05_05_JNS.1.gls 4/21/05 1:06 PM Page 870 J Neurosurg 102:870–878, 2005 Blood pressure in the artery distal to an intraarterial embolus during thrombolytic therapy for occlusion of a major artery: a predictor of cerebral infarction following good recanalization TAKATOSHI SORIMACHI, M.D., YUKIHIKO FUJII, M.D., NAOTO TSUCHIYA, M.D., TAKEO NASHIMOTO, M.D., MASATSUNE SAITO, M.D., KENICHI MORITA, M.D., YASUSHI ITO, M.D., AND RYUICHI TANAKA, M.D. Department of Neurosurgery, Nishiogi-chuo Hospital, Tokyo; and Department of Neurosurgery, Brain Research Institute, Niigata University, Niigata, Japan Object. The aim in this study was the investigation of back pressure in arteries distal to the occlusion site during intraarterial thrombolysis as well as the usefulness of back pressure measurement in combination with diffusion-weighted (DW) magnetic resonance (MR) imaging to predict the occurrence of ischemic lesions following good recanalization. Methods. Twenty-five consecutive patients with severe hemiparesis caused by embolism of the internal carotid artery (10 patients) and the proximal middle cerebral artery (15 patients) were treated using intraarterial thrombolysis. Systolic back pressure, measured through a microcatheter in the artery just distal to the emboli, ranged from 22 to 78 mm Hg. According to an angiographic inclusion criterion for good recanalization—that is, recanalization of the M2 or more distal arteries at the end of thrombolysis—21 of 25 patients underwent evaluation in this study. In 14 patients volumes of low-density areas on computerized tomography (CT) scans obtained 2 months postthrombolysis were smaller in comparison with volumes of hyperintense areas on DW MR images acquired before treatment, whereas these low-density areas were larger in seven patients. Compared with those on initial DW MR images, the volume of abnormalities on CT scans obtained 2 months posttreatment were significantly reduced in patients with a systolic back pressure greater than 30 mm Hg (16 patients) than in those with a back pressure of 30 mm Hg or less (five patients) (p , 0.05). Systolic back pressures greater than 30 mm Hg were associated with significantly better modified Rankin Scale scores than those 30 mm Hg or less (p , 0.05). Conclusions. Back pressure measurement in combination with DW MR imaging can be used to predict the occurrence of infarction as demonstrated on CT scans following thrombolysis. KEY WORDS • back pressure • diffusion-weighted imaging • fibrinolysis • magnetic resonance imaging • stump pressure IFFUSION-WEIGHTED MR imaging, which can display focal brain abnormalities during the early stages of ischemia, is one of the most widely used tools for predicting infarction in a clinical setting. The hyperintense areas on DW MR images are assumed to indicate irreversible injury; therefore, large areas of abnormality on such images are regarded as an exclusion criterion for intraarterial thrombolysis in cerebral ischemia.6,14,17,28 Hyperintense areas on initial DW MR images have been reported to normalize later in some cases of transient ischemic attack13 and postthrombolytic therapy,8,9,15 when early recanalization occurred. Nonetheless, no accurate indicator of the reversal of abnormalities on early DW MR images has been investigated. A good correlation reportedly exists between the stump pressure in the distal ICA during CEA and the incidence of postoperative neurological complications.1,7,10,12,22 D Abbreviations used in this paper: ADC = apparent diffusion coefficient; CEA = carotid endarterectomy; CT = computerized tomography; DW = diffusion-weighted; ICA = internal carotid artery; MCA = middle cerebral artery; MR = magnetic resonance; mRS = modified Rankin Scale. 