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Computed tomography and magnetic resonance observations in asymptomatic cerebral ischemic lesions
] Stroke Cerebrooasc Dis 1994;4:275-278
© 1994 National Stroke Association
Computed Tomography and Magnetic Resonance Observations in Asymptomatic Cerebral Ischemic Lesions
s. Passero, M.D., and N. Battistini, M.D.
yve ~ompared the .results ~f computed tomography and magnetic resonance imagmg m the evaluation of silent cerebral ischemic lesions in patients without a history of cerebrovascular events and those who present an initial cerebral ischemic episode. Key Words: Silent ischemic lesions-Cerebrovascular disease-Computed tomography-Magnetic resonance imaging .
Computed tomography (CT) may often reveal cerebral ischemic lesions in patients without previous history of cerebral ischemic events. Such silent lesions may have been truly asymptomatic or may have produced symptoms passed unreported or unrecognized as stroke. In general, studies on this issue concern patients with clinical evidence and/or history of cerebrovascular disease or with particular risk factor for stroke (1-13). The prevalence of unreported or asymptomatic cerebral ischemic lesions in subjects without a history of cerebrovascular disease and without particular risk factor is unknown. Furthermore, the prevalences observed in patients with cerebrovascular disease are probably influenced by the criteria of patient selection and by the imaging procedure used. The aims of the present study were: (a) to compare the prevalence and characteristics of silent cerebral ischemic lesions in unselected patients without any history of cerebrovascular events and in patients who present an initial cerebral ischemic episode and (b) to evaluate the phenomenon on the basis of the results obtained by two different imaging techniques, namely CT and magnetic resonance imaging (MRI).
From the Institute for Nervous and Mental Diseases, University of Siena, Siena, Italy. Address correspondence and reprint requests to Dr. S. Passero at Institute for Nervous and Mental Diseases, University of Siena, ViaIe Bracci, 53100 Siena, Italy.
Subjects and Methods The frequency and characteristics of silent cerebral ischemic lesions were analyzed by means of CT or MRI in a group of 194 patients (72 women and 122 men) who had experienced an initial transient ischemic attack (TIA) or stroke and in a group of 225 patients (114 women and 111 men) without history of previous cerebrovascular episodes. Of the 194 patients with cerebral ischemic events, 103 were studied by CT and 91 by MRI. Of the 225 patients without history of cerebrovascular disease, 118 underwent CT and 107 MRI as part of the diagnostic workup for other neurologic or psychiatric disorders. CT was performed on a General Electric 9800 scanner. MRI studies were performed using a superconducting magnet with a main field strength of 0.5 T (General Electric) . The timing of CT and MRI was random in patients without a history of cerebrovascular disease, whereas in patients with a cerebral ischemic event, imaging studies were performed within days or weeks of the clinical event. For each patient, CT or MRI were evaluated for the number, type, and topography of the lesions. Ischemic lesions were classified as small (lacunar) when the diameter of the lesion was less than or equal to 15 mm, or large when the diameter of the lesion was greater than 15 mm. Ischemic lesions were defined as focal areas of hypodensity of presumably vascular ] STROKE CEREBROVASCDIS, VOL. 4, NO.4, 1994
275
S. PASSEROAND N. BAITlSTINI
Magnetic Resonance Imaging
origin on CT or focal areas of low-signal intensity on MRI Tl-weighted images that were visible as hyperintense areas on T2-weighted images. Hyperintense punctuate lesions on T2-weighted images were not counted as ichemic lesions if they were not visible as low-intensity areas on Tl-weighted images. In patients without history of cerebral ischemic episodes, all ischemic lesions were considered as silent. In patients with an initial cerebral ischemic event, lesions were considered silent when unrelated to the qualifying clinical event.
As expected, MRIshowed much higher prevalences of silent cerebral ischemic lesions both in patients without history of stroke and in those with an initial ischemic episode (Table 3). Sixty-two percent of patients without history of stroke showed silent ischemic lesions, which, in most cases (95.5%), were small and more often (77.6%) localized in the white matter. Among patients with an initial cerebral ischemic episode, 79% showed silent ischemic lesions. Also, in this case, most were small deep lesions in the white matter, but basal ganglia were more often involved with respect to the patients without a history of cerebral ischemic episodes. larger infarcts were observed in 8 (11%) patients.
