Introduction
The distal anterior cerebral artery (DACA) is defined as the part of the ACA distal to the anterior communicating artery.2)6) DACA aneurysms are relatively rare and account for 2.1 to 9.2% (average, about 5%) of all intracranial aneurysms.3)8)9)11)13)15)16)20) The clinical characteristics of DACA aneurysms include multiplicity (coexistence of other aneurysms), association with vascular anomalies, subarachnoid hemorrhages (SAH) and intracerebral hemorrhages (ICH) in addition to high rates of rebleeding.1)5)6)14)18) The microsurgical treatment of DACA aneurysms is difficult because of their small size, distal location (they are usually buried in the frontal lobe), a narrow operative field, retraction of the frontal lobe and tight adhesions to adjacent tissue.1)3)5)11)13)17)20) In addition, it may complicate a successful and safe obliteration when the severe tortuousness of cerebral arteries, the relatively broad necks, and the difficulty in the selection of the aneurysm and in the handling of the microcatheter are encountered in endovascular treatment.4)7)12)19) These characteristics present a considerable technical challenge for both neurosurgeons and interventionalists. In this study, we retrospectively investigated the clinical characteristics and outcomes of patients with ruptured DACA aneurysms and discuss their optimal treatment strategy.
Materials and methods
Between February 2001 and January 2009, 488 patients presented with ruptured intracranial aneurysms. Of these, 24 patients (4.9%) had DACA aneurysms that were directly responsible for the SAH, and these patients were included in this study. Incidental and unruptured DACA aneurysms were excluded. We reviewed the medical records, radiological data and outpatient clinic charts. All 24 patients with SAH and DACA aneurysms were diagnosed using computed tomography (CT) scanning and conventional angiography. Our standard management protocol is early surgical or endovascular intervention as soon as possible within a few hours after ictus. The treatment modality was determined based on the initial CT scan (combining ICH) and conventional angiography (size, shape, and relation to parent artery). A microsurgical operation was performed with an interhemispheric approach. However, for two patients with multiple aneurysms, a combined approach was performed by using a pterional and interhemispheric approach or an extended pterional and frontal approach. The preoperative clinical and radiological conditions were evaluated according to Hunt-Hess grades and Fisher grades, respectively. The clinical outcomes of patients were evaluated at last follow-up with the Glasgow Outcome Scale (GOS) score.
Results
1. Clinical characteristics
The clinical characteristics of the patients are summarized in Table 1. The patients (6 men, 18 women) had a mean age of 52 years (range, 30 to 70 years). Fifteen patients had a Hunt-Hess grade of II, 5 had a grade of III, 3 had a grade of IV, and 1 had a grade of V. With respect to Fisher grades, 9 patients had a grade of II, 1 had a grade of III, and 14 had a grade of IV. Fourteen of the 24 patients (58%) had an associated ICH. Six of the 24 patients (25%) had multiple aneurysms (2 aneurysms in 4 patients, 3 in 2 patients and 4 in one patient). The location of the associated aneurysms were the left posterior communication artery (P-com), the anterior communication artery (A-com), both middle cerebral arteries (MCA), both superior hypophyseal arteries (SHA), and the right internal carotid artery (ICA) bifurcation. The location of the aneurysms was classified based on the segmental division of the ACA by Fisher or A1, A2, A3, A4 or A5.10) Twenty patients had DACA aneurysms in the A3 segment and 2 each in A2 and A4. The aneurysmal size was divided by the maximum diameter into small (< 6mm), medium (6~14mm), large (15~24mm) or massive (≥25mm). Twenty-one cases (88%) had small-sized aneurysms, 3 patients (12%) had medium-sized and none had a large- or massive-sized aneurysm. Among the 24 patients, 6 patients underwent endovascular treatment and 17 underwent microneurosurgery. The other patient was managed with only extra-ventricular drainage (EVD) because the patient’s legal guardian refused further treatment. Two of the 6 patients treated with endovascular coiling had multiple aneurysms (in the A-com and left SHA). Regardless of aneurysmal location, standard endovascular coiling was tried in 8 patients initially and it succeeded in 6 cases. Two patients with ruptured DACA aneurysms could not be embolized completely due to severe tortuousness and relatively broad necks, and thus, microsurgical clipping was performed as the definitive treatment. Seventeen patients underwent microsurgical treatment. Four cases had multiple aneurysms and 1 had a remnant DACA aneurysm after previous endovascular treatment.

