Surgery of incidental intracranial aneurysms

A series of nine patients with an unruptured asymptomatic aneurysm not associated with a ruptured aneurysm is discussed. Three had giant aneurysms. Two patients had bilateral aneurysms of the middle cerebral artery. Five had solitary aneurysms of the middle cerebral artery. One had an aneurysm of the anterior communicating artery. One had an ophthalmic aneurysm. All aneurysms were clipped. Two operations were necessary in the two patients with bilateral aneurysms. There was no mortality and no significant morbidity. Clipping of the aneurysm is recommended for those patients who have no other serious illness that significantly increases the surgical risk. If a combination of pituitary tumor and aneurysm is found, a subfrontal instead of transsphenoidal approach should be considered so as to treat both the tumor and aneurysm at the same operation.     

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.     

Wall stress analysis in small asymptomatic, symptomatic and ruptured abdominal aortic aneurysms.

OBJECTIVES: To evaluate the potential of wall stress analysis for the identification of abdominal aortic aneurysm (AAA) at elevated risk of rupture in spite of small diameter. MATERIALS AND METHODS: Thirty patients with small AAA, 10 asymptomatic, 10 symptomatic and 10 ruptured, were included. Demographic data and results from physical examinations were recorded in a retrospective fashion. After CT-evaluation and the creation of a patient specific 3D model, wall stress was calculated using the finite element method. RESULTS: No differences were observed in diameter between asymptomatic, symptomatic or ruptured aneurysms (5.1+/-0.2 cm vs. 5.1+/-0.2 cm vs. 5.3+/-0.2 cm respectively; p=0.57). Peak aortic wall stress at maximal systolic blood pressure is significantly higher in ruptured than asymptomatic aneurysms (51.7+/-2.4 N/cm(2) vs. 39.7+/-3.3 N/cm(2) respectively; p=0.04). Wall stress analysis at uniform blood pressure, performed to correct for higher blood pressure in the symptomatic and rupture group did not result in significant differences in peak wall stress (asymptomatic 31.7+/-2.3 N/cm(2); symptomatic 30.5+/-1.3 N/cm(2); rupture 36.7+/-4.0 N/cm(2); p=0.26). CONCLUSIONS: Wall stress analysis at maximal systolic blood pressure is a promising technique to detect aneurysms at elevated aneurysm rupture risk. Since no significant differences were found at uniform blood pressure, the need for adequate blood pressure control in aneurysm patients is reiterated.     

Endovascular treatment of abdominal aortic aneurysms

BACKGROUND: Endovascular treatment of abdominal aortic aneurysms is a rapidly evolving technique that has gained broad acceptance in the treatment of patients with abdominal aortic aneurysms. METHODS: A review of the English literature was done to determine the short- and long-term outcomes of endovascular repair of abdominal aortic aneurysms. Reports of complications such as endoleak, graft migration, graft limb occlusion, aneurysm rupture, and aneurysm enlargement were evaluated. RESULTS: Short-term results of endovascular repair of abdominal aortic aneurysms are excellent. The necessity for open conversions is less than 5%. The cumulative risk of aneurysm rupture is approximately 1% per year. The coverall incidence of graft limb occlusion was 2.8% in the follow-up period. The cumulative risk for a secondary procedure was 12% at 1 year, 24% at 2 years, and 35% at 3 years. Moderate and severe neck angulation was associated with an increased incidence of adverse events in the follow-up period. Endografts have the potential to become infected and develop aortoduodenal fistula. The treatment of ruptured aneurysms with endovascular grafts has been successful and a technique that is increasingly used. CONCLUSION: Endovascular treatment of abdominal aortic aneurysm is an effective technique with excellent short-term results. The long-term results remain to be determined. Ongoing surveillance is necessary to avoid late complications of aneurysm rupture.     

Treatment of ruptured and unruptured internal carotid artery aneurysms.

A consecutive series of 95 patients with a total of 131 intracranial cerebral aneurysms came under observation from 1972-1978. Of these, 78 patients had operations for 106 aneurysms. Over half of the patients (41) had operations for an aneurysm of the intracranial internal carotid artery; there were 16 incidental "asymptomatic" aneurysms also found. There was no surgical mortality in this group. Medical treatment, including bed rest, antihypertensive treatment and administration of epsilon amino caproic acid followed by microsurgical obliteration of the aneurysm offers the best results for the treatment of ruptured and unruptured aneurysms.     

