ASL and susceptibility-weighted imaging contribution to the management of acute ischaemic stroke

Biochemical, biomechanical and imaging biomarkers of ischemic stroke: Time for integrative thinking

Stroke is one of the leading causes of adult disability affecting millions of people worldwide. Post-stroke cognitive and motor impairments diminish quality of life and functional independence. There is an increased risk of having a second stroke and developing secondary conditions with long-term social and economic impacts. With increasing number of stroke incidents, shortage of medical professionals and limited budgets, health services are struggling to provide a care that can break the vicious cycle of stroke. Effective post-stroke recovery hinges on holistic, integrative and personalized care starting from improved diagnosis and treatment in clinics to continuous rehabilitation and support in the community. To improve stroke care pathways, there have been growing efforts in discovering biomarkers that can provide valuable insights into the neural, physiological and biomechanical consequences of stroke and how patients respond to new interventions. In this review paper, we aim to summarize recent biomarker discovery research focusing on three modalities (brain imaging, blood sampling and gait assessments), look at some established and forthcoming biomarkers, and discuss their usefulness and complementarity within the context of comprehensive stroke care. We also emphasize the importance of biomarker guided personalized interventions to enhance stroke treatment and post-stroke recovery.

Changes in iron load in specific brain areas lead to neurodegenerative diseases of the central nervous system

The causes of neurodegenerative diseases remain largely elusive, increasing their personal and societal impacts. To reveal the causal effects of iron load on Parkinson's disease (PD), Alzheimer's disease (AD), amyotrophic lateral sclerosis and multiple sclerosis, we used Mendelian randomisation and brain imaging data from a UK Biobank genome-wide association study of 39,691 brain imaging samples (predominantly of European origin). Using susceptibility-weighted images, which reflect iron load, we analysed genetically significant brain regions. Inverse variance weighting was used as the main estimate, while MR Egger and weighted median were used to detect heterogeneity and pleiotropy. Nine clear associations were obtained. For AD and PD, an increased iron load was causative: the right pallidum for AD and the right caudate, left caudate and right accumbens for PD. However, a reduced iron load was identified in the right and left caudate for multiple sclerosis, the bilateral hippocampus for mixed vascular dementia and the left thalamus and bilateral accumbens for subcortical vascular dementia. Thus, changes in iron load in different brain regions have causal effects on neurodegenerative diseases. Our results are crucial for understanding the pathogenesis and investigating the treatment of these diseases.

No-reflow phenomenon following stroke recanalization therapy: Clinical assessment advances: A narrative review

The no-reflow phenomenon (NRP) after successful vascular recanalization in acute ischemic stroke (AIS) has become a major cause of poor clinical prognosis and ineffective recanalization. However, there is currently no clear definition or unified clinical assessment method for the NRP. Therefore, it is urgent to clarify the clinical evaluation criteria for the NRP and develop new no-reflow evaluation techniques so that remedial treatment can be applied to AIS patients suffering from the NRP. In this brief review, a variety of NRP assessment methods and defining criteria for clinical practice are presented.

Simultaneous depiction of clot and MRA using 1 min phase contrast angiography in acute ischemic patients

[Background and Purpose] Clot location and range predict clinical outcomes for acute ischemic stroke (AIS). We developed a new technique for visualizing occlusion clots, namely, the DEpicting blood clot and MRA using Phase contrast angiography with Image Calculation for Thrombectomy (DEPICT) method. The purpose of this study was to assess the clinical usefulness of DEPICT. [Methods] We used DEPICT in 36 AIS patients to obtain MRA and black blood images with 1-min phase contrast angiography (PCA). We created the black blood images by subtracting the MRA from the T1WI using the source image of PCA. We evaluated the motion artifact, detectability of clot, and precision in location and range compared these to that of susceptibility vessel sign in T2*WI and measured contrast ration (CR) of clot between the cistern and brain tissue. Motion artifact was visually evaluated using a 3-point scale. Detectability and precision of the location and range of occlusion clots were assessed by comparison with findings from digital subtraction angiography (DSA). Gwet's AC₁ and kappa statistics were used to assess inter-observer agreement. [Results] DEPICT showed significant robustness for motion artifact compared with T2*WI (p = 0.0026, Wilcoxon signed-rank test). DEPICT showed 100% detectability for the clot. Further, DEPICT showed higher Gwet's AC₁ and kappa statistic values with DSA than T2*WI. CR demonstrated a positive value. [Conclusions] DEPICT technique based on 1-min PCA offers both MRA and black blood T1W images that can be used to accurately evaluate both location and range of the clot.

