Ultrasound imaging of preterm brain injury: fundamentals and updates

Intravenous administration of ultrasound contrast to critically ill pediatric patients

BACKGROUND

The off-label use of contrast-enhanced ultrasound has been increasingly used for pediatric patients.

OBJECTIVE

The purpose of this retrospective study is to report any observed clinical changes associated with the intravenous (IV) administration of ultrasound contrast to critically ill neonates, infants, children, and adolescents.

MATERIALS AND METHODS

All critically ill patients who had 1 or more contrast-enhanced ultrasound scans while being closely monitored in the neonatal, pediatric, or pediatric cardiac intensive care units were identified. Subjective and objective data concerning cardiopulmonary, neurological, and hemodynamic monitoring were extracted from the patient's electronic medical records. Vital signs and laboratory values before, during, and after administration of ultrasound contrast were obtained. Statistical analyses were performed using JMP Pro, version 15. Results were accepted as statistically significant for P-value<0.05.

RESULTS

Forty-seven contrast-enhanced ultrasound scans were performed on 38 critically ill patients, 2 days to 17 years old, 19 of which were female (50%), and 19 had history of prematurity (50%). At the time of the contrast-enhanced ultrasound scans, 15 patients had cardiac shunts or a patent ductus arteriosus, 25 had respiratory failure requiring invasive mechanical oxygenation and ventilation, 19 were hemodynamically unstable requiring continual vasoactive infusions, and 8 were receiving inhaled nitric oxide. In all cases, no significant respiratory, neurologic, cardiac, perfusion, or vital sign changes associated with IV ultrasound contrast were identified.

CONCLUSION

This study did not retrospectively identify any adverse clinical effects associated with the IV administration of ultrasound contrast to critically ill neonates, infants, children, and adolescents.

Cerebral Microvascular Imaging in Infants: Scan Technique and Potential Clinical Applications

ABSTRACT

Brain ultrasound in infants, although widely utilized, provides limited functional insights into the brain. Although color and power Doppler ultrasounds have allowed quantitative assessment of cerebral macrovascular flow dynamics, there is no standardized tool integrated into the current neurosonography protocol that allows cerebral microvascular flow assessment. The evaluation of anatomic and functional changes in cerebral microvessels is important, as microvascular alterations have been shown to precede macrovascular and tissue injury in a variety of neurologic diseases of infancy. In this regard, the cerebral microvascular imaging technique is a commercially available, advanced Doppler technique in which slow flow of cerebral microvessels can be detected via a static noise suppression algorithm. This article therefore shares the basic scan technique and clinical examples of the integrated use of microvascular imaging in neurosonography for infants, setting the stage for future clinical integration of the technique.

Magnetic Resonance Imaging-Based Distribution and Reversibility of Lesions in Pediatric Vigabatrin-Related Brain Toxicity

BACKGROUND

We aimed to systematically characterize the magnetic resonance imaging (MRI) findings in vigabatrin-related neurotoxicity in children and determine the reversibility of lesions based on follow-up images.

METHODS

We evaluated children with a history of refractory seizures who had a brain MRI while on vigabatrin therapy. We included available brain MRI studies before vigabatrin therapy initiation, during vigabatrin treatment, and after vigabatrin was discontinued. A pediatric neuroradiologist systematically assessed images on T2/fluid-attenuated inversion recovery (FLAIR) and diffusion-weighted imaging /apparent diffusion coefficient sequences to identify hyperintense lesions and/or restricted diffusion. The frequency of abnormal signal at each location was determined, as well as the reversibility of these after vigabatrin discontinuation.

