Diffusion tensor imaging of fetal brain: principles, potential and limitations of promising technique.

Human brain development is a complex process that begins in the third week of gestation. During early development, the fetal brain undergoes dynamic morphological changes. These changes result from events such as neurogenesis, neuronal migration, synapse formation, axonal growth and myelination. Disruption of any of these processes is thought to be responsible for a wide array of different pathologies. Recent advances in magnetic resonance imaging, especially diffusion-weighted imaging and diffusion tensor imaging (DTI), have enabled characterization and evaluation of brain development in utero. In this review, aimed at practitioners involved in fetal medicine and high-risk pregnancies, we provide a comprehensive overview of fetal DTI studies focusing on characterization of early normal brain development as well as evaluation of brain pathology in utero. We also discuss the reliability and limitations of fetal brain DTI. © 2022 International Society of Ultrasound in Obstetrics and Gynecology.

Biometric and morphological features on magnetic resonance imaging of fetal bladder in lower urinary tract obstruction: new perspectives for fetal cystoscopy.

OBJECTIVES: Incompatibility between currently available fetoscopes and the anatomical constraints of the distended fetal bladder, with the resulting curvature around the bladder neck, account for most technical difficulties during fetal cystoscopy in lower urinary tract obstruction (LUTO). The aim of this anatomical study was to assess by magnetic resonance imaging (MRI) the variation in three bladder angles (bladder-neck angle (BNA), vesicourethral angle (VUA) and angle between bladder dome and posterior urethra (DUA)), according to gestational age (GA), bladder volume and the presence of LUTO. METHODS: From our fetal medicine database, we retrieved for review 46 MRI examinations of male fetuses between 2015 and 2019, including 17 with LUTO, examined at a mean GA of 28.1 (range, 17.3-35.0) weeks and 29 age-matched controls, examined at 29.9 (range, 21.9-35.0) weeks. We measured bladder volume, bladder-wall thickness and the three bladder angles, and used the Mann-Whitney U-test to compare values between groups. Variations according to GA and bladder volume were determined using analysis of variance (ANOVA). A reliability study was performed using the Bland-Altman method and Lin's correlation coefficient was calculated. RESULTS: Both bladder volume and bladder-wall thickness were significantly greater in the LUTO group (P < 0.01). BNA was significantly larger in LUTO compared with control fetuses: the mean (range) was 127.1° (101.6-161.6°) vs 111.2° (88.5-157.3°) (P < 0.01). DUA averaged 117° and showed no difference between the groups (P = 0.92). No statistical comparison was performed on VUA since this was not measurable in most control fetuses. ANOVA showed no variation of any angle with bladder volume in both LUTO fetuses and control fetuses. BNA in LUTO fetuses was the only angle to vary with GA, being larger after, compared with at or before, 25 weeks (P = 0.04). The reliability study showed an acceptable bias for both intra- and interobserver reproducibility for all three angles. CONCLUSION: The findings that BNA is increased by approximately 15° in fetuses with LUTO and DUA averages 117° could aid in development of a customized fetal cystoscope and help to overcome the current technical challenges of fetal cystoscopy. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

[Fetal cerebral magnetic resonance imaging (MRI). Indications, normal and pathological patterns]. / Imagerie par résonance magnétique (IRM) foetale cérébrale : indications, aspects normaux et pathologiques.

Fetal MRI is a specific imaging modality, always performed after a reference ultrasound examination. The decision to perform an MRI-scan must take into account the anxiety constantly generated by the need for this unusual examination during pregnancy. To date, no side-effect associated with 1.5 tesla magnets has been described. Compared to ultrasonography, fetal brain MRI provides better contrast between grey and white matter, as well as better delineation of the brainstem (pontic curvature) and the cerebellum (lobules and fissures). However, it often remains difficult to inform parents about prognosis. Thereby, it is of utmost importance to be familiar with the definite criteria associated with a poor neurological prognosis such as lack of pontic curvature or as diffuse or bilateral cortical malformations. This has to be considered within the framework of French regulations which allow pregnancy termination with no time limit. The optimal timing to perform a fetal MRI-scan depends on the context. The period between 27 and 30 weeks of gestation is a good balance between gestational age and gyration or sulcation development. The main ultrasonographic findings requiring MRI are ventriculomegalies and posterior fossa abnormalities. MRI exploration can sometimes be performed despite a normal ultrasonography in case of genetic disorders such as tuberous sclerosis and lissencephalies. In addition to its diagnostic value towards decision to terminate pregnancy, fetal MRI can be used as "in vivo autopsy", in case of expected technical difficulties or refusal of post-abortion examinations by relatives. Technical advances (real time and specific sequences like diffusion tensor and spectroscopy) and prospective clinical studies will probably improve the efficiency of this method to assess neurological prognosis.

Prenatally diagnosed periventricular nodular heterotopia: Further delineation of the imaging phenotype and outcome.

OBJECTIVES: Periventricular nodular heterotopia (PNH) is a malformation of cortical development which presents with heterogeneous imaging, neurological phenotype and outcome. There is a paucity of comprehensive description detailing the prenatal diagnosis of PNH. The aim of this study is to report neuroimaging features and correlated outcomes in order to delineate the spectrum of prenatally diagnosed PNH. METHODS: It was a retrospective study over 15 years in five tertiary centers. All fetuses with prenatally diagnosed PNH were collected. Fetal ultrasound and MRI were reviewed and genetic screening collected. Prenatal findings were analyzed in correlation to fetopathological analyses and post-natal follow up. RESULTS: Thirty fetuses (22 females and 8 males) with PNH were identified. The two major ultrasound signs were ventriculomegaly associated with dysmorphic frontal horns (60%) and posterior fossa anomalies (73.3%). On MRI, two groups of PNH were identified: the contiguous and diffuse PNH (n = 15, 50%), often associated with megacisterna magna, and the non-diffuse, either anterior, posterior or unilateral PNH. FLNA mutations were found in 6/11 cases with diffuse PNH. Additional cortical malformations were exclusively observed in non diffuse PNH (9/15; 60%). Twenty-four pregnancies (80%) were terminated. Six children aged 6 months to 5 years are alive. Five have normal neurodevelopment (all had diffuse PNH) whereas one case with non diffuse PNH has developmental delay and epilepsy. CONCLUSION: PNH is heterogeneous but patients with diffuse PNH are a common subgroup with specific findings on prenatal imaging and implications for prenatal counseling.

