Arterial Spin Labeling: Techniques, Clinical Applications, and Interpretation.

Arterial spin labeling (ASL) is an emerging noninvasive MRI technique for assessing cerebral perfusion. An important advantage of ASL perfusion is the lack of a requirement for an exogenous tracer. ASL uses magnetically labeled water protons from arterial blood as an endogenous diffusible tracer. For this reason, ASL is an attractive perfusion imaging modality for children and for patients with contraindications or adverse reactions to gadolinium, patients with renal failure, and those who need repeated follow-up imaging. Another advantage of ASL is the possibility of quantifying cerebral blood flow, which provides an opportunity for comparative analysis among multiple longitudinal studies, unlike other MR perfusion techniques, which are semiquantitative and yield relative perfusion parameters. Advances in MRI technology and pulse sequence design have translated ASL beyond the research arena to successful clinical implementation. However, ASL is still underused in routine clinical practice. Some disadvantages of ASL include a lower signal-to-noise ratio and a longer acquisition time than those with dynamic susceptibility contrast-enhanced MRI. Additional factors limiting the use of ASL include variations in existing techniques and pulse sequence design, the complexity of implementation and postprocessing, insufficient experience with and/or knowledge of the potential clinical applications, and the absence of interpretation guidelines. The authors review the technical and physiologic basis of ASL perfusion, as well as artifacts, pitfalls, and its current clinical applications. A practical approach for interpreting ASL findings is also suggested.

Tips and tricks in the diagnosis of intracranial dural arteriovenous fistulas: A pictorial review.

Dural arteriovenous fistulas (DAVFs) are complex vascular abnormalities that account for 10-15% of intracranial vascular malformations. DAVFs are typically encountered in middle-aged adults, with a slightly female predominance. The causative factors are still uncertain; however, abnormal local hemodynamics and neoangiogenesis related to dural sinus or venous thrombosis can contribute to DAVF occurrence. The diagnosis is dependent on a high level of clinical suspicion and high-resolution imaging techniques. Computed tomography and/or magnetic resonance imaging aid in the diagnosis, but conventional angiography remains the most accurate method for the complete characterization and classification of DAVFs. The therapeutic approach can be conservative or more aggressive, based on symptom severity, sequelae risk and patient characteristics. This article is a pictorial review of adult intracranial DAVFs that highlights some tips and tricks for recognizing useful red flags in the suspicion of DAVFs.

Imaging of Creutzfeldt-Jakob Disease: Imaging Patterns and Their Differential Diagnosis.

Diagnosis of sporadic Creutzfeldt-Jakob disease (sCJD) remains a challenge because of the large variability of the clinical scenario, especially in its early stages, which may mimic several reversible or treatable disorders. The molecular basis of prion disease, as well as its brain propagation and the pathogenesis of the illness, have become better understood in recent decades. Several reports have listed recognizable clinical features and paraclinical tests to supplement the replicable diagnostic criteria in vivo. Nevertheless, we lack specific data about the differential diagnosis of CJD at imaging, mainly regarding those disorders evolving with similar clinical features (mimicking disorders). This review provides an update on the neuroimaging patterns of sCJD, emphasizing the relevance of magnetic resonance (MR) imaging, summarizing the clinical scenario and molecular basis of the disease, and highlighting clinical, genetic, and imaging correlations in different subtypes of prion diseases. A long list of differential diagnoses produces a comprehensive pictorial review, with the aim of enabling radiologists to identify typical and atypical patterns of sCJD. This review reinforces distinguishable imaging findings and confirms diffusion-weighted imaging (DWI) features as pivotal in the diagnostic workup of sCJD, as these findings enable radiologists to reliably recognize this rare but invariably lethal disease. A probable diagnosis is justified when expected MR imaging patterns are demonstrated and CJD-mimicking disorders are confidently ruled out. ©RSNA, 2017.

Thrombus Features in Hyperacute Ischemic Stroke: A Perspective on Using Length and Density Evaluation.

