Size and location of ruptured and unruptured intracranial aneurysms measured by 3-dimensional rotational angiography

OBJECTIVE: The aim of the study was to report about accurate size and location of a consecutive series of ruptured and unruptured aneurysms taking the complex 3-dimensional (3D) anatomy and parent vessel morphology into consideration by using the newly developed 3D rotational angiography (3D-RA). METHODS: One hundred eighteen consecutive patients with 155 saccular intracranial aneurysms were included in the study and received 3D-RA reconstructions for measurement of maximal height and width of the aneurysmal sac. Statistical evaluation compared values for ruptured (n = 83) and unruptured (n = 72) aneurysms. RESULTS: Mean height and width of unruptured aneurysms were 5.7 and 5.7 mm; of ruptured aneurysms, 6.7 and 6.1 mm (not significant, P = .7 for height and P = .9 for width). The majority of ruptured aneurysms, 81.9% and 59%, were smaller than 10 and 7 mm; likewise, 81.9% and 68.1% of unruptured aneurysms were smaller than 10 and 7 mm. The difference in frequency of small (<10/<7 mm) aneurysms between unruptured and ruptured aneurysms was not significant (P = 1.0 and .32, respectively). The majority (69.4%) of small ruptured aneurysms (<7 mm) were located in the anterior circulation. Most ruptured aneurysms were in the size group 4 to 6 mm in height and 2 to 4 mm in width, and a critical threshold size for aneurysm rupture could not be identified. CONCLUSIONS: An automated calibration procedure applied to all images and excellent visualization of aneurysm and parent vessel morphology using 3D-RA allow accurate size measurement of intracranial aneurysms which may be smaller than previously thought. Small aneurysm (<7 mm), also in the anterior circulation, should be carefully evaluated for treatment.     

Does a safe size-limit exist for unruptured intracranial aneurysms?

Summary Of 1076 patients with intracranial ruptured aneurysms (RA) included in the Danish Aneurysm Study, 948 had the RA verified by angiography. Of these cases 908 RA had a maximum diameter less than 25 mm. 162 RA were <5 mm, 474 and 272 were between 5–10 mm and 11–24 mm, respectively. The average diameter of the RA according to the day of angiography after the aneurysm rupture did not differ significantly within the first 10 days. In these circumstances, using this indirect method for estimation of aneurysm rupture according to the size, we also recommend that unruptured aneurysms with a size 10 mm or less should be seriously considerated for operation.     

Size of cerebral aneurysms and related factors in patients with subarachnoid hemorrhage

BACKGROUND: As the indication for surgical treatment of incidentally discovered small aneurysms remains controversial. METHODS: We retrospectively investigated the characteristics of small ruptured aneurysms and examined the relationship between the size and location of ruptured intracranial aneurysms and the sex, age, lifestyle, and medical history of 280 patients with ruptured aneurysm treated at our institute. RESULTS: The mean diameter of ruptured aneurysms in this series was 7.6 mm. In diameter, 135 (48.2%) ranged between 5 and 10 mm; 73 (26.1%) were smaller than 5 mm. The size of the ruptured aneurysms was significantly smaller (mean 6.5 mm) in patients with non- or poorly controlled hypertension than in normotensive patients (mean 8.3 mm) (p < 0.05). Ruptured aneurysms in the anterior communicating artery (AcomA) and anterior cerebral artery (ACA) were significantly smaller (p < 0.01) than those in the internal carotid artery or middle cerebral artery. Among 58 patients with multiple aneurysms, only 7 (12%) suffered rupture of aneurysms smaller than 5 mm (p < 0.01). Patients younger than 40 years and patients with a family history of subarachnoid hemorrhage appeared to predispose to the rupture of small-sized aneurysms, although those did not affect the statistical significance. CONCLUSIONS: This study shows that even aneurysms smaller than 10 mm may rupture. However, treatment decisions for unruptured aneurysm should not be based solely on the size of the unruptured aneurysms. Our data implies that even small aneurysms in the AcomA and ACA had an increased tendency for rupture, and that hypertensive patients were at higher risk for the rupture of small aneurysms.     

