the new vertical cranial biometric measurement with HC measurement can exclude these cases and thus improve diagnostic accuracy for Fmic. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Zika - A Pandemic in Progress?

The emerging threat of Zika virus outbreak with associated neurological abnormalities needs to be assessed in perspective in terms of its ability to cause a pandemic. This article attempts to throw some light on the issue.

Pränataldiagnostik bei fetaler Mikrozephalie

Diese Übersichtsarbeit behandelt die Mikrozephalie (MZ) aus der Perspektive der pränatalen Diagnostik. Eine MZ wird bei einem Kopfumfang unter der dritten Standardabweichung für das Gestationsalter vermutet. Diese Verdachtsdiagnose kann aus einem falschen Gestationsalter oder einer falsche Messung resultieren oder infolge einer Reihe häufiger Ätiologien wie offene Spina bifida, Enzephalozele, Holoprosenzephalie, Infektion, Aneuploidie, seltener auch Ursachen wie einer primären oder syndromalen MZ entstehen. Typische Ultraschallzeichen einer fetalen MZ sind die flache Stirn, der kleine Frontallappen, das reduzierte Gyrierungsmuster mit einem kurzen Balken, eine Pseudo-Kraniosynostose, ein dilatierter Subarachnoidalraum und oft eine Diskrepanz zwischen Kopf- und Bauchumfang. Mitunter kann eine schwere MZ schon in der Mitte der Schwangerschaft entdeckt werden, aber die meisten Formen fallen erst im III. Trimenon bzw. nach der Geburt auf. Die diagnostische Abklärung sollte auch das Angebot genetischer Untersuchungen einschließen, um monogen vererbte Formen mit hohem Wiederholungsrisiko z. B. bei autosomal-rezessiver Vererbung zu identifizieren. Die Arbeit diskutiert pränatalmedizinische und genetisch-diagnostische Abklärungsschritte bei fetaler MZ, die in Kombination mit den neuen genetischen Untersuchungstechniken hoffentlich in Zukunft zu einer höheren Aufklärungsrate führen werden.

The fetal profile line: a proposal for a sonographic reference line to classify forehead and mandible anomalies in the second and third trimester

OBJECTIVES

To test the fetal profile (FP) line, defined as the line that passes through the anterior border of the mandible and the nasion, as a reference line for forehead and mandible anomalies.

METHODS

Volumes of 248 normal and 24 pathological fetuses (16-36 and 19-37 weeks' gestation, respectively) were analysed retrospectively. When the FP line passes anteriorly, across or posteriorly to the frontal bone, this was defined as 'negative', 'zero' or 'positive', respectively. When the FP line was positive the distance (F distance) between the FP line and the frontal bone was measured.

RESULTS

No cases with a negative FP line were found in the normal fetuses. Before 27 weeks' gestation the FP line was always 'zero' except in one case. After 27 weeks' gestation the FP line was 'positive' in up to 25% (F distance (mean, range): 2.8, 2.1-3.6 mm). The FP line correctly identified 13 cases with retrognathia, 5 cases with frontal bossing and 3 cases with a sloping forehead.

CONCLUSION

Although large prospective studies are needed, the FP line may be a useful tool to detect second trimester profile anomalies such as retrognathia, sloping forehead and frontal bossing with the possibility of quantifying the latter.

Primary microcephaly in Hungary: epidemiology and clinical features

AIM

To describe the population-based epidemiological characteristics and clinical features of primary microcephaly in Hungary.

METHODS

A retrospective survey of patients born with microcephaly in a region (Dél-Alföld - South Great Plain) in Hungary between July 1, 1992 and June 30, 2006 was performed. Patients with microcephaly and without any environmental or obstetric risk factors and/or dysmorphism (primary microcephaly) were included in the study. The birth prevalence of primary microcephaly per 10,000 live births was calculated.

RESULTS

Ten patients (8 girls and 2 boys) were found with primary microcephaly among 185,486 live births, which corresponds to a birth prevalence of 0.54 per 10,000 live births (95% confidence interval: 0.20-0.87). Developmental delay and intellectual disability were the main clinical features. Dyskinesia was seen in one and epilepsy was diagnosed in two patients. The MRI revealed simplified gyral pattern in all patients.

CONCLUSION

Primary microcephaly is a very rare brain malformation, although the birth prevalence found in this survey is slightly higher than the few figures published earlier. As more and more genes and mutations responsible for primary microcephaly are discovered, the ascertainment of these rare cases is mandatory to provide the parents with genetic counselling.

Practice parameter: Evaluation of the child with microcephaly (an evidence-based review): report of the Quality Standards Subcommittee of the American Academy of Neurology and the Practice Committee of the Child Neurology Society

OBJECTIVE

To make evidence-based recommendations concerning the evaluation of the child with microcephaly.

METHODS

Relevant literature was reviewed, abstracted, and classified. RECOMMENDATIONS were based on a 4-tiered scheme of evidence classification.

