DWI-pc-ASPECT score in basilar artery occlusion: is 6 points or less always indicative of a bad outcome?

Abstract

Background and purpose

The prognosis of patients with acute basilar arterial occlusion after endovascular reperfusion therapy with diffusion-weighted imaging – posterior circulation–Alberta Stroke Program Early Computed Tomography Score (DWI-pc-ASPECTS) of 6 or less remains unclear. We aimed to assess the characteristics and prognosis of endovascular reperfusion therapy in patients with acute basilar arterial occlusion and DWI-pc-ASPECTS of 6 or less.

Methods

We analysed data collected from 1 January 2012 to 31 January 2018 in a prospective neuro-interventional registry of consecutive patients treated with endovascular reperfusion therapy. Clinical and imaging data on patients with DWI-pc-ASPECTS of 6 or less who underwent endovascular reperfusion therapy for acute basilar arterial occlusion were collected for this study. A good clinical outcome was defined as a modified Rankin scale of 2 or less at 90 days.

Results

Forty-five acute basilar arterial occlusion patients with DWI-pc-ASPECTS of 6 or less were included. Among them, 11 (24.4%) patients had a good clinical outcome at 90 days. Patients with a good clinical outcome had less severe neurological symptoms at presentation (National Institutes of Health Stroke Scale (NIHSS) 19.0 (12.0–25.0) vs. 8.0 (6.0–11.5); P = 0.003) and were younger (72.5 years (57.0–80.0 years) vs. 63.0 years (55.5–69.0 years), P = 0.096) than those with a poor clinical outcome. The symptomatic intracranial haemorrhage rate was significantly higher in the poor clinical outcome group (13 (38.2%)) than in the good clinical outcome group (0 (0.0%)) (P = 0.045). In particular, in patients aged over 70 years, a favourable outcome was low (18 (52.9%) vs. 1 (9.1%); P = 0.027) even after successful recanalisation. In a multivariate model, a low initial NIHSS score (odds ratio 1.21; 95% confidence interval 1.07–1.44; P = 0.0093) and age over 70 years (odds ratio 15.27; 95% confidence interval 1.85–379.79; P = 0.0321) were independent predictors of poor clinical outcome.

Conclusions

Even with DWI-pc-ASPECTS of 6 or less, good clinical outcome can be achieved after endovascular reperfusion therapy. Relatively mild initial symptoms and younger age can predict a better outcome in acute basilar arterial occlusion patients with DWI-pc-ASPECTS of 6 or less.

Introduction

Recent trials of endovascular reperfusion therapy (ERT) have proved it to be an effective treatment for patients with acute ischaemic stroke (AIS) with a large-vessel occlusion involving the anterior cerebral circulation.^1–4 However, little is known about the effectiveness of ERT for AIS involving basilar artery occlusion (BAO). BAO is associated with high mortality (85–95%) if recanalisation does not occur.^5,6 Thus, successful recanalisation is the best predictor of a good outcome among patients with BAO.^7,8 However, the improvement of interventionist's techniques and rapid advancements in thrombectomy devices have dramatically increased the rate of successful recanalisation.⁶

Nevertheless, successful recanalisation alone cannot be expected to improve the clinical outcome without appropriate patient selection.⁹ Although the optimal patient selection for ERT in BAO is controversial, there are few proved and readily available clinical indicators. Among the factors associated with predicting the clinical outcomes for BAO, diffusion-weighted an imaging-based posterior circulation-Acute Stroke Prognosis Early CT Score (DWI-pc-ASPECTS) had suggested those commonly relevant.^10,11 Several studies reported that compared with patients with DWI-pc-ASPECTS greater than 6, those with DWI-pc-ASPECTS of 6 or less benefit less from ERT for BAO, with a lower rate of good clinical outcome (GCO) despite successful recanalisation.^12–15

However, in real-world practice, even some patients with DWI-pc-ASPECTS of 6 or less with acute BAO can achieve a good prognosis after successful ERT. It is critical to evaluate if the treatment would benefit the patient and to understand patient characteristics within the population with DWI-pc-ASPECTS of less than 6; these aspects may critically influence the treatment decision-making for ERT. In addition, several studies have recently reported that the prognosis of mechanical thrombectomy is superior to that of medical treatment alone in patients with a low DWI-pc-ASPECTS score in the anterior circulation.^16–18 However, the characteristics and prognosis of acute BAO in patients with DWI-pc-ASPECTS of less than 6 have not been studied. Thus, we aimed to investigate the clinical characteristics and predictive prognostic factors for better clinical outcomes in acute BAO patients with DWI-pc-ASPECTS of less than 6 who underwent ERT.