Results The demographic characteristics in the four groups of patients and clinical subtype of event in patients who presented an initial cerebral ischemic episode are reported in Table 1. There were no significant age and sex differences between patients studied by CT and those studied by MRI.
Discussion With the advent of CT, it became evident that silent ischemic lesions were frequently found in patients with or without a history of cerebrovascular episodes. According to previous CT studies performed in patients with an initial cerebrovascular episode but without any history or prior cerebral ischemic event, the prevalence of silent cerebral ischemic lesions was about 12% (2,4,5). In populations of patients with history of TIAs, the prevalence ranged from 30% to 39% (7,13) and was higher (47%) when patients also had carotid stenosis (7). In surgical series, in which patients undergo CT before carotid endarterectomy, cerebral ischemic lesions were reported in 12-48% of patients with previous TIAs (3,11,12) and in 17-21% of those without previous ischemic episodes (1,9). In selected populations of patients with atrial fibrillation,
Computed Tomography Among the 118 patients without history of cerebral ischemic event, CT showed no evidence of cerebral ischemic lesions in 106 cases. In 12 .patients (10%), CT showed small deep infarcts, which in 5 cases involved only the white matter and in 7 the white matter and the basal ganglia. Among patients with an initial episode, CT showed silent ischemic lesions in 33 cases (32.0%). In most cases, these were small deep infarcts in the white matter alone (42:4%) or in the white matter and basal ganglia (45.4%). Only in 4 cases were these larger superficial infarcts (Table 2).
Table 1.
Demographic characteristics and clinical subtype of eventin 419 patients (194) and without (225) an initial cerebral ischemic episode (CIE) CT Without CIE
No. Sex (M/F) Mean age (years) Initial episode TIA RIND or minor stroke Stroke
118 57/61 66.3
MRI With CIE 103 64/39 64.2 27 (26.2%) 30 (29.1%) 46 (46.7%)
Without CIE 107 54/53 62.5
With CIE 91 58/33 61.7 27 (29.6%) 31 (34.0%) ~3 (36.2%)
TIA, transient ischemic attack; RIND, reversible ischemic neurological deficit. 276
J STROKECEREBROVASCDIS, VOL.4, NO.4, 1994
Witll
ASYMPTOMATICCEREBRAL ISCHEMIC LESIONSON MRl AND cr
CT study: prevalence and characteristics of silent cerebral ischemic lesions in patients with or withoutan initial ischemic episode (Clf)
Table 2.
Without CIE (n = 118)
No. of patients with silent lesions Unilateral Bilateral Size Small Large Small and large Location Small infarcts White matter Basal ganglia White matter and basal ganglia Large infarcts Superficial Deep
With CIE (n = 103)
No.
%
No.
%
12 2 10
10.1 16.7 83.3
33 13 20
32.0 39.4 60.6
29 4 0
87.4 12.1
14 0 15
42.4
4 0
12.1
12 0 0
5 0 7
100
41.7 58.3
0 0
45.4
MRI study: prevalence and characteristics ofsilent or unreported cerebral ischemic lesions in patients with or withoutan initial cerebral ischemic episode (Clf)
Table 3.
Without CIE (n = 107)
No. of patients with silent lesions Unilateral Bilateral Size Small Large Small and large Location Small infarcts White matter Basal ganglia White matter and basal ganglia Large infarcts Superficial Deep
even higher prevalence rates of silent infarction were reported (6,8,10). Our CT findings indicated that silent cerebral ischemic lesions occurred rather frequently (10%) in aged subjects without a history of cerebrovascular
WithCIE (n = 91)
No.
%
No.