FLAIR Vascular Hyperintensity: An Important MRI Marker in Patients with Transient Ischemic Attack

Purpose

We aimed to investigate the prevalence of fluid-attenuated inversion recovery (FLAIR) vascular hyperintensities (FVHs) and the clinical-radiological correlation in transient ischemic attack (TIA) patients.

Materials and Methods

We performed a retrospective analysis of TIA patients who had undergone magnetic resonance imaging (MRI) within 24 h of symptom onset. Two independent neuroradiologists investigated the presence of FVHs, large-artery severe stenosis or occlusion (LASO) in magnetic resonance angiograms, and the nature of factors associated with FVH.

Results

A total of 207 patients were enrolled in this study. FVHs were detected in 42 (20.3%) patients, in whom atrial fibrillation (AF) was confirmed in 25 (59.5%) cases and LASO was confirmed in 30 (71.4%) cases. The corresponding figures were 33 (20.0%) and 10 (6.1%), respectively, for the 165 FVH-negative patients. Logistic regression analysis showed that time from symptom onset to MRI (odds ratio [OR] = 0.82, 95% CI 0.76-0.97, p = 0.042), previous stroke (OR = 2.95, 95% CI 1.58-6.74, p = 0.002), AF (OR = 5.83, 95% CI 2.24-9.46, p < 0.001), and LASO (OR = 4.28, 95% CI 2.96-10.28, p < 0.001) were independently associated with FVH. Overall, the sensitivity and specificity of FVH for predicting LASO were 0.75 and 0.93, respectively, and the positive predictive value, negative predictive value, and accuracy were 0.71, 0.94, and 0.89, respectively. The area under the receiver operating characteristic curve was 0.839. FVH-positive TIA patients with LASO had less AF (14 [46.7%] versus 11 [91.7%], p = 0.019) and longer times from symptom onset to MRI (6.8 ± 2.8 h versus 4.8 ± 1.3 h, p = 0.004) than those without LASO.

Conclusion

The presence of FVH could be an important marker in TIA patients. Many factors, including LASO, AF, and time from symptom onset to MRI, are associated with the detection of FVH.

Multiple hypointense veins on susceptibility weighted imaging as a promising biomarker of impaired cerebral hemodynamics in chronic steno-occlusive disease: a multiparametric MRI study

PURPOSE

Patients with steno-occlusive arterial disease may develop cerebral hypoperfusion with possible neurologic sequelae. The aim of the study is to verify the possible role of SWI, as a marker of cerebral hypoperfusion, in the identification of patient subgroups with significant chronic occlusions/stenoses at risk of critical cerebral hypoperfusion.

METHODS

We retrospectively identified 37 asymptomatic patients with chronic intra-extracranial occlusion/stenosis of the anterior circulation from a prospective brain MRI register between 2016 and 2020. All patients underwent 3 Tesla MRI. The imaging protocol included the following: SWI, 3D-FLAIR, DWI sequences, and 3D-TOF MRA. SWI findings were graded for the presence of asymmetric intracranial cortical veins (grades 1 to 4). The presence of collateralization was assessed with concomitant multiphase-CTA. FLAIR was evaluated for the presence of distal hyperintense vessels (DHVs), a described marker of flow impairment, and possible collateralization. Cerebral blood flow and arterial transit artifacts (ATAs) were evaluated at pCASL in 29 patients.

RESULTS

SWI showed multiple hypointense vessels (MHVs) in 22/37 patients in the cerebral hemisphere ipsilateral to vessel occlusion/stenosis. SWI-MHV grade 1 was found in 15 patients (40.5%), grade 2 in 18 patients (48.7%), and grade 3 in 3 patients (8.1%); in one patient, SWI was graded as 4 (2.7%). A significant relationship was found among MHV, DHV, collaterals, ATAs, and hypoperfused areas on pCASL and with patients' previous neurological symptoms.

CONCLUSION

SWI-MVH correlates with chronic cerebral flow impairment and is related to hypoperfusion and collateralization. It may help identify a subgroup of patients benefitting from revascularization.