Methods

Study population

Consecutive AIS patients with BAO who were treated with first-line endovascular therapy between 1 January 2012 and 31 January 2018 were evaluated. They were retrospectively selected from a prospective neuro-interventional database and stroke registry. Clinical and radiological data were reviewed for these patients. We collected information pertaining to patient demographics, vascular risk factors, imaging findings, time from onset to femoral puncture, door to puncture, onset to recanalisation, procedure time, baseline National Institutes of Health Stroke Scale (NIHSS), modified Rankin scale (mRS) at 3 months, and the length of hospital stay. Patients were classified according to the Trial of ORG 10172 in Acute Stroke Treatment (TOAST) criteria. In addition, cerebral angiograms were reviewed for the location of occlusion and the reperfusion status after ERT. The inclusion criteria for thrombectomy for acute BAO were as follows: (a) Patients with complete occlusion of the basilar artery who had pretreatment DWI-pc-ASPECTS of 6 or less; (b) Patients for whom performing ERT for acute BAO was judged to be beneficial by discussion between neurologist and neurointerventionist about onset to door time, symptoms, patient information, and initial neuro-image. We excluded patients with: (a) onset to puncture time greater than 24 hours; (b) severe stenosis without complete occlusion; (c) other causes of stroke, such as arterial dissection, Moyamoya disease, and vasculitis; (d) pre-morbid mRS greater than 2; (e) combined ischaemic stroke of anterior circulation; and (f) any symptomatic intracerebral haemorrhage detected on the initial computed tomography (CT) or magnetic resonance imaging (MRI) (Figure 1).

Figure 1.

Flowchart of the patient selection process. DWI-pc-ASPECT: diffusion-weighted imaging – posterior circulation–Alberta Stroke Program Early Computed Tomography Score; DSA: digital subtraction angiography.

The history of all ischaemic events was obtained, and the physical and neurological status of each patient was evaluated by stroke neurologists from our institution. This study was approved by the institutional review board, and the need for written informed consent was waived because of the retrospective nature of the study. According to our management protocol for acute stroke, all patients underwent a non-enhanced CT scan and multimodal MRI before undergoing endovascular thrombectomy procedures.

Intervention procedures

All procedures were performed by the percutaneous transfemoral route under local anaesthesia. All endovascular treatments were performed by two neuro-interventionalists in our institution who treat all patients with large-vessel occlusion. After placement of a sheath introducer, unfractionated heparin was intravenously administered to maintain the activated clotting time at more than two times the normal. If stenting was predicted before the procedure, loading doses of clopidogrel (300 mg) with aspirin (300–500 mg) were prescribed.¹⁹

Typically, a 6-French guide catheter (Envoy or Envoy DA; Codman Neurovascular, Miami Lakes, FL, USA) or a 5–6 French long sheath (Shuttle-SL; Cook Medical, Bloomington, IN, USA) was employed for the procedure. A microcatheter with an internal diameter of 0.021 inches or 0.027 inches was navigated distally to the point of occlusion over a 0.014-inch steerable microwire. A microcatheter angiographic run was performed to define the vascular bed distal to the thrombus. Available thrombectomy methods, such as a stent retriever and suction thrombectomy, were used to achieve reperfusion in the direct thrombectomy group. Endovascular therapy was performed without sedation or under conscious sedation. The thrombectomy procedure was chosen at the discretion of a neurointerventionist; it involved the use of a stent retriever or a direct aspiration first path technique in the first instance. When stent retriever or aspiration thrombectomy was unsuccessful, additional mechanical approaches were alternatively performed. Intracranial angioplasty with or without stenting was performed when severe (>70%) underlying basilar artery atherosclerotic stenosis with the flow-limiting pattern was observed after ERT according to the NASCET criteria.¹³ The time to endovascular therapy was defined as the interval between the estimated time of the BAO and the start of endovascular therapy.