BACKGROUND: More insights in the etiopathogenesis of thrombi could be helpful in the treatment of patients with acute ischemic stroke (AIS). One of the most confident and early imaging findings of stroke includes arterial hyperdensity. The purpose of this study was to determine whether thrombi's density and length would be useful for predicting their origin. METHODS: We evaluated 68 consecutive patients with AIS to correlate the presence of thrombi and their imaging features with the stroke subtype. RESULTS: After excluding patients with small-artery occlusion mechanism and undetermined and other causes, the stroke etiologic subtypes were large-artery atherosclerosis (LAA) in 59.0% of the patients, cardioembolism in 31.0%, and cervical artery dissection (CAD) in 10.0%. CAD more often caused thrombi with the longest length and highest attenuation, while thrombi that originated from the LAA had the smallest length and lowest attenuation. The mean Hounsfield unit (HU) values of all thrombi (with and without hyperdensity) on noncontrast computed tomography were 62.4 (50.0-70.0) in CAD, 53.8 (42.0-65.0) in cardioembolism, and 48.6 (27.0-65.0) in LAA. The length measurements were 28.5 mm (12.0-52.0) in CAD, 13.7 mm (5.0-31.0) in cardioembolism, and 10.8 mm (3.0-25.0) in the LAA subtype. The minimum cutoff value of 60 HU and a length greater than 20 mm were able to discriminate the CAD thrombi with an accuracy of 86.8% and 92.6%, respectively. CONCLUSION: Our study findings show how important thrombus analysis is in patients with AIS. Thrombus analysis can allow early suspicion of CAD before dedicated imaging of the cervical arteries is performed.

Magnetic resonance imaging of anterior temporal lobe cysts in children: discriminating special imaging features in a particular group of diseases.

INTRODUCTION: We hypothesised that disorders with anterior temporal lobe (ATL) cysts might exhibit common peculiarities and distinguishable imaging features that could be useful for diagnosis. We reviewed a series of patients for neuroimaging contributions to specific diagnoses. METHODS: A literature search was conducted, and institutional imaging files were reviewed to identify MR examinations with ATL cysts in children. Patients were divided according to head size, calcifications, white matter and cortical abnormalities. Unsupervised hierarchical clustering of patients on the basis of their MR and CT items was performed. RESULTS: We identified 23 patients in our database in whom MR revealed ATL cysts. Our series included five patients with congenital muscular dystrophy (05/23=21.7 %), six with megalencephalic leukoencephalopathy with subcortical cysts (06/23=26.1 %), three with non-megalencephalic leukoencephalopathy with subcortical cysts (03/23=13.1 %), seven with congenital cytomegalovirus disease (07/23=30.4 %) and two with Aicardi-Goutières syndrome (02/23=8.7 %). After analysis, 11 clusters resulted in the highest discriminative indices. Thereafter, patients' clusters were linked to their underlying diseases. The features that best discriminated between clusters included brainstem abnormalities, cerebral calcifications and some peculiar grey and white matter abnormalities. A flow chart was drafted to guide the radiologist in these diagnoses. CONCLUSIONS: The authors encourage the combined interpretation of these features in the herein proposed approach that confidently predicted the final diagnosis in this particular group of disorders associated with ATL cysts.

Imaging Aspects of Toxic and Metabolic Myelopathies.

Metabolic and toxic myelopathies usually occurs due to several different causes. Metabolic myelopathy usually occurs due to deficiency of a nutrient, such as vitamin B12. Toxic myelopathy occurs secondary to the exposure to an external toxic agent. Although they may have a difficult diagnosis, determination of the specific cause of myelopathy is of utmost importance, because many causes are amenable to treatment. Although they have many clinical, electrophysiologic, and neuropathologic similarities, imaging may aid in the suspicion of toxic or metabolic myelopathy. The aim of this article, is to review the imaging features of the main toxic and metabolic myelopathies.

Vascular Myelopathies.

There are many vascular disorders that can affect the spinal cord, and their prevalence and etiology are highly influenced by age, sex, and risk factors. This article reviews the embryology and anatomy of the spinal cord, as well as several vascular conditions, describing their clinical and imaging presentation, emphasizing the different imaging modalities' contributions to increasing specificity and better defining the most appropriate therapy strategy for improving the patient's prognosis.

Intracranial vessel wall magnetic resonance imaging features of infectious vasculitis.