Penumbra quantification from MR SWI-DWI mismatch and its comparison with MR ASL PWI-DWI mismatch in patients with acute ischemic stroke

In acute-ischemic-stroke patients, penumbra assessment plays a significant role in treatment outcome. MR perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) mismatch ratio can provide penumbra assessment. Recently reported studies have shown the potential of susceptibility-weighted imaging (SWI) in the qualitative assessment of penumbra. We hypothesize that quantitative penumbra assessment using SWI-DWI can provide an alternative to the PWI-DWI approach and this can also reduce the overall scan-time. The purpose of the current study was to develop a framework for accurate quantitative assessment of penumbra using SWI-DWI and its validation with PWI-DWI-based quantification. In the current study, the arterial-spin-labelling (ASL) technique has been used for PWI. This retrospective study included 25 acute-ischemic-stroke patients presenting within 24 hours of the last noted baseline condition of stroke onset. Eleven patients also had follow-up MRI within 48 hours. MRI acquisition comprised DWI, SWI, pseudo-continuous-ASL (pCASL), FLAIR and non-contrast-angiography sequences. A framework was developed for the enhancement of prominent hypo-intense vein signs followed by automatic segmentation of the SWI penumbra ROI. Apparent-diffusion-coefficient (ADC) maps and cerebral-blood-flow (CBF) maps were computed. The infarct core ROI from the ADC map and the ASL penumbra ROI from CBF maps were segmented semiautomatically. The infarct core volume, SWI penumbra volume (SPV) and pCASL penumbra volume were computed and used to calculate mismatch ratios MRSWIADC and MRCBFADC . The Dice coefficient between the SWI penumbra ROI and ASL penumbra ROI was 0.96 ± 0.07. MRSWIADC correlated well (r = 0.90, p < 0.05) with MRCBFADC , which validates the hypothesis of accurate penumbra assessment using the SWI-DWI mismatch ratio. Moreover, a significant association between high SPV and the presence of vessel occlusion in the MR angiogram was observed. Follow-up data showed salvation of penumbra tissue (location and volumes predicted by proposed framework) by treatments. Additionally, functional-outcome analysis revealed 93.3% of patients with MRSWIADC > 1 benefitted from revascularization therapy. Overall, the proposed automated quantitative assessment of penumbra using the SWI-DWI mismatch ratio performs equivalently to the ASL PWI-DWI mismatch ratio. This approach provides an alternative to the perfusion sequence required for penumbra assessment, which can reduce scan time by 17% for the protocol without a perfusion sequence.

Controversies in Imaging of Patients with Acute Ischemic Stroke: AJR Expert Panel Narrative Review

The development of reperfusion therapies has profoundly impacted stroke care, initially with the advent of IV thrombolytic (IVT) treatment and, more recently, with the development and refinement of endovascular treatment (EVT). Progress in neuroimaging has supported the paradigm shift of stroke care, and advanced neuroimaging now has a fundamental role in triaging patients for both IVT and EVT. As the standard of care for acute ischemic stroke (AIS) evolves, controversies remain in certain clinical scenarios. This article explores the use of multimodality imaging for treatment selection of AIS in the context of recent guidelines, highlighting controversial topics and providing guidance for clinical practice. Results of major randomized trials supporting EVT are reviewed. Advantages and disadvantages of CT, CTA, MRI, and MRA in stroke diagnosis are summarized, with attention to level 1 evidence supporting the role of vascular imaging and perfusion imaging. Patient selection is compared between approaches based on time thresholds and physiologic approaches based on infarct core measurement using imaging. Moreover, various imaging approaches to core measurement are described. As ongoing studies push treatment boundaries, advanced imaging is expected to help identify a widening range of patients who may benefit from therapy.

Early Neurological Deterioration and Hypoperfusion Volume Ratio on Arterial Spin Labeling in Patients with Acute Ischemic Stroke

BACKGROUND

Arterial spin labeling (ASL) is a magnetic resonance imaging (MRI) technique used to quantify cerebral blood perfusion by labeling blood water as it flows throughout the brain. Hypoperfusion volume ratio (HVR) can be calculated using proportional hypoperfusion volume on ASL-based cerebral blood flow (CBF). This study aimed to explore the relation between HVR and early neurological deterioration (END) in AIS patients.