%
67 3 64
62.6 4.5 95.5
72 12 60
79.1 16.7 83.3
64 2 1
95.5 3.0 1.5
63 7 2
87.5 9.7 2.8
52 0 12
77.6
35 0 28
48.6 38.9
3 0
4.5
8 1
11.1 1.4
17.9
episode and were significantly more frequent (32%) in unselected patients who presented an initial cerebral ischemic event. Brain MRI was proven to be very sensitive for the detection of silent cerebrovascular lesions (14). In a
JSTROKE CEREBROVASC DIS,VOL 4, NO.4,
1994
277
S. PASSEROAND N. BAITISTINI
recent MRI study, Matsubayashi et al. (IS) found at least one lacunar infarct in 47% of 73 independent asymptomatic elderly individuals aged S8-83 years (mean, 70 years). In our MRI study, we found a similar, although slightly more elevated, prevalence rate of silent ischemic lesions in patients without a history of cerebrovascular events. In patients who presented an initial cerebral ischemic event, prevalence of silent lesions was significantly higher (79%). In our study, as in others, silent cerebral ischemic lesions were found to be predominantly small and deep in location, and this may be related to be the fact that small lesions in the white matter with sparing of the motor tracts are generally asymptomatic as are the small lesions of the basal ganglia with sparing of the adjacent internal capsule (2,6). Our results indicate that evidence of silent cerebral ischemic lesions by CT or MRI is a common finding in patients with an initial cerebral ischemic episode and to a lesser extent in individuals without history of cerebrovascular events. Our results also underline the importance of routine imaging studies in evaluating patients with cerebrovascular disease, since clinical symptoms alone are inaccurate indicators of the presence or absence of cerebral ischemic lesions. Cerebral imaging studies may be of substantial help in making an estimation of the extent of cerebrovascular disease in subjects without a history of cerebrovascular events but with risk factors for stroke including advanced age.
References 1. Berguer R, Sieggreen M, Lazo A, Hodakowski G. The silent brain infarct in carotid surgery. J VaseSurg 1986; 3:442. 2. Chodosh E,Foulkes M, Kase C, et al. Silent stroke in the NINCDS stroke data bank. Neurology 1988;38:1674. 3. Graber J, Vollman R, Johnson W, et al. Stroke after
278
J STROKE CEREBROVASCDIS, VOL. 4, NO.4, 1994
4.
5. 6. 7.
carotid endarterectomy: risk as predicted by preoperative computerized tomography. Am J Surg 1984;147: 492. Herderschee D, Hijdra A, Algra A, Koudstaal P, Kappelle L, van Gijn J, for the Dutch TIA study group. Silent stroke in patients with transient ischemic attack or minor ischemic stroke. Stroke 1992;23:1220. Kase C, Wolf P, Chodosh E, et al. Prevalence of silent stroke in patients presenting with initial stroke. The Framingham study. Stroke 1989;20:850. Kempster P, Garraty R, Gates P. Asymptomatic cerebral infarction in patients with chronic atrial fibrillation. Stroke 1988;19:955. Norris J, Zhu C. Silent stroke and carotid stenosis. Stroke 1992;23:483.
8. Petersen P, Madsen E, Brun B,Pedersen F, Gyldensted C, Boysen G. Silent cerebral infarction in chronic atrial fibrillation. Stroke 1987;18:1098. 9. Ricotta J, Ouriel K, Green R, De Weese J. Use of computerized tomography in selection of patients for elective and urgent carotid endarterectomy. Ann Surg 1985;202:783. 10. Sasaki W, Yanagiswa S, Maki K, Onodera A, Awaji T, Kanazawa T. High incidence of silent small cerebral infarction in the patients with atrial fibrillation. Circulation 1987;76(Suppl IV):104. 11. Sise M, Sedwitz M, Rowley W, Shackford S. Prospective analysis of carotid endarterectomy and silent cerebral infarction in 197patients. Stroke 1989;20:329. 12. Street D, O'Brien M, Ricotta J. Observations on cerebral computed tomography in patients having carotid endarterectomy. J Vase Surg 1988;7:798. 13. Turnbull I, Bannister C. CT observations on the natural history of asymptomatic cerebral infarction following transient ischaemic attacks. Neurol Res 1985;7: 190. 14. Awad I, Spetzler R, Hodak J, Awad C, Carey R. Incidental subcortical lesions identified on magnetic resonance imaging in the elderly: 1. Correlation with age and cerebrovascular risk factors. Stroke 1986;17: 1084. 15. Matsubayashi K, Shimada K, Kawamoto A, Ozawa T. Incidental brain lesions on magnetic resonance imaging and neurobehavioral functions in the apparently healthy elderly. Stroke 1992;23:175. 16. Tuszynski M, Petito C, Levy D. Risk factors and clinical manifestations of pathologically verified lacunar infarctions. Stroke 1989;20:990.