2. Clinical outcomes
Twenty of the 24 patients (83%) had a good clinical condition (Hunt-Hess grade I-III) before management and nineteen of these patients (95%) showed good clinical outcomes (GOS 4~5) after treatment. Two of the 4 patients (50%) with a poor clinical condition (Hunt-Hess grade IV and V) had good clinical outcomes. Twenty-one of the total 24 patients (88%) had a good clinical course after treatment for DACA aneurysms (Table 2). Among the 15 patients with Fisher Grade III-IV, 12 (80%) had a good clinical course at last follow-up. Thirteen of the 14 patients with an accompanying ICH had good clinical outcomes. Only one patient with ICH had a poor outcome (GOS 1). In microsurgical treatment, an intraoperative rupture during dissection occurred in 1 patient. This was the only procedure-related complication of the microneurosurgery. A vasospasm developed in one case but there was no neurologic deficit. One patient required a ventricular peritoneal shunt for hydrocephalus. Other complications included a delayed subdural hematoma, an intraventricular hemorrhage (IVH) of unknown origin and pneumonia. The delayed subdural hematoma was treated with surgical removal and the postoperative IVH was managed conservatively. There were two patients with pneumonia and one died (Table 3). Concerning the endovascular coiling treatment, there were no procedure-related or medical complications. Six patients received endovascular coiling treatment. Among them, 5 patients (GOS 5) had good clinical outcomes regardless of the preoperative clinical condition. In addition, 16 of the 17 patients who received microsurgical clipping treatments had good clinical outcome (13 with a GOS of 5, 3 with a GOS of 4; Table 2).
Illustrative cases
Case 1
A 63-year-old female was admitted for altered consciousness (Hunt-Hess grade III). Her CT scan showed a diffuse SAH around the basal cistern and interhemispheric cistern. Conventional angiography was performed immediately, and the left internal carotid angiogram demonstrated a tiny saccular aneurysm (less than 2mm) located at the A3 segment. The aneurysm was very small but had a relatively favorable neck for coil embolization. Under general anesthesia, the aneurysm was catheterized carefully by a microcatheter (Excelsior SL 10, Boston Scientific) and the tip of the microcatheter was placed at the aneurymal base to prevent any jumping into the very tiny sac. The aneurysm was successfully obliterated using one detachable coil (GDC, Boston Scientific) with no complications (Fig. 1).

Case 2
A 56-year-old female was admitted for a severe bursting headache (Hunt-Hess grade II). A brain CT scan revealed a diffuse SAH at the interhemispheric cistern. A conventional cerebral angiogram of the left ICA confirmed a saccular aneurysm located at the A3 segment. Endovascular coiling was planned mainly due to a relatively favorable dome to neck ratio. Under general anesthesia, the aneurysm was catheterized by a microcatheter (Excelsior SL 10, Boston Scientific) and was successfully obliterated using 6 detachable coils (GDC, Boston Scientific and HydroCoil, MicroVention) with no complications. The parent artery and the callosomarginal artery patencies were confirmed by using frequent subtraction angiography during coil embolization. The 18-month follow-up angiogram showed stable occlusion of the aneurysm (Fig. 2).

Case 3
A 70-year-old female was admitted for a severe bursting headache followed by altered consciousness (Hunt- Hess grade IV). Her CT scan showed a diffuse subarachnoid hemorrhage in the interhemispheric cistern. The left internal carotid angiogram demonstrated a small aneurysm at the junction of the pericallosal and callosomarginal arteries. The aneurysm had a large neck but endovascular treatment was initially tried considering of her poor neurologic status and old age. Under general anesthesia, the aneurysm was catheterized by a microcatheter (Excelsior SL 10, Boston Scientific) and coil embolization was tried but failed because of its large neck. Finally the patient underwent an aneurismal neck clipping and the aneurysm was successfully clipped through a unilateral interhemispheric approach. A postoperative three-dimensional CT angiogram showed complete obliteration of the aneurysm (Fig. 3).

Case 4
A 62-year-old female was admitted for altered consciousness (Hunt-Hess grade IV). A brain CT scan showed a diffuse subarachnoid hemorrhage around the basal and interhemispheric cisterns, and a thick hematoma in the frontal lobe. Both internal carotid angiograms and enlarged three-dimensional rotation images demonstrated a ruptured aneurysm at the azygos A2 segment and another three small unruptured aneurysms at the bifurcation of both middle cerebral arteries as well as at the left distal internal carotid artery. Open surgery was planned, not only to obliterate the multiple aneurysms but also to evacuate the frontal hematoma. Under general anesthesia, the patient was placed in the supine position with slight head elevation and neck extension. After unilateral craniotomy for both interhemispheric and left pterional approaches, the ruptured aneurysm and two unruptured aneurysms on the left side were clipped simultaneously after careful dissection through the interhemispheric and the Sylvian fissure. The remaining aneurysm on the right side was clipped in a consecutive session (Fig. 4).