SUBJECTS AND METHODS

Patients with AIS were recruited consecutively, and ASL and regular MRI scans were performed. HVR was calculated from 1.5 and 2.5s post labeling delay (PLD) ASL-CBF maps. END was defined as ≥2 points increment of NIHSS within 72 hours of stroke onset. Univariate and multivariate analysis were used to evaluate the relation between HVR and END. Receiver operating characteristic (ROC) curves were used to determine the ability of HVR in predicting END.

RESULTS

Of the 52 enrolled patients, 18 (34.5%) were determined with END. In patients with END, the median hypoperfusion volume was 20 mL [Inter Quartile Range)IQR, 6-72.5 mL] at 1.5s PLD, and 11.2 mL (IQR, 5.3-26 mL) at 2.5s PLD; Sixteen (88.9%) patients had HVR ≥50%, and 13 (72.2%) patients hypoperfusion volume at 2.5s PLD ASL were greater than diffusion-weighted imaging (DWI) infarct volume. In patients without END, median hypoperfusion volume was 7 mL (IQR, 4-30 mL) at 1.5s PLD, and 4 mL (IQR, 1.5-8.5 mL) at 2.5s; Eleven (32.4%) patients had HVR ≥50%, and 10 (29.4%) patients hypoperfusion volume at 2.5s PLD ASL were greater than DWI infarct volume. The proportion of HVR ≥50% and hypoperfusion volume >DWI infarct volume were more frequent in patients with END than patients without (all P<0.001). After adjusted for age, admission NIHSS, proportion of hypoperfusion volume > DWI infarct and arterial transit artifact (ATA) by logistic regression analysis, HVR ≥50% (OR=13.1, P=0.003) was an independent risk factor for END. ROC analysis demonstrated that the HVR could predict END with an area under the curve of 0.794 (P=0.001).

CONCLUSIONS

HVR obtained from the 1.5 and 2.5s PLD ASL may be a useful predictor of END in AIS. The value of HVR may be a marker for hemodynamic impairments.

BONE PERFUSION AND ADIPOSITY BEYOND THE NECROTIC ZONE IN FEMORAL HEAD OSTEONECROSIS: A QUANTITATIVE MRI STUDY

PURPOSE

To describe bone perfusion and adiposity beyond the necrotic zone with quantitative MRI techniques in osteonecrosis of the femoral head (ONFH).

METHOD

In this cross-sectional multicentre study, we recruited patients suffering from late-stage ONFH or hip osteoarthritis. Hip MRI included quantitative MRI sequences: chemical-shift imaging and dynamic contrast-enhanced MRI. We drew regions of interest inside the necrotic zone (inner necrosis and its border) and outside (femoral head, neck and greater trochanter) in ONFH. In the control group, regions of interest were drawn in the femoral head, femoral neck and the greater trochanter. For each region of interest, we measured fat fraction, and calculated semi-quantitative (area under the curve, initial slope) and pharmacokinetic perfusion parameters (K_trans and K_ep).

RESULTS

Thirty-two male adults (mean age 58 ± 9 years, range 38-74 years) were included. Sixteen patients formed the ONFH group and fifteen the control group; one was excluded. In the normal-appearing non-necrotic part of the femoral head, fat fraction was not significantly different in comparison with controls (p = 1), but _Ktrans was significantly lower than in controls (0.012 ± 0.018 vs. 0.027 ± 0.045; p = 0.05). This perfusion parameter reflects exchanges between blood microvessels and bone marrow.

CONCLUSIONS

Our results question the concept of adipose toxicity on the macroscopic scale, and bring up the concept of regional ischemic penumbra that goes beyond the visible necrotic zone. Further studies are required to test these hypotheses in larger populations and earlier disease states.

Addition of arterial spin-labelled MR perfusion to conventional brain MRI: clinical experience in a retrospective cohort study

OBJECTIVE

The usage of arterial spin labelling (ASL) perfusion has exponentially increased due to improved and faster acquisition time and ease of postprocessing. We aimed to report potential additional findings obtained by adding ASL to routine unenhanced brain MRI for patients being scanned in a hospital setting for various neurological indications.

DESIGN

Retrospective.

SETTING

Large tertiary hospital.

PARTICIPANTS

676 patients.

PRIMARY OUTCOME

Additional findings from ASL sequence compared with conventional MRI.

