The Pathophysiology of Watershed Infarction: A Three-Dimensional Time-of-Flight Magnetic Resonance Angiography Study

Etiopathology, Clinical and Imaging Characteristics of Border Zone Strokes

Introduction

A border zone infarct (BI) is defined as an infarction that is localized to watersheds or border zones in the brain. BI is further classified into cortical border zone infarct (CBZ) and internal border zone infarct (IBZ). This study was conducted to explore the clinical and radiological characteristics of BI.

Materials and Method

The study was conducted on eligible 400 acute ischemic stroke patients out of which 52 BI patients (diagnosed by the radiologist on DWI MRI images), patients >18 yrs of age were selected and divided into two groups of IBZ and CBZ infarct patients. The degree of intracranial and extracranial stenosis and characteristics on clinical presentation were assessed. The data were collected and analyzed using SPSS version 20.0 software at significance level p-value <0.05.

Results

25% and 75% of CBZ and IBZ patients, respectively, had history of presyncope or syncope before stroke. On vascular evaluation, 3.9% and 51.9% were in MCA and ICA stenosis group, respectively. Evidence of cardio embolism was found in 17.3% of patients. 53.3% of CBZ and 53.8% of IBZ patients were in ICA stenosis group, and 6.7% of CBZ and 7.7% of IBZ patients were in MCA stenosis group, with a statistically insignificant relation (p-value >0.05).

Conclusion

Association of BI with events causing hypotension or hypovolemia is well-established in our study, association of BI with large vessel atherosclerosis is common, and its contribution to CBZ and IBZ seems to be equal.

Diagnosis and treatment of Watershed strokes: a narrative review

Watershed strokes have been described previously as ischemic strokes located in vulnerable border zones between brain tissue supplied by the anterior, posterior, and middle cerebral arteries in the distal junction between two non-anastomotic arterial territories. Ischemic strokes in border zones are well-recognized entities and well-described in terms of imaging features, but the pathophysiological mechanism of brain injury production is not fully defined. Border zone ischemia is caused by cerebral hypoperfusion through decreased cerebral blood flow and arterial embolism in unstable atheroma plaque. It is often difficult to say which mechanisms are fully responsible for producing cerebral ischemic lesions. This review aimed to highlight the imaging aspect of watershed strokes and to correlate the clinical characteristics of this type of stroke with the diagnostic algorithm for optimal therapeutic management. Neurologists should promptly recognize this type of stroke and investigate its etiology in the shortest possible time.

Predictive factors for clinical outcomes in Filipino patients with watershed infarction: A single center study

Background and purpose

Watershed infarcts denote ischemic lesions involving the distal territories of two major arteries. For years, hypotheses on its pathophysiological mechanisms have been proposed. Yet, the cause is still widely debated. This study aimed to determine the mechanism of watershed strokes and compare their clinical outcomes to acute ischemic stroke from other causes and predict the factors affecting clinical outcomes in patients with watershed infarcts.

Methods

This single-center, comparative, six-years retrospective cohort study included patients with a diagnosis of Acute Ischemic Stroke. Patients were classified under watershed group or acute ischemic stroke based on their neuroimaging findings. Stroke mechanisms were determined between groups as well as the factors associated with clinical outcomes in watershed strokes.

Results

Among the 424 patients included in the study, large artery atherosclerosis was seen in greater frequency in patients with watershed infarcts regardless of the type (EWIs: n = 68, 73% vs IWIs: n = 89, 75%). No differences observed in the clinical outcomes between groups. Multiple variable analysis showed that age, female sex, high NIHSS score and presence of underlying malignancy were associated with clinical outcomes.

Conclusion

Clinical outcomes between watershed infarcts and acute ischemic strokes were similar. Hemodynamic compromise in the setting of severe stenosis is the underlying mechanism for both types of watershed strokes thus, the goal of treatment is to maintain adequate perfusion. High baseline NIHSS score, increased age, female gender and underlying malignancy were all poor predictors of clinical outcomes in patients with watershed strokes.

A score to predict the stroke recurrence of patients with embolic stroke of undetermined source

AIM

We aimed to develop a score and validate it in a prospective cohort to identify the patients with ESUS at high risk for stroke recurrence.

METHODS

We assessed the stroke recurrence in ESUS patients of the Third China National Stroke Registry. We performed multivariable logistic regression analysis to identify predictors of stroke recurrence in the derivation cohort. Based on the coefficient of each covariate of the fitted multivariable model, we generated an integer-based point scoring system. We validated the score in the validation cohort assessing its discrimination and calibration.

RESULTS

2415 patients were included: 1611 in the derivation and 804 in the validation sample. We developed a scoring system (0-15 points) by assigning 2 points for hypertension, 3 points for diabetes mellitus, 4 points for multiple stage infarction, 2 points for watershed involved infarction, 1 points for left atrial diameter index (per increasing 2.5 mm/m2) and 3 points for without statin at discharge. The rate of stroke recurrence was 5.9% per year (95% CI 4.2-7.6%) in patients with low risk(a score of 0-5), 9.4% (7.3-11.5%) in patients with intermediate risk (6-10), and 26.8% (16.5-37.1%) in patients with high risk (11-15). The AUC (area under curve of receiver operator characteristic curve) of the score in the derivation cohort and validation cohort was, respectively, 0.60 (0.55-0.65) and 0.63 (0.56-0.70). The score was well calibrated both in the derivation cohort (p = 0.36) and validation cohort (p = 0.26) with the Hosmer-Lemeshow test.