Rupture of previously documented asymptomatic unruptured aneurysms--aneurysm size: risk factor for aneurysm rupture

The natural history of asymptomatic unruptured aneurysms is not clear. We conducted a follow up study of 100 patients (since 1993) with 122 asymptomatic unruptured aneurysms that had not been operated on. We report five patients with previously documented asymptomatic unruptured aneurysms smaller than 10 mm in diameter that subsequently ruptured. Among the 100 patients, five had suffered subarachnoid hemorrhage (SAH) due to rupturing of an aneurysm. Of the 5 cases, 1 was male and 4 were female, with ages ranging from 59-73 years (mean age, 68 years). The aneurysms were on the MCA in 3, on the BA-SCA in 1, on the IC-PC in 1. The maximal diameter of the aneurysms at diagnosis ranged from 4.5 to 8 mm. The period from discovery to SAH was from 4 to 69 months and the cumulative rate of rupture of the aneurysms was 1.5 percent per year. Four of the 5 cases increased in size after the rupture. In our series, 2 of the 5 cases showed enlargement and the development of an aneurysmal bleb in the follow up MRA and 3D-CTA. The present study demonstrates that five asymptomatic unruptured aneurysms less than 10 mm in diameter subsequently ruptured. We ought to seriously consider the assertion published in the New England Journal of Medicine (Dec. 10, 1998), that unruptured aneurysms less than 10 mm in diameter have a very low probability of subsequent rupture.     

Natural history of unruptured intracranial aneurysms: probability of and risk factors for aneurysm rupture

OBJECT: The authors conducted a study to investigate the long-term natural history of unruptured intracranial aneurysms and the predictive risk factors determining subsequent rupture in a patient population in which surgical selection of cases was not performed. METHODS: One hundred forty-two patients with 181 unruptured aneurysms were followed from the 1950s until death or the occurrence of subarachnoid hemorrhage or until the years 1997 to 1998. The annual and cumulative incidence of aneurysm rupture as well as several potential risk factors predictive of rupture were studied using life-table analyses and Cox's proportional hazards regression models including time-dependent covariates. The median follow-up time was 19.7 years (range 0.8-38.9 years). During 2575 person-years of follow up, there were 33 first-time episodes of hemorrhage from previously unruptured aneurysms, for an average annual incidence of 1.3%. In 17 patients, hemorrhage led to death. The cumulative rate of bleeding was 10.5% at 10 years, 23% at 20 years, and 30.3% at 30 years after diagnosis. The diameter of the unruptured aneurysm (relative risk [RR] 1.11 per mm in diameter, 95% confidence interval [CI] 1-1.23, p = 0.05) and patient age at diagnosis inversely (RR 0.97 per year, 95% CI 0.93-1, p = 0.05) were significant independent predictors for a subsequent aneurysm rupture after adjustment for sex, hypertension, and aneurysm group. Active smoking status at the time of diagnosis was a significant risk factor for aneurysm rupture (RR 1.46, 95% CI 1.04-2.06, p = 0.033) after adjustment for size of the aneurysm, patient age, sex, presence of hypertension, and aneurysm group. Active smoking status as a time-dependent covariate was an even more significant risk factor for aneurysm rupture (adjusted RR 3.04, 95% CI 1.21-7.66, p = 0.02). CONCLUSIONS: Cigarette smoking, size of the unruptured intracranial aneurysm, and age, inversely, are important factors determining risk for subsequent aneurysm rupture. The authors conclude that such unruptured aneurysms should be surgically treated regardless of their size and of a patient's smoking status, especially in young and middle-aged adults, if this is technically possible and if the patient's concurrent diseases are not contraindications. Cessation of smoking may also be a good alternative to surgery in older patients with small-sized aneurysms.     