Vasculitis is a complication of several infectious diseases affecting the central nervous system, which may result in ischemic and/or hemorrhagic stroke, transient ischemic attack, and aneurysm formation. The infectious agent may directly infect the endothelium, causing vasculitis, or indirectly affect the vessel wall through an immunological mechanism. The clinical manifestations of these complications usually overlap with those of non-infectious vascular diseases, making diagnosis challenging. Intracranial vessel wall magnetic resonance imaging (VWI) enables the evaluation of the vessel wall and the diseases that affect it, providing diagnostic data beyond luminal changes and enabling the identification of inflammatory changes in cerebral vasculitis. This technique demonstrates concentric vessel wall thickening and gadolinium enhancement, associated or not with adjacent brain parenchymal enhancement, in patients with vasculitis of any origin. It permits the detection of early alterations, even before a stenosis occurs. In this article, we review the intracranial vessel wall imaging features of infectious vasculitis of bacterial, viral, and fungal etiologies.

Ischemic stroke with unknown onset of symptoms: current scenario and perspectives for the future.

BACKGROUND: Stroke is a major cause of disability worldwide and a neurological emergency. Intravenous thrombolysis and mechanical thrombectomy are effective in the reperfusion of the parenchyma in distress, but the impossibility to determine the exact time of onset was an important cause of exclusion from treatment until a few years ago. OBJECTIVES: To review the clinical and radiological profile of patients with unknown-onset stroke, the imaging methods to guide the reperfusion treatment, and suggest a protocol for the therapeutic approach. METHODS: The different imaging methods were grouped according to current evidence-based treatments. RESULTS: Most studies found no difference between the clinical and imaging characteristics of patients with wake-up stroke and known-onset stroke, suggesting that the ictus, in the first group, occurs just prior to awakening. Regarding the treatment of patients with unknown-onset stroke, four main phase-three trials stand out: WAKE-UP and EXTEND for intravenous thrombolysis, and DAWN and DEFUSE-3 for mechanical thrombectomy. The length of the therapeutic window is based on the diffusion weighted imaging-fluid-attenuated inversion recovery (DWI-FLAIR) mismatch, core-penumbra mismatch, and clinical core mismatch paradigms. The challenges to approach unknown-onset stroke involve extending the length of the time window, the reproducibility of real-world imaging modalities, and the discovery of new methods and therapies for this condition. CONCLUSION: The advance in the possibilities for the treatment of ischemic stroke, while guided by imaging concepts, has become evident. New studies in this field are essential and needed to structure the health care services for this new scenario.

ANTECEDENTES: O acidente vascular cerebral (AVC) é uma das principais causas de incapacidade em todo o mundo, e uma emergência neurológica. A trombólise intravenosa e a trombectomia mecânica são eficazes na reperfusão do parênquima em sofrimento, mas a impossibilidade de determinar o tempo exato de início era uma causa importante de exclusão ao tratamento até alguns anos atrás. OBJETIVOS: Revisar o perfil clínico-radiológico dos pacientes com AVC de tempo indeterminado, os métodos de imagem para guiar o tratamento de reperfusão, e sugerir um protocolo para a abordagem terapêutica. MéTODOS: Os diferentes métodos de imagem foram agrupados de acordo com os tratamentos atuais baseados em evidências. RESULTADOS: A maioria dos estudos não encontrou diferença entre as características clínicas e de imagem dos pacientes com AVC reconhecido ao despertar e AVC de tempo definido, o que sugere que o icto, no primeiro grupo, ocorre próximo ao acordar. Quanto ao tratamento do AVC de tempo indeterminado, quatro grandes estudos na fase três sobressaem: WAKE-UP e EXTEND para trombólise intravenosa, e DAWN e DEFUSE-3 para trombectomia mecânica. A ampliação da janela terapêutica fundamenta-se nos paradigmas de incompatibilidade da imagem ponderada de difusão­recuperação da inversão atenuada por fluidos (diffusion weighted imaging­fluid-attenuated inversion recovery, DWI-FLAIR, em inglês), do núcleo isquêmico e penumbra, e clínico-radiológico. Os desafios na abordagem do AVC de tempo indeterminado envolvem a ampliação da janela terapêutica, a reprodutibilidade das modalidades de imagem no mundo real, e a identificação de novos métodos e tratamentos para essa condição. CONCLUSãO: É evidente o avanço nas possibilidades de tratamento do AVC isquêmico guiado pelos conceitos de imagem. Novos estudos nesse campo são essenciais, com necessidade de estruturar os serviços de saúde para esse novo cenário.

