Discrepancies between cerebral perfusion and metabolism after subarachnoid haemorrhage: a magnetic resonance approach

Redefining secondary injury after subarachnoid hemorrhage in light of multimodal advanced neuroimaging, intracranial and transcranial neuromonitoring: beyond vasospasm

The classic idea that arterial narrowing, called vasospasm (VSP), represents the hallmark of secondary injury after subarachnoid hemorrhage, has been challenged. The more complex and pleiotropic pathophysiological repercussions from the irruption of arterial blood into the subarachnoid layers go beyond the ascribed VSP. Putting adjectives in front of this term, such as "symptomatic," "microdialytic," or "angiographic" VSP, is misleading. Delayed cerebral ischemia (DCI) is a better term but remains restrictive to severe hypoperfusive injury and neglects oligemia, edema, and metabolic nonischemic injuries. In recognition of these issues, the international conference on VSP integrated "neurovascular events" into its name ( www.vasospasm2013.com ) and a multidisciplinary research group was formed in 2010 to study subgroups of DCI/VSP and their respective significance.In three parts, this tiered article provides a broader definitional envelope for DCI and secondary neurovascular insults after SAH, with a rubric for each subtype of delayed neuronal dysfunction. First, it pinpoints the need for nosologic precision and covers current terminological inconsistency. Then, it highlights the input of neuroimaging and neuromonitoring in defining secondary injurious processes. Finally, a new categorization of deteriorating patients is proposed, going beyond a hierarchical or dichotomized definition of VSP/DCI, and common data elements are suggested for future trials.

Metabolic changes in patients with aneurysmal subarachnoid hemorrhage apart from perfusion deficits: neuronal mitochondrial injury?

BACKGROUND AND PURPOSE

Neuronal damage in aSAH apart from perfusion deficits has been widely discussed. We aimed to test if cerebral injury occurs in aSAH independently from visible perfusion deficit by measuring cerebral metabolites in patients with aSAH without infarction or impaired perfusion.

MATERIALS AND METHODS

We performed 3T MR imaging including (1)H-MR spectroscopy, DWI, and MR perfusion in 58 patients with aSAH and 11 age-matched and sex-matched control patients with incidental aneurysm. We compared changes of NAA, Cho, Glx, Lac, and Cr between all patients with aSAH and controls, between patients with and without visible perfusion deficit or infarction and controls, and between patients with and without visible perfusion deficit or infarction by using the Wilcoxon signed-rank test.

RESULTS

We found that NAA significantly (P < .005) decreased in all patients with aSAH. Cho was significantly increased in all patients compared with controls (P < .05). In patients without impaired perfusion or infarction, Glx was significantly decreased compared with both controls (P = .005) and patients with impaired perfusion or infarction (P = .006).

CONCLUSIONS

The significant decrease of NAA and Glx in patients with aSAH but without impaired perfusion or infarction strongly suggests global metabolic changes independent from visible perfusion deficits that might reflect neuronal mitochondrial injury. Further, impaired perfusion in aSAH seems to induce additional metabolic changes from increasing neuronal stress that might, to some extent, mask the global metabolic changes.

Current advances in the diagnosis of vasospasm

Symptomatic vasospasm leading to delayed ischemia and neurological deficits is one of the most serious complications after aneurysmal subarachnoid hemorrhage (SAH). Reliable and early detection of symptomatic vasospasm is one of the major goals in the management of patients with SAH. In awake patients, the close clinical neurological examination still remains the most important diagnostic measure. In comatous or sedated patients, cerebral angiography remains the mainstay of the diagnostic workup for vasospasm. However, angiography does not allow assessing the hemodynamic relevance of vasospasm and is not suited for early identification of cerebral hypoperfusion and ischemia. Therefore, a large panel of new monitoring techniques for the assessment of regional cerebral perfusion has been recently introduced into the clinical management of SAH patients. This article briefly reviews the most relevant methods for monitoring cerebral perfusion and discusses their clinical predictive value for the diagnosis of vasospasm. On the basis of the currently available monitoring technologies, an algorithm for the diagnosis of vasospasm is presented.

Perfusion CT to quantify the cerebral vasospasm following subarachnoid hemorrhage

BACKGROUND AND PURPOSE

After subarachnoid hemorrhage (SAH), vasospasm is frequent and increases the risk of stroke and poor clinical outcome. The purpose of this study was to identify the best perfusion parameters in perfusion-CT (PCT) able to predict vasospasm diagnosed by angiography after SAH.

