Magnetic Resonance Imaging in Ischemic Stroke and Cerebral Venous Thrombosis

Ischemic brain edema: Emerging cellular mechanisms and therapeutic approaches

Brain edema is one of the most devastating consequences of ischemic stroke. Malignant cerebral edema is the main reason accounting for the high mortality rate of large hemispheric strokes. Despite decades of tremendous efforts to elucidate mechanisms underlying the formation of ischemic brain edema and search for therapeutic targets, current treatments for ischemic brain edema remain largely symptom-relieving rather than aiming to stop the formation and progression of edema. Recent preclinical research reveals novel cellular mechanisms underlying edema formation after brain ischemia and reperfusion. Advancement in neuroimaging techniques also offers opportunities for early diagnosis and prediction of malignant brain edema in stroke patients to rapidly adopt life-saving surgical interventions. As reperfusion therapies become increasingly used in clinical practice, understanding how therapeutic reperfusion influences the formation of cerebral edema after ischemic stroke is critical for decision-making and post-reperfusion management. In this review, we summarize these research advances in the past decade on the cellular mechanisms, and evaluation, prediction, and intervention of ischemic brain edema in clinical settings, aiming to provide insight into future preclinical and clinical research on the diagnosis and treatment of brain edema after stroke.

Pictorial Review on Imaging Findings in Cerebral CTP in Patients with Acute Stroke and Its Mimics: A Primer for General Radiologists

The imaging evaluation of computed tomography (CT), CT angiography (CTA), and CT perfusion (CTP) is of crucial importance in the setting of each emergency department for suspected cerebrovascular impairment. A fast and clear assignment of characteristic imaging findings of acute stroke and its differential diagnoses is essential for every radiologist. Different entities can mimic clinical signs of an acute stroke, thus the knowledge and fast identification of stroke mimics is important. A fast and clear assignment is necessary for a correct diagnosis and a rapid initiation of appropriate therapy. This pictorial review describes the most common imaging findings in CTP with clinical signs for acute stroke or other acute neurological disorders. The knowledge of these pictograms is therefore essential and should also be addressed in training and further education of radiologists.

Role of the noninvasive imaging techniques in monitoring and understanding the evolution of brain edema

Human brain injury elicits accumulation of water within the brain due to a variety of pathophysiological processes. As our understanding of edema emerged two temporally (and cellular) distinct processes were identified, cytotoxic and vasogenic edema. The emergence of both types of edema is reflected by the temporal evolution and is influenced by the underlying pathology (type and extent). However, this two-edema compartment model does not adequately describe the transition between cytotoxic and vasogenic edema. Hence, a third category has been proposed, termed ionic edema, that is observed in the transition between cytotoxic and vasogenic edema. Magnetic resonance neuroimaging of edema today primarily utilizes T2-weighted (T2WI) and diffusion-weighted imaging (DWI). Clinical diagnostics and translational science studies have clearly demonstrated the temporal ability of both T2WI and DWI to monitor edema content and evolution. DWI measures water mobility within the brain reflecting cytotoxic edema. T2WI at later time points when vasogenic edema develops visualizes increased water content in the brain. Clinically relevant imaging modalities, including ultrasound and positron emission tomography, are not typically used to assess edema. In sum, edema imaging is an important cornerstone of clinical diagnostics and translational studies and can guide effective therapeutics manage edema and improve patient outcomes.