RESULTS

MRIs of 43 patients were reviewed: 13 before vigabatrin initiation, 18 during treatment, and 12 after vigabatrin discontinuation. In the MRIs acquired during vigabatrin treatment, most lesions on T2/FLAIR occurred in the globus pallidi, thalami, and midbrain. Correspondingly, the most common locations for restricted diffusion were the globus pallidi, thalami, and subthalamic nuclei. On MRI after vigabatrin discontinuation, complete resolution of lesions on T2/FLAIR in all patients was seen in the midbrain, dentate nuclei, subthalamic nuclei, and hypothalami. Complete resolution of restricted diffusion was observed in the globus pallidi, midbrain, dentate nuclei, hippocampi, anterior commissure, and hypothalami.

CONCLUSION

Globus pallidi and thalami are the most commonly affected structures in vigabatrin-related toxicity, and most vigabatrin-related neuroimaging findings are reversible.

Evaluation of a Cranial Ultrasound Screening Protocol for Very Preterm Infants

OBJECTIVES

Cranial ultrasound (cUS) screening is recommended for preterm neonates born before 32 weeks' gestational age (GA). The primary aim of this study was to determine if both a day 3 and day 8 cUS screening examination is necessary for all neonates.

METHODS

A retrospective observational study was performed at a tertiary-level Australian hospital. Frequencies of cranial ultrasound abnormality (CUA) were compared between routine screening performed at postnatal days 3, 8, and 42. Univariate and multivariate analyses of risk factors for intraventricular hemorrhage (IVH) was performed using logistic regression.

RESULTS

cUS examinations on 712 neonates born before 32 weeks' GA were included. Neonates were divided into 2 groups: 99 neonates in the 23-25 weeks 6 days GA (group A) and 613 neonates in the 26-31 weeks 6 days GA (group B). All CUA occurred more frequently in group A neonates and in the subset of group B neonates who had defined risk factors. Low-risk group B neonates had lower incidence of CUAs demonstrated on day 8 cUS than high-risk group B neonates, with no significant differences between day 3 and day 8. Logistic regression analysis identified a number of risk factors (vaginal delivery, small for GA, Apgar score <7 at 5 minutes, intubation, patent ductus arteriosus and infection) that were associated with increased frequency of IVH on day 8. In neonates born between 30 and 31 weeks 6 days GA, 35% had a CUA identified.

CONCLUSIONS

Low-risk preterm neonates born between 26 and 31 weeks 6 days GA, without complications, could be screened with a single early cUS examination around day 8 without missing substantial abnormality.

A concise guide to transtemporal contrast-enhanced ultrasound in children

Brain contrast-enhanced ultrasound offers insights into the brain beyond the anatomic information offered by conventional grayscale ultrasound. In infants, the open fontanelles serve as acoustic windows. In children, whose fontanelles are closed, the temporal bone serves as the ideal acoustic window due to its relatively smaller thickness than the other skull bones. Diagnosis of common neurologic diseases such as stroke, hemorrhage, and hydrocephalus has been performed using the technique. Transtemporal ultrasound and contrast-enhanced ultrasound, however, are rarely used in children due to the prevalent notion that the limited acoustic penetrance degrades diagnostic quality. This review seeks to provide guidelines for the use of transtemporal brain contrast-enhanced ultrasound in children.

Transtemporal brain contrast-enhanced ultrasound in children: preliminary experience in patients without neurological disorders

AIM

To evaluate the use of transtemporal brain contrast-enhanced ultrasound (CEUS) to assess cerebral blood perfusion in a cohort of children without neurological disorders.

METHODS

We included pediatric patients who were undergoing a clinically-indicated CEUS study. Brain scans were performed with a Siemens Sequoia scanner and a 4V1 transducer, that was placed on the left transtemporal bone. Brain scans were performed simultaneously with the images of the clinically-indicated organ of interest. Qualitative and quantitative analysis was performed to evaluate the hemispherical blood flow at the level of the midbrain during the wash-in and wash-out phases of the time-intensity curve. Clinical charts were reviewed to evaluate post-CEUS adverse events.