Imaging protocol

All patients underwent conventional MRI, including time-of-flight magnetic resonance angiography (MRA) of the circle of Willis and contrast-enhanced MRA or computed tomography angiography (CTA) of the circle of Willis and carotid vessels. A final diagnosis of complete occlusion of the intracranial or extracranial vessels was based on conventional angiography with sufficient contrast medium and a prolonged run imaging follow-up within 72 hours after endovascular treatment comprised three-dimensional time-of-flight or CTA and MRI, including T2*, fluid-attenuated inversion recovery, and diffusion-weighted imaging (DWI). The basilar artery was divided into three segments according to Archer's method.²⁰ The proximal third of the basilar artery from the vertebral artery junction to the anterior inferior cerebellar artery is the proximal segment; the middle third of the basilar artery from the origin of the anterior inferior cerebellar artery to the origin of the superior cerebellar artery is the middle segment, and the area above the origin of the superior cerebellar artery is the distal segment. The location of occlusion was defined as the site of the most inferior extension of the filling defect of the basilar artery.

Two neuroradiologists independently assessed the DWI-pc-ASPECTS on the DWI, according to Tei's method.¹⁵ Discrepancies were resolved by consensus.

Outcome evaluations

For this study, the patients with DWI-pc-ASPECTS of 6 or less were dichotomised into two age groups based on median values. Neurological status after revascularisation was re-evaluated by stroke neurologists, and the patients were monitored in the neuro-intensive care unit. Patients with a greater than 2-point increase on the NIHSS score were evaluated by MRI except for the patients who were contraindicated or had poor cooperation. Clinical outcome was assessed by mRS at 90 days and dichotomised as GCO (mRS ≤ 2) and poor clinical outcome (PCO, mRS > 2). Other clinical and imaging outcomes evaluated mortality at 3 months, length of hospital stay, the occurrence of any cerebral haemorrhage (defined as any haemorrhagic transformation or subarachnoid haemorrhage based on the follow-up images), symptomatic intracranial haemorrhage (defined as any parenchymal haematoma, subarachnoid haemorrhage, or intraventricular haemorrhage associated with a worsening of the NIHSS score by ≥4 within 24 hours from ERT),²¹ postprocedural infarct extension, and newly detected infarction. The degree of recanalisation was classified based on modified thrombolysis in cerebral infarction (mTICI) perfusion categories.²² The rate of successful recanalisation was defined as mTICI grade 2b or 3. The recanalisation time was defined as the time interval from the puncture to the first reperfusion with more than mTICI grade 2a or greater.

Statistical analysis

Differences in baseline categorical variables were compared using the Pearson chi-square test or Fisher's exact test, and differences in continuous variables were compared using Student's t-test or the Mann–Whitney U-test, as appropriate. Multivariate logistic regression analysis was performed to identify the independent variables contributing to PCOs. Variables with a P value less than 0.2 in univariate analysis were included as candidate variables in the multivariate analysis and were removed by backward stepwise selection. Additional analysis using forward selection confirmed the final model. A two-tailed P value less than 0.05 was considered statistically significant. All statistical analyses were performed using SPSS version 21.0 (IBM, Armonk, NY, USA).

Results

Between 1 January 2012 and 31 January 2018 a total of 82 AIS patients with BAO were consecutively treated by ERT in the single comprehensive stroke centre. During the study period, 69 patients with acute BAO had dichotomised for 6 or less and over 6, according to DWI-pc-ASPECTS (Supplementary data file 1). Finally, 45 patients met the inclusion criteria for the current study (Figure 1). The median patient age was 67 years (interquartile range (IQR) 56–76 years), and 32 (70.1%) were men. The median interval between symptom onset to femoral puncture was 547.0 minutes (IQR 250–892.0 minutes). The median initial NIHSS was 13 (IQR 9.0–22.0 days) (Table 1).

Table 1.

Baseline characteristics of acute basilar artery occlusion patients with DWI-pc-ASPECTS of 6 or less.