Natural history of unruptured intracranial aneurysms: probability of and risk factors for aneurysm rupture

OBJECT: The authors conducted a study to investigate the long-term natural history of unruptured intracranial aneurysms and the predictive risk factors determining subsequent rupture in a patient population in which surgical selection of cases was not performed. METHODS: One hundred forty-two patients with 181 unruptured aneurysms were followed from the 1950s until death or the occurrence of subarachnoid hemorrhage or until the years 1997 to 1998. The annual and cumulative incidence of aneurysm rupture as well as several potential risk factors predictive of rupture were studied using lifetable analyses and Cox's proportional hazards regression models including time-dependent covariates. The median follow-up time was 19.7 years (range 0.8-38.9 years). During 2575 person-years of follow up, there were 33 first-time episodes of hemorrhage from previously unruptured aneurysms, for an average annual incidence of 1.3%. In 17 patients, hemorrhage led to death. The cumulative rate of bleeding was 10.5% at 10 years, 23% at 20 years, and 30.3% at 30 years after diagnosis. The diameter of the unruptured aneurysm (relative risk [RR] 1.11 per mm in diameter, 95% confidence interval [CI] 1-1.23, p = 0.05) and patient age at diagnosis inversely (RR 0.97 per year, 95% CI 0.93-1, p = 0.05) were significant independent predictors for a subsequent aneurysm rupture after adjustment for sex, hypertension, and aneurysm group. Active smoking status at the time of diagnosis was a significant risk factor for aneurysm rupture (RR 1.46, 95% CI 1.04-2.06, p = 0.033) after adjustment for size of the aneurysm, patient age, sex, presence of hypertension, and aneurysm group. Active smoking status as a time-dependent covariate was an even more significant risk factor for aneurysm rupture (adjusted RR 3.04, 95% CI 1.21-7.66, p = 0.02). CONCLUSIONS: Cigarette smoking, size of the unruptured intracranial aneurysm, and age, inversely, are important factors determining risk for subsequent aneurysm rupture. The authors conclude that such unruptured aneurysms should be surgically treated regardless of their size and of a patient's smoking status, especially in young and middle-aged adults, if this is technically possible and if the patient's concurrent diseases are not contraindications. Cessation of smoking may also be a good alternative to surgery in older patients with small-sized aneurysms.     

A review of size and location of ruptured intracranial aneurysms

OBJECTIVE: To review our experience and examine the size at which aneurysms ruptured in our patient population. METHODS: Patient charts and angiograms for all patients admitted with a diagnosis of subarachnoid hemorrhage to the Thomas Jefferson/Wills Eye Hospital between April 1996 and March 2000 were reviewed. RESULTS: Of the 362 cases reviewed, definite measurements of the ruptured aneurysm were obtained in 245. The data clearly showed that most ruptured aneurysms presenting to our institution were less than 10 mm in diameter. We found that, regardless of location on the circle of Willis, 85.6% of all aneurysms presenting with rupture were less than 10 mm. Review by location shows that aneurysms of the anterior communicating artery most often presented with rupture at sizes less than 10 mm (94.4%). A large number of ruptured posterior communicating artery aneurysms also presented at sizes less than 10 mm (87.5%). This trend continued for all aneurysm sites in our review. The incidence of subarachnoid hemorrhage in Western countries is estimated at 10 per 100,000 people per year. Recent reports have indicated that aneurysms less than 10 mm in size are unlikely to rupture. CONCLUSION: We argue that the risk of small aneurysms rupturing is not insignificant, especially those of the anterior communicating artery. Our findings indicate that surgery on unruptured aneurysms should not be predicated on aneurysm size alone.     

Rupture of previously documented small asymptomatic saccular intracranial aneurysms. Report of three cases.

In a recent study from the Mayo Clinic on the natural history of intact saccular intracranial aneurysms, none of the aneurysms smaller than 10 mm in diameter ruptured. It was concluded that these aneurysms carry a negligible risk for future hemorrhage and that surgery for their repair could not be recommended. These findings and recommendations have been the subject of much controversy. The authors report three patients with previously documented asymptomatic intact saccular intracranial aneurysms smaller than 5 mm in diameter that subsequently ruptured. In Case 1, a 70-year-old man bled from a 4-mm middle cerebral artery aneurysm that had been discovered incidentally 2 1/2 years previously during evaluation of cerebral ischemic symptoms. A 10-mm internal carotid artery aneurysm and a contralateral 4-mm middle cerebral artery aneurysm had not ruptured. Case 2 was that of a 66-year-old woman who bled from a 4-mm pericallosal aneurysm that had been present 9 1/2 years previously when she suffered subarachnoid hemorrhage (SAH) from a 7 x 9-mm posterior inferior cerebellar artery aneurysm. Although the pericallosal aneurysm had not enlarged in the intervening years, a daughter aneurysm had developed. The third patient was a 45-year-old woman who bled from a 4- to 5-mm posterior inferior cerebellar artery aneurysm that had measured approximately 2 mm on an angiogram obtained 4 years previously; at that time she had suffered SAH due to rupture of a 5 x 12-mm posterior communicating artery aneurysm. These cases show that small asymptomatic intact saccular intracranial aneurysms are not innocuous and that careful consideration must be given to their surgical repair and long-term follow-up study.     

