Introduction

   MCA aneurysm occupies 25% of all intracranial aneurysms, and usually occurs in MCA bifurcations. Clinical aspects, operational approach, and recuperation of MCA bifurcation aneurysm is well known. 10% of MCA aneurysm occur in proximal MCA, and rarely about 1% occurs in distal MCA.²⁾⁴⁾⁹⁾ In this rare case of distal MCA, it is hard to find documentary reports on clinical aspects, treatment approach, and treatment results. This research report four cases of ruptured distal MCA aneurysm and wishes to be of use for documentary research and later treatment approaches.

Clinical Materials and Methods

   From retrospective study, 214 patients were diagnosed as intracranial aneurysm and had been operated in all, from May 2001 to May 2004, based on medical records and radiological characteristics. Sixty three were MCA aneurysm, and out of the 63, four cases of ruptured distal MCA. Distal vessels of MCA were categorized into four segments according to Gibo, et al：M2 (insular segment), M2-3 junction, M3 (opercular segment), M4 (cortical segment).³⁾ Measurements of ICH volume was calculated with the longest axis of hematoma being A, its perpendicular diameter being B, and height C being the number of sections counted on a hematoma picture from a CT scan of 10mm interval；thus the volume calculated as (A*B*C)/2. The result of the treatments was categorized using Glasgow Outcome Scale (GCS) as the following：mild or no disability, moderate disability as favorable outcome, severe disability, vegetative state, and death as poor outcome.

Result

   Out of the four cases, two were male and two were female, making it 1：1, ages ranging from 40 to 59 with an average of 48.3. All four cases manifested subarachnoid hemorrhage (SAH) by aneurysm rupture, and three were M2 segment ruptures, one was M3 segment rupture. At the time of hospitalization, in case of ruptured distal MCA aneurysm there were one Hunt-Huss grade II, two grade IV, and one grade V. In the cases of ruptured distal MCA aneurysms, 3 cases accompanied ICH, showing two Hunt-Hess grade IV and one grade V, displaying poor preoperative grades. In the three cases of distal MCA aneurysm accompanied by ICH, all M2 segments were ruptured, and M3 segments had mycotic aneurysm ruptures. Four cases of ruptured distal MCA aneurysm showed no intracranial aneurysm in other areas. Out of the ruptured distal aneurysm patients, the three with poor preoperative grade accompanied by ICH resulted in one death and two good recoveries, with no relation to the amount of ICH. In the case of mycotic aneurysm not accompanied by ICH, antibiotic treatment was carried out according to the blood culture testing results, because no neurologic deficit was found except headache. However three weeks later the size increased in the follow-up Transfemoral Cerebral Angiography (TFCA), so right frontotemporal craniotomy and clipping with excision of aneurysm was done and the patient was discharged from the hospital with no disability status.¹⁾⁸⁾

Illustrative Cases (Table 1)

1. Case 1：
   A 59-year-old male patient hospitalized due to sudden loss of consciousness, diagnosed as SAH accompanied by frontotemporal ICH along the left sylvian fissure by CT scan, Hunt-Huss grade IV. 75cc of ICH volume, and aneurysm found in the left M2 segment on TFCA. After left frontotemporal craniotomy, aneurysm clipping and temporal ICH evacuation, he was discharged with favorable outcome (Fig. 1).

2. Case 2：
   49-year-old female patient hospitalized due to headaches and sudden loss of consciousness, transferred from another hospital after CT scan diagnosing SAH accompanied by right temporal ICH. At the time of hospitalization left hemiparesis was diagnosed, Hunt-Hess grade IV. 45cc of ICH volume, aneurysm found in the right M2 segment on TFCA. Right frontotemporal craniotomy and aneurysm clipping with hematoma evacuation carried out. After three days, vasospasm showed, improved to triple H therapy, and discharged with favorable outcome.

3. Case 3：
   39-year-old female patient hospitalized with sudden loss of consciousness, SAH accompanied by right frontotemporal ICH showed in CT scan, Hunt-Hess grade V. First rebleeding after one hour of hospitalization, and second after five hours, diagnosed as IVH and an increase in ICH, three points in GCS. 30 cc of ICH volume. 1×2.5 cm sized aneurysm found in the right M2 segment on TFCA. Right frontotemporal craniectomy and aneurysm clipping with hematoma evacuation and decompressive frontal & temporal lobectomy applied, expired two days after the surgery.

4. Case 4：
   38-year-old male patient hospitalized with headaches and vomiting. SAH along the right sylvian fissure diagnosed, Hunt-Hess grade II. Past history showed that patient received valve replacement surgery in '95 due to mitral valve stenosis. 0.4x0.4cm sized aneurysm found in the right M3 segment on TFCA. Gram positive cocci showed from blood culture, diagnosed as mycotic aneurysm and antibiotics medicated. A follow-up TFCA carried out three weeks later showed the aneurysm increased to 0.7×0.4 cm, and right frontotemporal craniotomy and clipping with excision of aneurysm carried out. TFCA done one week after the surgery showed no mycotic aneurysm. Patient was discharged with no damage in the nervous system (Fig. 2).