870 We have reported the clinical usefulness of blood pressure measurement through a microcatheter in arteries feeding cerebral arteriovenous malformations32 and in cerebral aneurysms33 during intravascular surgery. To the best of our knowledge no prior study has been published in which back pressure was evaluated in intracranial arteries distal to the site of occlusion in cerebral ischemia. In this study, however, we measured the back pressure in arteries just distal to emboli by using a microcatheter during thrombolytic therapy for an embolism in a major cerebral artery. Our purpose in this study was the investigation of both the back pressure in arteries just distal to the occlusion site during intraarterial thrombolysis and the usefulness of back pressure measurement in predicting tissue damage after good recanalization as an adjunct to DW MR imaging. In analyzing the latter, we compared hyperintense areas on initial DW MR images with low-density areas on CT scans obtained after sufficient recanalization through thrombolysis. We then evaluated the relationship between back pressure and the changes in ischemic lesion volumes obtained during the comparison. J. Neurosurg. / Volume 102 / May, 2005 05_05_JNS.1.gls 4/21/05 1:06 PM Page 871 Systolic back pressure in intraarterial thrombolysis Clinical Material and Methods Patient Population Between April 2001 and June 2004, 25 consecutive patients (15 men and 10 women) younger than 85 years of age (mean age 6 standard deviation 73.4 6 8 years, range 56–84 years) who had experienced the sudden onset of severe hemiparesis as well as gaze palsy to the hemiparetic side within the last 4 hours of hospital admission were treated using intraarterial thrombolysis. All patients suffered from cerebral ischemia caused by occlusion of a major artery. Ten patients had blockage of the terminal ICA, and 15 of the proximal MCA. The patients’ initial neurological status, rated according to the National Institutes of Health Stroke Scale5 ranged from 16 to 28 (mean 21.8 6 4). Computerized tomography scanning was performed in all patients. Magnetic resonance imaging was performed a mean of 90.6 6 49.4 minutes (range 45–225 minutes) after the onset of symptoms. Intraarterial thrombolysis with mechanical disruption, via a microcatheter and a guidewire, was started from 60 to 255 minutes (mean 121 6 52.1 minutes) after the onset of symptoms. The details of thrombolysis with mechanical disruption have been described previously.31 During this procedure blood pressure was measured in the intracranial arteries just distal to the emboli. Thrombolysis was completed in 150 to 360 minutes (mean 209.8 6 56.1 minutes). Arterial recanalization was evaluated using digital subtraction angiography at the end of thrombolytic therapy. The angiographic inclusion criterion for good recanalization in this study was recanalization of the M2 or more distal arteries. Occlusion of either the M1 portion of the MCA or the ICA on angiography at the end of the procedure was regarded as insufficient recanalization, and the patient was excluded from further study. Computerized tomography scanning was performed 2 months after treatment. Patient outcome at 3 months after treatment was assessed according to the mRS.35 Our study protocol was approved by the institutional review committee of our facility, and informed consent was obtained from each patient’s family members. analysis system. The final lesion volume was calculated by multiplying the area obtained from each section by the slice thickness. If multiple scattered or noncontiguous abnormalities were noted, volumes were calculated by summing the individual volumes of all abnormal lesions. The volumes of newly developed lesions that appeared on CT scans 2 months after treatment compared with admission scans were calculated using the same method as that used for DW MR imaging. A change in lesion volume was expressed as an improvement in ischemic volume, or an index of radiological improvement following recanalization, and was calculated according to the following equation: (volume of hyperintense areas on the initial DW MR image 2 volume of low-density areas on the CT scan obtained 2 months posttreatment)/volume of hyperintense areas on the initial DW MR image. A positive value indicated shrinkage of the ischemic lesion, whereas a negative value signified expansion (deterioration). Regional distribution of the ischemic lesions was evaluated on both initial DW MR images and CT scans 2 months after treatment. Blood Pressure Measurement A microcatheter (Renegade-18; Boston Scientific, Natick, MA) was introduced beyond the embolus. Superselective angiography studies were performed through a