Misun Hwang

Novel Contrast-Enhanced Ultrasound Evaluation in Neonatal Hypoxic Ischemic Injury: Clinical Application and Future Directions

Sensitive, specific, and safe bedside evaluation of brain perfusion is key to the early diagnosis, treatment, and improved survival of neonates with hypoxic ischemic injury. Contrast‐enhanced ultrasound (US) imaging is a novel imaging technique in which intravenously injected gas‐filled microbubbles generate enhanced US echoes from an acoustic impedance mismatch. This article describes contrast‐enhanced US imaging in 2 neonates with hypoxic ischemic injury and future directions on developing quantitative contrast‐enhanced US techniques for improved characterization of perfusion abnormalities. The importance of studying the temporal evolution of brain perfusion in neonatal hypoxic ischemic injury is also highlighted.

Contrast-Enhanced Ultrasound and Elastography Imaging of the Neonatal Brain: A Review

Neonates presenting with neurologic symptoms require rapid, noninvasive imaging with high spatial resolution and tissue contrast. Magnetic resonance imaging (MRI) is currently the most sensitive and specific imaging modality for evaluation of neurological pathology. This modality does come with several challenges in the neonatal population, namely, the need to transport a possibly critically sick neonate to the MRI suite and the necessity of the neonate to remain still for a significant length of time, occasionally requiring sedation. Cranial ultrasound has provided radiologists and clinicians with an invaluable imaging modality that allows of rapid, bedside point of care evaluation without ionizing radiation. The major drawback of cranial ultrasound is its lower sensitivity and specificity for subtle/early lesions. Contrast‐enhanced ultrasound (CEUS) and elastography have the potential to improve sensitivity and specificity for a variety of neuropathology but also expand the indications for cranial ultrasound. Goal of this paper is to present and discuss CEUS and elastography for neonatal brain imaging.

Advanced Pediatric Neurosonography Techniques: Contrast-Enhanced Ultrasonography, Elastography, and Beyond: Advanced Pediatric Neurosonography Techniques

Recent technical advances in neurosonography continue broadening the diagnostic utility, sensitivity, and specificity of ultrasound for detecting intracranial abnormalities bed side. The clinical and functional applications of neurosonography have significantly expanded since the 1980s when transcranial Doppler sonography first allowed anatomic and hemodynamic delineation of the intracranial vessels through the thin temporal skull. In the past few years, contrast‐enhanced ultrasonography, elastography, 3D/4D reconstruction tools, and high‐resolution microvessel imaging techniques have further enhanced the diagnostic significance of neurosonography. Given these advances, a thorough familiarity with these new techniques and devices is crucial for a successful clinical application allowing improved patient care. It is essential that future neurosonography studies compare these advanced techniques against the current “gold standard” computed tomography and magnetic resonance imaging to assure the accuracy of their diagnostic potential. This review will provide a comprehensive update on currently available advanced neurosonography techniques.

Dysplasia and overgrowth: magnetic resonance imaging of pediatric brain abnormalities secondary to alterations in the mechanistic target of rapamycin pathway

The current classification of malformations of cortical development is based on the type of disrupted embryological process (cell proliferation, migration, or cortical organization/post-migrational development) and the resulting morphological anomalous pattern of findings. An ideal classification would include knowledge of biological pathways. It has recently been demonstrated that alterations affecting the mechanistic target of rapamycin (mTOR) signaling pathway result in diverse abnormalities such as dysplastic megalencephaly, hemimegalencephaly, ganglioglioma, dysplastic cerebellar gangliocytoma, focal cortical dysplasia type IIb, and brain lesions associated with tuberous sclerosis. We review the neuroimaging findings in brain abnormalities related to alterations in the mTOR pathway, following the emerging trend from morphology towards genetics in the classification of malformations of cortical development. This approach improves the understanding of anomalous brain development and allows precise diagnosis and potentially targeted therapies that may regulate mTOR pathway function.

Bedside contrast-enhanced ultrasound diagnosing cessation of cerebral circulation in a neonate: A novel bedside diagnostic tool

Imaging diagnosis of brain death is performed with either four-vessel cerebral angiography or radionuclide cerebral blood flow studies. Unfortunately, timely performance of either study at a critically ill period is not only cumbersome but not feasible in many cases. We present a case of a 6-month-old male three hours status post-cardiac arrest of unknown etiology who underwent contrast-enhanced ultrasound (CEUS) for diagnosis of near absent perfusion, or near brain death. The patient passed away 30 minutes after the exam and clinical diagnosis of brain death was confirmed. The case report highlights the utility of CEUS for diagnosis of brain death. This can have significant clinical implications in neonates who may not be eligible for commonly used, cumbersome radiologic studies for diagnosis of brain death.