Discussion
A DACA aneurysm is relatively rare. The incidence rate of DACA aneurysms in our series of patients is 4.9%. This rate is similar to previous papers that have reported an incidence of 2.1 to 9.2% (average, about 5%) of all intracranial aneurysms.3)8)9)11)13)15)16)20) With respect to sexual distribution, it is well known that DACA aneurysms occur more frequently in female patients than male.14) In our series, the ratio of men and women was in agreement with the previous literature (18 females and 6 males). DACA aneurysms have been found to have a size of 5 to 10mm.14) In our results, 21 of 24 cases (87%) were small-sized aneurysms (<6mm), and there were no large or massive aneurysms. Based on these results, the low incidence of large- and massive-sized DACA aneurysms seems to be due to a tendency of these aneurysms to rupture early. Therefore, DACA aneurysms should be treated as soon as possible, even if they are small-sized and/or in an incidental unruptured state. Another clinical characteristic of DACA aneurysms are multiplicity (coexistence of other aneurysms) and an association with other vascular anomalies.1)5)6)14)18) In our series, 6 of 24 patients (25%) had multiple aneurysms. The cause of these remains unclear, and so complete and careful angiography should be performed in patients with DACA aneurysms. The anatomic course of the ACA is demonstrated by Fischer’s division of the ACA into five segments.2)6) Most of the DACA aneurysms are found in the A3 segment of the ACA, which is also described as the pericallosal-callosomarginal artery.2)6) Particularly, it is known that DACA aneurysms in the A3 segment are more prevalent when the bifurcation of the artery is angled acutely at the genu of the corpus callosum.2)6) In our data, the aneurysms of 21 of the 24 patients (83.3%) were located in the A3 segment. Thus, knowing the exact location of the aneurysms is very important for successful treatment.
The microsurgical clipping of a ruptured DACA aneurysm has a few difficulties, as previously described by several authors, and these difficulties include dense adhesions, the aneurysm being buried in the surrounding tissue, difficulty in finding the aneurysm, and a narrow working space.1)3)5)11)13)17)20) Therefore, before surgery, neurosurgeons should be aware of these difficulties. For safe surgery, enough brain relaxation with cerebrospinal fluid removal via ventricular or lumbar drainage is mandatory before brain retraction or dissection. Brain navigation system using 3-dimentional CT angiograms can be helpful in confirming the location of small and deeply located aneurysm and in early control of the parent artery. Considering these factors, endovascular coiling treatment emerges as an effective alternative treatment. However, it may complicate a successful and safe obliteration when the severe tortuousness of cerebral arteries, the relatively broad necks and the difficulty in the selection of the aneurysm and in the handling of the microcatheter are encountered in endovascular treatment.4)7)12)19) In order to increase the success rate of endovascular treatment, improved techniques may be needed for controlling the microcatheter, like a smaller microcatheter and the availability of stent and balloon assistance. In addition, using balloon or stent remodeling techniques in such a small-caliber artery is not without risk and sometimes not possible. Thorough risk-benefit considerations should be weighed before deciding on a treatment modality. Even though an aneurysm was clipped successfully or coiled completely, close observation is necessary after treatment because the aneurysm can regrow. We experienced one regrowing aneurysm one year after a coiling procedure in another institute. Although endovascular recoiling is the main treatment for an aneurysm that has recurred after coiling, surgical neck clipping was applied in our case mainly due to an unfavorable neck for simple endovascular coiling.
In previous reports, there were several predictive factors that affected the clinical outcomes of ruptured DACA aneurysms, such as age, Hunt-Hess grade, the size and location of the aneurysm, the timing of treatment and association with an ICH.13)17) In our study, favorable outcomes were found in 95% of patients with Hunt-Hess grades I-III, but only 50% of patients with Hunt-Hess grade IV and V. Considering previous papers and our results, preoperative clinical condition (Hunt-Hess grade) was the most important factor for predicting clinical outcome. The incidence of an ICH associated with ruptured DACA aneurysms varies from 40 to 73%.11)14)16)20) An ICH is associated more frequently with DACA aneurysms compared to other aneurysms. In our study, 14 out of 24 patients (58.3%) had an associated ICH. The high incidence of an ICH is obviously related to the narrow pericallosal cistern and dense attachment to the adjacent brain surface. However, only one of the 14 patients with an ICH had a poor clinical outcome (GOS 1) in our results. These results can be explained because the ICH in patients with ruptured DACA aneurysms was located at the frontal lobe and more peripheral regions of the brain, and not in central and eloquent areas. However, the relationship between the amount of ICH and clinical outcome needs further study.
Conclusions
DACA aneurysms have been known to have relatively higher treatment-related morbidity and mortality rates compared to other supratentorial ruptured aneurysms. In this study, acceptable favorable outcomes were achieved in patients with good preoperative scores who were treated with either clipping or coiling. Although thick SAH, associated ICH and severe consciousness deterioration seemed to predict worse prognosis of the ruptured aneurysms, immediate and active treatment of ruptured DACA aneurysms should be mandatory for better outcomes.
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