RESULTS

Our patient cohorts consisted of 676 patients with 257 with acute infarcts and 419 without an infarct. Additional findings from ASL were observed in 13.9% (94/676) of patients. In the non-infarct group, additional findings from ASL were observed in 7.4% (31/419) of patients, whereas in patients with an acute infarct, supplemental information was obtained in 24.5% (63/257) of patients.

CONCLUSION

The addition of an ASL sequence to routine brain MRI in a hospital setting provides additional findings compared with conventional brain MRI in about 7.4% of patients with additional supplementary information in 24.5% of patients with acute infarct.

Brain hemodynamic changes in amnestic mild cognitive impairment measured by pulsed arterial spin labeling

We used pulsed arterial spin labeling (PASL) to investigate differences in cerebral blood flow (CBF) between 26 patients with amnestic mild cognitive impairment (aMCI) and 27 controls with normal cognition (NC). Hypoperfusion was observed in the right temporal pole of the middle temporal gyrus and the right inferior temporal gyrus in the aMCI compared with NC group. Interestingly, hyperperfusion was observed in the left temporal pole of the middle temporal gyrus, left superior temporal gyrus, bilateral precuneus, postcentral gyrus, right inferior parietal lobule, and right angular gyrus in the aMCI group, which likely resulted from a compensatory mechanism to maintain advanced neural activities. We found that mean CBF in the right inferior temporal gyrus, precuneus, and postcentral gyrus was positively correlated with cognitive ability in the aMCI but not NC group. Collectively, our data indicate that PASL is a useful noninvasive technique for monitoring changes in CBF and predicting cognitive decline in aMCI.

A potential new role for ASL perfusion imaging: Diagnosis of metronidazole induced encephalopathy - Two companion cases

Metronidazole induced encephalopathy (MIE) is a rare condition due to prolonged high dose administration of metronidazole. MIE with corresponding increased perfusion on MRI arterial spin labeling (ASL) of the involved regions of the brain appears not to have been reported in the literature to date. We present two such cases, a 59-year-old male with recurrent C difficile colitis with classic MR imaging characteristics of MIE, and a companion case of a 65-year-old female with gangrenous cholecystitis also presumed to have MIE. Despite aggressive medical management, both patients expired. Our cases demonstrate a correlation with ASL hyperperfusion to affected brain regions thought to be due to edema or inflammation. Perfusion imaging may play a role in diagnosis of MIE.

Evaluation of cerebral blood flow in older patients with status epilepticus using arterial spin labeling

Introduction

Although older patients with status epilepticus (SE) have a high mortality rate and poor outcome, it is difficult to perform emergent electroencephalography (EEG) to diagnose SE in community hospitals. Arterial spin labeling (ASL) is a non-invasive magnetic resonance imaging (MRI) technique that can rapidly assess cerebral blood flow (CBF). Further, ASL can detect increased CBF in the ictal period. Therefore, ASL may be a useful tool for diagnosing SE in older patients. However, its effectiveness in this population is unknown.

Methods

We retrospectively investigated differences in CBF abnormalities between older patients (≥70 years) and non-older patients (<70 years) with SE using ASL. Participants were diagnosed with convulsive status epilepticus (CSE) or non-convulsive status epilepticus (NCSE) based on symptoms, brain MRI, and EEG.

Results

ASL detected CBF abnormalities in 40% of older patients with CSE or NCSE. Rates of CBF abnormalities in older patients were not significantly different compared with that in non-older patients.

Conclusions

ASL did not detect a higher rate of CBF abnormalities in older patients, but may help physicians diagnose SE in older patients in a community hospital setting if emergent EEG cannot be immediately performed.

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ASL is a non-invasive MRI technique.

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ASL can assess CBF in a short time.

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ASL showed abnormality in CBF in 40% of older patients with SE.

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ASL detected CBF abnormality more often in older patients with NCSE than with CSE.

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ASL may be an aid to diagnosing SE in older patients.

