CT perfusion during delayed cerebral ischemia after subarachnoid hemorrhage: distinction between reversible ischemia and ischemia progressing to infarction

High-sensitivity THz-ATR imaging of cerebral ischemia in a rat model

The fast label-free detection of the extent and degree of cerebral ischemia has been the difficulty and hotspot for precise and accurate neurosurgery. We experimentally demonstrated that the fresh cerebral tissues at different ischemic stages within 24 hours can be well distinguished from the normal tissues using terahertz (THz) attenuated total reflection (ATR) imaging system. It was indicated that the total reflectivity of THz wave for ischemic cerebral tissues was lower than that for normal tissues. Especially, compared to the images stained with 2,3,5-triphenyl tetrazolium chloride (TTC), the ischemic tissues can be detected using THz wave with high sensitivity as early as the ischemic time of 2.5 hours, where THz images showed the ischemic areas became larger and diffused as the ischemic time increasing. Furthermore, the THz spectroscopy of cerebral ischemic tissues at different ischemic times was obtained in the range of 0.5-2.0 THz. The absorption coefficient of ischemic tissue increased with the increase of ischemic time, whereas the refractive index decreased with prolonging the ischemic time. Additionally, it was found from hematoxylin and eosin (H&E) staining microscopic images that, with the ischemic time increasing, the cell size and cell density of the ischemic tissues decreased, whereas the intercellular substance of the ischemic tissues increased. The result showed that THz recognition mechanism of the ischemia is mainly based on the increase of intercellular substance, especially water content, which has a stronger impact on absorption of THz wave than that of cell density. Thus, THz imaging has great potential for recognition of cerebral ischemia and it may become a new method for intraoperative real-time guidance, recognition in situ, and precise excision.

Pathophysiology of Early Brain Injury and Its Association with Delayed Cerebral Ischemia in Aneurysmal Subarachnoid Hemorrhage: A Review of Current Literature

Background: Delayed cerebral ischemia (DCI) is a common and serious complication of aneurysmal subarachnoid hemorrhage (aSAH). Though many clinical trials have looked at therapies for DCI and vasospasm in aSAH, along with reducing rebleeding risks, none have led to improving outcomes in this patient population. We present an up-to-date review of the pathophysiology of DCI and its association with early brain injury (EBI). Recent Findings: Recent studies have demonstrated that EBI, as opposed to delayed brain injury, is the main contributor to downstream pathophysiological mechanisms that play a role in the development of DCI. New predictive models, including advanced monitoring and neuroimaging techniques, can help detect EBI and improve the clinical management of aSAH patients. Summary: EBI, the severity of subarachnoid hemorrhage, and physiological/imaging markers can serve as indicators for potential early therapeutics in aSAH. The microcellular milieu and hemodynamic pathomechanisms should remain a focus of researchers and clinicians. With the advancement in understanding the pathophysiology of DCI, we are hopeful that we will make strides toward better outcomes for this unique patient population.

The value of whole-brain CT perfusion imaging combined with dynamic CT angiography in the evaluation of pial collateral circulation with middle cerebral artery occlusion

BACKGROUND

Middle cerebral artery (MCA) occlusion is extremely common, especially unilateral artery, which can result in a significant incidence of cerebral infarction.

OBJECTIVE

To assess the value of whole-brain computed tomography perfusion (CTP) imaging combined with dynamic CT angiography (dCTA) in the evaluation of pial collateral circulation in patients with MCA occlusion.

METHODS

Whole-brain CTP and dCTA images were acquired in 58 patients with unilateral MCA occlusion. All patients were divided into three groups according to the American Society of Interventional and Therapeutic Neuroradiology/Society of Interventional Radiology (ASITN/SIR) collateral score (by CTA). The CTP parameters were analysed, including relative cerebral blood flow (rCBF), relative cerebral blood volume (rCBV), relative mean transit time (rMTT), and relative time to peak (rTTP). Patients were followed up with the modified Rankin scale (mRS). All cases in this study were confirmed by DSA.

