477 MR and CT of Lacunar Infarcts Jeffrey J. Brown 1, 2 Twenty-two patients with clinical signs and symptoms compatible with lacunar tran­ John R. Hesselink 1 sient ischemic attack or stroke of varying chronicity were evaluated with MR imaging. John F. Rothrock3 CT was also performed in 21 of these patients. MR revealed small, deep cerebral lesions in locations appropriate to the clinical symptoms in 19 patients. Lacunar infarcts were imaged by CT in 11 patients; however, no lesions were identified on CT that were not detected with MR. Presumed lacunar infarcts were identified on MR images in 17 additional patients. Lacunae generally appeared as focal areas of decreased signal intenSity on T1-weighted images and as focal areas of increased signal intensity on T2- weighted images. T2-weighted MR images detected a greater number of lacunar infarcts than did mixed T1-/T2-weighted images, which in turn detected more lacunae than did T1-weighted images. In general, acute lacunar infarcts (within 1 week of onset or recurrence of clinical symptoms) were seen only on T2-weighted images, while chronic lesions (more than 1 week) were seen on both T1- and T2-weighted images. Our results indicate that MR is superior to CT for evaluating lacunar infarcts, and second, that T2-weighted images are more sensitive than T1- and mixed T1-/T2- weighted images for detecting lacunar infarcts. Lacunar stroke accounts for up to 19% of all cerebral infarctions [1]. Although patients with lacunar disease generally manifest one of a number of well-defined lacunar syndromes, there is an overlap in the clinical presentation of acute lacunar infarction with ischemic insults to the cerebral cortex, especially in the setting of unstable carotid artery disease [2]. An important role of the neuroradiologist in evaluating a stroke patient is to help characterize the pathophysiology of the ischemic event, as this may guide the clinician in the choice of therapy. The purpose of this study was to evaluate the efficacy of MR imaging in the This articles appears in the May/June 1988 evaluation of patients with presumed lacunar transient ischemic attacks or stroke, issue of AJNR and the August 1988 issue of AJR. to compare the sensitivity of MR and CT in the setting of acute and chronic lacunar Received April 24, 1987; accepted after revision disease, and to describe the MR characteristics of lacunar infarctions. November 4, 1987. Presented in part at the annual meeting of the American Society of Neuroradiology, San Diego, Subjects and Methods January 1986. Twenty-two patients with presumed lacunar transient ischemic attacks or stroke were 1 Department of Radiology, and the Magnetic Resonance Institute, University of California, School evaluated with MR. CT was also performed in all but one of these patients. Each patient had of Medicine, San Diego, CA 92103. Address reprint a history, or current manifestations, of lacunar ischemia, including pure motor deficit, pure requests to J . R. Hesselink, UCSD Medical Center, sensory deficit, or motor/subcortical sensory deficit with or without associated dysarthria but 225 Dickinson St. , San Diego, CA 92103. without dysphasia or visual impairment. The patients included 10 men and 12 women, 42- 2 Present address: Department of Radiology, 83 years old. Ten of the patients (group 1) presented with multiple lacunar attacks defined University of California School of Medicine, San as two or more discrete episodes of anterior circulation cerebral ischemia within 24 hr of Francisco, CA 94143. initial evaluation or three or more such episodes within 72 hr preceding evaluation. Eighty 3 Department of Neurology, and Magnetic Res­ percent or greater resolution of neurologic deficits between attacks was required for inclusion onance Institute, University of California, School of Medicine, San Diego, CA 92103. in this acute group. MR and CT scanning were performed within 48 hr of the most recent symptomatic episode in each case. Five patients (group 2), considered to have recent or AJNR 9:477-482, May/June 1988 0195-6108/88/0903-0477 subacute lacunar stroke, were evaluated within 30 days (48 hr, 4 days, 5 days, 11 days, and © American Society of Neuroradiology 30 days) after the onset of clinical symptoms, and seven patients (group 3) with a history of 478 BROWN ET AL. AJNR:9, May/June 1988 remote or chronic lacunar stroke were evaluated more than 3 months partial-volume averaging, and inherent limitations in contrast after the onset of symptoms. and spatial resolution of both imaging techniques. The per­ Presumed lacunar infarcts were identified in 17 additional patients centages stated below are based on the total number of (group 4) in a retrospective review of MR images obtained over a 4- lacunae