	All	Poor clinical outcome	Good clinical outcome	P value
	(N = 45)	(N = 34)	(N = 11)
Age, years	69.0 (57.0–78.0)	72.5 (57.0–80.0)	63.0 (55.5–69.0)	0.096
Sex, male	32 (70.1%)	24 (70.6%)	8 (72.7%)	>0.999
Comorbidities
Hypertension	28 (62.2%)	19 (55.9%)	9 (81.8%)	0.236
Diabetes mellitus	12 (26.7%)	6 (17.6%)	6 (54.5%)	0.044
Smoking	12 (26.7%)	6 (17.6%)	6 (54.5%)	0.044
Alcohol	3 (6.7%)	2 (5.9%)	1 (9.1%)	>0.999
Hypercholesterolemia	11 (24.4%)	7 (20.6%)	4 (36.4%)	0.513
Atrial fibrillation	15 (33.3%)	11 (32.4%)	4 (36.4%)	0.833
History of stroke	10 (22.2%)	9 (26.5%)	1 (9.1%)	0.431
Cancer	6 (13.3%)	5 (14.7%)	1 (9.1%)	>0.999
Acute management
Tissue plasminogen activator	9 (20.0%)	6 (17.6%)	3 (27.3%)	0.795
Angioplasty	22 (48.9%)	15 (44.1%)	7 (63.6%)	0.436
Stent	16 (35.6%)	9 (26.5%)	7 (63.6%)	0.061
Location of occlusion				0.190
Proximal	15 (33.3%)	10 (29.4%)	5 (45.5%)
Mid	8 (17.8%)	8 (23.5%)	0 (0.0%)
Distal	22 (48.9%)	16 (47.1%)	6 (54.5%)
TOAST classification				0.368
Large-artery atherosclerosis	24 (53.3%)	17 (50.0%)	7 (63.6%)
Cardioembolism	13 (28.9%)	9 (26.5%)	4 (36.4%)
Other determined aetiology	2 (4.4%)	2 (5.9%)	0 (0.0%)
Undetermined aetiology	6 (13.3%)	6 (17.6%)	0 (0.0%)
Onset to puncture (min)	555.0 (223.0–954.0)	551.0 (255.0–892.0)	673.0 (190.0–1164.0)	0.663
Onset to recanalisation (min)	668.0 (346.0–994.0)	648.0 (390.0–944.0)	737.0 (242.0–1208.0)	0.606
Median duration of procedure (min)	68.0 (47.0–104.0)	77.0 (47.0–108.0)	52.0 (42.0–63.5)	0.119
Mean initial NIHSS	16.5 ± 8.4	18.7 ± 7.8	9.8 ± 7.0	0.002
Pre-stroke mRS				0.326
0	39 (86.7%)	28 (82.4%)	11 (100.0%)
−1	2 (4.4%)	2 (5.9%)	0 (0.0%)
−2	4 (8.9%)	4 (11.8%)	0 (0.0%)

TOAST: Trial of ORG 10172 in Acute Stroke Treatment; FAT: first abnormal time; NIHSS: National Institutes of Health Stroke Scale; mRS: modified Rankin scale.

PCO and GCO patients with DWI-pc-ASPECTS of 6 or less

When dichotomising our cohort, 34 of 45 (75.6%) were PCOs, and 11 of 45 (24.4%) were GCOs. Baseline characteristics of the two groups are shown in Table 1. There was no significant difference in baseline characteristics between patients with PCO and GCO. There was a significant difference in the initial mean NIHSS scores between the two groups (18.7 ± 7.8 vs. 9.8 ± 7.0, P = 0.002). In the PCO group, the patients presented with proximal basilar occlusion (29.4%), mid-basilar occlusions (23.5%) and distal basilar occlusion (47.1%), whereas the respective values for the GCO group were 45.5%, 0% and 54.5%, respectively. No differences in the proportion of patients receiving intravenous tissue-type plasminogen activator, angioplasty and stent placement were noted between the groups.