microcatheter to assess the precise site of occlusion and the size of the embolus. Arterial pressure just distal to the embolus was measured by connecting the microcatheter to a pressure transducer (model DX-312; Nihon Koden Corporation, Tokyo, Japan) and a digital pressure monitor (model KC013P; Nihon Koden Corporation).32,33 When the distal end of the embolus was located in the M2 portion of the MCA, blood pressure was measured in the M2 supplying mainly the parietal lobe. Systolic blood pressure, that is, systolic back pressure, was used in this study. Statistical Analysis Imaging Methods Statistical evaluation was performed using the Mann– Whitney U-test for between-group comparisons. A probability value less than 0.05 was considered statistically significant. Magnetic resonance imaging studies were performed using a 1-tesla unit (Signa; General Electric, Waukesha, WI) with a birdcage headcoil. In each case, DW MR imaging was performed using diffusion gradients in three orthogonal directions, with a maximal b value of 1000 seconds/mm2. The DW MR imaging studies were performed using a single-shot, multisection, spin echo–echo planar imaging sequence with the following parameters: TR 5000 msec, TE 120 msec, flip angle 90˚, matrix size 128 3 128, and field of view 22 3 22 cm. Nineteen axial sections with a thickness of 6 mm and an intersection gap of 1 mm were obtained. For CT studies we used a scanner (HiSpeed DX/I; General Electric) according to the following parameters: 120 kV, 220 mA, matrix size 512 3 512, section thickness 5 mm, and field of view 25 3 25 cm. In each case lesion volumes on DW MR images obtained on admission were identified through visual inspection for regions of hyperintensity and then were measured by outlining regions of interest by hand with the aid of an image Results The clinical characteristics of all 25 patients are presented in Table 1. In each patient hyperintense areas were demonstrated on initial DW MR images. Systolic back pressure ranged from 22 to 78 mm Hg (mean 39.5 6 14.1 mm Hg). Two patients died: one (Case 3) of thrombocytopenia 7 days after treatment and another (Case 19), in whom the M1 occlusion remained after thrombolysis, of transtentorial herniation 6 days after thrombolysis. The occluded vessels were recanalized in 24 patients; in only one patient (Case 7) with a right C4 occlusion was the procedure discontinued without recanalization. In two patients (Cases 18 and 19), including one who died, the M1 portion of the MCA was the occlusion site demonstrated on angiograms obtained immediately after thrombolysis. Four patients were excluded from analysis: two (Cases 3 and 19) who died and two (Cases 7 and 18) who survived with insufficient recanalization. In the remaining 21 patients with good recanalization, hyperintense areas on initial DW MR images were com- J. Neurosurg. / Volume 102 / May, 2005 871 05_05_JNS.1.gls 4/21/05 1:06 PM Page 872 T. Sorimachi, et al. TABLE 1 Summary of clinical features in 25 patients with ischemic lesions* Case No. Age (yrs), Sex Initial Occlusion Site Time From Symptom Onset to End of Thrombolysis (min) Occlusion Site After Thrombolysis Systolic Back Pressure (mm Hg) Vol of HIAs on Initial DWI (ml) State of Ischemic Vol mRS Score at 3 Mos Posttreatment 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 70, F 81, F 85, M 70, M 74, M 76, M 69, F 74, F 82, F 66, M 58, M 78, F 83, M 69, M 84, M 78, M 71, M 82, F 68, F 59, M 74, M 80, F 56, M 73, M 77, F rt M1 proximal lt M1 distal lt M1 proximal rt M1 distal lt M1 proximal lt C2 rt C4 lt M1 distal lt C3 rt C1 lt C1 lt C4 lt C3 rt C2 lt M2 proximal rt M1 proximal rt M1 distal rt C2 rt C1 lt M2 proximal rt M1 proximal lt M1 distal rt M1 proximal lt M2 proximal lt M2 proximal 160 180 265 165 210 150 240 150 210 170 150 330 180 220 180 300 230 210 240 150 360 270 225 180 150 none temporal M3 frontal M3 none frontocentral M4 angular M4 C4 parietal M3 angular M4 none none M2 angular M4 central M4 frontal M3 parietotemporal M3 parietal M4 M1 middle M1 middle frontal M4 frontal M3 none none none central M4 35 27 29 34 29 45 59 50 30 48 32 75 25 32 39 32 45 35 39 78 48 32 22 34 33 82 69 26 29 39 133 97 27 131 315 284 64 225 162 185 84 137 33 144 17 