Ultrasound and CT of the posterior fossa in neonates

Ultrasound, CT and MRI may all be used in the evaluation of the posterior fossa in neonates depending on the clinical scenario. Ultrasonography is particularly valuable for the evaluation of the neonatal brain because of the lack of ionizing radiation and the ability to perform exams at the bedside and, importantly, advancements in ultrasound technology now allow for diagnostic-quality imaging. While CT is still the initial imaging modality of choice in most neurologic emergencies, in the neonate, ultrasound is the first line in nontraumatic emergencies. The goal of this chapter is to discuss the ultrasound technique for evaluation of the cerebellum, to describe the normal sonographic and CT appearance of posterior fossa and to provide the classical findings of the most common cerebellar abnormalities. While ultrasound is able to accurately diagnosis a majority of cerebellar abnormalities in neonates, subsequent MR imaging remains essential to confirm findings and to detect associated abnormalities.

Head Ultrasound in Neonatal Hypoxic-Ischemic Injury and Its Mimickers for Clinicians: A Review of the Patterns of Injury and the Evolution of Findings Over Time

Hypoxic-ischemic injury (HII) of the neonatal brain and resulting clinical hypoxic-ischemic encephalopathy remains a significant cause of morbidity and mortality in the neonatal population. Ultrasound (US) has emerged as a powerful screening tool for evaluation of a neonate with suspected HII. The pattern of injury on brain imaging has crucial implications in therapies and predicted neurodevelopmental outcomes. US has become increasingly effective at determining the pattern, timing, and extent of injury in HII as well as differentiating these findings from a host of diagnoses that can result in a similarly appearing clinical picture. Repeated US studies over a patient’s course can define the evolution of findings from the acute through chronic phase in addition to identifying any complications of therapy. US also has the added benefits of easy portability, no need for patient sedation, and a relatively low cost when compared to other imaging modalities like magnetic resonance imaging (MRI). It is crucial that clinicians understand the full capabilities of advanced US in identifying an underlying diagnosis, directing appropriate therapy, monitoring disease progress, and finally in predicting outcomes, thus improving the care of neonates with encephalopathy. The following article demonstrates the breadth of uses for US in the full-term neonate with encephalopathy, its limitations, the patterns of injury seen, and their evolution over time. We will also briefly review several clinical mimickers of HII for comparison.

Ultrasound Imaging for Traumatic Brain Injury: Ultrasound Imaging for Traumatic Brain Injury

Traumatic brain injury (TBI) is challenging to assess even with recent advancements in computed tomography and magnetic resonance imaging. Ultrasound (US) imaging has previously been less utilized in TBI compared to conventional imaging because of limited resolution in the intracranial space. However, there have been substantial improvements in contrast‐enhanced US and development of novel techniques such as intravascular US. Also, continued research provides further insight into cerebrovascular parameters from transcranial Doppler imaging. These advancements in US imaging provides the community of TBI imaging researchers and clinicians new opportunities in clinically monitoring and understanding the pathologic mechanisms of TBI.

1302: CLINICIAN ULTRASOUND SCREENING FOR CATHETER-ASSOCIATED THROMBOSIS IN CRITICALLY ILL CHILDREN

www.ccmjournal.org Critical Care Medicine • Volume 46 • Number 1 (Supplement) Learning Objectives: Vascular catheter associated thrombosis (CAT) is an iatrogenic hazard to patient safety in the ICU as a source for ischemic and embolic vessel disease. This is particularly significant for the young patient, due to vessel obstruction from adult-sized catheters, sizedependent anticoagulant dosing, and projected life-years affected by CAT or its sequelae. Despite the crucial importance of durable vascular access in the critically ill child, an organized approach for screening for CAT in children and infants with central venous access is nonexistent. Methods: This is an IRB-approved pilot study examining the prospective use of ultrasound (US) by pediatric intensive care unit (PICU) practitioners in early identification of symptomatic CAT at a medical and surgical PICU. Patients < 18 years receiving central venous catheters in vessels, without previous thrombotic disease, were approached by the study team for consent. Enrolled patients received US examinations daily when safe. A simplified 4 image US protocol that could be completed in less than 15 min. was implemented, and thrombosis was defined as evidence of vessel noncompressibility in a region demonstrating a paucity of Doppler-detectable blood flow. Results: 25 catheters (14 CVC, 11 PICC) have been examined in 22 patients ranging from < 1 month to 16 years. 11 (44%) of the catheters demonstrated thrombosis confirmed by radiologist secondary read. 7 (28%) of the thrombi caused obstructive symptoms and the other four were asymptomatic. 10 of 11 thrombi were detected with CUS before other indicators of CAT were recognized. 2 patients identified with CAT by clinicians were negative according to a full diagnostic US (DUS). No patients with confirmed CAT were missed using CUS. This yielded a sensitivity of 1.00 and specificity of 0.86 (PPV 0.85, NPV 1.00) and suggests the modality is useful for screening. 3 patients identified with CAT using CUS did not demonstrate thrombosis using DUS, however the presence of CAT was confirmed by radiologist interpretation of the CUS images. The frequency of CAT in this population (44%) is higher than that reported in retrospective studies published to date (2–18%), and suggests that CAT can be readily missed in the ICU. Conclusions: CAT is detectable by clinicians with excellent screening accuracy using available PICU US equipment. Ongoing development and optimization of ICU US protocols for CAT screening is warranted to reduce the burden of thromboembolic disease in the critically ill patient.