© 1994 National Stroke Association
Computed Tomography and Magnetic Resonance Observations in Asymptomatic Cerebral Ischemic Lesions
s. Passero, M.D., and N. Battistini, M.D.
yve ~ompared the .results ~f computed tomography and magnetic resonance imagmg m the evaluation of silent cerebral ischemic lesions in patients without a history of cerebrovascular events and those who present an initial cerebral ischemic episode. Key Words: Silent ischemic lesions-Cerebrovascular disease-Computed tomography-Magnetic resonance imaging .
Computed tomography (CT) may often reveal cerebral ischemic lesions in patients without previous history of cerebral ischemic events. Such silent lesions may have been truly asymptomatic or may have produced symptoms passed unreported or unrecognized as stroke. In general, studies on this issue concern patients with clinical evidence and/or history of cerebrovascular disease or with particular risk factor for stroke (1-13). The prevalence of unreported or asymptomatic cerebral ischemic lesions in subjects without a history of cerebrovascular disease and without particular risk factor is unknown. Furthermore, the prevalences observed in patients with cerebrovascular disease are probably influenced by the criteria of patient selection and by the imaging procedure used. The aims of the present study were: (a) to compare the prevalence and characteristics of silent cerebral ischemic lesions in unselected patients without any history of cerebrovascular events and in patients who present an initial cerebral ischemic episode and (b) to evaluate the phenomenon on the basis of the results obtained by two different imaging techniques, namely CT and magnetic resonance imaging (MRI).
From the Institute for Nervous and Mental Diseases, University of Siena, Siena, Italy. Address correspondence and reprint requests to Dr. S. Passero at Institute for Nervous and Mental Diseases, University of Siena, ViaIe Bracci, 53100 Siena, Italy.
Subjects and Methods The frequency and characteristics of silent cerebral ischemic lesions were analyzed by means of CT or MRI in a group of 194 patients (72 women and 122 men) who had experienced an initial transient ischemic attack (TIA) or stroke and in a group of 225 patients (114 women and 111 men) without history of previous cerebrovascular episodes. Of the 194 patients with cerebral ischemic events, 103 were studied by CT and 91 by MRI. Of the 225 patients without history of cerebrovascular disease, 118 underwent CT and 107 MRI as part of the diagnostic workup for other neurologic or psychiatric disorders. CT was performed on a General Electric 9800 scanner. MRI studies were performed using a superconducting magnet with a main field strength of 0.5 T (General Electric) . The timing of CT and MRI was random in patients without a history of cerebrovascular disease, whereas in patients with a cerebral ischemic event, imaging studies were performed within days or weeks of the clinical event. For each patient, CT or MRI were evaluated for the number, type, and topography of the lesions. Ischemic lesions were classified as small (lacunar) when the diameter of the lesion was less than or equal to 15 mm, or large when the diameter of the lesion was greater than 15 mm. Ischemic lesions were defined as focal areas of hypodensity of presumably vascular ] STROKE CEREBROVASCDIS, VOL. 4, NO.4, 1994
275
S. PASSEROAND N. BAITlSTINI
Magnetic Resonance Imaging
origin on CT or focal areas of low-signal intensity on MRI Tl-weighted images that were visible as hyperintense areas on T2-weighted images. Hyperintense punctuate lesions on T2-weighted images were not counted as ichemic lesions if they were not visible as low-intensity areas on Tl-weighted images. In patients without history of cerebral ischemic episodes, all ischemic lesions were considered as silent. In patients with an initial cerebral ischemic event, lesions were considered silent when unrelated to the qualifying clinical event.
As expected, MRIshowed much higher prevalences of silent cerebral ischemic lesions both in patients without history of stroke and in those with an initial ischemic episode (Table 3). Sixty-two percent of patients without history of stroke showed silent ischemic lesions, which, in most cases (95.5%), were small and more often (77.6%) localized in the white matter. Among patients with an initial cerebral ischemic episode, 79% showed silent ischemic lesions. Also, in this case, most were small deep lesions in the white matter, but basal ganglia were more often involved with respect to the patients without a history of cerebral ischemic episodes. larger infarcts were observed in 8 (11%) patients.
