Aneurysm Location

Surgical accessibility of the aneurysm is the most important factor predicting treatment failure in patients undergoing microsurgical aneurysm clipping. Unlike surgical aneurysm treatment, endovascular treatment is less dependent on the location of the aneurysm. The morphologic aneurysm characteristics, as delineated by cerebral angiography, are the major determinants of endovascular treatment outcome (Fig. 1). The impact of aneurysm location in the selection of the treatment modality is reflected in the ISAT study. Patients with ruptured posterior circulation aneurysms (and to a lesser degree patients with middle cerebral artery aneurysms) are underrepresented (12).

Posterior Circulation

The basilar apex aneurysms are technically challenging to treat microsurgi-cally because of their deep location and their intimate relationship to the thala-moperforating arteries. On the other hand, in a review study, the endovascular treatment results and complications in patients with basilar bifurcation aneurysms were in the same range as those in patients with an aneurysm located elsewhere.

Lempert et al. (21) reported a morbidity of 2.8% and a procedure-related mortality of 0% in 109 patients with ruptured posterior circulation aneurysms treated with coiling. Nearly one-half of these aneurysms (49%) were located in

Basilar Bifurcation Aneurysms

Fig. 1. Three-dimensional rotational angiography (3D RA) can help elucidate aneurysm characteristics that will guide the choice of intervention. (Top) From 2D angiography this right internal carotid artery (ICA) giant aneurysm causing right cranial nerve III palsy and V1-2, discomfort was initially felt to have a very wide neck originating from the cavernous segment. (Bottom) Three-dimensional RA showed that it originated from the clinoidal segment with a favorable dome-to-neck ratio. Thus treatment was changed to coiling without assist. Previously the plan was open neurosurgical takedown of the right ICA. The patient had experienced right hemisphere hypoperfusion during balloon occlusion testing of the right ICA. This precluded endovascular takedown of the right ICA, as bypass to the right middle cerebral artery from the right superficial temporal artery would have been required to maintain right hemisphere perfusion.

Fig. 1. Three-dimensional rotational angiography (3D RA) can help elucidate aneurysm characteristics that will guide the choice of intervention. (Top) From 2D angiography this right internal carotid artery (ICA) giant aneurysm causing right cranial nerve III palsy and V1-2, discomfort was initially felt to have a very wide neck originating from the cavernous segment. (Bottom) Three-dimensional RA showed that it originated from the clinoidal segment with a favorable dome-to-neck ratio. Thus treatment was changed to coiling without assist. Previously the plan was open neurosurgical takedown of the right ICA. The patient had experienced right hemisphere hypoperfusion during balloon occlusion testing of the right ICA. This precluded endovascular takedown of the right ICA, as bypass to the right middle cerebral artery from the right superficial temporal artery would have been required to maintain right hemisphere perfusion.

the basilar bifurcation. Late rebleeding was seen in one patient (0.9%) with a partially treated aneurysm. Mean duration of clinical follow-up was 13.1 mo. A 22.4% recanalization rate was reported, at a mean angiographic follow-up 7.1 mo (21).

Bavinzski et al. (22) reported mortality and permanent morbidity rates directly related to the intervention of 2.2 and 4.4%, respectively, in 45 basilar artery aneurysms treated with GDCs, 35 of which were ruptured. A single rerupture was observed during 74.8 patient years of follow-up, corresponding to a rate of 1.3% per yr (22). An annual rerupture rate of 2.9% was reported by Eskridge et al. (23) for 61 patients with basilar tip aneurysms, on a mean follow-up of 1.1 yr. Samson et al. (24) reported the results of surgical clipping in a series of 303 basilar apex aneurysms, one-third of which were unruptured. At 6-mo follow-up, 81% of patients were neurologically intact or had minor deficits, 10% were dead, and 9% had a poor outcome. No recurrent SAH was seen at a mean follow-up of 8 yr. Residual aneurysm was observed in 6% on follow-up angiog-raphy. Lawton et al. (25) reported a surgical mortality rate of 9% and a permanent neurologic morbidity associated with treatment in 5% in a series of 57 basilar apex aneurysms, 47% of which were large or giant in size.

In a retrospective comparative study, endovascular treatment demonstrated a 50% combined morbidity/mortality rate in the surgical group compared with 10% in the endovascular group in a cohort of ruptured and unruptured basilar artery apex aneurysms. There were no reruptures during approx 24 patient-years of follow-up (26).

Middle Cerebral Artery Aneurysms

MCA aneurysms are often wide based and tend to incorporate the proximal segment of the M2 branches. This unfavorable angioanatomy poses a challenge to the endovascular surgeon and renders most aneurysms in this location unsuitable for coiling (27). In a prospective study, coiling of ruptured MCA aneurysms was found to be associated with a poorer outcome than coiling of aneurysms located elsewhere in the anterior circulation (5).

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