[Eyelid hemangiomas in infants: contribution of MRI]. / Les hémangiomes palpébraux du nourisson: apport de l'IRM.

OBJECTIVES: To describe the MR imaging features and patterns of local extension of hemangiomas of the eyelid in correlation with the clinical presentation. PATIENTS AND METHODS: Retrospective study including 21 MRI (GE, 1.5T, T1 +/- Gadolinium, T2 +/- fat saturation, 3 planes) examinations performed for eyelid hemangiomas with occlusion>50% and/or ocular deviation. All examinations were reviewed by two observers using a standardized list of criteria. RESULTS: All hemangiomas had a heterogeneous signal described as "salt and pepper" on T2W sequences. The extension was extra-orbital in 8 cases, intra-orbital in 13 cases, extra-conal in 9 cases, intra-conal in 4 cases. The "fat sat T2" sequence provided the best anatomical details. There was a strong correlation between ocular deviation at clinical examination and intra-orbital extension, but no correlation between the extent of eyelid involvement and orbital location of the hemangioma. Dysplastic cerebellum anomalies related to the PHACES syndrome were present in 3 patients. CONCLUSION: MRI of the brain and orbits provides information that appears essential for optimal management of infants with hemangioma of the eyelid.

[Congenital malformations of the lung, the radiologist's point of view]. / Malformations pulmonaires congénitales, le point de vue du radiologue.

Congenital lung malformations include a complex range of developmental abnormalities. Currently, most are diagnosed prenatally or during early childhood. They may, however, be discovered later, incidentally or in connection with non-specific symptoms, sometimes severe. Knowledge of their radiological appearances is necessary for their detection. Proper technique and analysis of cross-sectional imaging, computed tomography and magnetic resonance imaging, allow a definitive diagnosis in most patients and pre-treatment evaluation of surgical cases. This review will describe the radiological aspects of congenital pulmonary malformations, especially those which may occur in late childhood or adult life. When present, alternative diagnoses will be discussed. A distinction will be made between anomalies originating from bronchopulmonary structures, such as bronchial atresia, bronchogenic cyst, congenital lobar overinflation, cystic adenomatoid malformation, and forms related to vascular anomalies (vascular rings, anomalous left pulmonary artery, pulmonary underdevelopment, proximal interruption of the pulmonary artery, pulmonary sequestration, scimitar syndrome).

[Prenatal symptoms and diagnosis of inherited metabolic diseases]. / Maladies héréditaires du métabolisme : signes anténatals et diagnostic biologique.

Inherited metabolic diseases are mostly due to enzyme deficiency in one of numerous metabolic pathways, leading to absence of a compound downstream from and the accumulation of a compound upstream from the deficient metabolite(s). Diseases of intoxication by proteins (aminoacidopathies, organic acidurias, urea cycle defects) and by sugars (galactosemia, fructosemia) usually do not give prenatal symptoms since mothers protect their fetuses from pathological metabolite accumulation. A well-known exception is hypoplasia of corpus callosum, as is sometimes observed in nonketotic hyperglycinemia and sulfite oxidase deficiency. Conversely, women with phenylketonuria "poison" their fetus if they are not treated (spontaneous abortions, intrauterine growth restriction [IUGR], cardiac malformations, and brain disease). Amino acid synthesis defects can lead to prenatal symptoms: microcephaly in serine deficiency (detectable by amino acid analysis in fetal cord blood), and brain malformations in glutamine synthetase deficiency. Impaired folate metabolism is involved in a large fraction of neurodevelopmental defects referred to as spina bifida, yet the underlying genetic component(s) are largely unknown. Energy metabolism diseases caused by defects in the synthesis or utilization of relevant metabolites lead to organ dysfunctions or malformations, but prenatal diagnosis is usually impossible unless genetic analysis can rely on a previously affected child in the family. A somewhat intermediate condition is defects of mitochondrial beta-oxidation of fatty acids, as they may sometimes be symptomatic prenatally (notably the HELLP syndrome or other presentations), and in this case, organic acid and acylcarnitine analysis in amniotic fluid can be informative in the absence of an index case. In contrast, complex molecule diseases commonly give prenatal symptoms that may permit the diagnosis even in the absence of index cases: hydrops fetalis and skeletal anomalies in lysosomal storage diseases, hydrops fetalis in congenital disorders of glycosylation (CDG) and transaldolase deficiency, brain malformations in O-glycosylation defects, brain malformations, kidney cysts and skeletal anomalies in peroxysomal diseases (Zellweger syndrome), syndactyly, genitalia malformations, and IUGR in Smith-Lemli-Opitz (SLO) syndrome. Although many metabolic disorders show biochemical abnormalities during fetal development that are informative for prenatal diagnosis, only a fraction of them are clinically/sonographically symptomatic before birth, thus allowing for prenatal diagnosis in the absence of an index case, i.e., serine deficiency, some fatty acid beta-oxidation defects, transaldolase deficiency, lysosomal diseases, CDG, Zellweger syndrome, and SLO syndrome.