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