detected by MR and/or CT rather than on the true month period. This group included nine men and eight women 47- total number of lacunae in our study population. Absolute 81 years old. Since no recent ischemic episodes were reported, these infarcts were considered to be of the remote type. numbers would require careful pathologiC study of each case. MR images were obtained on a superconducting 1.5-T MR sys­ In the prospective portion of the study (groups 1-3), CT tem: A slice thickness of 5 mm was used with a 2.5-mm gap between detected 28% of the lacunae that were imaged by MR in slices. Axial images were obtained on a 256 x 256 matrix with a 20- patients studied by both techniques. No lacunae identified on cm field of view. T1-weighted pulse sequences consisted of 600/25/ CT were missed by MR. The T2-weighted sequence was the 2 (TRfTE/excitations), mixed T1 -fT2-weighted sequences of 2000/ most sensitive MR technique, detecting 98% of the lacunae 25- 35/2, and T2-weighted sequences of 2000/60-70/2. High-reso­ that were imaged (Table 2). The one lacuna not detected on lution CT was performed on aGE 9800 or Technicare 2020 scanner T2-weighted images was imaged only on T1-weighted im­ with a 10-mm slice thickness and contiguous sectioning. ages. Sixty-seven percent of the total number of lacunae T2-weighted and mixed T1-fT2-weighted images were obtained in identified were detected on mixed T1-fT2-weighted images all patients. T1-weighted images were obtained in 30 of 39 patients; five additional patients had T1-weighted images, but the anatomic and 40% on T1-weighted images. sites shown to contain lacunar lesions by CT or T2-weighted imaging In the patients analyzed in a retrospective manner (group were not included on the images. CT was performed in 21 of 22 4),98% of the lacunae were seen on T2-weighted MR images patients in the prospective groups (groups 1-3) and in three of 17 (Table 2). The one lacuna not seen on T2-weighted images patients in group 4. The CT scans and MR images were reviewed to was detected on both T1- and mixed T1-fT2-weighted im­ determine the number of lacunar infarctions detected by each imaging ages. Eighty-eight percent of lacunae were visualized with sequence. mixed T1-fT2-weighted images and 46% with T1-weighted For the purpose of this study, lacunar infarcts were defined as images. In patients who had both CT and MR imaging, CT discrete areas of decreased attenuation on CT or abnormal signal detected 64% of the lacunae that were seen on MR. Again, intenSity on MR ranging from 2 to 15 mm in diameter and located in no lacunae detected by CT were missed by MR . the basal ganglia, internal capsule, thalamus, brainstem, or corona radiata inferiorly to the level of the lateral ventricles. Data from both Lacunae generally appeared as focal areas of decreased the prospective and retrospective portions of the study were com­ signal intensity on T1-weighted images and as foci of in­ bined to make some basic observations about the MR appearance creased signal intenSity on T2-weighted images (Table 3, of lacunar infarcts with different imaging sequences. In addition to Figs. 1 and 2). In addition, lacunae were significantly brighter noting the morphologic features on the MR image, Signal-intensity on second-echo (T2-weighted) images than on first-echo values were obtained of each lacuna by using a normal-appearing (mixed T1-fT2-weighted) images. A total of eight lacunae in white-matter structure, such as the splenium of the corpus callosum, seven patients had an atypical appearance on the mixed T1-/ as an intemal standard. The signal-intensity values were expressed T2-weighted images, characterized by a perimeter of high as ratios of the signal intensity of the lacunar infarcts compared with signal intensity (signal-intensity ratio = 1.020 ± 0.007) sur­ the normal white matter. A ratio of greater than one indicates that rounding a lower-intensity center (Signal-intensity ratio = the lacuna has a signal intensity greater than that of white matter; conversely, a ratio of less than one corresponds to a lacuna with low 1.007 ± 0.005) (Fig . 3). We postulate that this appearance is signal intenSity relative to white matter. from central cavitation with surrounding gliosis. All data are expressed as the group mean ± 1 SO . The Wilcoxon Of the 22 patients in groups 1-3, 19 had evidence of signed ranks test was used to compare signal-intensity ratios ob­ lacunar infarction on MR and 11 on CT. The MR images and tained with each imaging technique to one. The two-sample Wilcoxon CT scans were normal in three. The acute and subacute test was used to compare signal-intensity ratios among groups 1-4 lacunae (group 2) were detected with a T2-weighted se­ with each imaging technique.