METHODS

Seventy-six patients with SAH were investigated by PCT and cerebral angiography. Using regions of interest (ROI) on parametric maps of mean transit time (MTT), time to peak (TTP), cerebral blood volume (CBV) and cerebral blood flow (CBF), PCT data were compared to an arteriographic score in two categories (severe vasospasm: ≥ 50% and non-severe vasospasm: <50%) for each artery. Best PCT predictors of the arteriographic score were tested using multiparametric logistic regression.

RESULTS

Among the 76 patients, PCT data were reliable in 65 patients. Twenty-seven patients had a severe vasospasm. Logistic regression showed that MTT was the best predictor of the arteriographic score. Using MTT, odds ratios having a vasospasm were superior to 3.1 and the occurrence of a vasospasm was accurately predicted in 78.5 to 100%, depending on the artery considered. However, no absolute value of the MTT could be identified to predict the occurrence of vasospasm. In fact, abnormal values of MTT ranged from 123 to 221% (m=146%) of the control values.

DISCUSSION AND CONCLUSIONS

PCT may accurately identify severe vasospasm and might be used as a convenient noninvasive imaging modality to monitor patients with SAH. When detected, severe vasospasm could be confirmed and managed using angiography and endovascular treatment, appropriately.

MR spectroscopy in patients after surgical clipping and endovascular embolisation of intracranial aneurysms

BACKGROUND

In MR spectroscopy, we evaluated cerebral metabolic changes in patients 2-4 years after clipping or endovascular therapy of intracranial aneurysms. MATERIAL/METODHS: A prospective study was conducted in 36 patients after SAH, treated surgically (n=23) or by endovascular embolisation (n=13). Control group consisted of 20 healthy volunteers. The clinical evaluation was based on the Glasgow Coma Scale, Hunt and Hess grade, and Glasgow Outcome Scale. MR spectroscopy was performed with 1.5T system with PRESS sequence, at echo time of 35 ms, in frontal lobes unchanged in MR examination. Ratios of N-acetylaspartate (NAA), choline (Cho), myo-inositol (mI) and glutamine/glutamate complex (Glx) to creatine were assessed.

RESULTS

Only a slight, statistically insignificant reduction of NAA/Cr and an insignificant increase of mI/Cr were noted; other metabolite ratios were close to the ones in the control group. Similar results were obtained in patients after surgical clipping and after endovascular therapy. Only in patients with aneurysms of anterior communicating artery complex (AcoA), the NAA/Cr ratio showed a significant reduction as compared to that of non-AcoA patients and of the control group. No significant changes of metabolite ratios were found in patients with internal carotid artery (ICA) and middle cerebral artery (MCA) aneurysms, with regard to aneurysm lateralisation.

CONCLUSIONS

Surgical clipping and endovascular embolisation of ICA, MCA and posterior circulatory aneurysms do not induce changes in metabolite concentration in frontal lobes assessed in MR spectroscopy. In patients with AcoA aneurysms, 2-4 years after obliteration, there were found persistent metabolic changes in unchanged brain tissue of the frontal lobes, corresponding to neuronal damage (dysfunction).

[Brain perfusion and metabolism imaging techniques]

Due to recent efforts in improving spatial and temporal resolution in imaging techniques, it is now possible to get relevant information about brain perfusion and metabolism in humans. This information can significantly impact on brain pathophysiology, diagnosis assessment and therapy options, particularly in patients having brain ischemia. Among these imaging and metabolism techniques are dynamic perfusion computed tomography, perfusion MRI, positron emission tomography and NMR spectroscopic imaging. The goal of this article is an overview of these four techniques, with their own technical description, advantages and drawbacks. Details are provided about brain parameters given by each technique and their clinical relevance, the accessibility of the technique in the emergency setting and the optimal window to use it during the patient's evolution.

Using CT in the Diagnosis and Management of Patients with Cerebral Vasospasm

Cerebral vasospasm remains a serious complication of aneurysmal subarachnoid hemorrhage. Efforts in improving its clinical outcome have been focused on early diagnosis and applying effective treatment regimens. Standard diagnostic modalities currently used do not fully address this complex disease. The use of CT angiography and CT perfusion are discussed, with emphasis on its potential role in not only detecting vasospasm, but also in guiding management decisions and assessing clinical outcome.