Procedural and angiographic outcomes

No differences between the PCO or GCO groups were observed in terms of the median time from onset to femoral puncture (551.0 minutes (IQR 255.0–892.0 minutes) vs. 673.0 minutes (IQR 190.0–1164.0 minutes); P = 0.663)), onset to first revascularisation (648.0 minutes (IQR 390.0–944.0 minutes) vs. 737.0 minutes (IQR, 242.0–1208.0 minutes)); P = 0.606), or the median duration of procedure (77.0 minutes (IQR 47.0–108.0 minutes) vs. 52.0 minutes (IQR 42.0–63.5 minutes); P = 0.119)), respectively (Table 1). Regarding revascularisation, there was no difference in successful recanalisation (30 (88.2%) vs. 11 (100.0%); P = 0.56) between the PCO and GCO groups. The balloon angioplasty and the use of rescue stent placement were comparable in the groups. Infarct volume on follow-up imaging was comparable in both groups (Table 2).

Table 2.

Clinical and imaging outcomes in groups of patients with DWI-pc-ASPECT of 6 or less.

	All	Poor clinical outcome	Good clinical outcome	P value
	(N = 45)	(N = 34)	(N = 11)
Age > 70 years	19 (42.2%)	18 (52.9%)	1 (9.1%)	0.027
NIHSS at discharge	13.5 (3.0–29.0)	22.0 (12.0–30.0)	3.0 (1.5–3.0)	<0.001
Recovery after ERT (ΔNIHSS)	0.0 (−6.0–6.0)	−1.0 (−8.0–2.0)	5.0 (3.0–10.5)	0.004
Mortality at 90 days	10 (22.2%)	10 (29.4%)	0 (0.0%)	0.105
Length of hospital stay, days	11.0 (7.0–15.0)	12.5 (8.0–17.0)	8.0 (7.0–11.0)	0.103
mTICI, 2b–3	41 (91.1%)	30 (88.2%)	11 (100.0%)	0.560
1	2 (4.4%)	2 (5.9%)	0 (0.0%)	>0.999
2a	2 (4.4%)	2 (5.9%)	0 (0.0%)	>0.999
2b	23 (51.1%)	20 (58.8%)	3 (27.3%)	0.141
3	18 (40.0%)	10 (29.4%)	8 (72.7%)	0.028
Any haemorrhage on follow-up imaging	18 (40.0%)	16 (47.1%)	2 (18.2%)	0.179
HI-1	10 (22.2%)	10 (29.4%)	0 (0.0%)
HI-2	2 (4.4%)	0 (0.0%)	2 (18.2%)
PH-1	0 (0.0%)	0 (0.0%)	0 (0.0%)
PH-2	4 (8.9%)	4 (11.8%)	0 (0.0%)
Subarachnoid haemorrhage	2 (4.4%)	2 (5.9%)	0 (0.0%)
Symptomatic intracranial haemorrhage	13 (28.9%)	13 (38.2%)	0 (0.0%)	0.045

DWI-pc-ASPECT: diffusion-weighted imaging – posterior circulation–Alberta Stroke Program Early Computed Tomography Score; NIHSS: National Institutes of Health Stroke Scale; ERT: endovascular reperfusion therapy; mTICI: modified treatment in cerebral ischaemia; HI: haemorrhagic infarction; PH: parenchymal haematoma.

Clinical outcome

NIHSS at discharge (NIHSS 22.0 (IQR 12.0–30.0) vs. 3.0 (IQR 1.5–3.0); P < 0.001) was significantly higher in PCO than GCO. Early neurological improvement after ERT (ΔNIHSS −1.0 (IQR −8.0–2.0) vs. 5.0 (IQR 3.0–10.5); P = 0.004) was significantly lower in PCO than GCO, respectively. Of the patients with DWI-pc-ASPECTS of 6 or less and over 70 years of age, 18/19 were in the PCO group at 90 days (Table 2). Importantly, in the DWI-pc-ASPECTS 6 point group, the GCO was 54.5%, but below 5, mRS of 2 or less at 90 days was only 14.7% (Supplementary Figure 1). On univariate analysis, follow-up imaging showed significantly higher infarct volume in the PCO group than in the GCO group (13 (38.2%) vs. 0 (0.0%); P = 0.045). Mortality did not statistically differ (10 (29.4%) vs. 0 (0.0%); P = 0.105) at 90 days; however, there were no deaths in the GCO group. Regarding haemorrhagic complications, there were no significant between-group differences, with an overall rate of any haemorrhage and symptomatic haemorrhage of (16 (47.1%) vs. 2 (18.2%), and 6 (17.7%) vs. 2 (18.2%); P = 0.179) in the PCO and GCO groups, respectively (Table 2).

