Surgical management of aneurysms of the bifurcation of the internal carotid artery

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Abstract

Internal carotid artery (ICA) bifurcation aneurysms are rare and easily bleed in younger patients, but are difficult to treat surgically, due to perforators surrounding and adherent to the aneurysm. A series of 25 patients treated by clipping under the operating microscope are analyzed and compared with previous cases. Twenty-five patients, 11 men and 14 women (mean age 51 years), were treated by the same neurosurgeon. Seventeen patients presented with subarachnoid hemorrhage (Hunt & Kosnik Grade I in three, II in five, III in two, IV in seven), five with unruptured ICA bifurcation aneurysms, and three with unruptured ICA bifurcation aneurysms but another ruptured aneurysm. There were 23 small, one large, and one giant ICA bifurcation aneurysms. The projection was superior in 12, anterior in seven, and posterior in six cases. Pterional approach was employed for all cases. Outcomes were evaluated at discharge with the Glasgow Outcome Scale. Favorable outcomes (good recovery (GR) and moderate disability (MD)) were obtained in ten of 17 patients with ruptured ICA bifurcation aneurysm. Favorable outcomes were significantly greater in Grades I and II (three in I, four in II) than in Grades III and IV (one in III, two in IV; P=0.0498). Seven of eight patients with unruptured ICA bifurcation aneurysm had favorable outcomes. Temporary clipping and projection of the aneurysm did not affect the outcome. Causative factors of unfavorable outcomes were primary brain damage in cases of small and large aneurysms and perforator damage in the case of giant aneurysm. Poor clinical grade and vasospasm are the causative factors of poor outcome in patients with ruptured ICA bifurcation aneurysm. Preservation of perforators is crucial in cases of giant aneurysm. Clipping of unruptured ICA bifurcation aneurysms is recommended since they tend to bleed at a lower age than other aneurysms.

Introduction

Aneurysms of the bifurcation of the internal carotid artery (ICA) have a very low incidence in adults by accounting for only 5% of all intracranial aneurysms [1], [2], [3], [4], [5], and are less common even among aneurysms of the ICA [4]. ICA bifurcation aneurysms bleed easily in younger adults [6], [7], [8], [9], [10], [11], [12] and show male predominancy [6], [8], [10], [12], [13], [14], [15], in contrast to the aneurysms at other locations of the ICA. ICA bifurcation aneurysms could be regarded separately from other aneurysms of the ICA because of the embryogenetic factor in the origin [14].

Surgical management of these aneurysms is more troublesome than for other types of ICA aneurysms. This difficulty is related to the need for deep retraction to achieve exposure, and to the many perforators originating from the anterior cerebral artery (ACA), middle cerebral artery (MCA), anterior choroidal artery, and posterior communicating artery (PcomA) [16], [17], [18] which hinder microdissection of the aneurysm [5], [19], [20], [21]. ICA bifurcation aneurysms have been treated in series of ICA aneurysms [2], [5], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], but there has been no specific discussion of more than 20 cases of ICA bifurcation aneurysms [6], [7], [10], [12], [34], [35]. Consequently, no analysis is available of the outcome according to clinical grade, timing of the operation, causative factors of unfavorable outcomes, outcome for giant or incidental aneurysm, and postoperative computed tomography (CT) findings.

The present study investigated the clinical features of ICA bifurcation aneurysms in a series of 25 patients, to assess the causative factors of unfavorable outcomes, and to propose the optimum treatment of ICA bifurcation aneurysms.

Section snippets

Clinical material and evaluation

Twenty-five patients with ICA bifurcation aneurysms, 11 males and 14 females aged 36–81 years (mean 51.2 years), were operated on under the operating microscope by the same neurosurgeon (H.N.) between 1974 and 1999, out of a total of 905 patients (2.8%) with aneurysm treated during the same period [36]. Clinical features of the 25 patients are shown in Table 1. Clinical state just before the operation was assessed according to the Hunt and Kosnik scale [37] and outcome was evaluated at

Overall surgical results

Table 1 summarizes the outcomes of all patients. Ten of the 17 patients with ruptured ICA bifurcation aneurysms had favorable outcomes (GR in ten, MD in zero), but two patients had severe disability (SD), two patients were in the vegetative state (VS) and three patients died (D). Patients in Grades I and II had significantly better outcomes than patients in Grades III and IV (P=0.0498, Fisher's exact test). Two patients in Grade I were operated on in the chronic stage resulting in GR in both.

Historical background

Dott first successfully coated an ICA bifurcation aneurysm with a muscle patch in a 53-year-old male patient in 1933 [40]. Since then, ICA bifurcation aneurysms have been treated by many neurosurgeons without (Table 2) or with the operating microscope (Table 3). Forty-three series including ours have been reported between 1933 and 2000, totaling 822 patients of whom 507 (61.7%) were treated surgically. The mortality rate for conservative therapy was 43%, and that for carotid ligation was 41%

Conclusions

ICA bifurcation aneurysms have a tendency to bleed at a lower age, but no male predominance is seen. Analysis of the surgical results shows that clipping is the treatment of choice in cases of small and large aneurysm. The causative factors of unfavorable outcomes are vasospasm and poor clinical grade, but not perforator damage. Temporary clipping and projection of the aneurysm do not affect the surgical outcome. The outcome of incidental aneurysms is excellent in spite of small low density

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