Time Course in the Development of Cerebral Vasospasm after Experimental Subarachnoid Hemorrhage: Clinical and Neuroradiological Assessment of the Rat Double Hemorrhage Model

OBJECTIVE

The "double hemorrhage" model in the rat is frequently used to simulate delayed cerebral vasospasm (CVS) after subarachnoid hemorrhage (SAH) in humans. However, an exact neurological and angiographic characterization of the CVS is not available for this model so far and is provided in the present investigation. Additionally, perfusion weighted imaging (PWI) at 3 tesla magnetic resonance (MR) tomography was implemented to assess the reduction in cerebral blood flow (CBF).

METHODS

In a prospective, randomized setting CVS was induced by injection of 0.2 ml autologous blood twice in the cisterna magna of 45 male Sprague-Dawley rats. The surviving animals were examined on Days 2, 3, 5, 7 and 9 and compared to a sham operated control group (n = 9). Rats were neurologically graded between 0 and 3, followed by MRI and selective digital subtraction angiography (DSA). The relative CBF was set in relation to the perfusion of the masseter muscle.

RESULTS

The neurological state was significantly worsened on Day 2 (Grade 3), 3 (Grade 3), and 5 (Grade 2) (medians). The relative CBF/muscle BF ratio (2.5 +/- 0.8 (SAH) versus 9.2 +/- 1.3 (sham) (mean +/- SEM) and the basilar artery (BA) diameter (0.15 +/- 0.02 mm (SAH) versus 0.32 +/- 0.01 mm (sham) were significantly decreased on Day 5. Correlation between relative CBF/muscle BF ratio and BA diameter was 0.70.

CONCLUSION

A valid and reproducible CVS simulation was proven by neurological score, DSA, and PWI on Day 5. Furthermore, our data demonstrate the practicability and validity of MR PWI for the monitoring of CVS in a rat SAH model.

Prediction of Cerebral Vasospasm in Patients Presenting with Aneurysmal Subarachnoid Hemorrhage: A Review

OBJECTIVE:

Cerebral vasospasm is a devastating medical complication of aneurysmal subarachnoid hemorrhage (SAH). It is associated with high morbidity and mortality rates, even after the aneurysm has been treated. A substantial amount of experimental and clinical research has been conducted in an effort to predict and prevent its occurrence. This research has contributed to significant advances in the understanding of the mechanisms leading to cerebral vasospasm. The ability to accurately and consistently predict the onset of cerebral vasospasm, however, has been challenging. This topic review describes the various methodologies and approaches that have been studied in an effort to predict the occurrence of cerebral vasospasm in patients presenting with SAH.

METHODS:

The English-language literature on the prediction of cerebral vasospasm after aneurysmal SAH was reviewed using the MEDLINE PubMed (1966–present) database.

RESULTS:

The risk factors, diagnostic imaging, bedside monitoring approaches, and pathological markers that have been evaluated to predict the occurrence of cerebral vasospasm after SAH are presented.

CONCLUSION:

To date, a large blood burden is the only consistently demonstrated risk factor for the prediction of cerebral vasospasm after SAH. Because vasospasm is such a multifactorial problem, attempts to predict its occurrence will probably require several different approaches and methodologies, as is done at present. Future improvements in the prevention of cerebral vasospasm from aneurysmal SAH will most likely require advances in our understanding of its pathophysiology and our ability to predict its onset.

Computed Tomographic Perfusion in the Management of Aneurysmal Subarachnoid Hemorrhage: New Application of an Existent Technique

OBJECTIVE:

Cerebral blood flow (CBF) alterations are common after aneurysmal subarachnoid hemorrhage (SAH). Treatment of delayed cerebral ischemia in this setting depends on timely and accurate diagnosis. Techniques to measure cerebral blood flow are useful and important. Computed tomographic (CT) perfusion imaging is a technique for the measurement of CBF, cerebral blood volume, and time to peak. It is a fast and inexpensive brain imaging modality that offers promise in the management of patients with SAH.

METHODS:

CT perfusion imaging was performed in 10 patients with aneurysmal SAH when neurological changes raised suspicions of cerebral ischemia. Quantitative values for CBF, cerebral blood volume, and time to peak were obtained in each study. The case history, CT perfusion results, and an analysis of how patient management was influenced are presented for each patient.