Predictors of clinical outcome

On multivariate analysis, being over the age of 70 years and the high initial NIHSS score were independent predictors of PCO on adjusting for variables (Table 3).

Table 3.

Predictors of poor clinical outcome at 90 days in acute basilar artery occlusion patients with DWI-pc-ASPECT of 6 or less.

	Unadjusted OR (95% CI)	P value	Adjusted OR (95% CI)	P value
Age > 70 years	11.3 (1.9–218.3)	0.028	15.3 (1.9–379.8)	0.032
Symptomatic intracranial haemorrhage	4.0 (0.9–28.9)	0.105
Initial NIHSS	1.2 (1.7–1.4)	0.008	1.2 (1.1–1.4)	0.009

DWI-pc-ASPECT: diffusion-weighted imaging – posterior circulation–Alberta Stroke Program Early Computed Tomography Score; OR: odds ratio; CI: confidence interval; NIHSS: National Institutes of Health Stroke Scale.

Discussion

To our knowledge, this study was the first to evaluate the characteristics and effects of ERT in acute BAO patients with DWI-pc-ASPECTS of 6 or less. In acute BAO patients with DWI-pc-ASPECTS of 6 or less, GCO was present in 11 (24.4%) patients, and overall mortality was 10 (22.2%). Also, our data demonstrate that patients with a DWI-pc-ASPECT score of 6 have higher chances of a favourable outcome, while those with a score below 5 do not (Table 2 and Supplementary Table 2). There was a large difference between the GCO and PCO groups in terms of mortality, infarct volume on follow-up imaging, and haemorrhagic complications; however, the difference was not statistically significant because of the small number of patients. The successful recanalisation was not associated with a favourable outcome but did not aggravate the haemorrhage or increase the 90-day mortality rate. The patients with higher initial NIHSS had a poor prognosis despite the successful revascularisation. The mean initial NIHSS was less than 10 in the GCO group. Importantly, in patients with acute BAO with DWI-pc-ASPECTS of 6 or less, the functional outcomes at 90 days had a worse tendency in those over 70 years old. Although the number of patients was small, there was no favourable outcome (mRS ≤ 2) in patients over 80 years of age (Figure 2).

Figure 2.

Clinical outcome (modified Rankin scale 0–6) of acute basilar artery occlusion in patients who had DWI-pc-ASPECT (diffusion-weighted imaging – posterior circulation–Alberta Stroke Program Early Computed Tomography Score) of 6 or less according to their age. The proportion of outcomes (modified Rankin scale 0–2 vs. 3–6) within each age group is shown.

There are several small studies on ERT performed in acute BAO which suggested the patient's age, reperfusion status and initial thalamus involvement were associated with clinical prognosis.^12,23,24 However, there is no well-designed prospective trial about ERT for BAO. It was difficult to perform the randomised clinical trials probably because of the relatively low incidence, and the varied presentation of acute BAO. Thus, optimal patient selection for ERT in acute BAO remains challenging. The treatment decision is based on recommendations derived from subgroups of large retrospective studies or based on anecdotal expert opinions.^25,26 Therefore, making prompt treatment decisions in an emergency for acute BAO patients has been difficult because there is no strict indication for performing ERT.

For optimal patient selection for ERT in acute BAO patients, it is important to choose an appropriate initial imaging technique among other things. In this regard, DWI-pc-ASPECTS has higher sensitivity than non-contrast CT for detecting brain infarction volume and location in the posterior circulation. Typically, most conservative studies have reported that DWI-pc-ASPECTS had a poor prognosis at 6 points.^12,13,15 However, it is doubtful whether the cut-off value of 6 points is robust. Recent reports have shown that if the ERT achieved successful recanalisation, even DWI-ASPECTS of 6 or less in an anterior circulation ischaemic stroke has a better prognosis than medical treatment alone. However, similar to our study, ERT was effective at 6 points of DWI-pc-ASPECTS, but not at 5 points or less.^16–18

