Long Insular Artery Infarction: Characteristics of a Previously Unrecognized Entity

Definition of Vascular Territories

According to the figure of the coronal microangiogram of a postmortem brain obtained by Kumabe et al,¹¹ the subcortical white matter and basal ganglia on coronal images was divided into the 3 individual vascular territories: the WMMA territory, the LIA territory, and the LSA territory, as shown in Fig 1A. The fact that stroke associated with sacrificed insular perforators during resection of an opercular glioma was located from the top of the insular cortex to the periventricular corona radiata is in accordance with this anatomic vascular distribution.¹¹ In this study, to standardize radiologic interpretation, we drew a virtual line from the tip of the anterior horn to the top of the superior limb of the insular cleft in reference to the microangiogram of the LIA¹¹ (referred to as the A-I line), because this corresponds closely to the previously reported vascular territory of the LIA (Fig 1B).^9,10 Radiologic classifications were independently made by 1 neurologist with 10 years of experience under the supervision of a neuroradiologist with >20 years of experience, and by 1 neuroradiologist with 13 years of experience. When these investigators reached different decisions, the judgment from the neurologist supervised by the neuroradiologist was adopted. They were instructed to classify those infarctions involving the A-I line into the LIA group and to classify those situated under the A-I line and extending vertically (craniocaudal) as the LSA group. (Infarctions presenting over the A-I line were not included in this report.)

Patient Selection

With institutional ethics committee approval, clinical records of all patients with ischemic stroke who presented at our hospital between April 2003 and August 2010 and underwent MR imaging, including DWI and MRA, within 7 days of symptom onset were retrospectively reviewed. Patients with an isolated infarct in the LIA or LSA territories were included in this study. On the basis of the geographic distribution of a hyperintense area on coronal reconstructed images from DWI, patients were classified into the LIA group or LSA group, as described above (Figs 1 and 2). Patients with multiple infarcts or a large subcortical infarct (>15 mm) were excluded.

Clinical and Demographic Data

The following clinical data were obtained on each patient: 1) age; 2) sex; 3) vascular risk factors including hypertension, diabetes mellitus, hyperlipidemia, and smoking; 4) blood pressure value on admission; 5) NIHSS score on admission; 6) classic lacunar syndrome, which consisted of pure motor stroke, pure sensory stroke, sensorimotor stroke, ataxic hemiparesis, and dysarthria–clumsy hand syndrome; 7) mode of neurologic symptom onset, being either abrupt, gradual, or on awakening; 8) frequency of poor outcome, defined as a modified Rankin Scale ≥3 at 3 months after onset; and 9) embolic sources.

We also identified the following vascular risk factors: hypertension, defined as prior diagnosis or blood pressure >140/90 mm Hg persisting for >2 weeks after admission; diabetes mellitus, defined as prior diagnosis or fasting serum blood glucose >126 mg/dL or hemoglobin A1c >6.5%; hyperlipidemia, defined as prior diagnosis or fasting, serum low-attenuation lipoprotein cholesterol >140 mg/dL or fasting serum total cholesterol >220 mg/dL; and smoking, defined as regular daily cigarette use within the past 2 years.

Mode of neurologic symptom onset was defined in the following manner: abrupt, an abruptly started single episode reaching maximum severity within 30 minutes after onset; gradual, an episode reaching maximum severity >30 minutes after onset with gradually progressing or fluctuating symptoms; and on awakening, an episode with stroke symptoms noticed on awakening.

In this study, embolic sources included both cardiac and aortic sources. On the basis of a previously described definition, cardiac sources of embolism were further divided into groups associated with embolic high-risk sources and embolic moderate-risk sources.¹³ Atrial fibrillation, left ventricular aneurysm or thrombus, left atrial thrombus, recent transmural anterior myocardial infarction, rheumatic valvular disease, mechanical prosthetic valve, endocarditis, and primary intracardiac tumors were regarded as embolic high-risk sources. Embolic moderate-risk sources consisted of mitral annular calcification, mitral valve prolapse, cardiomyopathy, segmental wall-motion abnormality, patent foramen ovale, atrial flutter, sick sinus syndrome, valve strands, and left atrial spontaneous echo contrast. Aortic sources of embolism included ipsilateral occlusive arterial disease and aortic atheroma. Criteria for occlusive arterial disease were the presence of stenosis ≥50% by the NASCET criteria¹⁴ or occlusion in the ipsilateral extracranial carotid artery and stenosis ≥50% or occlusion in the ipsilateral intracranial carotid artery by measurement with MRA. Aortic atheroma was defined as an aortic plaque with thickness of ≥4 mm, mobile elements, or ulceration on transesophageal echocardiography (TEE). All patients underwent 12-lead electrocardiography, 24-hour electrocardiography monitoring, color-flow duplex carotid sonography, and transthoracic echocardiography to detect an embolic source. TEE was suggested to patients showing abrupt onset with no embolic source and was performed after informed consent was obtained.

MR Imaging

MR imaging was performed on a 1.5T MR imaging unit (Intera Achieva Pulsar scanner; Philips Healthcare, Best, the Netherlands) with echo-planar capabilities. An acquisition time of approximately 4 minutes was used for DWI. Images were acquired by using a single-shot echo-planar imaging technique with the following parameters: 6000/88 ms (TR/TE), with a motion-probing gradient in 15 orientations; b-value = 1000 s/mm²; and averaging 2 times. A parallel imaging technique was used to record data with a 128 × 128 spatial resolution for a 230 × 230 mm FOV. A total of 41 sections were obtained, with a section thickness of 3 mm and no intersection gap. Coronal DWI was reconstructed from DWI data by using the multiplanar reconstruction of the PACS.

Analyses

Statistical analysis was undertaken by using a commercially available software package (Statistical Package for the Social Sciences for Windows, Version 11; IBM, Armonk, New York). The degree of interrater agreement was determined by calculation of the κ statistic. Baseline characteristics were compared with a χ² test (for proportions), a t test (for means), or a Mann-Whitney test (for medians), between the 2 groups. Differences with a P value < .05 were considered statistically significant.