RESULTS

Five patients were evaluated (mean age 5.8 ± 5.1 years). Qualitatively, more avid enhancement in the midbrain than the cortex was observed. Structures depicted ranged between the centrum semiovale at the level of the lateral ventricles and the midbrain. A quantitative analysis conducted on four patients demonstrated less avid perfusion on the contralateral (i.e. right) side, with a mean left/right ratio ranging between 1.51 and 4.07. In general, there was a steep positive wash-in slope starting at approximately 10 s after contrast injection, reaching a peak intensity around 15-26 s on the left side, and 17-29 s on the right side. No adverse events were reported.

CONCLUSION

Transtemporal brain CEUS is feasible and safe in the pediatric population and allows qualitative and quantitative assessment of cerebral perfusion.

Ultrasound Elastography in Neurosurgery: Current Applications and Future Perspectives

BACKGROUND

Similar to clinical palpation, Ultrasound elastography (USE) helps distinguish between tissues by providing information on their elasticity. While it has been widely explored and has been applied to many body organs, USE has not been studied as extensively for application in neurosurgery. The current systematic review was performed to identify articles related to the use of interoperative USE in neurosurgery.

METHODS

Search included MEDLINE(R) database. Only original peer-reviewed full-text articles were included. No language or publication year restrictions were imposed. Two independent reviewers assessed the search results for relevance. The identified articles were screened by title, abstract, and full-text review.

RESULTS

Seventeen articles were included in the qualitative analysis and 13 articles were related to oncology, epilepsy (n = 3), and spine (n = 1). In oncology, USE was found useful in defining tumor stiffness, aiding surgical planning, detecting residual tumors, discriminating between tumor and brain tissue, and differentiating between different tumors. In epilepsy, USE could improve the detection of epileptogenic foci, thereby enhancing the prospect of complete and safe resection. The application in spinal surgery was limited to demonstrating that a compressed spinal cord is stiffer than the decompressed one.

CONCLUSIONS

USE was found to be a safe, quick, portable, and economic tool that was a useful intraoperative adjunct to provide information corresponding to a variety of neurosurgical diseases, at different stages of surgery. This review describes the current intraoperative neurosurgical applications of USE, the concept of elasticity, and different USE modalities as well as the technical challenges, limitations, and possible future implications.

Neonatal neurosonography practices: a survey of active Society for Pediatric Radiology members

BACKGROUND

While neonatal brain US is emerging as an imaging modality with greater portability, widespread availability and relative lower cost compared to MRI, it is unknown whether US is being maximized in infants to increase sensitivity in detecting intracranial pathology related to common indications such as hemorrhage, ischemia and ventriculomegaly.

OBJECTIVE

To survey active members of the Society for Pediatric Radiology (SPR) regarding their utilization of various cranial US techniques and reporting practices in neonates.

MATERIALS AND METHODS

We distributed an online 10-question survey to SPR members to assess practice patterns of neonatal cranial US including protocol details, use of additional sonographic views, perceived utility of spectral Doppler evaluation, and germinal matrix hemorrhage and ventricular size reporting preferences.

RESULTS

Of the 107 institutions represented, 90% of respondents were split evenly between free-standing children's hospitals and pediatric departments attached to a general hospital. We found that most used template reporting (72/107, 67%). The anterior fontanelle approach was standard practice (107/107, 100%). We found that posterior fontanelle views (72% sometimes, rarely or never) and high-frequency linear probes to evaluate far-field structures (52% sometimes, rarely or never) were seldom used. Results revealed a range of ways to report germinal matrix hemorrhage and measure ventricular indices to assess ventricular dilatation. There was substantial intra-institutional protocol and reporting variability as well.

CONCLUSION

Our results demonstrate high variability in neurosonography practice and reporting among active SPR members, aside from the anterior fontanelle views, template reporting and linear high-resolution near-field evaluation. Standardization of reporting germinal matrix hemorrhage and ventricular size would help ensure a more consistent application of neonatal US in research and clinical practice.