87 37 96 34 33 0.39 21.54 –– 0.79 22.62 0.20 20.38 0.48 20.08 0.50 0.80 21.31 20.05 0.51 0.65 0.46 0.57 24.97 –– 0.65 20.25 0.92 20.17 0.32 0.85 0 5 dead 0 4 2 3 0 5 0 2 3 5 4 2 1 0 5 dead 0 4 1 4 3 1 * DWI = DW imaging; HIA = hyperintense area; –– = not applicable. pared with low-density areas on CT scans obtained 2 months posttreatment. In 14 patients low-density areas on CT scans obtained 2 months after treatment indicated a smaller lesion volume in comparison with hyperintense areas on initial DW MR images (improvement), whereas in seven patients the CT scans revealed larger lesion volumes than those on the DW MR images (deterioration). Figure 1 depicts the relationship between the systolic back pressure and the rate of improved ischemic volume. In CT scans 2 months posttreatment all five patients with systolic back pressure of 30 mm Hg or less demonstrated a larger lesion volume than had been revealed on initial DW MR images (deterioration). In two of 16 patients with systolic back pressure greater than 30 mm Hg, the intervals from the onset of symptoms to completion of thrombolysis were longer than 300 minutes. In both of these patients the volumes of low-density areas on CT scans were larger than those of hyperintense areas on initial DW MR images (deterioration). In the remaining 14 patients, who had intervals of 300 minutes or less between symptom onset and procedure completion, lesion volumes were smaller on postthrombolysis CT scans than those on initial DW MR images (improvement). Improvement in patients with a systolic back pressure greater than 30 mm Hg (mean 0.41 6 0.29 mm Hg; 16 patients) was significantly better than that in those with a systolic back pressure of 30 mm Hg or less (mean 20.89 6 1.32 mm Hg; five patients; p , 0.05). Regional distribution of the ischemic lesion in the 14 patients whose conditions improved is indicated in Table 2. In the patients in whom a reduction in ischemic volume (improvement) was demonstrated, 67, 38, 20, and 17% of the 872 hyperintense areas on the corona radiata, temporal and frontal regions, and putamen, respectively, were ameliorated after thrombolysis, whereas no hyperintense area in either the parietal region or insula was improved. Figure 2 left shows the relationship between the improvement in ischemic volume and mRS score 3 months after thrombolysis. Patients with improvement of ischemic lesions (14 patients) had significantly better mRS scores than those with aggravation of ischemic lesions (deterioration, seven patients; p , 0.05). One patient with improvement had an mRS score of 4 because of a leg embolism; the remaining 13 patients with improvement had an mRS score of 3 or better. Figure 2 right illustrates the relationship between systolic back pressure and mRS score. Patients with systolic back pressure greater than 30 mm Hg (16 patients) a significantly better mRS score was demonstrated than in those with a back pressure of 30 mm Hg or less (five patients; p , 0.05). Illustrative Cases Case 2 This 81-year-old woman with a history of arterial fibrillation presented to the emergency room 40 minutes after the acute onset of aphasia and right hemiplegia. Emergent DW MR imaging performed 60 minutes after onset revealed hyperintense areas in the left frontal and parietal regions and the insula (Fig. 3A). Angiography confirmed the left M1 occlusion (Fig. 3B). Systolic back pressure was 27 mm Hg in the M2 just distal to the occlusion. Thrombolysis with J. Neurosurg. / Volume 102 / May, 2005 05_05_JNS.1.gls 4/21/05 1:06 PM Page 873 Systolic back pressure in intraarterial thrombolysis TABLE 2 Regional distribution of ischemic lesions in 14 patients whose lesion volume improved Location No. of HIAs on Initial DWI No. of LDAs on CT* % Amelioration of Ischemic Regions frontal region parietal region temporal region putamen corona radiata insula internal capsule 10 7 8 6 9 5 0 8 7 5 5 3 5 0 20 0 38 17 67 0 –– * The CT scans were obtained 2 months posttreatment. Abbreviation: LDA = low-density areas. FIG. 1. Graph demonstrating the relationship between systolic back pressure and improvement in ischemic volume. The improvement in ischemic volume is calculated according to the following equation: (volume of