Fetal neuroimaging: an update on technical advances and clinical findings.

This paper is based on a literature review from 2011 to 2016. The paper is divided into two main sections. The first section relates to technical advances in fetal imaging techniques, including fetal motion compensation, imaging at 3.0 T, 3-D T2-weighted MRI, susceptibility-weighted imaging, computed tomography, morphometric analysis, diffusion tensor imaging, spectroscopy and fetal behavioral assessment. The second section relates to clinical updates, including cerebral lamination, migrational anomalies, midline anomalies, neural tube defects, posterior fossa anomalies, sulcation/gyration and hypoxic-ischemic insults.

Diagnostic imaging of fetal and pediatric orbital abnormalities.

OBJECTIVE: The orbit contains structures from which a wide spectrum of disease can arise. This article focuses on orbital anatomy and a simple compartmental approach to evaluating the orbit on diagnostic imaging. The characteristic findings of key fetal structural diseases and a wide spectrum of pediatric orbital disorders, including inflammatory disorders and developmental lesions, and the differential diagnosis of benign versus malignant masses will be discussed. CONCLUSION: Orbital abnormalities in fetuses may be recognized using ultrasound and MRI. Anophthalmia, hypertelorism, and hypotelorism either may be part of a genetic syndrome or may be related to a developmental abnormality of the fetal skull. In the pediatric population, cross-sectional imaging with CT and MRI offers a means to assess which compartments of the orbit are affected. Aggressive masses have characteristic features and must be evaluated for intracranial extension.

Defining the reliability of sonoanatomy identification by novices in ultrasound-guided pediatric ilioinguinal and iliohypogastric nerve blockade.

BACKGROUND: The ilioinguinal (II)/iliohypogastric (IH) nerve block is a safe, frequently used block that has been improved in efficacy and safety by the use of ultrasound guidance. We assessed the frequency with which pediatric anesthesiologists with limited experience with ultrasound-guided regional anesthesia could correctly identify anatomical structures within the inguinal region. Our primary outcome was to compare the frequency of correct identification of the transversus abdominis (TA) muscle with the frequency of correct identification of the II/IH nerves. We used 2 ultrasound machines with different capabilities to assess a potential equipment effect on success of structure identification and time taken for structure identification. METHODS: Seven pediatric anesthesiologists with <6 mo experience with ultrasound-guided regional anesthesia performed a total of 127 scans of the II region in anesthetized children. The muscle planes and the II and IH nerves were identified and labeled. The ultrasound images were reviewed by a blinded expert to mark accuracy of structure identification and time taken for identification. Two ultrasound machines (Sonosite C180plus and Micromaxx, both from Sonosite, Bothell, WA) were used. RESULTS: There was no difference in the frequency of correct identification of the TA muscle compared with the II/IH nerves (chi(2) test, TA versus II, P = 0.45; TA versus IH, P = 0.50). Ultrasound machine selection did show a nonsignificant trend in improving correct II/IH nerve identification (II nerve chi(2) test, P = 0.02; IH nerve chi(2) test, P = 0.04; Bonferroni corrected significance 0.17) but not for the muscle planes (chi(2) test, P = 0.83) or time taken (1-way analysis of variance, P = 0.07). A curve of improving accuracy with number of scans was plotted, with reliability of TA recognition occurring after 14-15 scans and II/IH identification after 18 scans. CONCLUSIONS: We have demonstrated that although there is no difference in the overall accuracy of muscle plane versus II/IH nerve identification, the muscle planes are reliably identified after fewer scans of the inguinal region. We suggest that a reliable end point for the inexperienced practitioner of ultrasound-guided II/IH nerve block may be the TA/internal oblique plane where the nerves are reported to be found in 100% of cases.

MRI of the fetal eyes: morphologic and biometric assessment for abnormal development with ultrasonographic and clinicopathologic correlation.

BACKGROUND: Currently ocular biometric measurements are defined by US and are measured from the orbital walls. These bony landmarks cannot be seen by MRI, and therefore these measurements cannot be directly applied. OBJECTIVE: To define measurements of normal growth of the fetal eyes using MRI. MATERIALS AND METHODS: Transorbital views were analyzed in 198 fetal MR examinations. The ocular diameter (OD) and interocular and binocular distances (IOD and BOD) were measured and were plotted against gestational age. Fetuses with abnormalities affecting the eyes were evaluated separately. RESULTS: Of 198 scans, 146 had suitable images, 35 of which were abnormal. Normal growth of BOD, IOD and OD were determined, and compared with the respective already established US data. CONCLUSION: Normal growth charts were derived from a cohort of 111 normal fetuses. Because the margins of the vitreous are inside the bony orbit, at the same gestational age measurements of the BOD and OD are always less than the corresponding measurements by US, and those of the IOD are always more. Normal growth charts for MRI can now be used to support suspected diagnoses of orbital and ocular pathologies and the syndromes that give rise to them, and many examples are demonstrated.

The fetal cerebellar vermis: assessment for abnormal development by ultrasonography and magnetic resonance imaging.

Fetal magnetic resonance provides a new tool in the imaging of the posterior fossa and is proving useful in cases that are difficult to assess sonographically by allowing further assessment of the fourth ventricle, cisterna magna, and vermian growth and development. We describe various criteria with which to evaluate vermian growth, including vermian biometry and the relationship between the superior and inferior lobes. We demonstrate 2 markers of normal vermian development: the primary fissure and fastigial point. We illustrate the tegmento-vermian angle, "closure" of the fourth ventricle, and communication of the fourth ventricle with the basal cisterns during development and in several disorders. We correlate those features with the expected embryological course of development and illustrate identification of these features and associated abnormalities of the posterior fossa, brain stem, and central nervous system in mid-trimester scans of fetuses with abnormal development. Correlation with contemporaneous ultrasound examinations is demonstrated.

The cisterna magna septa: vestigial remnants of Blake's pouch and a potential new marker for normal development of the rhombencephalon.

OBJECTIVE: The purpose of this study was to show the normal sonographic embryologic anatomy of the cisterna magna septa, fourth ventricle, and cerebellar vallecula at various stages of development and our experience with their variable appearance in multiple planes and to discuss the probable relationship between the cisterna magna septa, Dandy-Walker continuum, mega cisterna magna, and persistent Blake's pouch. METHODS: Retrospective and prospective selection of examples of cisterna magna septa was performed over approximately a 12-month period. Standard and nonstandard imaging planes were adopted as necessary. RESULTS: The septa are typically seen inferoposterior to the cerebellar vermis, usually straight and parallel, arising at the cerebellovermian angle and coursing posteriorly to the occipital bone. The cisterna magna septa become contiguous with the roof of the fourth ventricle inferior to the cerebellar vermis. The cerebrospinal fluid space enclosed between the cisterna magna septa is in direct contiguity with the fourth ventricle via the vallecula and is always completely anechoic because it develops intra- and not extra-axially. CONCLUSIONS: We propose that the cisterna magna septa represent the walls of Blake's pouch, a phylogenetic vestigial structure observed during ontogeny. Additionally, our observations support current opinion that a persistent Blake's pouch and mega cisterna magna represent (less severe) abnormalities within the Dandy-Walker continuum. The cisterna magna septa therefore are a marker of normal development of the roof of the rhombencephalon. Deviation from their normal appearances should prompt a closer assessment for associated abnormalities of the cerebellum, vermis, and brain stem by additional imaging in orthogonal planes with either sonography or magnetic resonance imaging.