CONCLUSION

The developed score can improve risk stratification after ESUS in secondary care settings.

Left hemispheric cortical watershed infarcts triggered by carotid sinus self-massage

A 69-year-old man was presented to our emergency department with acute onset of hemianopsia, aphasia and dizziness. He reported that while he was sitting in front of his computer at home, he had performed a bilateral self-massage of his carotid arteries when suddenly the symptoms occurred. A neurological examination revealed a hemianopsia with a visual field loss on the right side. In addition, a mild aphasic syndrome with agraphia and a word-finding disorder (National Institutes of Health Stroke Scale (NIHSS): 3 points) was diagnosed. The initial brain CT scan with CT angiography showed neither an intracerebral haemorrhage nor a cerebral infarction. Also, no occlusion or any signs of artery dissection or a flow relevant stenosis of the brain supplying arteries were found. After excluding other contraindications, an intravenous thrombolysis with weight-adapted alteplase was performed. The symptoms of the patient significantly improved in the short-term follow-up. Three days after admission no neurological deficits remained. The MRI of the brain revealed multifocal, small, left hemispherical strokes in the middle cerebral artery territory. In general, watershed infarcts after carotid sinus self-massage follow a rare ischaemic stroke mechanism. This case emphasises the importance of a detailed anamnestic evaluation to determine the aetiological classification of ischaemic stroke as well as educating patients' (poststroke) behaviour.

A narrative review of the pathophysiology of ischemic stroke in carotid plaques: a distinction versus a compromise between hemodynamic and embolic mechanism

Atherosclerotic carotid artery stenosis causes about 10–20% of all ischemic strokes through two main mechanisms: hemodynamic impairment in case of significant stenosis and thromboembolism from an atherosclerotic plaque regardless of the degree of stenosis. The latter is the most frequent mechanism and appear to result from embolization from a vulnerable atherosclerotic plaque or acute occlusion of the carotid artery and propagation of thrombus distally. Downstream infarcts may occur in a territory of major cerebral artery or at the most distal areas between two territories of major cerebral arteries, the so-called watershed (WS), or border zone area. Although WS infarcts, especially deep WS infarct, were historically thought to be due to hemodynamic compromise, the role of microembolism has also been documented, both mechanisms may act synergistically to promote WS infarcts. Routine and more advanced imaging techniques may provide information on the underlying mechanism involved in ipsilateral ischemic stroke. A better understanding of ischemic stroke pathogenesis in carotid stenosis may limit the use of routine non-selective shunt, whose benefit-risk balance is debated, to patients with hemodynamic impairment.

After reviewing existing evidence underpinning the contribution of the two mechanisms in downstream ischemic stroke and the various imaging techniques available to investigate them, we will focus on the pathogenesis of WS infarcts that remains debated.

Chronic Lymphocytic Leukemia Presenting as a Subcortical Watershed Infarct

Internal watershed infarcts (WI) involve white matter between deep and superficial arterial systems of middle cerebral artery. These infarcts are considered to be either from low blood flow or microembolism. Anemia is an extremely rare cause of watershed infarcts. Very few cases of hemolytic anemia causing watershed cerebral infarcts have been reported. Chronic lymphocytic leukemia (CLL) is frequently complicated with secondary autoimmune cytopenia such as autoimmune hemolytic anemia (AIHA), immune thrombocytopenia (ITP), and pure red cell aplasia. AIHA is present in about 7–10% of patients with CLL. AIHA from CLL presenting as WI is an extremely rare phenomenon with no previously published case reports to the best of our knowledge.

Cerebral border zone infarction: an etiological study

Background

Border zone infarcts (BZI) are ischemic lesions at the junction between two main arterial territories which may be either cortical or internal BZI.

Methods

This study was conducted on 76 cerebral BZI patients and 20 healthy control subjects. Patients were divided to group I included 26 internal BZI, group II included 19 cortical BZI and group III included 21 mixed internal/cortical BZI patients. Included subjects were submitted to neurological examination, laboratory investigations, ECG, echocardiogram, brain CT and/or MRI and extra and intracranial blood vessels imaging by duplex and CT angiography.

Results

Hypertension was significantly higher among groups I and III compared to group II while atrial fibrillation (AF) was significantly higher in groups II and III than group I (p < 0.05). Sonographic duplex assessment of extra and intracranial blood vessels revealed significant increase in mean flow velocities of CCA, ICC and MCA on both side in groups I and III compared to group II (p < 0.05). CT angiography revealed non-significant differences between BZI patients and control as well as in between the three BZI patient's groups regarding the existence of vertebral artery hypoplasia and/or circle of Willis anomalies.

Conclusions

Vascular stenosis is the main etiological factor in internal BZI while AF is the predominant etiological factor of cortical BZI. Congenital vascular anomalies play roles in the localization of BZI but cannot predispose to it except when comorbid with hemodynamic disturbances.