hyperintense areas on the initial DW MR image 2 volume of low-density areas on the CT scan obtained 2 months postthrombolysis)/volume of hyperintense areas on the initial DW MR image. A positive value indicates reduction of ischemic volume, whereas a negative value signifies a volume increase. Patients with systolic back pressure greater than 30 mm Hg (16 patients) showed significantly better improvement than those with a systolic back pressure of 30 mm Hg or less (five patients; p , 0.05). Dotted line indicates 30 mm Hg of systolic back pressure; shaded circles indicate two patients in whom recanalization was achieved more than 300 minutes after the onset of the ischemia. mechanical disruption was performed, and almost complete recanalization was achieved 180 minutes after symptom onset (Fig. 3C). No remarkable change in symptoms was observed after the procedure. A CT scan obtained 2 months postthrombolysis demonstrated low-density areas in the left temporal region and the corona radiata; lesions had not been demonstrated at these sites on initial MR imaging (Fig. 3D). Case 4 This 70-year-old man with a history of arterial fibrillation presented to the emergency room 60 minutes after the acute onset of left hemiplegia. Emergency DW MR imaging performed 80 minutes after onset revealed hyperintense areas in the right frontal region, putamen, and corona radiata (Fig. 4A). Angiography confirmed the right M1 occlusion (Fig. 4B). Systolic back pressure was 34 mm Hg in the M2 just distal to the occlusion. Thrombolysis with mechanical disruption was performed, and complete recanalization was FIG. 2. Outcome 3 months after treatment. Left: Graph depicting the relationship between the improvement in ischemic volume and mRS score. A reduction in ischemic lesion volume (improvement, 14 patients) results in significantly better mRS scores compared with the scores following an increase in lesion volume (deterioration, seven patients; p , 0.05). Shaded circles indicate two patients in whom recanalization was achieved more than 300 minutes after the onset of the ischemia. Right: Relationship between systolic back pressure and mRS score. Systolic back pressures greater than 30 mm Hg (16 patients) result in significantly better mRS scores than pressures of 30 mm Hg or less (five patients; p , 0.05). Dotted line indicates 30 mm Hg of systolic back pressure. Shaded circles indicate two patients in whom recanalization was achieved more than 300 minutes after the onset of the ischemia. J. Neurosurg. / Volume 102 / May, 2005 873 05_05_JNS.1.gls 4/21/05 1:07 PM Page 874 T. Sorimachi, et al. FIG. 3. Case 2. Images demonstrating an increased lesion volume. A: Diffusion-weighted MR images obtained on admission, revealing hyperintense areas in the left frontal and parietal regions and the insula. B: Left ICA angiograms demonstrating occlusion of the M1 portion of the MCA (left, anteroposterior view; right, lateral view). C: Left ICA angiograms obtained immediately after thrombolysis (left, anteroposterior view; right, lateral view). The MCA is almost completely recanalized. D: Computerized tomography scans obtained 2 months posttreatment, exhibiting low-density areas in the left frontal, parietal, and temporal regions and insula and corona radiata. 874 J. Neurosurg. / Volume 102 / May, 2005 05_05_JNS.1.gls 4/21/05 1:07 PM Page 875 Systolic back pressure in intraarterial thrombolysis FIG. 4. Case 4. Images demonstrating an improved lesion volume. A: Diffusion-weighted MR images obtained on admission, revealing hyperintense areas in the right frontal region, corona radiata, and putamen. B: Right ICA angiograms displaying occlusion of the M1 portion of the MCA (left, anteroposterior view; right, lateral view). C: Right ICA angiograms obtained immediately after thrombolysis (left, anteroposterior view; right, lateral view). The MCA is completely recanalized. D: Computerized tomography scans obtained 2 months posttreatment, exhibiting a low-density area in the right putamen. J. Neurosurg. / Volume 102 / May, 2005 875 05_05_JNS.1.gls 4/21/05 1:07 PM Page 876 T. Sorimachi, et al. achieved 165 minutes after symptom onset (Fig. 4C). All symptoms resolved after the procedure. A CT scan obtained 2 