Leukoaraiosis May Confound the Interpretation of CT Perfusion in Patients Treated with Mechanical Thrombectomy for Acute Ischemic Stroke

Perfusion Status in Lacunar Stroke: A Pathophysiological Issue

The pathophysiology of lacunar infarction is an evolving and debated field, where relevant information comes from histopathology, old anatomical studies and animal models. Only in the last years, have neuroimaging techniques allowed a sufficient resolution to directly or indirectly assess the dynamic evolution of small vessel occlusion and to formulate hypotheses about the tissue status and the mechanisms of damage. The core-penumbra concept was extensively explored in large vessel occlusions (LVOs) both from the experimental and clinical point of view. Then, the perfusion thresholds on one side and the neuroimaging techniques studying the perfusion of brain tissue were focused and optimized for LVOs. The presence of a perfusion deficit in the territory of a single small perforating artery was negated for years until the recent proposal of the existence of a perfusion defect in a subgroup of lacunar infarcts by using magnetic resonance imaging (MRI). This last finding opens pathophysiological hypotheses and triggers a neurovascular multidisciplinary reasoning about how to image this perfusion deficit in the acute phase in particular. The aim of this review is to summarize the pathophysiological issues and the application of the core-penumbra hypothesis to lacunar stroke.

CT Perfusion in Lacunar Stroke: A Systematic Review

BACKGROUND

The main theory underlying the use of perfusion imaging in acute ischemic stroke is the presence of a hypoperfused volume of the brain downstream of an occluded artery. Indeed, the main purpose of perfusion imaging is to select patients for endovascular treatment. Computed Tomography Perfusion (CTP) is the more used technique because of its wide availability but lacunar infarcts are theoretically outside the purpose of CTP, and limited data are available about CTP performance in acute stroke patients with lacunar stroke.

METHODS

We performed a systematic review searching in PubMed and EMBASE for CTP and lacunar stroke with a final selection of 14 papers, which were examined for data extraction and, in particular, CTP technical issues and sensitivity, specificity, PPV, and NPV values.

RESULTS

A global cohort of 583 patients with lacunar stroke was identified, with a mean age ranging from 59.8 to 72 years and a female percentage ranging from 32 to 53.1%.CTP was performed with different technologies (16 to 320 rows), different post-processing software, and different maps. Sensitivity ranges from 0 to 62.5%, and specificity from 20 to 100%.

CONCLUSIONS

CTP does not allow to reasonable exclude lacunar infarct if no perfusion deficit is found, but the pathophysiology of lacunar infarct is more complex than previously thought.

Spatial accuracy of computed tomography perfusion to estimate the follow-up infarct on diffusion-weighted imaging after successful mechanical thrombectomy

BACKGROUND

Volumetric accuracy of using computed tomography perfusion (CTP) to estimate the post-treatment infarct in stroke patients with successful recanalization after mechanical thrombectomy (MT) has been studied a lot, however the spatial accuracy and its influence factors has not been fully investigated.

METHODS

This retrospective study reviewed the data from consecutive anterior large vessel occlusion (LVO) patients who had baseline CTP, successful recanalization after MT, and post-treatment diffusion-weighed imaging (DWI). Ischemic core on baseline CTP was estimated using relative cerebral blood flood (CBF) of < 30%. The infarct area was outlined manually on post-treatment DWI, and registered to CTP. Spatial agreement was assessed using the Dice similarity coefficient (DSC) and average Hausdorff distance. According to the median DSC, the study population was dichotomized into high and low Dice groups. Univariable and multivariable regression analyses were used to determine the factors independently associated with the spatial agreement.

RESULTS

In 72 included patients, the median DSC was 0.26, and the median average Hausdorff distance was 1.77 mm. High Dice group showed significantly higher median ischemic core volume on baseline CTP (33.90 mL vs 3.40 mL, P < 0.001), lower proportion of moderate or severe leukoaraiosis [27.78% vs 52.78%, P = 0.031], and higher median infarct volume on follow-up DWI (51.17 mL vs 9.42 mL, P < 0.001) than low Dice group. Ischemic core volume on baseline CTP was found to be independently associated with the spatial agreement (OR, 1.092; P < 0.001).

CONCLUSIONS

CTP could help to spatially locate the post-treatment infarct in anterior LVO patients who achieving successful recanalization after MT. Ischemic core volume on baseline CTP was independently associated with the spatial agreement.

Mediating roles of leukoaraiosis and infarcts in the effects of unilateral carotid artery stenosis on cognition

Background and objectives

Leukoaraiosis and infarcts are common in patients with carotid artery stenosis (CAS), and CAS severity, leukoaraiosis and infarcts all have been implicated in cognitive impairments. CAS severity was not only hypothesized to directly impede specific cognitive domains, but also transmit its effects indirectly to cognitive function through ipsilateral infarcts as well as periventricular leukoaraiosis (PVL) and deep white matter leukoaraiosis (DWML). We aimed to delineate the contributions of leukoaraiosis, infarcts and CAS to different specific cognitive domains.

Materials and methods

One hundred and sixty one participants with unilateral CAS (&gt;50%) on the left (n = 85) or right (n = 76) side and 65 volunteers without significant CAS (&lt;50%) were recruited. The PVL, DWML, and infarct severity were visually rated on MRI. A comprehensive cognitive battery was administered and standardized based on age norms. Correlation and mediation analyses were adopted to examine the direct and indirect influence of CAS, leukoaraiosis, and infarct on specific cognitive domains with adjustment for education, hypertension, diabetes mellitus, and hyperlipidemia.