The benign course of cavernous carotid artery aneurysms.

Recently, the benign nature of aneurysms of the cavernous carotid artery has been questioned. In a review of cases evaluated from 1980 to 1990 with this developmental aneurysm, the authors found 70 patients with 79 cavernous carotid artery aneurysms. As expected, the great majority (59 patients) had ophthalmoplegia as the initial problem. Retro-orbital pain (three cases) and a carotid-cavernous fistula (five cases) were infrequently the sole manifestation. Mirror-image asymptomatic aneurysms were found in nine patients and asymptomatic cavernous aneurysms were found in three additional patients. Thirty-four patients not surgically treated were followed for a mean of 2.8 years, and 36 surgical patients were followed for a mean of 4.1 years prior to treatment. Of the 79 aneurysms, one (1.3%) ruptured into the subarachnoid space during this period. Other than optic neuropathy or cranial neuropathy, no patient had a permanent neurological deficit; the 12 asymptomatic aneurysms remained asymptomatic. It is concluded that an aneurysm of the cavernous carotid artery is rarely associated with life-threatening complications, and treatment should be considered principally for patients with intolerable pain or problems related to vision.     

Elective surgery for small abdominal aortic aneurysms.

BACKGROUND AND PURPOSE: Surgical repair for abdominal aortic aneurysm has become more frequent and the mortality associated with elective surgery has been reduced, but the overall mortality for ruptured aneurysm remains unacceptably high. The dilemma for the vascular surgeon is whether to operate early and electively on asymptomatic small aneurysms, less than 5 cm in diameter, or to delay surgery, adopting a wait-and-see attitude. The purpose of this retrospective study was to review a recent 5-year experience of elective aneurysm surgery, with special emphasis on the perioperative outcome of surgical repair of asymptomatic small aneurysms, in order to evaluate whether early mortality and morbidity justify an aggressive approach. METHODS: The report concerns a series of 141 consecutive patients who underwent aneurysm repair for small (n = 65, group I) and large aneurysms (n = 76, group II). For each group, the age, sex, risk factors and associated diseases, operative and aortic cross-clamping times, estimated blood loss, blood transfusion volume, type of operation and graft, perioperative morbidity and mortality, and causes of death were recorded and compared. RESULTS: The majority of patients were males. The mean age of the patients was lower in group I than in group II. No statistically significant difference was found from the comparison of the risk factors and associated diseases in groups I and II. The mean operating time was 82 minutes in group I, 98 minutes in group II, and the aortic cross-clamping time was also shorter in group I (37 min versus 52 min), whereas blood loss was greater, with a statistically significant difference (P < 0.05). The operative mortality rate was higher in group II than in group I (1.3% versus 0%, P = NS). CONCLUSIONS: Elective small aneurysm repair is recommended in good-risk patients for the following reasons: (i) the operative mortality and morbidity rates are lower in small than in large aneurysm patients, and (ii) the small aneurysm repair is technically easier and safer to perform. In addition, there are two other considerations that are more difficult to quantify, but may support an aggressive approach: the cost-benefit ratio is better with early diagnosis and elective surgery, before an emergency operation is required, and personal choice and psychological reasons can induce patients to prefer early elective repair to periodic monitoring by ultrasound or computed tomography scans.     

Long term prognosis of symptomatic and asymptomatic cerebral aneurysms

The authors analyze the follow-up series of 58 patients with diagnosed cerebral aneurysms who were either not treated surgically or, in surgically treated cases, in which the aneurysmal neck was not clipped. The patients are divided in three groups: untreated ruptured; ruptured treated by coating, vessel ligation or aneurysmal dome clipping; and asymptomatic cases. During the follow-up period of three to ten years, there were no bleedings from asymptomatic aneurysms and only one rebleeding from symptomatic operated aneurysms. As can be expected in the group of ruptured unoperated aneurysms, the rate of rebleeding was 40.9% with a mortality rate of 31.7%. The natural history of asymptomatic aneurysms is unclear regarding the risk of bleeding, and regardless of the obtained follow-up results in our cases, we think that all diagnosed cerebral aneurysms must be treated surgically. Certainly, individual cases must be evaluated.     

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.     

