Division of Neurosurgery, Institute of Brain Diseases, Tohoku University School of Medicine, Sendai 982

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1 Tohoku J. exp. Med., 1978, 126, Distribution of Intracranial Aneurysm TAKASHI YOSHIMOTO, TAKAMASA KAYAMA, NAMIO KODAMA and JIRO SUZUKI Division of Neurosurgery, Institute of Brain Diseases, Tohoku University School of Medicine, Sendai 982 YOSHIMOTO, T., KAYAMMA, T., KODAMA, N. and SUZUKI, J. Distribution of Intracranial Aneurysm. Tohoku J. exp. Med., 1978, 126 (2), The 1,080 cases of intracranial saccular aneurysms, which were seen at our clinic during the period from June 1961 to September 1975, were subjected to the analysis on the location of the aneurysms, age distribution and sex incidence. intracranial aneurysm; distribution We reported the statistical studies on the 3548 cases of intracranial aneurysms in the neurosurgical clinics in Japan (Suzuki et al. 1971). Recently we noted that more than one thousand cases of intracranial aneurysm were seen and examined at our clinic alone. In the present study, the distribution of intracranial aneurysms, based on our 1080 saccular aneurysm cases, is investigated. MATERIALS 1,116 cases of various kinds of intracranial aneurysms were seen in our clinic during the period from June 1961 to September The 1,116 cases included 1080 saccular aneurysm cases, 11 sclerotic, 3 traumatic, 1 mycotic, 2 anomalous, 1 giant cell arteritis TABLE 1. Various types of intracranial aneurysms (Tohoku Univ. June 1961-Sept. 1975) CVD, cerebro-vascular disease; AVM, arterio-venous malformation; HICH, hypertensive intracerebral hematoma. Received for publication, January 7,

2 126 T. Yoshimoto et al. and 18 aneurysm cases accompanied with other cerebrovascular diseases (Table 1). For the object of this study only cases of saccular aneurysms were subjected to the analysis. RESULTS The 1,080 cases of intracranial saccular aneurysms were analyzed for the frequency of aneurysm sites. There were 366 cases of the anterior communicating artery, 286 cases of the internal carotid artery, 182 cases of the middle cerebral artery, 50 cases of the anterior cerebral artery, 30 cases of the vertebro-basilar arteries and 166 cases of multiple aneurysms (Table 2). TABLE 2. Site distribution Fig. 1. Location of 1,307 saccular aneurysms in 1,080 cases. In cases of multiple aneurysms there were 127 cases of two aneurysms, 25 cases of three, 9 of four, 4 of five and 1 case of eight. The total cases including 914 cases of a single aneurysm and 166 cases of multiple aneurysms had 1,307 aneurysms. There were 462 aneurysms (35.3%) on the anterior communicating artery, 422 aneurysms (32.2%) on the internal carotid artery, 298 aneurysms

3 Distribution of Intracranial Aneurysm 127 (22,8%) on the middle cerebral artery, 80 aneurysms (6.1%) on the anterior cerebral artery and 45 aneurysms (3.4%) on the vertebro-basilar artery (Fig. 1). The age ranged from 16-year-old male to 86-year-old female. The peak incidence occurred in the sixth decade with 32.2 percent followed by the fifth decade with 31.0 percent (Table 3). Our series revealed distinct difference of site distribution between age groups younger than 30 years and all other decennial age groups. Of the 44 cases younger than 30 years, only 1 case had an aneurysm of the middle cerebral artery. On the other hand, 17 of 44 cases showed aneurysms of the internal carotid artery. No significant differences could be seen between the group older than 60 years and the overall age group (Table 4). TABLE 3. Age distribution TABLE 4. Site distributions in younger and older age groups TABLE 5. Age distribution and sex incidence

4 128 T. Yoshimoto et al. TABLE 6. Distiribution of aneurysm cases according to number of aneurysms, sex and age The sex incidence in our series was male-predominant. There were 578 male with 54 percent and 502 female with 46 percent. Male predominance exhibited a maximum ratio of 2.5 to 1 for the ages below 20 years, but the gap diminished gradually until the fifth decade. And, female became predominant after 50 years (Table 5). No significant differences were seen between the age distribution in cases of single and multiple anerusysm. However, about a quarter of the female cases over the sixth decade were the cases of multiple aneurysms (Table 6). DISCUSSION Ramamurthi (1969) reported that the incidence of intracranial aneurysm in South-East Asian countries including Japan is considerably lesser than that in European countries and the United States. However, we reported that 3,548 cases with 3,898 aneurysms in total had been seen in 111 Japanese neurosurgical clinics for a period of about 10 years (Suzuki et al. 1971). The number of aneurysms in our clinic had increased progressively year by year and the 1000th case was operated on intracranially in September 1975 (Fig. 2). Fig. 2. Saccular aneurysm seen each year in Tohoku University.