Results

Carotid artery stenosis severity was associated with ipsilateral leukoaraiosis and infarct. Left CAS had direct effects on most cognitive domains, except for visual memory and constructional ability, and transmitted its indirect effects on all cognitive domains through ipsilateral PVL, and on constructional ability and psychomotor through infarcts. Right CAS only had negative direct effects on visual memory, psychomotor, design fluency and color processing speed, and transmitted its indirect effects on visual memory, word and color processing speed through ipsilateral infarcts. The trends of direct and indirect cognitive effects remained similar after covariate adjustment.

Conclusion

Left and right CAS would predominantly lead to verbal and non-verbal cognitive impairment respectively, and such effects could be mediated through CAS-related leukoaraiosis and infarct. Given that cognition is subject to heterogeneous pathologies, the exact relationships between markers of large and small vessel diseases and their composite prognostic effects on cognition requires further investigation.

Automated Processing of Head CT Perfusion Imaging for Ischemic Stroke Triage: A Practical Guide to Quality Assurance and Interpretation

Recent successful trials of thrombectomy launched a shift to imaging-based patient selection for stroke intervention. Many centers have adopted CT perfusion imaging (CTP) as a routine part of stroke workflow, and the demand for emergent CTP interpretation is growing. Fully automated CTP postprocessing software that rapidly generates standardized color-coded CTP summary maps with minimal user input and with easy accessibility of the software output is increasingly being adopted. Such automated postprocessing greatly streamlines clinical workflow and CTP interpretation for radiologists and other frontline physicians. However, the straightforward interface overshadows the computational complexity of the underlying postprocessing workflow, which, if not carefully examined, predisposes the interpreting physician to diagnostic errors. Using case examples, this article aims to familiarize the general radiologist with interpreting automated CTP software data output in the context of contemporary stroke management, providing a discussion of CTP acquisition and postprocessing, a stepwise guide for CTP quality assurance and troubleshooting, and a framework for avoiding clinically significant CTP interpretative pitfalls in commonly encountered clinical scenarios. Interpreting radiologists should apply the outlined approach for quality assurance and develop a comprehensive search pattern for the identified pitfalls, to ensure accurate CTP interpretation and optimize patient selection for reperfusion.

Severe Cerebral Small Vessel Disease Burden Is Associated With Poor Outcomes After Endovascular Thrombectomy in Acute Ischemic Stroke With Large Vessel Occlusion

Background

Despite recent advancements in the treatment of acute ischemic stroke (AIS) with large vessel occlusion (LVO), infarct progression over time and functional outcomes remain variable. This variation in outcomes may be partially attributed to an underlying state of chronic cerebral hypoperfusion and ischemia affecting small cerebral perforating arterioles, venules, and capillaries of the brain; broadly termed cerebral small vessel disease (CSVD). We investigated the association between CSVD burden and the degree of disability following successful recanalization with endovascular thrombectomy (EVT) in patients with AIS presenting with LVO.

Methodology

We conducted a single center retrospective analysis of all patients presenting with AIS LVO between May 2016 and May 2019. Patients who were premorbidly independent and presented within six hours from the last known well (LKW) with a proximal anterior circulation occlusion confirmed on computed tomography (CT) angiography of the head or neck were treated with EVT. Patients presenting after six hours and up to 24 hours from LKW with a target ischemic core to perfusion mismatch profile on CT or magnetic resonance (MR) perfusion, or a clinical imaging mismatch on MR diffusion-weighted imaging, were also treated. Patients with successful revascularization, defined as a thrombolysis in cerebral infarction score 2b or 3, were included and evaluated for CSVD burden. The presence of CSVD was quantified using the Fazekas scale (0-3). All patients were further evaluated for disability at 90 days using the modified Rankin Scale (mRS, range 0-6). An mRS score of ≤2 was defined as a good functional outcome.

Results

Of the 190 patients evaluated, absent (Fazekas grade 0), mild (Fazekas grade 1), moderate (Fazekas grade 2), and severe (Fazekas grade 3) CSVD was present in 33 (17.4%), 84 (44.2%), 35 (18.4%), and 38 (20.0%) patients, respectively. Patients with severe CSVD (Fazekas grade 3) were found to be older, had a higher presenting National Institute of Health Stroke Scale (NIHSS), and had greater proportions of preexisting atrial fibrillation and dementia compared to patients with no CSVD (Fazekas grade 0). Using a multivariate ordinal logistic regression model to adjust for age, presenting NIHSS, thrombus location, LKW to groin puncture time, use of tissue plasminogen activator, ischemic infarct volume, development of a symptomatic intracerebral hemorrhage, and treatment with hemicraniectomy, patients with Fazekas grade 3 were significantly more likely to have poor 90-day functional outcomes compared to patients with Fazekas grade 0 (odds ratio 10.25, 95% confidence interval [3.3-31.84]).

Conclusions

Based on our analytical cohort of AIS LVO patients treated with EVT, we found that patients with severe CSVD burden had worse functional outcomes at 90 days and increased mortality. These results provide evidence that the burden of CSVD may be considered an independent risk factor of poor clinical outcome and a predictor of mortality in patients with AIS presenting with LVO, despite successful radiographic recanalization with EVT.