Endovascular treatment for basilar tip aneurysms

The aim of this study was to analyze the effect of endovascular treatment of basilar (BA) tip aneurysms. The authors performed a retrospective analysis of 79 aneurysms of the BA tip that had been treated using endovascular coil embolization for the last 11 years. Fifty-six patients were women, and 23 were men. The average age of the patients was 63.7 years (range, 35-83 year). The average maximum diameter of the aneurysms was 8.0 mm (range, 2-30 mm). Forty-seven patients (60%) presented with acute subarachnoid hemorrhage (SAH), 1 patient (1%) had an unruptured aneurysm with mass effect, and 31 patients (39%) had incidental aneurysms. Immediate anatomic outcomes demonstrated complete occlusion (CO) in 53 aneurysms (67%), residual neck (RN) in 22 aneurysms (28%), and residual aneurysm (RA) in 4 aneurysms (5%). One patient died from rebleeding 6 hours after the embolization. Another patient suffered from rebleeding 6 years after the initial embolization, and was successfully treated with re-embolization. Four patients suffered from asymptomatic P1 occlusion. No symptomatic complication was observed in the unruptured group. Retreatment was performed in 5 patients, including 4 broad-neck large ruptured aneurysms and 1 giant thrombosed aneurysm. Angiographic and clinical results have been improving in recent cases in this study. Technical advances such as highly compliant balloon remodeling microcatheter and 3D-reconstructed digital angiography contributed to this improvement. Our results indicate that endovascular treatment of BA tip aneurysm is safe and effective. The long-term stability after coil embolization is still a matter of concern. Further improvement is expected.     

Solitary aneurysms of the iliac arterial system: an estimate of their frequency of occurrence

Solitary iliac artery aneurysms are rare, and most reports have been presented as case reports. By combining autopsy records and operating records, a total of 13 cases were found: during a 15-year period (1971 to 1985), 42,010 of the inhabitants of Malm? died (population 230,000) and 35,265 (including 9014 forensic autopsies) underwent autopsy (84%). Solitary iliac artery aneurysms were found in seven (0.03%) of the 26,251 patients who underwent autopsy at the hospital; six of those had been asymptomatic and one was ruptured. Among the 9014 persons who underwent forensic medical autopsy, there were two with ruptured solitary iliac artery aneurysms. Four patients had clinically detected solitary iliac artery aneurysms, three of which were ruptured. All patients underwent surgery, and two of the three patients with ruptured solitary iliac artery aneurysms left the hospital well. The rupture rate of iliac aneurysm among those found at autopsy was one of seven (14%) and among those clinically detected three of four.     

锁孔微创入路手术治疗颅内动脉瘤的风险因素及对策分析

目的 探讨颅内动脉瘤在锁孔手术中破裂的风险因素、适应证选择、手术难点、预防动脉瘤破裂的方法及应急处理措施.方法 回顾性分析1999年至2005年115例动脉瘤患者的临床资料.将动脉瘤破裂风险较低的43例患者通过锁孔微创入路手术治疗（锁孔组）,其余72例患者采用常规开颅手术治疗（常规组）.锁孔组43例患者手术中翼点锁孔入路20例,眶上锁孔入路18例,纵裂锁孔入路5例.常规组72例患者风险高而采用常规翼点开颅31例,额下开颅11例,纵裂开颅7例,翼点-额下联合10例,翼点-纵裂联合6例,额下-纵裂联合4例,翼点-额下-纵裂联合3例.结果 锁孔组术中动脉瘤渗漏6例,破裂出血3例,发生率为7%,无手术死亡.2例在锁孔手术中无法夹闭动脉瘤而改为常规开颅.常规组术中发生动脉瘤渗漏18例,破裂出血9例,发生率为13%,手术后死亡2例.结论 尽管锁孔手术有微创、伤口美观、术后恢复快等优点,但在风险低的患者中动脉瘤渗漏和破裂的风险仍然不能忽视.     

Concurrent treatment of acute pancreatitis and multiple visceral artery aneurysms using endovascular techniques

Multiple aneurysms involving the celiac axis are extremely rare. Celiac artery aneurysms account for only 4% of all visceral aneurysms with 40% having concomitant aneurysms such as gastroduodenal artery (GDA) aneurysms. Development of a GDA aneurysm is associated with pancreatitis. If a GDA aneurysm ruptures, traditional repair is through open surgical techniques with significant morbidity and mortality as up to 50% occur in the setting of chronic pancreatitis. However, a ruptured GDA aneurysm causing pancreatitis has not been described previously. We report a case of successful endovascular treatment of a ruptured GDA aneurysm and concomitant celiac artery aneurysm leading to the resolution of acute pancreatitis.     