5 Distribution of Intracranial Aneurysm 129 One of the reasons why aneurysm cases, especially surgical ones, have increased progressively from the 1960's in Japan had been attributed to the advance and development of the cerebral angiography for the cerebral stroke. At present, the incidence per population of intracranial aneurysms in Japan is not lesser, but probably higher than Western countries. It is rather curious that the incidence has remained low in many South-East Asian countries. The Japanese National Health Statistics on the cases of death reported cerebral stroke as the most popular, cancer as the second, heart attack as the third (Fig. 3). The order of these causes is different from those in the United States and European countries. Moreover, according to the statistics of mortality rate of cerebrovascular disease by World Health Statistics Annual in 1970, the Fig. 3. Causes of death in Japan. Japan National Health Statistics (1972). Fig. 4. Mortality rate of cerebrovascular disease. World Health Statistics Annual (1970).

6 130 T. Yoshimoto et al. TABLE 7. Site and side * Only single aneurysm cases including 56 cases with both aneurysm and arteriovenous incidence of cerebral stroke in Japan was the highest among the reported countries (Fig. 4). Our statistical study covering the north-eastern districts (Tohoku) in Japan has been compared with studies of distribution of intracranial aneurysm of the United States Cooperative Study in 1966 (USA Coop) (Sahs et al. 1969), and of the Japanese neurosurgical clinics in 1969 (JNC) (Suzuki et al. 1971). The total numbers of aneurysm cases in these statistics were 2,672 cases in the USA Coop, 3,548 cases in the JNC and 1,080 cases in the Tohoku. In the USA Coop and the JNC, the internal carotid artery was most frequently involved, followed by the anterior communicating artery. In the Tohoku the anterior communicating artery was the highest and the internal carotid artery the lowest among the three investigations (Table 7). However, all studies were in agreement in that the most frequent sites were the internal carotid artery, anterior communicating Fig. 5. Age of aneurysm cases in U.S.A. and Japan. œ- œ, Tohoku ( ) 308 cases; ü- ü, Tohoku ( ) 772 cases; - Japan (1969) 3,430 cases; -, U.S.A. (1966) 2,627 cases.

7 Distribution of Intracranial Aneurysm 131 distribution of aneurysms malformation. Fig. 6. Sex incidence of aneurysm cases. Fig. 7. Sex ratio (F/M) of the incidence of aneurysms by decennial age. œ- œ ( ) 308 cases -, Tohoku (1975), 1,080 cases ü- ü ( ) 772 cases USA Coop (1966), 2,627 cases artery and middle cerebral artery. These three arteries altogether account for 89.1% of the total cases in the USA Coop, 87% in the JNC and 90.3% in the Tohoku.

8 132 T. Yoshimoto et al. In age distribution, more than 90 percent of the saccular aneurysms were found in the age range between 30 and 69 years with a peak at the fifth decade in the JNC and our 1960's series (Tohoku), while peaks were in the sixth decade in the USA Coop and our 1970's series (Tohoku). The cases of aneurysm were few in the first, second and eighth decades in every series (Fig. 5). The sex incidence in Japan with male predominance was contrary to that of the USA Coop. However, female cases in our clinic have increased according to our recent series (Fig. 6). Sex ratio in each decade changes with a clear-cut tendency in the USA Coop and the Tohoku. The younger the decade is, the more predo minant males are, and the older the decade is, the more predominant females are. In the USA Coop, females became predominant above 40 years and the ratio of female predominance was very distinct. On the other hand, in the Tohoku females became predominant above 50 years and the ratio was not remarkable (Fig. 7). References 1) Ramamurthi, B. (1969) Incidence of intracranial aneurysms in India. J. Neurosurg., 30, ) Sahs, A.L., Perret, G.E., Locksley, H.B. & Nishioka, H. (1969) Intracranial Aneurysms and Subarachnoid Hemorrhage, J.B. Lippincott Co., Philadelphia-Toronto, pp ) Suzuki, J., Hori, S. & Sakurai, Y. (1971) Intracranial aneurysms in neurosurgical clinics in Japan. J. Neurosurg., 35,

Division of Neurosurgery, Institute of Brain Diseases, Tohoku University School of Medicine, Sendai 982

Division of Neurosurgery, Institute of Brain Diseases, Tohoku University School of Medicine, Sendai 982 Tohoku J. exp. Med., 1979, 128, 267-271 The Correlation between Hypertension in Past History and the Incidence of Cerebral Aneurysms RYUNGCHAN KWAK, KAZUO Mizoi, IRO SUZUKI RYUICHI KATAKURA and J Division