RESULTS

The CTP parameters of the MCA blood supply area on the affected side of patients with different degrees of stenosis were significantly different from those on the unaffected side. There are significant differences in the CTP parameters and openings of the Willis circle in patients with different degrees of stenosis. Significant differences were found in the number of patients with good prognosis.

CONCLUSIONS

Whole-brain CT perfusion combined with dynamic CTA can structurally and functionally evaluate the establishment of pial collateral circulation and its effect on cerebral hemodynamic changes.

Multidisciplinary and standardized management of patients with delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage

BACKGROUND

The appropriate management of delayed cerebral ischemia (DCI) after aneurysmal subarachnoid hemorrhage (aSAH) remains uncertain. We aimed to evaluate the effect of implementing a standardized protocol for detection and management of DCI after aSAH on cerebral infarction and functional outcome.

METHODS

We studied two cohorts of aSAH patients, one before (pre-implementation cohort: January 2012 to August 2014) and one after (post-implementation cohort: January 2016 to July 2018) implementation of a multidisciplinary approach, with standardized neurological and radiological assessment and risk-based medical treatment of DCI. We assessed the presence of new hypodensities on CT within 6 weeks after aSAH and categorized cerebral infarction into overall and DCI-related infarctions (hypodensities not within 48 h after IA repair and not attributable to aneurysm occlusion or intraparenchymal hematoma). Functional outcome was assessed at 3 months using the extended Glasgow outcome scale (eGOS), dichotomized into unfavorable (eGOS: 1-5) and favorable (eGOS: 6-8). We calculated odds ratios (OR) with corresponding 95% confidence intervals (CI's), and adjusted for age, WFNS grade, Fisher score, and treatment modality (aOR).

RESULTS

In the post-implementation (n = 158) versus the pre-implementation (n = 143) cohort the rates for overall cerebral infarction were 29.1% vs 46.9% (aOR: 0.41 [0.24-0.69]), for DCI-related cerebral infarction 17.7% vs. 31.5% (aOR: 0.41 [0.23-0.76]), and for unfavorable functional outcome at 3 months 37.3% vs. 53.8% (aOR: 0.30 [0.17-0.54]). For patients with DCI, the rates for unfavorable functional outcomes at 3 months in the post-implementation versus the pre-implementation cohort were 42.3% vs. 77.8% (aOR: 0.1 [0.03-0.27]).

CONCLUSIONS

A multidisciplinary approach with more frequent and standardized neurological assessment, standardized CT and CT perfusion monitoring, as well as tailored application of induced hypertension and invasive rescue therapy strategies, is associated with a significant reduction of cerebral infarction and unfavorable functional outcome after aneurysmal aSAH.

Delayed Cerebral Ischemia after Subarachnoid Hemorrhage

Delayed cerebral ischemia (DCI) is the most feared complication of aneurysmal subarachnoid hemorrhage (aSAH). It increases the mortality and morbidity associated with aSAH. Previously, large cerebral artery vasospasm was thought to be the sole major contributing factor associated with increased risk of DCI. Recent literature has challenged this concept. We conducted a literature search using PUBMED as the prime source of articles discussing various other factors which may contribute to the development of DCI both in the presence or absence of large cerebral artery vasospasm. These factors include microvascular spasm, micro-thrombosis, cerebrovascular dysregulation, and cortical spreading depolarization. These factors collectively result in inflammation of brain parenchyma, which is thought to precipitate early brain injury and DCI. We conclude that diagnostic modalities need to be refined in order to diagnose DCI more efficiently in its early phase, and newer interventions need to be developed to prevent and treat this condition. These newer interventions are currently being studied in experimental models. However, their effectiveness on patients with aSAH is yet to be determined.