Neurological imaging findings in hospitalized COVID-19 patients: a retrospective observational study in two Brazilian reference centers.

BACKGROUND: A variety of neurological manifestations have been attributed to COVID-19. OBJECTIVE: To investigate the occurrence of neurological symptoms and neuroimaging findings in patients hospitalized in two Brazilian reference centers. METHODS: We performed a retrospective cohort study of patients who had laboratory-confirmed COVID-19 presenting in two hospitals in Brazil between March 4 and July 7, 2020, who underwent brain imaging. RESULTS: We recorded 1,359 patients with laboratory-confirmed COVID-19. Brain imaging was performed in 250 (18.4%) patients with neurological symptoms, and nine of them (3.6%) had acute or subacute ischemic stroke neuroimaging findings. Six of the nine patients initially presented with respiratory symptoms while the other three patients presented to the emergency room with acute stroke signs. CONCLUSIONS: We described the neuroimaging findings of patients infected with COVID-19 who presented with neurological symptoms in two major hospitals in Brazil. We reinforce the importance of being aware of cerebrovascular complications, both in severe hospitalized patients and in patients who present to the emergency room with acute neurological symptoms, even in the elderly.

Current uses of intracranial vessel wall imaging for clinical practice: a high-resolution MR technique recently available.

Intracranial vessel wall imaging plays an increasing role in diagnosing intracranial vascular diseases. With the growing demand and subsequent increased use of this technique in clinical practice, radiologists and neurologists should be aware of the choices in imaging parameters and how they affect image quality, clinical indications, methods of assessment, and limitations in the interpretation of these images. Due to the improvement of the MRI techniques, the possibility of accurate and direct evaluation of the abnormalities in the arterial vascular wall (vessel wall imaging) has evolved, adding substantial data to diagnosis when compared to the indirect evaluation based on conventional flow analyses. Herein, the authors proposed a comprehensive approach of this technique reinforcing appropriated clinical settings to better use intracranial vessel wall imaging.

Ischemic stroke with unknown onset of symptoms: current scenario and perspectives for the future / Acidente vascular cerebral isquêmico com tempo indeterminado de início dos sintomas: cenário atual e perspectivas para o futuro

Abstract Background Stroke is a major cause of disability worldwide and a neurological emergency. Intravenous thrombolysis and mechanical thrombectomy are effective in the reperfusion of the parenchyma in distress, but the impossibility to determine the exact time of onset was an important cause of exclusion from treatment until a few years ago. Objectives To review the clinical and radiological profile of patients with unknown-onset stroke, the imaging methods to guide the reperfusion treatment, and suggest a protocol for the therapeutic approach. Methods The different imaging methods were grouped according to current evidence-based treatments. Results Most studies found no difference between the clinical and imaging characteristics of patients with wake-up stroke and known-onset stroke, suggesting that the ictus, in the first group, occurs just prior to awakening. Regarding the treatment of patients with unknown-onset stroke, four main phase-three trials stand out: WAKE-UP and EXTEND for intravenous thrombolysis, and DAWN and DEFUSE-3 for mechanical thrombectomy. The length of the therapeutic window is based on the diffusion weighted imaging-fluid-attenuated inversion recovery (DWI-FLAIR) mismatch, core-penumbra mismatch, and clinical core mismatch paradigms. The challenges to approach unknown-onset stroke involve extending the length of the time window, the reproducibility of real-world imaging modalities, and the discovery of new methods and therapies for this condition. Conclusion The advance in the possibilities for the treatment of ischemic stroke, while guided by imaging concepts, has become evident. New studies in this field are essential and needed to structure the health care services for this new scenario.