Magnetic resonance imaging of arterial stroke mimics: a pictorial review

Acute ischaemic stroke represents the most common cause of new sudden neurological deficit, but other diseases mimicking stroke happen in about one-third of the cases. Magnetic resonance imaging (MRI) is the best technique to identify those 'stroke mimics'. In this article, we propose a diagnostic approach of those stroke mimics on MRI according to an algorithm based on diffusion-weighted imaging (DWI), which can be abnormal or normal, followed by the results of other common additional MRI sequences, such as T2 with gradient recalled echo weighted imaging (T2-GRE) and fluid-attenuated inversion recovery (FLAIR). Analysis of the signal intensity of the parenchyma, the intracranial arteries and, overall, of the veins, is crucial on T2-GRE, while anatomic distribution of the parenchymal lesions is essential on FLAIR. Among stroke mimics with abnormal DWI, T2-GRE demonstrates obvious abnormalities in case of intracerebral haemorrhage or cerebral amyloid angiopathy, but this sequence also allows to propose alternative diagnoses when DWI is negative, such as in migraine aura or headaches with associated neurological deficits and lymphocytosis (HaNDL), in which cortical venous prominence is observed at the acute phase on T2-GRE. FLAIR is also of major interest when DWI is positive by better showing evocative distribution of cerebral lesions in case of seizure (involving the hippocampus, pulvinar and cortex), hypoglycaemia (bilateral lesions in the posterior limb of the internal capsules, corona radiata, striata or splenium of the corpus callosum) or in posterior reversible encephalopathy syndrome (PRES). Other real stroke mimics such as mitochondrial myopathy, encephalopathy, lactic acidosis, stroke-like episodes (MELAS), Susac's syndrome, brain tumour, demyelinating diseases and herpes simplex encephalitis are also included in our detailed and practical algorithm. KEY POINTS: • About 30% of sudden neurological deficits are due to non-ischaemic causes. • MRI is the best technique to identify stroke mimics. • Our practical illustrated algorithm based on DWI helps to recognise stroke mimics.

Arterial Spin Labeling Imaging of a Giant Aneurysm Leading to Subarachnoid Hemorrhage following Cerebral Infarction

An 83-year-old Japanese man was admitted with dysarthria and right hemiparesis. He had had a large intracranial aneurysm on the left internal carotid artery 5 years before admission and had been followed up under conservative treatment. On admission, diffusion-weighted imaging revealed a hyperintense signal on the left anterior choroidal artery territory. Time-of-flight magnetic resonance angiography demonstrated poor visibility of the middle and anterior cerebral arteries and the inferior giant aneurysm, suggesting distal emboli from aneurysm thrombosis or a reduction of blood outflow due to aneurysm thrombosis. Arterial spin labeling (ASL) signal increased in the giant aneurysm, suggesting blood stagnation within the aneurysmal sac, and decreased in the left hemisphere. We diagnosed cerebral infarction due to aneurysm thrombosis, and started antithrombotic therapy. On day 2, he suddenly died of subarachnoid hemorrhage due to rupturing of the giant aneurysm. When thrombosis occurs in a giant aneurysm, increasing ASL signal within the aneurysm and decreasing ASL signal with poor visibility on magnetic resonance angiography in the same arterial territory may indicate the danger of impending rupture of the giant aneurysm.

Beyond the embolus: "do not miss" diffusion abnormalities of ischaemic and non-ischaemic neurological disease

Abstract

Given the rapid evolution and technological advances in the diagnosis and treatment of acute ischaemic stroke (AIS), including the proliferation of comprehensive stroke centres and increasing emphasis on interventional stroke therapies, the need for prompt recognition of stroke due to acute large vessel occlusion has received significant attention in the recent literature. Diffusion-weighted imaging (DWI) is the gold standard for the diagnosis of acute ischaemic stroke, as images appear positive within minutes of ischaemic injury, and a high signal-to-noise ratio enables even punctate infarcts to be readily detected. DWI lesions resulting from a single arterial embolic occlusion or steno-occlusive lesion classically lateralise and conform to a specific arterial territory. When there is a central embolic source (e.g. left atrial thrombus), embolic infarcts are often found in multiple vascular territories. However, ischaemic disease arising from aetiologies other than arterial occlusion will often not conform to an arterial territory. Furthermore, there are several important entities unrelated to ischaemic disease that can present with abnormal DWI and which should not be confused with infarct. This pictorial review explores the scope and typical DWI findings of select neurologic conditions beyond acute arterial occlusion, which should not be missed or misinterpreted.

Teaching points

• DWI abnormalities due to acute arterial occlusion must be promptly identified.

• DWI abnormalities not due to arterial occlusion will often not conform to an arterial territory.

• Several important non-ischaemic entities can present on DWI and should not be confused with infarct.