Aneurysmal Subarachnoid Hemorrhage: Review of the Pathophysiology and Management Strategies

PURPOSE OF REVIEW

Aneurysmal subarachnoid hemorrhage remains a devastating disease process despite medical advances made over the past 3 decades. Much of the focus was on prevention and treatment of vasospasm to reduce delayed cerebral ischemia and improve outcome. In recent years, there has been a shift of focus onto early brain injury as the precursor to delayed cerebral ischemia. This review will focus on the most recent data surrounding the pathophysiology of aneurysmal subarachnoid hemorrhage and current management strategies.

RECENT FINDINGS

There is a paucity of successful trials in the management of subarachnoid hemorrhage likely related to the targeting of vasospasm. Pathophysiological changes occurring at the time of aneurysmal rupture lead to early brain injury including cerebral edema, inflammation, and spreading depolarization. These events result in microvascular collapse, vasospasm, and ultimately delayed cerebral ischemia. Management of aneurysmal subarachnoid hemorrhage has remained the same over the past few decades. No recent trials have resulted in new treatments. However, our understanding of the pathophysiology is rapidly expanding and will advise future therapeutic targets.

Routine use of perfusion computed tomography for the detection of delayed cerebral ischemia in unconscious patients after aneurysmal subarachnoid hemorrhage

BACKGROUND

Delayed cerebral ischemia (DCI) after aneurysmal subarachnoid hemorrhage (aSAH) is difficult to diagnose in unconscious patients, but it is essential for the prognosis. We analyzed the diagnostic value of routinely performed perfusion computed tomography (rPCT) to detect DCI-related hypoperfusion in this subgroup of patients.

METHODS

Retrospective analysis of unconscious aSAH patients who underwent rPCT according to a predefined protocol. We exclusively analyzed PCT examinations in patients who were clinically and functionally asymptomatic with regard to transcranial Doppler ultrasound (TCD) and invasive neuromonitoring at the time of the PCT examination. The perfusion maps were quantitatively evaluated to detect DCI-related hypoperfusion. Possible clinical risk factors for the occurrence of DCI-related hypoperfusion in rPCT imaging were analyzed by multivariate analyses.

RESULTS

One hundred thirty-six rPCTs were performed in 55 patients. New onset of DCI-related hypoperfusion was observed in 18% of rPCTs. The positive predictive value of rPCT to detect angiographic CVS was 0.80. Between examination days 6 and 10, the rate of DCI-related hypoperfusion was increased significantly (p < 0.05). After rPCT imaging with proof of DCI-related hypoperfusion, short-term follow-up showed secondary cerebral infarction (SCI) in 38%, compared with 5% for patients with normal perfusion on rPCT. The parameters "high risk phase (examination days 6-10)" and "new onset of DCI-related SCI" were significantly associated with the occurrence of DCI-related hypoperfusion in rPCT.

CONCLUSIONS

In unconscious and asymptomatic aSAH patients, rPCT identifies DCI-related hypoperfusion in a relevant number of examinations. However, despite timely endovascular rescue therapy, a significant proportion of secondary infarction still occurs in this subgroup.

Detection of delayed cerebral ischemia using objective pupillometry in patients with aneurysmal subarachnoid hemorrhage

OBJECTIVE

Cerebral vasospasm causing delayed cerebral ischemia (DCI) is a source of significant morbidity after subarachnoid hemorrhage (SAH). Transcranial Doppler is used at most institutions to detect sonographic vasospasm but has poor positive predictive value for DCI. Automated assessment of the pupillary light reflex has been increasingly used as a reliable way of assessing pupillary reactivity, and the Neurological Pupil Index (NPi) has been shown to decrease hours prior to the clinical manifestation of ischemic injury or herniation syndromes. The aim of this study was to investigate the role of automated pupillometry in the setting of SAH, as a potential adjunct to TCD.