Cerebral Venous Thrombosis: Review of Diagnosis, Follow-Up, Late Complications and Potential Pitfalls

Cerebral venous thrombosis is a less common but relevant cause of stroke in adults. The clinical manifestations are nonspecific leading frequently diagnostic delays, so imaging findings are is of vital importance. Conventional imaging modalities, namely computed tomography and magnetic resonance imaging (MRI), allow identification of the thrombus and parenchymal involvement due to venous congestion to a variable degree, but this entity may appears as a nonexpected finding in a nonvenographic study. computed tomography and MRI venographies allow noninvasive confirmation of the diagnosis and adequate characterization of the extent of the thrombus and acute complications, both of them being robust diagnostic techniques. MR venography also can be done without the use of contrast media, which is especially important in certain clinical situations. Cerebral venous thrombosis needs follow-up, and imaging plays a key role in detection of late complications of the disease, including dural arteriovenous fistulas and intracranial hypertension due to veno-occlusive disease. Knowledge of other diseases and conditions that may mimic a thrombus is needed to avoid wrong diagnosis. In this article, we conduct a pictorial comprehensive review of cerebral venous thrombosis, including also the technical aspects of different imaging modalities, diagnosis and acute complications, follow-up, late complications and potential imaging mimics.

Prospective evaluation of the utility of magnetic resonance imaging in patients with non-MRI-conditional pacemakers and defibrillators

BACKGROUND

Magnetic resonance imaging (MRI) in patients with legacy cardiovascular implantable electronic devices (CIEDs) in situ is likely underutilized. We hypothesized the clinical benefit of MRI would outweigh the risks in legacy CIED patients.

METHODS

This is a single-center retrospective study that evaluated and classified the utility of MRI using a prospectively maintained database. The outcomes were classified as aiding in diagnosis, treatment, or both for the patients attributable to the MRI. We then assessed the incidence of adverse effects (AE) when the MRI was performed.

RESULTS

In 668, MRIs performed on 479 patients, only 13 (1.9%) MRIs did not aid in the diagnosis or treatment of the patient. Power-on reset events without clinical sequelae in three scans (0.45%) were the only AE. The probability of an adverse event happening without any benefit from the MRI scan was 1.1 × 10^-4 . A maximum benefit in diagnosis using MRI was obtained in ruling out space-occupying lesions (121/185 scans, 65.4%). Scans performed in patients for elucidating answers to queries in treatment were most frequently done for disease staging at long term follow-up (167/470 scans, 35.5%). Conservative treatment (184/470 scans, 39%) followed by medication changes (153/470 scans, 28.7%) were the most common treatment decisions made.

CONCLUSIONS

The utility of MRI in patients with non-MRI-conditional CIEDs far outweighs the risk of adverse events when imaging is done in the context of a multidisciplinary program that oversees patient safety.

Dural venous sinus thrombosis: The combination of noncontrast CT, MRI and PC-MR venography to enhance accuracy

Aim The aim of this article is to determine whether a combination of noncontrast CT (NCCT), three-dimensional-phase contrast magnetic resonance venography (3D PC-MRV), T1- and T2-weighted MRI sequences can help to identify acute and subacute dural venous sinus thrombosis (DVST) with greater accuracy. Methods A total of 147 patients with DVST ( n = 30) and a control group ( n = 117) underwent NCCT, T1- and T2-weighted MRI sequences, and 3D PC-MRV from 2012 to 2016. Two experienced observers interpreted the images retrospectively for the presence of DVST. Nonvisualization of the dural venous sinuses on 3D PC-MRV and signal changes supporting acute or subacute thrombus on T2- and T1-weighted images were considered a direct sign of DVST. Also, using circle region of interest (ROI) techniques, attenuation measurement from each sinus was obtained on NCCT. Sensitivity and specificity were computed for these modalities separately and in combination for diagnosis of DVST using digital subtraction angiography as the reference standard. Results Nonvisualization of venous sinuses on 3D PC-MRV (sensitivity 100%, specificity 71%) in combination with both applying Hounsfield unit (HU) threshold values of greater than 60 on NCCT (sensitivity 70%, specificity 94%) and acquiring signal changes supporting DVST on T2- and T1-weighted images (sensitivity 83%, specificity 96%), were found to have 100% sensitivity and 100% specificity in the identification of acute or subacute DVST. Conclusion The combination of NCCT, T1- and T2-weighted MRI and 3D PC-MRV may allow the diagnosis of acute or subacute DVST and may obviate the need for contrast usage in patients with renal impairment or contrast allergies.