months later exhibited a low-density area in the right putamen (Fig. 4D). Ischemic lesions in the frontal region and corona radiata, which had been demonstrated on the initial DW MR image, did not appear on the CT scan. Discussion To our knowledge this is the first published study on back pressure measurement during intraarterial thrombolysis. Systolic back pressure ranged from 22 to 78 mm Hg. Reversible DW MR Image Abnormality The area of lowered perfusion-weighted and normal DW MR images (DW MR image/perfusion-weighted MR image mismatch) is an index of the penumbra, or tissue that has potentially reversible ischemia.4,24,29,34 Normalization of the DW MR image abnormality after early recanalization has been reported in clinical studies on both transient ischemic attack13 and thrombolytic therapy,8,9,15 and in animal studies.20,21 Moseley, et al.,23 speculated that the decrease in the ADC resulting in hyperintensity on DW MR images is related to cytotoxic edema. Acute energy and ionic failure, which results in cytotoxic edema, does not per se indicate irreversible damage and may in part recover even after prolonged ischemia.2,3,30 No accurate method of predicting reversible DW MR imaging abnormalities in the early ischemic period has been reported. Note that ADC mapping is a useful tool in predicting the development of infarction in cases of prolonged occlusion.25 When early recanalization occurs, however, ADC decreases do not reliably indicate tissue infarction. Even severely decreased ADC values have been reported to normalize in the context of strokes in humans following early recanalization through thrombolytic therapy.8,9,14 In addition, a significant decrease below a specific ADC threshold value is not necessarily associated with histological changes in animal experiments.11,16,20 With sustained ischemia, both the magnitude of the ADC reduction and the size of the abnormality on DW MR imaging generally increase with time.8,19,26,27 Diffusion-weighted MR imaging performed immediately after admission does not seem to indicate accurately the condition of ischemic tissue immediately before recanalization and during treatment because of the time lag. The occurrence of infarction in brain tissue exposed to local anemia depends on the duration and severity of the ischemia.2,20 In this study back pressure was used as an index for the severity of ischemia. Back pressure values do not seem to change remarkably over time unless collateral circulation is aggravated by thrombus extension and/or edema development. After a change in intensity on DW MR images caused by acute energy and ionic failure (ischemic depolarization), neuronal death occurs if the ischemia continues.2,3,30 An interval between ischemic depolarization and neuronal death might be longer in ischemia with high back pressure in comparison to ischemia with low back pressure because of good collateral circulation. Back Pressure Measured in an ICA Distal to Occlusion Back pressure in a completely occluded artery is mainly determined by back flow via collateral circulation. The following factors are considered to affect collateral circulation: 876 patient age, occlusion site of artery, thrombus formation, tissue edema, second embolus in further distal artery, and general blood pressure. Many authors have reported on stump pressure in the distal ICA during CEA. There is a good correlation between stump pressure and the incidence of postoperative neurological complications.12,22 Nonetheless, there is no general consensus on the appropriate stump pressure cutoff value that indicates the need for some form of brain protection. Various values of critical stump pressure have been reported: 25,1,22 35,7 40,10 and 50 mm Hg.12 Data in this study showed that a back pressure of 30 mm Hg or less in intracranial arteries could be correlated with enlargement of ischemic lesions. The different factors between back pressure during intraarterial thrombolysis and stump pressure during CEA include the occlusion sites of cerebral arteries, the occlusion period, and the process used to evaluate ischemic damages. In this study a portion of the abnormalities on DW MR imaging could be ameliorated in patients with systolic back