Utility of Cerebral Microvascular Imaging in Infants Undergoing ECMO

PURPOSE

Infants who require extracorporeal membrane oxygenation (ECMO) therapy have an increased risk of neurological complications and mortality. Microvascular imaging (MVI) is an advanced Doppler technique that allows high-resolution visualization of microvasculature in the brain. We describe the feasibility and utility of MVI for the evaluation of cerebral microvascular perfusion in patients undergoing ECMO.

METHODS

We retrospectively analyzed brain MVI scans of neonates undergoing ECMO. Two pediatric radiologists qualitatively assessed MVI scans to determine the presence or absence of tortuosity, symmetry, heterogeneity, engorgement, and hypoperfusion of the basal ganglia-thalamus (BGT) region, as well as the presence or absence of white matter vascular engorgement and increased peri-gyral flow in the cortex. We tested the association between the presence of the aforementioned brain MVI features and clinical outcomes.

RESULTS

We included 30 patients, 14 of which were male (46.7%). The time of ECMO duration was 11.8 ± 6.9 days. The most prevalent microvascular finding in BGT was lenticulostriate vessel tortuosity (26/30, 86.7%), and the most common microvascular finding in the cortex was increased peri-gyral flow (10/24, 41.7%). Cortical white matter vascular engorgement was significantly associated with the presence of any poor outcome as defined by death, seizure, and/or cerebrovascular events on magnetic resonance imaging (p = 0.03).

CONCLUSION

MVI is a feasible modality to evaluate cerebral perfusion in infants undergoing ECMO. Additionally, evidence of white matter vascular engorgement after ECMO cannulation could serve as a predictor of poor outcomes in this population.

High-resolution neurosonographic examination of the lenticulostriate vessels in neonates with hypoxic-ischemic encephalopathy

OBJECTIVE

To assess the feasibility of visualizing lenticulostriate vessels (LV) using a linear high-resolution ultrasound probe and characterize LV morphology to determine whether morphological alterations in LV are present in neonatal hypoxic-ischemic encephalopathy (HIE) as compared to the unaffected infants.

METHODS

We characterized LV by their echogenicity, width, length, tortuosity, and numbers of visualized stems/branches in neurosonographic examinations of 80 neonates. Our population included 45 unaffected (non-HIE) and 35 with clinical and/or imaging diagnosis of HIE. Of the neonates with clinical diagnosis of HIE, 16 had positive MRI findings for HIE (HIE+MRI) and 19 had negative MRI findings (HIE-MRI). Annotations were performed twice with shuffled data sets at a 1-month interval and intrarater reliability was assessed. Focused comparison was conducted between non-HIE, HIE+MRI and HIE-MRI neonates whose images were acquired with a high frequency linear transducer.

RESULTS

Studies acquired with the two most frequently utilized transducers significantly differed in number of branches (p = 0.002), vessel thickness (p = 0.007) and echogenicity (p = 0.009). Studies acquired with the two transducers also significantly differed in acquisition frequency (p < 0.001), thermal indices (p < 0.001) and use of harmonic imaging (p < 0.001). Groupwise comparison of vessels imaged with the most frequently utilized transducer found significantly fewer branches in HIE + MRI compared to HIE-MRI negative and non-HIE patients (p = 0.005).

CONCLUSION

LV can be visualized in the absence of pathology using modern high-resolution neurosonography. Visualization of LV branches varies between HIE + MRI, HIE-MRI neonates and controls.

ADVANCES IN KNOWLEDGE

High-resolution neurosonography is a feasible technique to assess LV morphology in healthy neonates and neonates with HIE.

Current understanding and future potential applications of cerebral microvascular imaging in infants

Microvascular imaging is an advanced Doppler ultrasound technique that detects slow flow in microvessels by suppressing clutter signal and motion-related artifacts. The technique has been applied in several conditions to assess organ perfusion and lesion characteristics. In this pictorial review, we aim to describe current knowledge of the technique, particularly its diagnostic utility in the infant brain, and expand on the unexplored but promising clinical applications of microvascular imaging in the brain with case illustrations.