RESULTS

Microcephaly is an important neurologic sign but there is nonuniformity in its definition and evaluation. Microcephaly may result from any insult that disturbs early brain growth and can be seen in association with hundreds of genetic syndromes. Annually, approximately 25,000 infants in the United States will be diagnosed with microcephaly (head circumference <-2 SD). Few data are available to inform evidence-based recommendations regarding diagnostic testing. The yield of neuroimaging ranges from 43% to 80%. Genetic etiologies have been reported in 15.5% to 53.3%. The prevalence of metabolic disorders is unknown but is estimated to be 1%. Children with severe microcephaly (head circumference <-3 SD) are more likely ( approximately 80%) to have imaging abnormalities and more severe developmental impairments than those with milder microcephaly (-2 to -3 SD; approximately 40%). Coexistent conditions include epilepsy ( approximately 40%), cerebral palsy ( approximately 20%), mental retardation ( approximately 50%), and ophthalmologic disorders ( approximately 20% to approximately 50%).

RECOMMENDATIONS

Neuroimaging may be considered useful in identifying structural causes in the evaluation of the child with microcephaly (Level C). Targeted and specific genetic testing may be considered in the evaluation of the child with microcephaly who has clinical or imaging abnormalities that suggest a specific diagnosis or who shows no evidence of an acquired or environmental etiology (Level C). Screening for coexistent conditions such as cerebral palsy, epilepsy, and sensory deficits may also be considered (Level C). Further study is needed regarding the yield of diagnostic testing in children with microcephaly.

Holoprosencephaly with neurogenic hypernatremia: a new case

BACKGROUND

Holoprosencephaly (HPE) is the most common developmental defect of the forebrain and mid-face in humans. It is a disorder of neural induction in which a genetic programming defect results in noncleavage of the forebrain in the sagittal plane and variable hypoplasia of paramedian structures. It occurs in 5-12/10,000 live births. Clinically, there is a nearly continuous spectrum of malformations consistent with HPE. Endocrinopathies, such as diabetes insipidus, hypothyroidism, hypocorticism, and growth hormone deficiency, are frequently associated with HPE. Seizures may occur.

CASE REPORT

We report a new case of semilobar-HPE complicated by neurogenic hypernatremia and no signs of dehydration in a child with microcephaly, spasticity, mental and psychomotor retardation, frontal bones hypoplasia, and mild facial dysmorphism.

Norman-Roberts syndrome: characterization of the phenotype in early fetal life

PURPOSE

Our purpose is to describe the prenatal manifestation of Norman-Roberts syndrome and to expand the knowledge of the fetal phenotype of this rare condition. The recurrence in two sibs might contribute to the hypothesis of a recessive condition.

METHODS

Three cases are presented in which the diagnosis was suggested by a prenatal ultrasound examination and confirmed by pathology of the fetuses, after termination of pregnancy. The major sign was the ultrasound detection of microcephaly at the 22nd and 23rd week of gestation. Fetal Magnetic Nuclear Resonance, the pathological examination with histological studies, was applied to arrive at the diagnosis of Norman-Roberts syndrome.

CONCLUSION

To the best of our knowledge, this is the second description of prenatal cases of Norman-Roberts syndrome. The combined clinical and pathological data is a contribution that might help to increase the identification of this rare condition and to correctly define the risk of its recurrence.

Assessment of fetal intracranial pathologies first demonstrated late in pregnancy: cell proliferation disorders

A considerable number of central nervous system pathologies remain undiagnosed during the first two trimesters of pregnancy. This group of disorders includes anomalies of brain proliferation, migration and cortical organization. Due to the fact that a detailed ultrasound examination of the fetal brain is usually not performed during the third trimester the diagnosis of these disorders is usually only made in families with a previously affected child or in many cases be mere chance. In this article we review the feasibility of prenatal diagnosis of disorders of brain proliferation: microcephaly, macrocephaly, hemimegalencephaly and neoplastic and non-neoplastic abnormal cell types. We discuss the differential diagnosis and offer a stepwise approach to the diagnosis of the more common disorders.

Methodologic issues in epidemiologic studies of congenital microcephaly

In this methodological paper, we explore a number of issues that pose problems for those who seek the antecedents of congenital microcephaly. We pay particular attention to three concerns: Who is a case? How should cases be classified? To whom should cases be compared?

Brains and faces in holoprosencephaly: pre- and postnatal description of 30 cases

OBJECTIVE

To investigate the prenatal appearance of the holoprosencephaly spectrum.

METHODS

A database of 1750 fetuses with congenital anomalies identified by ultrasound was prospectively collected from 1987 to 2000. Among them, 30 cases (1.7%) with holoprosencephaly were prenatally identified and described.

RESULTS

The prevalence of holoprosencephaly in the Health Region of the National Center for Fetal Medicine in Norway was 1.26 : 10 000; the sex distribution (male : female) was 1.4 : 1. Holoprosencephaly was found in one dichorionic twin pregnancy and one pair of conjoined twins. Among the 30 cases of holoprosencephaly, 18 were alobar, five were semilobar, two were lobar, two were lobar variants, and three were anencephalic. The facial features varied considerably. Sixty-seven per cent (20/30) had associated structural anomalies that were not related to the cerebral and facial holoprosencephaly condition. Thirty-seven per cent (11/30) had detectable chromosome aberrations and 23% (7/30) had nonchromosomal syndromal origin. The size or shape of the head was abnormal in 83% (25/30) of holoprosencephaly cases.

CONCLUSION

This study indicates that holoprosencephaly represents a heterogeneous entity with different etiologies and clinical appearances. The fact that holoprosencephaly features are found associated with particular conditions such as fronto-nasal dysplasia (2/30; 6.7%), agnathia-otocephaly (3/30; 10%), and anencephaly (3/30; 10%), suggests that these may be underreported conditions in other large holoprosencephaly series.