METHODS

Our analysis included patients that had been diagnosed with aneurysmal SAH and admitted to the neuro-intensive care unit of the University of Texas Southwestern Medical Center between November 2015 and June 2017. A dynamic infrared pupillometer was used for all pupillary measurements. An NPi value ranging from 3 to 5 was considered normal, and from 0 to 2.9 abnormal. Sonographic vasospasm was defined as middle cerebral artery velocities greater than 100 cm/sec with a Lindegaard ratio greater than 3 on either side on transcranial Doppler. Most patients had multiple NPi readings daily and we retained the lowest value for our analysis. We aimed to study the association between DCI and sonographic vasospasm, and DCI and NPi readings.

RESULTS

A total of 56 patients were included in the final analysis with 635 paired observations of daily TCD and NPi data. There was no statistically significant association between the NPi value and the presence of sonographic vasospasm. There was a significant association between DCI and sonographic vasospasm, χ2(1) = 6.4112, p = 0.0113, OR 1.6419 (95% CI 1.1163-2.4150), and between DCI and an abnormal decrease in NPi, χ2(1) = 38.4456, p < 0.001, OR 3.3930 (95% CI 2.2789-5.0517). Twelve patients experienced DCI, with 7 showing a decrease of their NPi to an abnormal range. This change occurred > 8 hours prior to the clinical decline 71.4% of the time. The NPi normalized in all patients after treatment of their vasospasm.

CONCLUSIONS

Isolated sonographic vasospasm does not seem to correlate with NPi changes, as the latter likely reflects an ischemic neurological injury. NPi changes are strongly associated with the advent of DCI and could be an early herald of clinical deterioration.

Efficiency of Iterative Metal Artifact Reduction Algorithm (iMAR) Applied to Brain Volume Perfusion CT in the Follow-up of Patients after Coiling or Clipping of Ruptured Brain Aneurysms

Metal artifacts resulting from coiling or clipping of a brain aneurysm degrade image quality and reduce diagnostic usefulness of computed tomography perfusion CTP. Our aim was to assess the diagnostic value of the iterative metal artifact reduction algorithm (iMAR) in CTP studies after coiling or clipping of ruptured intracranial aneurysms. Fifty-eight CTP exams performed in 32 patients were analysed. iMAR was applied to the source images from the CT scanner. Perfusion maps were generated from datasets both with and without iMAR, and both datasets were compared qualitatively and quantitatively. Qualitative analysis included evaluation of intensity of artifacts, image quality, presence of new artifacts, and the reader’s confidence in their diagnosis as well as diagnostic impression. Quantitative analysis included evaluation of tissue attenuation curves, evaluation of region of interest (ROI)-based measurement of perfusion values at levels that do and do not contain metal, compared to previously published reference ranges of perfusion values. Our results showed that application of iMAR reduced artifacts and significantly improved image quality. New artifacts were observed adjacent to metallic implants, but did not limit the evaluation of other regions. After correction for artifact readers’ confidence in their diagnosis increased from 41.3% to 87.9%, and the diagnostic impression changed in 31% of the exams. No difference between tissue attenuation curves was found. For slices without metal, no difference was noted between values measured before and after iMAR, and the total number of ROIs in the reference range of perfusion values was unchanged. At the level of the metal implant, 89.85% of ROIs obtained before using iMAR showed calculation errors. After using iMAR, only 1.7% showed errors. Before iMAR 3.1% of values were in the reference range, whereas after iMAR this increased to 33.1%. In conclusion, our results show that iMAR is an excellent tool for reducing artifacts in CTP. It is therefore recommended for use in clinical practice, particularly when severe artifacts are present, or when hypoperfusion is suspected at the level of the coil or clip. After the application of iMAR, the perfusion values at the level of the metal can be better calculated, but may not lie within the reference range; therefore, quantitative analysis at the level of artifacts is not advisable.