Renal artery aneurysms. Natural history and prognosis

Eighty-three patients out of 8,525 undergoing renal angiography during the years 1970-1979 were found to have renal artery aneurysm, which in six patients were bilateral and in 11 multiple. This corresponds to an incidence of almost 1% in this group of patients. Sixty-nine patients were treated conservatively and followed for a mean of 4.3 years. At that time nine patients had died. The cause of death was in no case related to the aneurysm. None of the 60 living patients had symptoms which could be related to the aneurysm. Reports of 36,656 autopsies, including most of the sudden deaths occurring in southern Sweden during a ten-year period, were analyzed. Nineteen cases of ruptured arterial aneurysms in the branches of abdominal aorta were found, but in no case were the renal arteries involved. It is concluded that the risk for rupture of a renal artery aneurysm is extremely small. The indications to operate renal artery aneurysms are discussed.     

Usefulness of CT angiography for demonstrating cerebral aneurysms

We report the usefulness of computed cerebral angiotomography (CT angiography) for demonstrating cerebral aneurysm and the clinical significance of CT angiography for ruptured cerebral aneurysm. Our modified method of CT angiography was easy and less time-consuming. Fifteen seconds after starting a single bolus injection, 1 ml/kg/25 seconds via cubital vein, of contrast medium (60% urograffin), 5 serial 5 mm thick-CT slices were scanned in every 6.5 seconds including 2 seconds of interval, beginning from an axial level 20 mm above the orbitomeatal line and ending at a level 40 mm. A total of 103 patients were examined in this report, consisting of 70 unruptured asymptomatic, 8 unruptured symptomatic (oculomotor nerve palsy) and 25 subarachnoid hemorrhage (SAH). Seven unruptured aneurysms in 4 asymptomatic cases, 2 unruptured aneurysms in 2 symptomatic cases 27 aneurysms in 24 SAH cases were suspected by CT angiography. Of these 36 aneurysms suspected by CT angiography 32 aneurysms were confirmed by cerebral angiography. The detection rate of CT angiography in this report was 89%, higher than those of previous reports. Thirteen aneurysms were located at internal carotid-posterior communicating artery (ICPC) junction. 11 at anterior communicating artery (Acom), 7 at middle cerebral artery (MCA). CT angiography showed a false positive findings in 4 cases, which were all located at Acom. Four aneurysms were not detected in CT angiography, which were all located at MCA and were very small (2-3 mm) in diameter. There were no deteriorated cases during and after CT angiography. We suggest that CT angiography is a useful and safe method for predicting the location of not only unruptured but ruptured aneurysms.     

Late results of small untreated abdominal aortic aneurysms

We report our experience with 73 patients who were initially selected for nonoperative management of an abdominal aortic aneurysm less than 5 cm in diameter. Size of the aneurysm was determined by ultrasound (34); arteriography (16); computerized tomography (17); plain x-ray (4); and magnetic resonance imaging (2). End points of the study were subsequent elective resection, rupture, death from cause other than rupture, or an intact aneurysm followed for a minimum of three years. Overall, 28 (38%) aneurysms were subsequently resected on an elective basis; four (5%) ruptured; 15 (21%) were intact at the time of the patient's death; and 26 (36%) remained intact during follow-up of 3 to 6.5 years. Indications for elective resection were aneurysm enlargement (21); symptoms suggesting impending rupture (3); and improvement in medical condition (4). In the 43 aneurysms initially less than 4 cm diameter, 16 (37%) had elective resection and one (2%) ruptured, and in the 30 that were 4–4.9 cm, 12 (40%) were resected and three (10%) ruptured. The four aneurysms that ruptured had enlarged to greater than 5 cm prior to rupture. We conclude that aneurysms less than 4 cm can be safely followed. Aneurysms 4–4.9 cm should be considered for operation, depending upon the size of the aneurysm, patient's life expectancy, and risk factors for surgery. Any aneurysm that enlarges should be resected, especially if the aneurysm becomes larger than 5 cm in diameter.Presented at the Annual Meeting of the Southern California Vascular Surgical Society, September 21–23, 1990.     