Results The demographic characteristics in the four groups of patients and clinical subtype of event in patients who presented an initial cerebral ischemic episode are reported in Table 1. There were no significant age and sex differences between patients studied by CT and those studied by MRI.
Discussion With the advent of CT, it became evident that silent ischemic lesions were frequently found in patients with or without a history of cerebrovascular episodes. According to previous CT studies performed in patients with an initial cerebrovascular episode but without any history or prior cerebral ischemic event, the prevalence of silent cerebral ischemic lesions was about 12% (2,4,5). In populations of patients with history of TIAs, the prevalence ranged from 30% to 39% (7,13) and was higher (47%) when patients also had carotid stenosis (7). In surgical series, in which patients undergo CT before carotid endarterectomy, cerebral ischemic lesions were reported in 12-48% of patients with previous TIAs (3,11,12) and in 17-21% of those without previous ischemic episodes (1,9). In selected populations of patients with atrial fibrillation,
Computed Tomography Among the 118 patients without history of cerebral ischemic event, CT showed no evidence of cerebral ischemic lesions in 106 cases. In 12 .patients (10%), CT showed small deep infarcts, which in 5 cases involved only the white matter and in 7 the white matter and the basal ganglia. Among patients with an initial episode, CT showed silent ischemic lesions in 33 cases (32.0%). In most cases, these were small deep infarcts in the white matter alone (42:4%) or in the white matter and basal ganglia (45.4%). Only in 4 cases were these larger superficial infarcts (Table 2).
Table 1.
Demographic characteristics and clinical subtype of eventin 419 patients (194) and without (225) an initial cerebral ischemic episode (CIE) CT Without CIE
No. Sex (M/F) Mean age (years) Initial episode TIA RIND or minor stroke Stroke
118 57/61 66.3
MRI With CIE 103 64/39 64.2 27 (26.2%) 30 (29.1%) 46 (46.7%)
Without CIE 107 54/53 62.5
With CIE 91 58/33 61.7 27 (29.6%) 31 (34.0%) ~3 (36.2%)
TIA, transient ischemic attack; RIND, reversible ischemic neurological deficit. 276
J STROKECEREBROVASCDIS, VOL.4, NO.4, 1994
Witll
ASYMPTOMATICCEREBRAL ISCHEMIC LESIONSON MRl AND cr
CT study: prevalence and characteristics of silent cerebral ischemic lesions in patients with or withoutan initial ischemic episode (Clf)
Table 2.
Without CIE (n = 118)
No. of patients with silent lesions Unilateral Bilateral Size Small Large Small and large Location Small infarcts White matter Basal ganglia White matter and basal ganglia Large infarcts Superficial Deep
With CIE (n = 103)
No.
%
No.
%
12 2 10
10.1 16.7 83.3
33 13 20
32.0 39.4 60.6
29 4 0
87.4 12.1
14 0 15
42.4
4 0
12.1
12 0 0
5 0 7
100
41.7 58.3
0 0
45.4
MRI study: prevalence and characteristics ofsilent or unreported cerebral ischemic lesions in patients with or withoutan initial cerebral ischemic episode (Clf)
Table 3.
Without CIE (n = 107)
No. of patients with silent lesions Unilateral Bilateral Size Small Large Small and large Location Small infarcts White matter Basal ganglia White matter and basal ganglia Large infarcts Superficial Deep
even higher prevalence rates of silent infarction were reported (6,8,10). Our CT findings indicated that silent cerebral ischemic lesions occurred rather frequently (10%) in aged subjects without a history of cerebrovascular
WithCIE (n = 91)
No.
%
No.