There was a significant difference in the initial median NIHSS (P < 0.001) between the GCO and PCO. Although the images representing the two groups of ischaemic cores show similar results, the patient's symptoms provide important information in predicting prognosis. DWI-pc-ASPECTS does not reflect the critical location or volume of the ischaemic core. Thus, even if the DWI-pc-ASPECTS is the same, the presence or absence of invasion of the critical region of the brainstem or the difference in the ischaemic volume may be reflected in the difference in the initial NIHSS, which may lead to clinical outcomes. The evidence suggests that lesions seen in DWI are not irreversible and that DWI reversal can occur after ERT. In addition, despite DWI-pc-ASPECTS of 6 or less, mild initial symptoms were predictors of GCO, which may be related to the local energy metabolism requirements, haemodynamic factors, and excitatory reflecting local neurotransmitters.²⁷ The posterior circulation is considered to be highly developed, with a robust collateral arterial network and involves reverse filling of the distal basilar artery, which results in resistance to the tissue clock characterising the rapid necrosis.⁵ However, when ischaemia exceeds the threshold of resistance, serious irreversible damage occurs. Recent randomised trials have shown the ‘late window paradox’ presented in the anterior circulation stroke. If the abundant collateral flow for keeping the small ischaemic core size, better results can be obtained even if late ERT is performed.^28–30

In addition, the results of this study showed that death or functional impairment was found in 94.7% of patients at 3 months after ERT for BAO in patients with DWI-pc-ASPECTS of 6 or less and aged over 70 years (Figure 3). ERT outcome data on anterior circulation occlusion in very elderly patients reported positive results, but BAO had different clinical features. ERT in octogenarian patients showed a severe presentation with worse clinical outcome and mortality ratios than in younger patients.²⁵ Although posterior circulation is known to be well tolerated by ischaemic insult, older patients have a relatively small penumbra, thus leading to a faster progression of penumbra to the ischaemic core due to the insufficient vascular reserve.^25,31,32

Figure 3.

Modified Rankin scale at 3 months between ages 70 years and older and under 70 years in acute basilar artery occlusion patients treated by endovascular reperfusion treatment.

The limitation of this study is the small number of patients. Currently, studies on BAO are limited regarding the number of patients they include, and thus meaningful results are limited. Therefore, prospective, large-scale studies are needed to establish treatment guidelines for acute BAO. However, this is the first study to provide clinical information for determining the suitability of ERT in patients with posterior circulation stroke having DWI-pc-ASPECTS of 6 or less. We also did not compare patients with DWI-pc-ASPECTS of 6 or less in whom ERT was not performed. However, previous studies report a mortality rate of approximately 40% and severe neurological disability in more than 65% of survivors.³³ Therefore, in this study, the outcomes of ERT performed in patients with DWI-pc-ASPECTS of 6 or less is considered acceptable. Finally, in our data, octogenarian patients with acute BAO did not show good prognosis even with successful ERT. Nonetheless, there is still a limit to whether the decision to use ERT progress based on age. Because the number of patients in this study was very small, it is likely that biased information was reflected. In addition, Mourand et al. reported that age was not included in the prognostic factors in acute BAO.³⁴ Therefore, prospective and systematic large-scale studies are needed.

In conclusion, to our knowledge, this is the first study investigating the clinical characteristics and prognosis of acute BAO patients with DWI-pc-ASPECTS of 6 or less who arrived at the hospital within a therapeutic time window. The purpose of the current study is to help guide the clinical decision-making and to encourage the practical conversation between stroke neurologist (or neuro-interventionist) and patients (or family) about ERT as a treatment option for acute BAO in patients with DWI-pc-ASPECTS of 6 or less. In particular, DWI-pc-ASPECT of 6 or greater is the prognostic indicator of the good chances of a favourable outcome.

Author contribution

JGK and DHL conceptualised and designed the study. JGK, DWL, YSS, DCS and DHL reviewed the articles and collected the data. JGK, DWL, YSS, DCS and DHL recruited patients. JGK, JCC, DWL and DHL analysed the data. All authors contributed to data interpretation, write-up, editing and revisions of the final manuscript. All authors have contributed to the production of the final version of this manuscript.

Availability of data and material

The data and materials used in the present study are available from the corresponding author on request.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Ethics approval and consent to participate

Ethical approval was granted according to national requirements, and the need for written informed consent was waived by the institutional review board at the Asan Medical Center.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Provenance and peer review

Not commissioned; externally peer reviewed.