Delayed Ischemic Neurologic Deficit after Aneurysmal Subarachnoid Hemorrhage

Delayed ischemic neurologic deficit (DIND) is the main preventable cause of poor outcomes in aneurysmal subarachnoid hemorrhage (SAH) patients. Of 50% of survivors from a SAH, approximately 30% of patients will present clinical vasospasm (VS). The cornerstone of the DIND management comprises prevention and early identification. Several diagnostic methods have been proposed differing in efficacy, invasiveness, and costs. Serial neurological examination is the most reliable method to detect a new neurological deficit. On the other hand, comatose patients require advanced monitoring methods which identify changes in the microcirculatory environment, brain autoregulation, and spreading depolarization. Multimodality monitoring with continuous electroencephalography, microdialysis, and intracranial pressure monitoring represents altogether the current state-of-art technology for the intensive care of SAH patients. Moreover, advances in genetic biomarkers to predict clinical VS have shown consistent accuracy which may in the near future allow the early prediction of DIND through a simple blood test. Several clinical trials have tested drugs with theoretical effects on DIND prevention or treatment. Nevertheless, nimodipine remains the Holy Grail in the prevention of clinical VS. Among rescue therapies, the endovascular treatment through intra-arterial vasodilator (verapamil or nicardipine) infusion is the most employed method for DIND reversal; however, there is no good quality evidence comparing results of intra-arterial infusion of vasodilators versus balloon angioplasty. Although we have addressed the most refined technology in the management of SAH and DIND, the clinical experience and strict follow-up in neurointensive care will be determinant for favorable long-term outcomes.

Hemodynamic Disturbances in the Early Phase After Subarachnoid Hemorrhage: Regional Cerebral Blood Flow Studied by Bedside Xenon-enhanced CT

BACKGROUND

The mechanisms leading to neurological deterioration and the devastating course of delayed cerebral ischemia (DCI) after subarachnoid hemorrhage (SAH) are still not well understood. Bedside xenon-enhanced computerized tomography (XeCT) enables measurements of regional cerebral blood flow (rCBF) during neurosurgical intensive care. In the present study, CBF characteristics in the early phase after severe SAH were explored and related to clinical characteristics and early clinical course outcome.

MATERIALS AND METHODS

Patients diagnosed with SAH and requiring mechanical ventilation were prospectively enrolled in the study. Bedside XeCT was performed within day 0 to 3.

RESULTS

Data from 64 patients were obtained. Median global CBF was 34.9 mL/100 g/min (interquartile range [IQR], 26.7 to 41.6). There was a difference in CBF related to age with higher global CBF in the younger patients (30 to 49 y). CBF was also related to the severity of SAH with lower CBF in Fisher grade 4 compared with grade 3. rCBF disturbances and hypoperfusion were common; in 43 of the 64 patients rCBF<20 mL/100 g/min was detected in more than 10% of the region-of-interest (ROI) area and in 17 patients such low-flow area exceeded 30%. rCBF was not related to the localization of the aneurysm; there was no difference in rCBF of ipsilateral compared with contralateral vascular territories. In patients who initially were in Hunt & Hess grade I to III, median global CBF day 0 to 3 was significantly lower for patients who were in poor neurological state at discharge compared with patients in good neurological state, 25.5 mL/100 g/min (IQR, 21.3 to 28.3) versus 37.8 mL/100 g/min (IQR, 30.5 to 47.6).

CONCLUSIONS

CBF disturbances are common in the early phase after SAH. In many patients, CBF was heterogenic and substantial areas with low rCBF were detected. Age and CT Fisher grade were factors influencing global cortical CBF. Bedside XeCT may be a tool to identify patients at risk of deteriorating so they can receive intensified management, but this needs further exploration.

Prediction of outcome after aneurysmal subarachnoid haemorrhage using data from patient admission

OBJECTIVES

The pathogenesis leading to poor functional outcome after aneurysmal subarachnoid haemorrhage (aSAH) is multifactorial and not fully understood. We evaluated a machine learning approach based on easily determinable clinical and CT perfusion (CTP) features in the course of patient admission to predict the functional outcome 6 months after ictus.