Resumo Antecedentes O acidente vascular cerebral (AVC) é uma das principais causas de incapacidade em todo o mundo, e uma emergência neurológica. A trombólise intravenosa e a trombectomia mecânica são eficazes na reperfusão do parênquima em sofrimento, mas a impossibilidade de determinar o tempo exato de início era uma causa importante de exclusão ao tratamento até alguns anos atrás. Objetivos Revisar o perfil clínico-radiológico dos pacientes com AVC de tempo indeterminado, os métodos de imagem para guiar o tratamento de reperfusão, e sugerir um protocolo para a abordagem terapêutica. Métodos Os diferentes métodos de imagem foram agrupados de acordo com os tratamentos atuais baseados em evidências. Resultados A maioria dos estudos não encontrou diferença entre as características clínicas e de imagem dos pacientes com AVC reconhecido ao despertar e AVC de tempo definido, o que sugere que o icto, no primeiro grupo, ocorre próximo ao acordar. Quanto ao tratamento do AVC de tempo indeterminado, quatro grandes estudos na fase três sobressaem: WAKE-UP e EXTEND para trombólise intravenosa, e DAWN e DEFUSE-3 para trombectomia mecânica. A ampliação da janela terapêutica fundamenta-se nos paradigmas de incompatibilidade da imagem ponderada de difusão-recuperação da inversão atenuada por fluidos (diffusion weighted imaging-fluid-attenuated inversion recovery, DWI-FLAIR, em inglês), do núcleo isquêmico e penumbra, e clínico-radiológico. Os desafios na abordagem do AVC de tempo indeterminado envolvem a ampliação da janela terapêutica, a reprodutibilidade das modalidades de imagem no mundo real, e a identificação de novos métodos e tratamentos para essa condição. Conclusão É evidente o avanço nas possibilidades de tratamento do AVC isquêmico guiado pelos conceitos de imagem. Novos estudos nesse campo são essenciais, com necessidade de estruturar os serviços de saúde para esse novo cenário.

Neurological imaging findings in hospitalized COVID-19 patients: a retrospective observational study in two Brazilian reference centers / Achados de neuroimagem em pacientes hospitalizados por COVID-19: um estudo retrospectivo e observacional em dois serviços brasileiros de referência

ABSTRACT Background: A variety of neurological manifestations have been attributed to COVID-19. Objective: To investigate the occurrence of neurological symptoms and neuroimaging findings in patients hospitalized in two Brazilian reference centers. Methods: We performed a retrospective cohort study of patients who had laboratory-confirmed COVID-19 presenting in two hospitals in Brazil between March 4 and July 7, 2020, who underwent brain imaging. Results: We recorded 1,359 patients with laboratory-confirmed COVID-19. Brain imaging was performed in 250 (18.4%) patients with neurological symptoms, and nine of them (3.6%) had acute or subacute ischemic stroke neuroimaging findings. Six of the nine patients initially presented with respiratory symptoms while the other three patients presented to the emergency room with acute stroke signs. Conclusions: We described the neuroimaging findings of patients infected with COVID-19 who presented with neurological symptoms in two major hospitals in Brazil. We reinforce the importance of being aware of cerebrovascular complications, both in severe hospitalized patients and in patients who present to the emergency room with acute neurological symptoms, even in the elderly.

RESUMO Introdução: Diversas manifestações neurológicas têm sido atribuídas à COVID-19. Objetivo: Investigar a ocorrência de sintomas neurológicos e achados de neuroimagem em pacientes internados em dois centros de referência brasileiros. Métodos: Estudo retrospectivo que avaliou pacientes internados em dois hospitais no Brasil entre 4 de março e 7 de julho de 2020, com confirmação laboratorial de infecção pelo COVID-19 e que foram submetidos a tomografia computadorizada ou ressonância magnética do crânio em razão de sintomas neurológicos. Resultados: Obtivemos 1.359 pacientes com confirmação laboratorial de infecção pelo COVID-19. Deles, 250 (18,4%) apresentaram sintomas neurológicos e foram submetidos a exames de imagem do crânio e nove (3,6%) demonstraram achados de neuroimagem compatíveis com acidente vascular cerebral (AVC) isquêmico agudo ou subagudo. Em seis dos nove pacientes, observaram-se inicialmente tosse e dispneia graves, enquanto outros três chegaram ao pronto-socorro com sinais de AVC agudo. Conclusões: Foram descritos os achados de neuroimagem em pacientes infectados com COVID-19 em dois grandes centros de referência brasileiros. Reforçamos a importância de estar atento aos quadros neurológicos, especialmente de AVC, tanto em pacientes graves hospitalizados quanto em pacientes que chegam ao pronto-socorro com sintomas neurológicos agudos, mesmo em idosos.

