Transvaginal 3D and Doppler ultrasonography of the fetal brain

Transvaginal sonographic approach to the fetal brain, which provides detailed information about the fetal intracranial morphology, opened a new field in medicine, "neurosonography." The clinical significance of 3D ultrasound for prenatal diagnosis has been discussed since three-dimensional ultrasound was introduced in obstetrics. Three-dimensional ultrasound has several functions: surface reconstruction, multiplanar image analysis, three-dimensional sono-angiography, and volume calculation. In this article, we introduce transvaginal three-dimensional ultrasound for the assessment of fetal head and brain. Surface mode shows not only fetal head abnormality such as acrania but also normal cranial bones and sutures in the first trimester. Rotation of the brain volume image and multiplanar analysis enable tomographic visualization as magnetic resonance imaging. Sono-angiography shows the brain circulation three-dimensionally and extracted volume images of target organ provide information on detailed intracranial conditions. The technology is easy, noninvasive, and reproducible methods, and produces comprehensible and objective information.

Clinical application of three-dimensional ultrasound in fetal brain assessment

AIM

To clarify the usefulness of three-dimensional (3D) ultrasound in the assessment of the fetal head and brain, according to 3D ultrasound surface reconstruction, multiplanar image analysis, three-dimensional angiography, and volume calculation.

METHODS

We examined 326 normal fetuses between 10 and 40 weeks of gestation using 3D ultrasound (Voluson, 530D, Medison, Seoul, Korea), mainly with transvaginal 3D transducer. Fetal head structures, such as the skull, brain structure, and brain circulation, were presented by surface mode, multiplanar imaging mode, and three-dimensional Doppler mode. After automatic volume acquisition of the fetal head, image analyses were performed off-line, and 3D View software was used for volume imaging of the lateral ventricle and choroid plexus in randomly selected 30 normal fetuses. Seven fetuses with intracranial abnormalities were evaluated by 3D ultrasound functions.

RESULTS

Surface mode of 3D ultrasound objectively depicted in vivo development of the cranial bones and formation of the cranial sutures and fontanelles in normal fetuses. Multiplanar image analysis of the brain structure presented a fetal brain in more cutting sections than conventional 2D ultrasound. Transvaginal 3D angiography was successful in 13% of normal fetuses and rotation of 3D circulatory image allowed the analysis of the intracranial vessels. Volume imaging showed the intracranial structures, such as the lateral ventricle and choroid plexus. Intracranial abnormalities were longitudinally evaluated by 3D ultrasound and objective images helped in reaching prenatal diagnoses.

CONCLUSION

Advanced 3D ultrasonography and software for volume analysis can provide additional objective information about the fetal skull formation, brain structure, and brain circulation.

Transvaginal Doppler assessment of fetal intracranial venous flow

OBJECTIVE

To investigate physiologic blood-flow-velocity waveform patterns of the fetal cerebral venous system during normal pregnancies by transvaginal Doppler studies and to evaluate cases with abnormal venous-flow patterns.

METHODS

Internal cerebral veins and the three dural sinuses, those of the superior sagittal sinus, vein of Galen, and straight sinus, were examined in normal cephalic-presenting fetuses of 20-40 weeks' gestation. For analysis, the venous index was defined as maximum minus minimum velocity divided by maximum velocity. Different cases with intracranial abnormalities were evaluated with emphasis on abnormal venous blood-flow patterns.

RESULTS

Internal cerebral veins had pulsatile patterns with a venous index of 0.22 in 47.6% of fetuses, whereas all fetuses had pulsations in the dural sinuses. The vein of Galen had a significantly lower venous index (0.31) than the superior sagittal sinus (0.39) and the straight sinus (0.36), indicating that the amplitude of the intracranial venous pulsation might increase as the flow runs from the periphery toward the proximal portion. Significant regression lines of venous index were obtained, indicating the stability of the pulsation during pregnancy. A flat pattern of superior sagittal sinus flow was found in three cases of hydrocephalus and one of craniosynostosis.

CONCLUSION

We showed the normal patterns of fetal cerebral venous blood-flow velocity and the abnormal patterns which might be associated with increased intracranial pressure. Doppler assessment of the intracranial venous system enabled us to evaluate intracranial abnormalities accompanied by increased intracranial pressure that might have prognostic clinical importance.