%
67 3 64
62.6 4.5 95.5
72 12 60
79.1 16.7 83.3
64 2 1
95.5 3.0 1.5
63 7 2
87.5 9.7 2.8
52 0 12
77.6
35 0 28
48.6 38.9
3 0
4.5
8 1
11.1 1.4
17.9
episode and were significantly more frequent (32%) in unselected patients who presented an initial cerebral ischemic event. Brain MRI was proven to be very sensitive for the detection of silent cerebrovascular lesions (14). In a
JSTROKE CEREBROVASC DIS,VOL 4, NO.4,
1994
277
S. PASSEROAND N. BAITISTINI
recent MRI study, Matsubayashi et al. (IS) found at least one lacunar infarct in 47% of 73 independent asymptomatic elderly individuals aged S8-83 years (mean, 70 years). In our MRI study, we found a similar, although slightly more elevated, prevalence rate of silent ischemic lesions in patients without a history of cerebrovascular events. In patients who presented an initial cerebral ischemic event, prevalence of silent lesions was significantly higher (79%). In our study, as in others, silent cerebral ischemic lesions were found to be predominantly small and deep in location, and this may be related to be the fact that small lesions in the white matter with sparing of the motor tracts are generally asymptomatic as are the small lesions of the basal ganglia with sparing of the adjacent internal capsule (2,6). Our results indicate that evidence of silent cerebral ischemic lesions by CT or MRI is a common finding in patients with an initial cerebral ischemic episode and to a lesser extent in individuals without history of cerebrovascular events. Our results also underline the importance of routine imaging studies in evaluating patients with cerebrovascular disease, since clinical symptoms alone are inaccurate indicators of the presence or absence of cerebral ischemic lesions. Cerebral imaging studies may be of substantial help in making an estimation of the extent of cerebrovascular disease in subjects without a history of cerebrovascular events but with risk factors for stroke including advanced age.
References 1. Berguer R, Sieggreen M, Lazo A, Hodakowski G. The silent brain infarct in carotid surgery. J VaseSurg 1986; 3:442. 2. Chodosh E,Foulkes M, Kase C, et al. Silent stroke in the NINCDS stroke data bank. Neurology 1988;38:1674. 3. Graber J, Vollman R, Johnson W, et al. Stroke after
278
J STROKE CEREBROVASCDIS, VOL. 4, NO.4, 1994
4.
5. 6. 7.
carotid endarterectomy: risk as predicted by preoperative computerized tomography. Am J Surg 1984;147: 492. Herderschee D, Hijdra A, Algra A, Koudstaal P, Kappelle L, van Gijn J, for the Dutch TIA study group. Silent stroke in patients with transient ischemic attack or minor ischemic stroke. Stroke 1992;23:1220. Kase C, Wolf P, Chodosh E, et al. Prevalence of silent stroke in patients presenting with initial stroke. The Framingham study. Stroke 1989;20:850. Kempster P, Garraty R, Gates P. Asymptomatic cerebral infarction in patients with chronic atrial fibrillation. Stroke 1988;19:955. Norris J, Zhu C. Silent stroke and carotid stenosis. Stroke 1992;23:483.
8. Petersen P, Madsen E, Brun B,Pedersen F, Gyldensted C, Boysen G. Silent cerebral infarction in chronic atrial fibrillation. Stroke 1987;18:1098. 9. Ricotta J, Ouriel K, Green R, De Weese J. Use of computerized tomography in selection of patients for elective and urgent carotid endarterectomy. Ann Surg 1985;202:783. 10. Sasaki W, Yanagiswa S, Maki K, Onodera A, Awaji T, Kanazawa T. High incidence of silent small cerebral infarction in the patients with atrial fibrillation. Circulation 1987;76(Suppl IV):104. 11. Sise M, Sedwitz M, Rowley W, Shackford S. Prospective analysis of carotid endarterectomy and silent cerebral infarction in 197patients. Stroke 1989;20:329. 12. Street D, O'Brien M, Ricotta J. Observations on cerebral computed tomography in patients having carotid endarterectomy. J Vase Surg 1988;7:798. 13. Turnbull I, Bannister C. CT observations on the natural history of asymptomatic cerebral infarction following transient ischaemic attacks. Neurol Res 1985;7: 190. 14. Awad I, Spetzler R, Hodak J, Awad C, Carey R. Incidental subcortical lesions identified on magnetic resonance imaging in the elderly: 1. Correlation with age and cerebrovascular risk factors. Stroke 1986;17: 1084. 15. Matsubayashi K, Shimada K, Kawamoto A, Ozawa T. Incidental brain lesions on magnetic resonance imaging and neurobehavioral functions in the apparently healthy elderly. Stroke 1992;23:175. 16. Tuszynski M, Petito C, Levy D. Risk factors and clinical manifestations of pathologically verified lacunar infarctions. Stroke 1989;20:990.