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From the Department of Neurosurgery, Kumamoto University, School of Medicine, Kumamoto, Japan.
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Methods— We examined angiograms obtained from 107 moyamoya patients; 70 manifested ischemic and 37 had hemorrhagic lesions. Patients with intracerebral aneurysms or both hemorrhagic and ischemic lesions in the same cerebral hemisphere were not included. Patients were divided into those <20 years of age (n=47) and those 20 years of age (n=60). The right and left hemispheres in each patient were individually classified as hemorrhagic, ischemic, or asymptomatic. Each hemisphere was assessed for dilatation and branch extension of the anterior choroidal artery (AChA) and posterior communicating artery (P-CoM) and for the degree of proliferation of basal moyamoya vessels. These data were then statistically analyzed for correlation with intracranial bleeding events.
Results— The degree of proliferation of basal moyamoya vessels was not statistically correlated with hemorrhagic events. On the other hand, there was a correlation between hemorrhage and dilatation and abnormal branching of the AChA. In 27 of 37 hemorrhagic hemispheres (73.0%), this artery was dilated, and its abnormal branches served as collateral supply vessels to other regions. This phenomenon was observed in 4 of 5 hemorrhagic hemispheres from young patients; it was noted in fewer than one third of ischemic and asymptomatic hemispheres from this age group. Similarly, 71.9% of hemorrhagic hemispheres from adult patients manifested AChA dilatation and branching, and the difference between hemorrhagic hemispheres and those that were ischemic or asymptomatic was statistically significant (P<0.01). Although the incidence of dilatation and abnormal branching of the P-CoM was relatively low in hemorrhagic hemispheres from adult patients (18.8%), it was significantly higher than in the ischemic and asymptomatic hemispheres from this age group. Using dilatation and abnormal branching of the AChA and/or P-CoM as assessment criteria, we obtained high specificity (86.4%) and sensitivity (84.4%) for hemorrhagic events in adult moyamoya patients.
Conclusions— In adult moyamoya patients, dilatation and abnormal branching of the AChA and/or P-CoM are strong predictors of hemorrhagic events.
Key Words: angiography • hemorrhage • moyamoya disease
| Introduction |
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Because the site of intracranial bleeding in many moyamoya patients is the basal ganglia, thalamus, and near lateral ventricle wall,9–11 basal moyamoya vessels have been suspected as its origin.1,12–15 However, in some patients with hemorrhage, few basal moyamoya vessels are found, and their location is away from the bleeding site . We noted that among hemorrhagic moyamoya patients, including some exhibiting this phenomenon, the anterior choroidal artery (AChA) was frequently dilated and exhibited abnormal extension of many branches () and that the bleeding site was within the AChA territory. Therefore, we examined the arteries that normally supply the central or basal brain region in an effort to identify characteristic features of hemorrhagic moyamoya disease.
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We focused on vessels that supply the basal regions of the brain such as the basal ganglia, thalamus, and near lateral ventricle where intracranial bleeding frequently occurs in moyamoya patients.1,4,9–11 Our focus was on the AChA, posterior communicating artery (P-CoM), and basal moyamoya vessels, except for the ethmoidal and vault moyamoya vessels because the territories they feed are not frequent bleeding sites.
The right and left cerebral hemispheres (n=214) in each patient were separately identified as ischemic (including those with infarction and transient ischemic attacks, n=102), hemorrhagic (n=37), or asymptomatic (n=75). The AChA in each hemisphere was recorded as grade 0 (normal), 2 (dilated with distal branching), or 3 (dilated with abnormal branches serving as collateral supply vessels to other regions;. Basal moyamoya vessels were graded as absent (grade 0), few in number (grade 1), and densely proliferated (grade 2; . Findings on the P-CoM were recorded as negative; normal, dilated, or positive; or dilated with abnormal branch extensions . We also noted the site of occlusion or stenosis (O/S) of the ICA as following; site 1, ICA top or A1/M1; site 2, just distal to AChA; site 3, between the AChA and P-CoM; or site 4, proximal to P-CoM .
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The 107 patients were divided into a young (<20 years of age; n=47) and an adult (20 years of age; n=60) group because childhood moyamoya patients tend to manifest ischemia and adults predominantly experience hemorrhage. We examined the correlation between angiographic findings and symptoms using the Mann-Whitney U and 2 tests. Differences of P<0.01 were considered statistically significant.
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Angiographic Findings on Moyamoya Vessels and the AChA
Compared with ischemic and asymptomatic hemispheres, those with hemorrhage tended to manifest a higher degree of moyamoya vessel proliferation, regardless of the age of the patient . However, the difference was not statistically significant.
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Overall, in 33 of 37 hemorrhagic hemispheres (89.2%), the AChA was dilated and manifested branching (grades 1 and 2). More than 70% of the hemorrhagic hemispheres in both age groups had grade 2 AChA; the difference was statistically significant compared with ischemic and asymptomatic hemispheres (P<0.01).
Angiographic Findings on the P-COM
As shown in , approximately one fifth of the hemorrhagic hemispheres in both age groups showed P-CoM dilatation and branching. The difference between hemorrhagic and nonhemorrhagic hemispheres was statistically significant at P<0.01 (2 test) in both age groups.