The aspect ratio (dome/neck) of ruptured and unruptured aneurysms

OBJECT: In this retrospective study the authors examined the aspect ratio (AR; the maximum dimension of the dome/width of the neck of an aneurysm) and compared the distribution of this ratio in a group of ruptured and unruptured aneurysms. A similar comparison was performed in relation to the maximum dimension of the aneurysm alone. The authors sought to evaluate the utility of these measures for differentiating ruptured and unruptured aneurysms. METHODS: Measurements were made of 774 aneurysms in 532 patients at three medical centers. One hundred twenty-seven patients harbored only unruptured lesions, 290 only ruptured lesions, and 115 both ruptured and unruptured lesions. Cases were included if angiograms were available for measurement and the status of the individual patient's aneurysm(s) was known. The odds of a lesion falling in the ruptured aneurysm group increased with both the lesion's maximum size and the AR. The odds ratio for rupture rose progressively only for the AR. The distribution curves showed that ruptured aneurysms were larger and had greater ARs. The mean size of unruptured aneurysms was 7 mm and that of ruptured ones was 8 mm; the corresponding mean ARs were 1.8 and 3.4, respectively. The odds of rupture were 20-fold greater when the AR was larger than 3.47 compared with an AR less than or equal to 1.38. Only 7% of ruptured aneurysms had an AR less than 1.38 compared with 45% of unruptured lesions. CONCLUSIONS: The AR is probably a useful index to calculate. A high AR might reasonably influence the decision to treat actively an unruptured aneurysm independent of its maximum size. Prospective studies are warranted.     

Intracranial saccular aneurysm enlargement determined using serial magnetic resonance angiography

OBJECT: The goal of this study was to determine the frequency of enlargement of unruptured intracranial aneurysms by using serial magnetic resonance (MR) angiography and to investigate whether aneurysm characteristics and demographic factors predict changes in aneurysm size. METHODS: A retrospective review of MR angiograms obtained in 57 patients with 62 unruptured, untreated saccular aneurysms was performed. Fifty-five of the 57 patients had no history of subarachnoid hemorrhage. The means of three measurements of the maximum diameters of these lesions on MR source images defined the aneurysm size. The median follow-up period was 47 months (mean 50 months, range 17-90 months). No aneurysm ruptured during the follow-up period. Four patients (7%) harbored aneurysms that had increased in size. No aneurysms smaller than 9 mm in diameter grew larger, whereas four (44%) of the nine aneurysms with initial diameters of 9 mm or larger increased in size. Factors that predicted aneurysm growth included the size of the lesion (p < 0.001) and the presence of multiple lobes (p = 0.021). The location of the aneurysm did not predict an increased risk of enlargement. CONCLUSIONS: Patients with medium-sized or large aneurysms and patients harboring aneurysms with multiple lobes may be at increased risk for aneurysm growth and should be followed up with MR imaging if the aneurysm is left untreated.     