Fetal craniofacial structure and intracranial morphology in a case of Apert syndrome

Apert syndrome is characterized by craniosynostosis, midfacial hypoplasia and bilateral syndactyly. We document in detail the intrauterine natural history of Apert syndrome by serial sonographic examination. Ultrasound examination of a 19-week fetus revealed an abnormal appearance of the skull. The subsequent examination including transvaginal brain scanning demonstrated a deformed occipital part of the cerebrum and lateral ventricles, frontal bossing, a low nasal bridge and an abnormal appearance of the fetal hands and feet. The distortion of the fetal profile became progressively worse with advancing gestation. Towards the end of pregnancy, anterior prominence of the cerebrum, ventricles and corpus callosum was demonstrated and mild non-progressive ventriculomegaly was seen. The female 3152-g newborn with the typical facial appearance of Apert syndrome, bilateral syndactyly of the fingers and toes and isolated cleft palate was delivered at 37 weeks. Postnatal three-dimensional computed tomography scan demonstrated the fusion of the coronal suture and a wide mid-line calvarial defect, and cranial magnetic resonance imaging confirmed the prenatal sonographic findings. Although the karyotype was normal, genomic DNA analysis of the fibroblast growth factor receptor 2 revealed Ser252Trp, which is specified in the mutational basis of Apert syndrome. The time course of the prenatal findings in this case may help increase understanding of the intrauterine natural history of Apert syndrome.

Transvaginal sonography of the fetal brain: detection of abnormal morphology and circulation

AIM

To analyze the incidence, transvaginal detection age, sonographic appearance, clinical course, and outcomes of pregnancy in cases with abnormal fetal brain structure and/or circulation, and to evaluate the clinical significance of sonographic abnormalities.

METHODS

Serial observation of the fetal brain and intracranial Doppler assessment by transvaginal approach at four-week intervals were performed in 306 singleton fetuses from the first trimester and 13 referral cases at our ultrasound units from January 1996 to December 1997. Detection of abnormalities was followed by subsequent serial scans every one or two weeks.

RESULTS

Morphological abnormalities were found in 66 cases: open neural tube defect (9 cases), disorders of prosencephalic development (2), ventriculomegaly with cerebellar hypoplasia (1), hydrocephalus (1), craniosynostosis (1), unclassified brain anomaly (1), brain atrophy (1), isolated choroid plexus cysts (19), choroid plexus cysts with cerebellar hypoplasia (2), lateral ventricular asymmetry (26), and subependymal cyst (3). Chromosomal aberration was found in 4 cases. Artificial abortion was performed in 10 cases and fetal demise occurred in 2 cases. Isolated choroid plexus cysts, isolated ventricular asymmetry and subependymal cyst were not clinically significant. Two abnormal flow patterns of superior sagittal sinus, sharp doubled pulsatile pattern, and disappearance of normal pulsatile pattern were found in different situations.

CONCLUSION

Serial transvaginal observation of the fetal brain provided evidence of hitherto unreported intracranial abnormalities: subependymal cyst, craniosynostosis, medullary kink in Chiari malformation, brain damage, and abnormal venous flows. Venous flow assessment may be of great potential in predicting fetal neurological well-being.

Transvaginal power Doppler angiography of the fetal brain

Using transvaginal B-mode sonography combined with power Doppler flow mapping on a total of 65 fetuses between 12 and 30 weeks of gestation, fetal intracerebral arteries and veins and blood flow were demonstrated in the coronal and sagittal planes. Clear images of the fetal brain and intracerebral vascular flow were obtained in 36 of the 65 cases. Bilateral vertebral arteries, the basilar artery and posterior cerebral arteries were imaged in the coronal plane at 12 weeks of gestation. Bilateral carotid and middle cerebral arteries were also depicted in the coronal plane at 13 weeks of gestation. The middle cerebral arteries and their branches were depicted via the anterior fontanelle in the coronal plane at 20 weeks of gestation. The anterior cerebral artery and its branches were demonstrated in the sagittal plane at 26 weeks of gestation. The fetal cerebral venous systems of the superior sagittal sinus, internal cerebral vein, vein of Galen and straight sinus were clearly imaged in the mid-sagittal plane. Although we encountered several problems with this new technology of transvaginal power Doppler sonography, we were able to demonstrate its potential to assess fetal intracranial blood flow during pregnancy.