Discussion

   MCA is an area intracranial aneurysm, with most of them being MCA bifurcation, but about 1% occurs in distal MCA. The clinical aspects, treatment, and recuperation of MCA bifurcation aneurysms are well known due to microsurgeries and numerous cases, and the same goes for proximal MCA aneurysms.^2)3)5)10) In the case of distal MCA, Poppen first reported in 1951, and 25 distal MCA patients were researched in a report by Rinne, et al., out of 561 MCA patients, taking up 4% of all MCA aneurysms.⁹⁾ In Korea's case Chung YS, et al. found 13 distal MCAs out of 194 MCA cases in search for proximal MCA aneurysms.²⁾ However most of the reports only included the incidence of distal MCA aneurysm to MCA analyzation, neglecting clinical aspects or treatment methods of distal MCA. In 2004, a paper released by Horiuchi, et al. dealed with and analyzed 9 cases of ruptured distal MCA aneurysm, the most in a single research. Distal MCA is categorized into four segments according to Gibo, et al., M2 (insular segment), M2-3 junction, M3 (opercular segment), and M4 (cortical segment).
   According to the report by Horiuchi, et al., out of 791 MCA cases nine were distal MCA aneurysms taking up 1.1%, and seven of them were female and two were male. Out of the nine eight were saccular aneurysm, and one was mycotic aneurysm; eight cases were accompanied by ICH, and five aneurysms of distal MCA segments were found location in M2 segment, two at the M2-3 junction, one at the M3 segment, and another one in the M4 segment. In five cases multiple aneurysm were found. Eight cases were clipped in Transsylvian approach, and one care was trapped. Despite the poor preoperative grade due to ICH, it is reported to gain a favorable outcome.⁴⁾ Our study showed 2 male and 2 female cases out of all four, showing male to female ratio equal. Out of the four ruptured distal MCA aneurysms, three were M2 segment rupture and one was M3 segment rupture. In the case of ruptured distal MCA aneurysm, no multiple aneurysm was found on other areas, three cases being saccular aneurysm and the other one case being mycotic aneurysm. At the time of hospitalization Hunt-Huss grade was one II, two IV, and one V in the case of ruptured distal MCA aneurysm. In the cases of ruptured distal MCA aneurysm three cases were accompanied by intracranial hemorrhage, with two Hunt-Hess grade IV and one grade V, all ruptured in M2 segments, and mycotic aneurysm rupture in the rest of M3 segments. In the case of MCA aneurysm ICH incidence is reported to be about 45%, and there is a high chance that due to this cause the outcomes are worse than other anterior circulation aneurysms.^2)5)10) In the case of distal MCA aneurysm it is hard to put them into statistical analysis due to lack of number of cases, but in the case of Horuichi, et al. eight cases out of all nine were accompanied by ICH, and our study showed three cases out of all four ruptured distal MCA aneurysms were accompanied by ICH, displaying 80% incidence, which is higher than MCA. Also, two studies on ruptured distal MCA manifested area revealed that eight cases out of thirteen showed M2 segment. In the case of multiple aneurysm, five out of nine cases were accompanied in studies of Horuichi, et al., but in our studies none was found except for the unruptured diatal aneurysm, therefore further research is needed. For treatment methods, microsurgical repair method is used more frequently than endovascular surgeries.

   This is because the approach is more useful in effectively removing mass effect by ICH. Most cases apply clipping after transsylvian approach, and some needs trapping. Therefore some cases of distal MCA aneurysm requires trapping of the parent artery, and preparation for superficial temporal artery (STA) and MCA anastomosis before surgery is required. Especially in the case of dissecting aneurysm, STA-MCA anastomosis after trapping of resecting is carried out for preservation of circulation distal to the aneurysm.⁷⁾ David WN, et al. reported that in operation of distal MCA aneurysm surgery, intracranial to intracranial vascular anastomosis with microanastomotic device was carried out with two difficult cases, and gained good result, so it should be taken into consideration in case of giant aneurysm or fusiform aneurysm.⁶⁾ In case of distal MCA aneurysm surgery, dissection is harder to perform than proximal MCA；for lack of surgical experience and the fact that many anatomical variations of distal MCA are embedded together in the brain. In this class the surgery was performed without any special equipment for locating the aneurysm, but intraoperative angiography should be considered if there is no confidence in anatomy or approach of distal MCA, or if the location of aneurysm is ambiguous in preoperatibve angiography. Horiuchi et al. reported about post-surgery recuperation that despite the poor preoperative grades due to ICH early surgery gained favorable outcome, while Rinne, et al. reported that unfavorable outcome was achieved due to ICH.⁴⁾⁹⁾ In general, there is a report that in case of MCA aneurysm rupture the more the ICH volume, the worse recuperation is, but there are no reports on the possibility of the volume of ICH being a recuperation factor,⁵⁾¹⁰⁾ and our study showed no relationship between the volume of ICH and post-surgery recuperation；out of three ICH cases, one patient with 30cc of ICH volume deceased, and the other two, with 45cc and 75cc each, showed good recovery. In case of mycotic aneurysm, it takes up 2 to 6% of all intracranial aneurysm, manifesting in distal MCA. Surgical indications are：1) the presence of a significant symptomatic mass such as a hematoma or abscess, 2) a ruptured aneurysm located distally, 3) enlargement of an aneurysm during appropriate antibiotic treatment, 4) failure of an aneurysm to resolve despite a full course of appropriate antibiotic therapy, and 5) neurological deteriorration during antibiotic therapy.¹⁾⁸⁾ In discovery of distal MCA aneurysm, mycotic aneurysm must be ruled out with past history on endocarditis such as cardiac valve disiease.

Conclusion

   Distal MCA aneurysm is very rare, and is accompanied by ICH more frequently than other MCA aneurysms. Poor preoperative grade is shown due to mass effect by ICH, but shows good recuperation due to early surgery. In case of mycotic aneurysm or giant aneurysm, it is difficult to do clipping, therefore trapping or wrapping with STA-MCA anastomosis for distal artery circulation should be considered. Also in case of distal MCA, there are many anatomical variations and many cases when aneurysm is embedded in brain parenchyme, leading to difficulty in dissection, and intraoperative angiography can be helpful to the operation. In case distal MCA aneurysm should be found, it is not often but there is a chance of mycotic aneurysm, therefore a history of heart surgery or infective endocarditis must be checked and evaluated.

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