Difference in configuration of ruptured and unruptured intracranial aneurysms determined by biplanar digital subtraction angiography

Summary ¶Summary There is an ongoing discussion about the risk of bleeding from unruptured intracranial aneurysms. Management guidelines were developed recently and some of the recommendations for decision making are based on the anatomical configuration of the aneurysm. The common assumption is that the presence of multiple lobes or a daughter sac indicates a higher risk of rupture. We have investigated the anatomical configuration of ruptured and unruptured intracranial aneurysms using biplanar digital subtraction angiography (DSA). The objective was to determine, whether there was a difference between ruptured and unruptured aneurysms regarding lobulation, the presence of a daughter sac or the shape as measured by the height/neck ratio.Biplanar DSA images of 124 patients were retrospectively analyzed. A total of 53 unruptured and 94 ruptured aneurysms were found (=147 aneurysms in total). Aneurysms of less than 10mm diameter accounted for 82% of all aneurysms. Overall, 10% of unruptured aneurysm showed a multilobular appearance on DSA compared with 20% of ruptured aneurysms (Fishers exact test, p=0.10). In the 5–9mm aneurysm group, multiple lobes were found significantly more frequent in ruptured aneurysms (26% vs. 4%, Fishers exact test, p<0.05). A height/neck ratio of less than 1.5 was not found in unruptured aneurysms (0/26) but in 21% (12/57) of ruptured aneurysms (p<0.05).Our data provide scientific support for using morphological features for the decision making process in the management of unruptured intracranial aneurysms. An irregular multilobar appearance was significantly more common in aneurysms of 5–9mm size that ruptured.Published online October 9, 2003     

Unruptured intracranial aneurysms in elderly patients.

A total of 556 patients with 769 intracranial aneurysms, of which 256 were unruptured and 513 were ruptured, were included in the present study. The patients were divided into three age groups: those aged 59 years or younger, those aged 60 to 69 years, and those aged 70 years or older. Small aneurysms of 4 mm or less in diameter were more common in the series of unruptured aneurysms than in the ruptured aneurysms. The rupture rate in anterior communicating artery aneurysms was the highest, and it increased with age. A follow-up study was performed on 47 patients with 55 unruptured aneurysms, and only one giant basilar artery aneurysm ruptured during the average follow-up period of 5.2 years. Direct operation was performed on 52 patients with unruptured aneurysms. While the surgical mortality rate was 0%, the morbidity rate was 6% (three of 52 cases), which was not directly related to the patients' age. When considering surgery for unruptured aneurysms, rupture rate of aneurysms at each site is one of the most important factors, especially in elderly patients.     

Angiographic characteristics of ruptured paraclinoid aneurysms: risk factors for rupture

Background

The diagnosis and treatment of unruptured paraclinoid aneurysms has been increasing with the recent advent of diagnostic tools and less invasive endovascular therapeutic options. Considering the low incidence of rupture, investigation of the characteristics of ruptured paraclinoid aneurysm is important to predict rupture risk of the paraclinoid aneurysms. The objective of this study is to evaluate probable factors for rupture by analyzing the characteristics of ruptured paraclinoid aneurysms.

Methods

A total of 2,276 aneurysms (1,419 ruptured and 857 unruptured) were diagnosed and treated endovascularly or microsurgically between 2001 and 2011. Among them, 265 were paraclinoid aneurysms, of which 37 were ruptured. Removing 12 blister-like aneurysms, 25 ruptured and 228 unruptured saccular aneurysms were included and the medical records and radiological images were retrospectively analyzed.

Results

Of 25 aneurysms, 16 (64.0 %) were located in the superior direction. Five were inferior located lesions (20 %) and four were medially located lesions (16.0 %). Laterally located lesions were not found. The mean size of aneurysms was 9.4?±?5.6 mm. Ten aneurysms (40.0 %) were ≥?10 mm in size. Thirteen aneurysms (52.0 %) were lobulated. The superiorly located aneurysms were larger than the other aneurysms (10.3?±?5.8 mm vs. 7.7?±?4.9 mm) and more frequently lobulated (ten of 16 vs. three of nine). In a comparative analysis, the ruptured aneurysms were located more in the superior direction compared with unruptured aneurysms (64 vs. 23.2 %, p?<?0.0001). Large aneurysms (36.0 vs. 7.9 %, p?<?0.0001), longer fundus diameter (mean 9.4?±?5.6 vs. 4.8?±?3.3 mm, p?=?0.001), dome-to-neck ratio (mean 1.8?±?0.9 vs. 1.2?±?0.5, p?<?0.0001), and lobulated shape aneurysms were more likely to be ruptured aneurysms (13 of 25 ruptured aneurysms, 52.0 %, p?=?0.001).