Collateral blood vessels in acute ischemic stroke: a physiological window to predict future outcomes.

Collateral circulation is a physiologic pathway that protects the brain against ischemic injury and can potentially bypass the effect of a blocked artery, thereby influencing ischemic lesion size and growth. Several recent stroke trials have provided information about the role of collaterals in stroke pathophysiology, and collateral perfusion has been recognized to influence arterial recanalization, reperfusion, hemorrhagic transformation, and neurological outcomes after stroke. Our current aim is to summarize the anatomy and physiology of the collateral circulation and to present and discuss a comprehensible review of the related knowledge, particularly the effects of collateral circulation on the time course of ischemic injury and stroke severity, as well as imaging findings and therapeutic implications.

Multidetector computed tomography angiography in clinically suspected hyperacute ischemic stroke in the anterior circulation: an etiological workup in a cohort of Brazilian patients.

OBJECTIVE: The potential of computed tomography angiography (CTA) was assessed for early determination of stroke subtypes in a Brazilian cohort of patients with stroke. METHOD: From July 2011 to July 2013, we selected patients with suspected hyperacute stroke (< 6 hours). Intracranial and cervical arteries were scrutinized on CTA and their imaging features were correlated with concurrent subtype of stroke. RESULTS: Stroke was documented in 50/106 selected patients (47.2%) based on both clinical grounds and imaging follow-up (stroke group), with statistically significant arterial stenosis and vulnerable plaques on CTA. Intracranial large artery disease was demonstrated in 34% of patients in the stroke group. Partial territorial infarct prevailed (86%) while artery-to-artery embolization was the most common stroke mechanism (52%). CONCLUSION: Multidetector CTA was useful for the etiologic work-up of hyperacute ischemic stroke and facilitated the knowledge about the topographic pattern of brain infarct in accordance with its causative mechanism.

Current uses of intracranial vessel wall imaging for clinical practice: a high-resolution MR technique recently available / Usos atuais do estudo de parede vascular intracraniana na prática clínica: uma técnica de RM de alta resolução recentemente disponível

ABSTRACT Intracranial vessel wall imaging plays an increasing role in diagnosing intracranial vascular diseases. With the growing demand and subsequent increased use of this technique in clinical practice, radiologists and neurologists should be aware of the choices in imaging parameters and how they affect image quality, clinical indications, methods of assessment, and limitations in the interpretation of these images. Due to the improvement of the MRI techniques, the possibility of accurate and direct evaluation of the abnormalities in the arterial vascular wall (vessel wall imaging) has evolved, adding substantial data to diagnosis when compared to the indirect evaluation based on conventional flow analyses. Herein, the authors proposed a comprehensive approach of this technique reinforcing appropriated clinical settings to better use intracranial vessel wall imaging.

RESUMO O estudo angiográfico intracraniano não invasivo está sendo amplamente utilizado no diagnóstico de doenças vasculares intracranianas. Com a crescente demanda e o aumento subsequente do uso dessa técnica na prática clínica, radiologistas e neurologistas devem estar cientes das opções nos parâmetros de imagem e como estes afetam a qualidade da imagem, as indicações clínicas, os métodos de avaliação e as limitações na interpretação dessas imagens. Devido ao aprimoramento das técnicas de imagem por RM, a possibilidade de avaliação precisa e direta das anormalidades na parede vascular arterial (vessel wall imaging) evoluiu, agregando dados substanciais ao diagnóstico quando comparados à avaliação indireta baseada em análises de fluxo convencionais. Neste artigo, os autores discorrem sobre a avaliação e interpretação dos achados de imagem desta nova técnica e suas aplicações clínicas.