METHODS

Out of 630 consecutive subarachnoid haemorrhage patients (2008-2015), 147 (mean age 54.3, 66.7% women) were retrospectively included (Inclusion: aSAH, admission within 24 h of ictus, CTP within 24 h of admission, documented modified Rankin scale (mRS) grades after 6 months. Exclusion: occlusive therapy before first CTP, previous aSAH, CTP not evaluable). A random forests model with conditional inference trees was optimised and trained on sex, age, World Federation of Neurosurgical Societies (WFNS) and modified Fisher grades, aneurysm in anterior vs. posterior circulation, early external ventricular drainage (EVD), as well as MTT and T_max maximum, mean, standard deviation (SD), range, 75th quartile and interquartile range to predict dichotomised mRS (≤ 2; > 2). Performance was assessed using the balanced accuracy over the training and validation folds using 20 repeats of 10-fold cross-validation.

RESULTS

In the final model, using 200 trees and the synthetic minority oversampling technique, median balanced accuracy was 84.4% (SD 0.7) over the training folds and 70.9% (SD 1.2) over the validation folds. The five most important features were the modified Fisher grade, age, MTT range, WFNS and early EVD.

CONCLUSIONS

A random forests model trained on easily determinable features in the course of patient admission can predict the functional outcome 6 months after aSAH with considerable accuracy.

KEY POINTS

• Features determinable in the course of admission of a patient with aneurysmal subarachnoid haemorrhage (aSAH) can predict the functional outcome 6 months after the occurrence of aSAH. • The top five predictive features were the modified Fisher grade, age, the mean transit time (MTT) range from computed tomography perfusion (CTP), the WFNS grade and the early necessity for an external ventricular drainage (EVD). • The range between the minimum and the maximum MTT may prove to be a valuable biomarker for detrimental functional outcome.

Intracortical electrophysiological correlates of blood flow after severe SAH: A multimodality monitoring study

Subarachnoid hemorrhage (SAH) is a devastating form of stroke. Approximately one in four patients develop progressive neurological deterioration and silent infarction referred to as delayed cerebral ischemia (DCI). DCI is a complex, multifactorial secondary brain injury pattern and its pathogenesis is not fully understood. We aimed to study the relationship between cerebral blood flow (CBF) and neuronal activity at both the cortex and in scalp using electroencephalography (EEG) in poor-grade SAH patients undergoing multimodality intracranial neuromonitoring. Twenty patients were included, of whom half had DCI median 4.7 days (interquartile range (IQR): 4.0-5.6) from SAH bleed. The rate of decline in regional cerebral blood flow (rCBF) was significant in both those with and without DCI and occurred between days 4 and 7 post-SAH. The scalp EEG alpha-delta ratio declined early in those with DCI. In the group without DCI, CBF and cortical EEG alpha-delta ratio were correlated (r = 0.53; p <  0.01) and in the group without DCI, inverse neurovascular coupling was observed at CPP <  80 mmHg. We found preliminary evidence that as patients enter the period of highest risk for the development of DCI, the absence of neurovascular coupling may act as a possible pathomechanism in the development of ischemia following SAH.

Case Studies in Neurocritical Care

The practice of neurocritical care encompasses multiple acute neurologic and neurosurgical diseases and requires detailed knowledge of neurology and critical care. This article presents 5 cases that illustrate just some of the conditions encountered in the daily practice of neurocritical care and exemplify some of the common diagnostic, therapeutic, and prognostic challenges facing the neurointensivist. Life-threatening medical complications after severe acute ischemic stroke, seizures and extreme agitation from autoimmune encephalitis, refractory seizures after subdural hemorrhage, neurologic and systemic complications related to aneurysmal subarachnoid hemorrhage, and status epilepticus after cardiac arrest are discussed in this article.