Conclusions

Rupture risk of the paraclinoid aneurysm is very low. However, superiorly located paraclinoid aneurysms appear more likely to rupture than other locations. Angiographically, more conservative indication for the treatment of paraclinoid aneurysm should be recommended except for superior located lesions.     

Quantified aneurysm shape and rupture risk

OBJECT: The authors investigated whether quantified shape or size indices could better discriminate between ruptured and unruptured aneurysms. METHODS: Several custom algorithms were created to quantifiy the size and shape indices of intracranial aneurysms by using three-dimensional computerized tomography angiography models of the brain vasculature. Data from 27 patients with ruptured or unruptured aneurysms were evaluated in a blinded fashion to determine whether aneurysm size or shape better discriminated between the ruptured and unruptured groups. Five size and eight shape indices were calculated for each aneurysm. Two-tailed independent Student t-tests (significance p < 0.05) were used to determine statistically significant differences between ruptured and unruptured aneurysm groups for all 13 indices. Receiver-operating characteristic-area under curve analyses were performed for all indices to quantify the predictability of each index and to identify optimal threshold values. None of the five size indices were significantly different between the ruptured and unruptured aneurysms. Five of the eight shape indices were significantly different between the two lesion groups, and two other shape indices showed a trend toward discriminating between ruptured and unruptured aneurysms, although these differences did not reach statistical significance. CONCLUSIONS: Quantified shape is more effective than size in discriminating between ruptured and unruptured aneurysms. Further investigation will determine whether quantified aneurysm shape will prove to be a reliable predictor of aneurysm rupture.     

Study of multiple cerebral aneurysms comprised of both ruptured and unruptured aneurysm--an analysis of incidence rate with respect to site and size

The purpose of this investigation was to study the incidence rate of rupture with respect to the site and size of multiple cerebral aneurysms that include both ruptured and unruptured aneurysms. Site and size were investigated in 58 cases of this type of multiple cerebral aneurysm. All cerebral aneurysms were examined with MR angiography, 3D-CT angiography and digital subtraction angiography, as well as seeing measured using 3D-CT or digital subtraction angiography. As regards the site of the 58 ruptured cerebral aneurysms under study, 18 were internal carotid aneurysms (C2 or C3: 4 cases, IC-PC: 12 cases, IC-ancho.: 1 case, IC terminal: 1 case), 25 were anterior communicating aneurysms, 10 were middle cerebral aneurysms, 4 were anterior cerebral aneurysms and 1 case was a VA-PICA aneurysm. The ruptured internal carotid aneurysms were 4.0-21.0 mm in size, the anterior communicating aneurysms were 1.8-13 mm, the middle cerebral aneurysms were 2.0-21.3 mm, the anterior cerebral aneurysms were 3.2-9.1 mm, and the VA-PICA aneurysm was 4.4 mm. The sites of the 89 unruptured cerebral aneurysms break down as follows: 29 were internal carotid aneurysms (C2 or C3: 4 cases, IC-PC: 10 cases, IC-ancho.: 10 cases, IC terminal: 5 cases), 18 were anterior communicating aneurysms, 34 were middle cerebral aneurysms, and there were 5 cases of posterior circulation aneurysm. In size, the unruptured internal carotid aneurysms were 1.0-18.3 mm, the anterior communicating aneurysms were 1.0-6.5 mm, the middle cerebral aneurysms were 1.0-10.3 mm, the anterior cerebral aneurysms were 1.0-3.3 mm, and the posterior circulation aneurysms were 2.2-17.3 mm. Out of 58 ruptured cerebral aneurysms, 44 were of the largest size category, and 53 (91.4%) were in the largest size category and/or anterior communicating aneurysms. The accumulated incidence rate of rupture of anterior communicating aneurysms rose suddenly upon reaching 2 mm in size, and after reaching 3 mm, these aneurysms accounted for a nearly uniform 55%-60% of the incidence rate of rupture. The accumulated incidence rate of rupture of IC-PC aneurysms rose drastically at 4 mm in size with the data describing a parabolic slope when graphed. IC-PC aneurysms represented a uniform 55% of the incidence rate of rupture after reaching 8 mm in size. The accumulated incidence rate of rupture of middle cerebral aneurysms rose in a gently sloping parabola beginning at 4 mm, and stabilized at 20% upon reaching 10 mm. These results suggest that each site is associated with a characteristic size and rate of aneurismal rupture. Special attention should thus be paid to large and anterior communicating aneurysms when operating on multiple cerebral aneurysms.     