Clinical and anatomic outcomes after endovascular coiling of middle cerebral artery aneurysms: report on 30 treated aneurysms and review of the literature

BACKGROUND: Endovascular treatment of middle cerebral artery (MCA) aneurysms has not been extensively studied. We report our experience on a select group of patients that underwent coil embolization of an MCA bifurcation aneurysm. METHODS: From August 1999 to January 2005, 29 patients harboring 30 MCA aneurysms were treated with coil embolization. These patients were felt to have favorable characteristics for endovascular therapy including absence of thrombus in the aneurysm, absence of an efferent artery off of the aneurysm, and ability to reconstruct the wide neck with stent reconstruction. We retrospectively reviewed their records and angiographic images to evaluate for technical result and complications. RESULTS: The mean age of our cohort was 59 +/- 13 years with 19 patients presenting with a ruptured aneurysm. Complete obliteration was achieved in 24 (80%) of 30 of aneurysms on postprocedural angiography and no patient showed aneurysm regrowth at 6-month follow-up. Twenty-seven (93%) of 29 patients had no change in baseline neurological function post-embolization. There were two procedural-related complications: one intraprocedural rupture of an aneurysm and one thromboembolic stroke in the ipsilateral MCA territory. CONCLUSIONS: Coil embolization of MCA bifurcation aneurysms has a high rate of complete obliteration with acceptable morbidity in our selected group of patients.     

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.     

Cerebral aneurysms in identical twins

The hypothesis that genetic factors play a role in the genesis of cerebral aneurysms may be supported by clinical analysis of cerebral aneurysms in identical twins. In addition to reporting the present case, we review the literature on clinical features and genetical considerations in this matter. A forty-two-year-old male presented with subarachnoid hemorrhage (SAH) due to a left MCA aneurysm. At the age of 39, his identical twin brother also had SAH due to a ruptured left MCA aneurysm. This identical twin brother and his father's sisters died of SAH. Venous blood of the patient and his parents was collected to determine apolipoprotein E, angiotensinogen, angiotensin-converting enzyme, and very low density lipoprotein receptor genes. This analysis suggested a strong genetic association of apolipoprotein E epsilon4 with the pathogenesis. Including our cases, 13 cases of cerebral aneurysms in identical twins have been reported. There was a total of 37 aneurysms. Six twins had the same sites of aneurysm. These aneurysms show a tendency to be small in size, and to cause a high frequency of SAH occurring at a similar age. In young adults, cerebral aneurysms in identical twins tend to rupture. A screening diagnosis should be carried out as early as possible on an asymptomatic twin when the other has been discovered to have a ruptured cerebral aneurysm. Preventive treatment and systemic genome-wide linkage study should be conducted.     

False localization of rupture site in patients with multiple cerebral aneurysms and subarachnoid hemorrhage

OBJECTIVE: Patients with subarachnoid hemorrhage and multiple intracranial aneurysms present a unique challenge to the neurosurgeon. Unless all aneurysms can be clipped through a single craniotomy, the surgeon must accurately determine which aneurysm has ruptured. Misjudgment may result in disastrous postoperative rebleeding from the untreated but true ruptured lesion. We assessed the risk of false localization of the rupture site and subsequent rebleeding and documented the problems in predicting the true rupture site when patients have multiple intracranial aneurysms. METHOD: We reviewed the records of a consecutive series of 93 patients treated over a period of 12 years who presented with their first subarachnoid hemorrhage and who had multiple intracranial aneurysms. The rupture site was determined on the basis of computed tomographic and angiographic findings, and the supposed ruptured aneurysm was clipped within 2 days of hemorrhage in each patient. Additional aneurysms that could not be accessed in the same surgical session were operated on at a later stage. All patients' records were reviewed, and all computed tomographic scans and angiograms, including repeat studies performed in some patients, were retrospectively reevaluated by the authors, who had no knowledge of the patients' clinical information. RESULTS: The location of the aneurysm that ruptured was verified at the time of surgery or during the autopsy in 76 patients (82%). The aneurysm that ruptured was the one predicted as ruptured by the surgeon before surgery in 69 patients (91%) and in retrospect in 72 patients (95%). Five of the 6 patients in whom the ruptured aneurysm was not correctly identified were thought to have only a single aneurysm. Four patients rebled after surgery, and 2 patients died as a result of the rebleeding. CONCLUSION: In the reported series, the most common cause of rebleeding soon after aneurysm surgery was failure to obliterate the ruptured aneurysm, usually because it was missed on the initial angiogram. The results support not only meticulous radiological investigation of all intracranial arteries before surgery but also thorough surgical inspection of the target aneurysm in all cases of subarachnoid hemorrhage even after one candidate lesion has been discovered.