RESULTS:

A total of 17 CT perfusion studies were performed. Five studies showed evidence of cerebral ischemia, leading to endovascular treatment of vasospasm. Eight studies excluded cerebral ischemia, and two studies identified cerebral hyperemia, resulting in adjustments in hyperdynamic therapy. CT perfusion was used to help predict a poor prognosis and withhold aggressive intervention in two patients with poor Hunt and Hess grades. Time-to-peak values identified regions of cerebral ischemia more readily than CBF or cerebral blood volume values.

CONCLUSION:

CT perfusion imaging can be used to identify patients with delayed cerebral ischemia after SAH and to guide medical and endovascular therapy. The findings can lead to alterations in patient management.

Jugular bulb oximetry for prediction of vasospasm following subarachnoid hemorrhage

BACKGROUND

Cerebral vasospasm adversely impacts the outcome of those suffering aneurysmal subarachnoid hemorrhage (SAH). Prediction of vasospasm could improve outcomes. We hypothesized that preclinical vasospasm would be heralded by an increase in cerebral oxygen extractions (AVDO2) which could be detected by jugular bulb oximetry. A pilot study was conducted to address this hypothesis.

METHODS

Fourteen consenting patients with aneurysmal SAH, undergoing early surgery, were entered into the study. Four patients were withdrawn from the study secondary to failure of catheters or religious belief. At the time of craniotomy, a jugular bulb catheter was placed. Post-operatively, arterial and jugular bulb blood samples were taken every 12 hours to calculate AVDO2. As this was an observational study, no change in management occurred based on measurements.

RESULTS

Four of 10 patients had clinical vasospasm. These patients had a significant rise in AVDO2 approximately one day prior to the onset of neurologic deficits (P<0.001). Symptoms resolved along with a significant improvement in AVDO2 on instituting hypertensive, hemo-dilutional, and hypervolemic therapy in these patients. The six patients who did not exhibit clinical vasospasm did not demonstrate significant rise in AVDO2.

CONCLUSIONS

Jugular bulb oximetry is simple and cost effective. Increases in AVDO2 using this technique were predictive of clinically evident vasospasm in the subsequent hours to days. This investigation supports a larger study to assess the utility of jugular bulb oximetry in predicting vasospasm in aneurysmal SAH.

Vasospasm after subarachnoid hemorrhage: interest in diffusion-weighted MR imaging

BACKGROUND AND PURPOSE

Vasospasm secondary to subarachnoid hemorrhage (SAH) is responsible for severe ischemic complications. Although effective, angioplasty must be performed at a very early stage to produce any clinical recovery. Diagnostic investigations to assess arterial narrowing (transcranial Doppler, angiography) or cerebral perfusion (xenon CT, single-photon emission CT) do not provide evidence of the extent of parenchymal ischemia. In stroke, diffusion-weighted MR imaging (DWI) appears to be the most sensitive procedure to detect cerebral ischemia. We studied asymptomatic vasospasm in patients with aneurysmal SAH to assess whether DWI provides predictive markers of silent ischemic lesions and/or progression toward symptomatic ischemia.

METHODS

Seven asymptomatic vasospasm patients (average blood velocity rates >120 cm/s), 3 patients with symptomatic vasospasm, and 4 patients with SAH but without vasospasm were studied at regular intervals by DWI, and their apparent diffusion coefficients (ADCs) were calculated.

RESULTS

All patients with vasospasm including those without symptoms presented abnormalities on DWI with a reduction of the ADC prevalently in the white matter. No such abnormalities were observed in patients without vasospasm. The abnormalities on DWI resolved completely in 4 of the 7 patients, with no parenchymal lesion. Resolution was partial in 3 patients whose white matter still presented residual round, focal ischemic lesions.

CONCLUSIONS

Being able to correlate abnormalities on DWI with parenchymal involvement in asymptomatic patients would be of considerable clinical significance. It is hoped that larger studies will be undertaken to determine whether the ADC has a reversibility threshold, because this would facilitate patient management.

Imaging developing brain infarction

Continued advances in neuroimaging technology have made it practical to image multiple aspects of evolving brain infarction during the potential window period of therapeutic opportunity in stroke. Recent methodologic developments include computed tomography angiography and perfusion, and the description of quantitative parameters for magnetic resonance blood oxygen level-dependent perfusion imaging. In pathophysiologic studies, metabolism and function in the ischemic focus and the peri-infarct tissue have been further characterized. Clinical studies have focused on the applications of computed tomography and magnetic resonance imaging for prethrombolysis patient selection. These methods have an important role in the evaluation and development of new pharmaceutical agents and will be increasingly used in clinical practice as new therapies become available.