Ruptured intracranial aneurysms: an autopsy study of 133 patients

The autopsy findings of 133 patients with ruptured intracranial aneurysms were reviewed: 24 (18%) had multiple aneurysms. Intraventricular hemorrhage was seen in 53 patients (40%), and intracerebral hematoma was seen in 52 (39%). Intraventricular hemorrhage was seen most frequently in patients with anterior communicating artery aneurysms [21 of 40 (53%)]. Intracerebral hematoma occurred most frequently in patients with middle cerebral artery aneurysms [11 of 28 (39%)]. Hemorrhages arising from anterior communicating artery aneurysms had two types of penetration routes into the lateral ventricle. The first was through the inferomedial portion of the frontal lobe, and the second was through the corpus callosum. The second type was poorly visualized in horizontal sections of the brain. Of 40 patients with anterior communicating artery aneurysms, the first type of penetration route was observed in 15, and the second type was found in 3. The second type is rare, and if the hemorrhage is not massive, it may be overlooked in axial computed tomography scans. Of the 109 ruptured aneurysms, 18 (17%) were 4 mm or less in diameter, 50 (46%) were 5-9 mm in diameter, and 41 (38%) were 10 mm or larger in diameter. In the 21 patients with multiple aneurysms, unruptured aneurysms were smaller than ruptured aneurysms in 17 of 27 (63%), equal size in 9 (33%), and larger in 1 (4%). Regarding rerupture, the larger the ruptured aneurysms were, the higher the percentage of rerupture, that is, 11% of 18 ruptured aneurysms of 4 mm or less in diameter, 32% of 50 of 5-9 mm in diameter, and 37% of 41 of 10 mm or larger in diameter had reruptured. It seems that the larger the size of the aneurysm, the higher the risk of rerupture as well as of initial rupture.     

A proposed parent vessel geometry-based categorization of saccular intracranial aneurysms: computational flow dynamics analysis of the risk factors for lesion rupture

OBJECT: The authors created a simple, broadly applicable classification of saccular intracranial aneurysms into three categories: sidewall (SW), sidewall with branching vessel (SWBV), and endwall (EW) according to the angiographically documented patterns of their parent arteries. Using computational flow dynamics analysis (CFDA) of simple models representing the three aneurysm categories, the authors analyzed geometry-related risk factors such as neck width, parent artery curvature, and angulation of the branching vessels. METHODS: The authors performed CFDAs of 68 aneurysmal geometric formations documented on angiograms that had been obtained in patients with 45 ruptured and 23 unruptured lesions. In successfully studied CFDA cases, the wall shear stress, blood velocity, and pressure maps were examined and correlated with aneurysm rupture points. Statistical analysis of the cases involving aneurysm rupture revealed a statistically significant correlation between aneurysm depth and both neck size (p < 0.0001) and caliber of draining arteries (p < 0.0001). Wider-necked aneurysms or those with wider-caliber draining vessels were found to be high-flow lesions that tended to rupture at larger sizes. Smaller-necked aneurysms or those with smaller-caliber draining vessels were found to be low-flow lesions that tended to rupture at smaller sizes. The incidence of ruptured aneurysms with an aspect ratio (depth/neck) exceeding 1.6 was 100% in the SW and SWBV categories, whereas the incidence was only 28.75% for the EW aneurysms. CONCLUSIONS: The application of standardized categories enables the comparison of results for various aneurysms' geometric formations, thus assisting in their management. The proposed classification system may provide a promising means of understanding the natural history of saccular intracranial aneurysms.     