pressure exceeding 30 mm Hg when recanalization was achieved within 300 minutes after the onset of symptoms. On the other hand, ischemic lesions enlarged in patients with systolic back pressure of 30 mm Hg or less even when the occluded vessels were sufficiently recanalized. With regard to regional distribution, several hyperintense areas in the corona radiata and temporal region on DW MR images transformed to a normal appearance on CT scans obtained later. Perforating vessels originating from the M1 portion of the MCA supply the corona radiata, and recanalization of the M1 usually occurs in the early period of thrombolysis. This might explain the frequent improvement of ischemic lesions in the corona radiata. Collateral circulation from the posterior cerebral artery might be related to the frequent preservation of the temporal lobe. It was easy, quick, and safe to measure back pressure by simply connecting the microcatheter to the transducer after local angiography.32,33 Back pressure measurement, which could predict the development of infarction, seems to be a useful prognostic strategy. We used several mechanical disruption techniques by using a microcatheter and a microguidewire in intraarterial thrombolysis.31 A more invasive technique with a greater incidence of recanalization has a higher complication rate. In contrast, the safer technique with a lower complication rate has a lower recanalization rate. In cases of high back pressure values we chose less invasive techniques because we could take a longer time for recanalization. When the back pressure value was low, however, it was better to attempt early recanalization using more invasive techniques. Brain protection methods, including barbiturate therapy and induced hypertension, may be useful in cases of low back pressure. Limitations of the Study We measured blood pressure in the M2 parietal branch in patients with emboli extending from the M1 to the proximal M2. Back pressure in the M2 frontal branch was not measured because catheterization of the frontal branch usually took more time, which could delay recanalization. In cases of terminal ICA occlusion we did not measure back pressure in the anterior cerebral artery for the same reason. In this study ischemic lesions after thrombolysis were evaluated using CT scanning studies, although T2-weightJ. Neurosurg. / Volume 102 / May, 2005 05_05_JNS.1.gls 4/21/05 1:07 PM Page 877 Systolic back pressure in intraarterial thrombolysis ed MR imaging is more sensitive than CT scanning for the detection of ischemic lesions. In comparison with CT scanning, T2-weighted MR imaging takes a longer time period and tends to display motion artifacts. Patients with occlusion of a major artery are often restless; therefore, in this study we used CT scanning rather than T2-weighted MR imaging. Newly developed ischemic lesions can be confirmed by comparing CT scans obtained on admission and those obtained 2 months after thrombolytic therapy. Selective neuronal loss has been observed in regions of normal-appearing T2 signal on postischemic MR images.18 Neither CT scanning nor T2-weighted MR imaging can accurately demonstrate the true extent of neuronal damage. In this study, patients whose CT scans had revealed a reduction in ischemic lesions experienced significantly better outcomes than those whose scans demonstrated enlargement. This result indicates that CT scanning is an appropriate tool for evaluating ischemic damage with regard to clinical impairment. Conclusions Back pressure values, measured through a microcatheter during intraarterial thrombolysis, ranged from 22 to 78 mm Hg in this study. Back pressure measurements in combination with DW MR imaging could predict the development of infarction following thrombolysis. Thus, back pressure values might indicate appropriate strategies during intraarterial thrombolysis. Acknowledgment We thank Mr. Kenichi Miyoshi for his excellent technical assistance. References 1. Akl BF, Blakeley WR, Lewis CE, Edwards WS: Carotid endarterectomy: is a shunt necessary? Am J Surg 130:761–765, 1975 2. Astrup J, Siesjo BK, Symon L: Thresholds in cerebral ischemia— the ischemic penumbra. 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