Site of O/S of the ICA
demonstrates the distribution of the O/S site in the ICA. In 80.6% of adult hemorrhagic hemispheres, the lesion was just distal to the AChA (site 2); this site was involved in 45.9% and 20.8% of ischemic and asymptomatic hemispheres, respectively. The incidence of site 4 and 3 O/S was highest in ischemic hemispheres, and site 4 O/S was not found in hemorrhagic hemispheres.
Predictive Indicator(s) of a Hemorrhagic Event
To determine the most important factor(s) for predicting a hemorrhagic event in adult moyamoya patients, we assessed different parameters for their positive or negative predictive value, specificity, and sensitivity for hemorrhagic events (). Although the findings of grade 1 or 2 AChA showed the highest sensitivity (90.6%), the specificity was not as high (70.5%). Finally, our findings suggest that the combination of a dilated AChA in which the branches provide collateral flow (grade 2) or dilated P-CoM with abnormal branch extensions represents an indicator with good sensitivity (84.4%) and specificity (86.4%) for predicting a hemorrhagic event.
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| Discussion |
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Under normal conditions, the AChA supplies areas such as the medial portion of the globus pallidus, anterior perforating substance, internal capsule, choroid plexus, tail of the caudate nucleus, and thalamus. The normal P-CoM gives off branches to the optic chiasm, oculomotor nerve, tuber cinereum, cerebral crura, ventral thalamus, and caudal portion of the caudate nucleus.16,17 Thus, the normal branches of the AChA and P-CoM provide blood to areas near the lateral ventricle, basal ganglia, and thalamus. In moyamoya patients, these normal branches sometimes extend to other regions, and their function as collateral vessels results in blood flow increases. Rupture of dilated branches of the AChA and/or P-CoM may produce intraventricular or thalamic hematomas, hematomas near the lateral ventricle, and hematomas of the basal ganglia that are frequently found in hemorrhagic moyamoya patients. It is considered that the postmortem data may support (or disprove) our hypothesis. Thus, we examined 3 autopsy cases with hemorrhagic moyamoya disease and tried to identify the bleeding vessels. However, we could not identify the branches of AChA and P-CoM. Although it is difficult to pinpoint the bleeding vessels, in our series, hemorrhagic events coincided with dilatation and branch extension of the AChA and/or P-CoM , suggesting that these vessels may have been the origin of bleeding.
According to the morphometric analysis of Yamashita et al,15 most dilated arteries show fibrosis and marked attenuation of the media with occasional segmentation of the elastic lamina. As a result of hemodynamic stress or aging, dilated arteries with attenuated walls may acquire a predisposition for focal protrusion (microaneurysm formation) of the arterial wall. Subsequent rupture is thought to be a mechanism resulting in hemorrhage in patients with moyamoya disease. Such microscopic arterial changes may occur in the branches of the AChA and P-CoM.
The normal AChA is 0.5 mm in diameter and 3.0 cm in length. On angiograms, the last visible portion of the AChA enters the plexus of the temporal horn, visualized as the angiographic "brush" of the plexus. Furthermore, the fine vessels of the normal P-CoM are scarcely visible angiographically.16,17 Thus, the angiographically evident dilatation and branching of the AChA and P-CoM recorded in our study may signal increased blood flow and hemodynamic stress in these vessels. In 30% of nonhemorrhagic hemispheres from our young moyamoya patients, the dilated AChA had branches that served as collateral vessels; in adult ischemic and asymptomatic hemispheres, this phenomenon was more rare . This suggests that in young patients the AChA may function as a major collateral route and that it may play the same role for moyamoya vessels.
In nonhemorrhagic hemispheres, blood flow in the AChA decreases or disappears as the O/S site gets closer to the area proximal to the P-CoM . Furthermore, if the stenotic lesion is located just proximal to the P-CoM, neither the dilated AChA nor the basal moyamoya vessels are visible on angiograms. We posit this as the reason that no basal moyamoya vessels were discernible in about one fourth of the ischemic and asymptomatic hemispheres examined . We also suspect that O/S just distal to the AChA induces the greatest change in this vessel and results in severe hemodynamic stress. In adults with hemorrhagic moyamoya, the site of O/S may have stopped progressing at a younger age, and the presence of prolonged hemodynamic stress and/or some factors related to aging18 may eventually have led to bleeding.
Intracranial bleeding is a major prognostic factor in moyamoya patients,9,11 and currently we have no reliable indicator(s) for predicting a hemorrhagic event. In our series, angiograms were obtained within a few days of the initial hemorrhagic event, and the findings reflect the status before any rebleeding episodes. Of 32 adult patients who suffered hemorrhage, 17 who did not undergo bypass surgery experienced rebleeding during the follow-up period. Of these, 16 (94.1%) manifested a dilated AChA whose branches served as collateral vessels and/or a dilated P-CoM on angiograms obtained before the rebleeding episode. From these findings and the data shown , we suggest that dilatation and branch extension of the AChA and P-CoM are sensitive and specific predictive indicators of rebleeding.
Direct bypass surgery is thought to prevent recurrent intracranial bleeding in moyamoya patients.19–21 A direct bypass may decrease the blood flow in the AChA and P-CoM, and the findings reported here may help to identify moyamoya patients at greatest risk for hemorrhage and thus make it possible to apply preventive surgical therapy before the occurrence of a potentially lethal repeated hemorrhage. However, because this study was retrospective, a large prospective study is needed to confirm our conclusions.
| Acknowledgments |
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Received March 6, 2002; revision received August 8, 2002; accepted August 13, 2002.
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