Small unruptured aneurysm verification (SUAVe Study, Japan)--interim report

A prospective study (SUAVe Study, Japan) is in progress at 13 national hospitals to determine the surgical indications for small unruptured intracranial aneurysm. These hospitals are observing the natural history of small unruptured aneurysms (under 5 mm diameter) without surgical treatment. Since October 2000, 455 aneurysms (393 patients) with 75 aneurysms excluded by film judgment committees have been registered, of which 380 aneurysms (329 cases) have been followed up for a mean of 13.8 months (5 aneurysms for 36 months, 68 for 24 months, 164 for 12 months, and 64 for 6 months). Four aneurysms have already ruptured (3 multiple and 1 single). The annual rupture rate was 0.8% (95% confidence interval 0.2-3%). Another 18 aneurysms have enlarged including seven aneurysms treated for enlargement over 2 mm in size. Considering this finding, the annual rupture rate might rise slightly. The important factors for rupture and enlargement were multiplicity of aneurysm, female, patient aged over 70 years old, and location of aneurysm (anterior communicating artery, basilar artery). The growth rate may be faster in multiple aneurysms than in single aneurysms.     

Problems of surgical treatment for multiple intracranial aneurysms]

A series of 105 patients presenting with multiple aneurysms and subarachnoid hemorrhage (SAH) were operated on for ruptured and unruptured aneurysms between 1976 and 1984. Clinical factors other than the severity of SAH affecting the outcomes included: 1) Misdiagnosis of the location of a ruptured aneurysm among multiple aneurysms resulted in poor outcomes because of multiple surgical approaches or rebleeding during the acute period. 2) Combinations of aneurysmal locations requiring multiple surgical approaches, such as interhemispheric and transsylvian, during the acute stage caused worse outcomes than with multi-stage surgeries. If an unruptured aneurysm could not be reached during the initial exposure, multi-stage surgery was safe if the ruptured aneurysm had been clipped during the acute period. 3) Complications occurring during unruptured aneurysm surgery. The patient's age, the location and size of the unruptured aneurysms were significant factors in the clinical prognosis. Surgery for unruptured aneurysm caused 1.8% morbidity in patients between 28 and 55 years, but 18.0% morbidity in patients over 56 years of age. Surgery for internal carotid artery aneurysms resulted in 14.8% overall morbidity. Surgery for middle cerebral and anterior cerebral artery aneurysms caused below 5% morbidity. Postoperative morbidity in patients with aneurysms less than 5 mm in diameter was 1.3%, and with aneurysms measuring 10 mm or more, 20%. The optimum treatment for multiple aneurysms with SAH should be based on all factors of the patient's condition, including the unruptured aneurysms.     

Simulation of the natural history of cerebral aneurysms based on data from the International Study of Unruptured Intracranial Aneurysms

OBJECT: Despite recent publications of large-scale study data, controversy over the management of unruptured cerebral aneurysms continues. The low rupture rates in the International Study of Unruptured Intracranial Aneurysms (ISUIA) apparently contradicted surgeons' experiences with ruptured aneurysms. In the present study, based on data from the ISUIA, a mathematical model describing the natural history of cerebral aneurysms was developed. With this model, the author aimed to examine the validity of data from the ISUIA and to provide a better treatment guideline for unruptured aneurysms. METHODS: The author made a computer simulation of the natural history of cerebral aneurysms that was used to calculate such figures as the prevalence of unruptured aneurysms, incidence of subarachnoid hemorrhage (SAH), and age and size distribution of both unruptured and ruptured aneurysms. The lifetime lesion rupture probability for individual patients with various ages and aneurysm sizes was also computed, thereby providing a useful index to help patients in the medical decision-making process. The computer model produced a sample of unruptured aneurysms in the general population with a prevalence of 4.2% and a median diameter of 5.8 mm. These unruptured aneurysms--affected by the rupture rate reported in the ISUIA--had a yearly SAH incidence of 19.6 per 100,000 persons. The median diameter of these aneurysms was 9.4 mm. CONCLUSIONS: Findings in the present study validated the results of the ISUIA by showing that the seemingly low rupture rates could explain the statistical data for ruptured aneurysms. With the featured model, the author calculated the lifetime probability of lesion rupture--a useful measure for deciding on the optimal treatment for unruptured aneurysms.