The removal of the anterior clinoid process is required for clipping of cavernous sinus aneurysms internal carotid-ophthalmic artery aneurysms (IC-OP AN) and lower positioned internal carotid-posterior communicating artery aneurysms (IC-PC AN). The anterior clinoid process has tradionally been removed introdurally after exposure of the optic nerve and ICA. Recently the extradural removal of the anterior clinoid process and roof of the optic nerve has been reported. It is a matter for discussion whether to remove the anterior clinoid process and the roof of the optic nerve intradurally or extradurally.
In this paper, we have identified the indication and method of removing the ala minor when operating on cavernous sinus aneurysms, IC-OP aneurysms and IC-PC aneurysms.
The proximal neck of lower positioned IC-PC aneurysms; was lower than the anterior clinoid process. For clipping of lower positioned IC-PC aneurysms, removal of the anterior clinoid process was required. It is very difficult to tell the condition of the anterior clinoidal bone from pre-operative angiography. When operating for IC-PC aneurysms, we usually don't open the neck for the spare of the carotid artery. But carotid artery preparation in the neck is recommended when preoperative angiograms show an extremely lower positioned IC-PC aneurysm. As the neck of the aneurysm and anterior clinoid process is near, intradural removal of the anterior clinoid process is recommended. Extradural removal of the anterior clinoid process might cause the rupture of lower positioned IC-PC aneurysms, and it is difficult to control bleeding from the extradural space.
When operating the IC-OP aneurysms, intradural removal of the anterior clinoid process and unroofing of the optic canal was performed after the preparation of the carotid artery in the neck. Intradural removal of the anterior clinoid process is advisalble when operating for IC-OP aneurysms because it is very important to determine the course of the ophthalmic artery. The ophthalmic artery usually runs beneath the optic nerve.
When operating for cavernous sinus aneurysms, extensive removal of the ala minormbone is required. Intradural procedure restricts the space, so it is usually difficult to remove the ala minor bone extensively. It is advisable to remove the anterior clinoid process and the roof of the optic canal extradullary.
With basilar tip aneurysms, extradural removal of the ala minor bone is useful because this procedure allows wide retraction of the optic nerve and the internal carotid artery.
In conclusion, removal of the ala minor bone was required when operating for cavernous sinus aneurysms, IC-OP aneurysms and lower positioned IC-PC aneurysms. Intradural removal of the ala minor bone is preferable for clipping of IC-OP aneurysms and lower positioned IC-PC aneurysms. Extradural removal of the ala minor bone is better when operating for cavernous sinus aneurysms.

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Surgical problems and our strategies for large carotid cave aneurysms (medially faced C₃ aneurysms) were pointed out as follows.
Exposure of proximal neck: Anterior clinoid process is removed extradurally, after keeping the proximal (neck) and distal (intracranial) ICA.
Optic nerve injury: Dural sheath of the optic nerve, ophthalmic artery and Dawson's artery are preserved.
Ischemic complication: Local heparinization of ICA and irrigation of aneurysm sac during temporary trapping to prevent the embolism. Balloon Matas test before surgery.
Positioning of the clips: Dissection of aneurysm enough to reform the kinked ICA. For broad neck aneurysm, multiple clipping technique with a new type of curved blade fenestrated clip was used.

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In this paper, the authors present their surgical experience with 26 cases of paraopthalmic aneurysms, and describe the clinical features, surgical technique and outcome. Direct clipping of giant aneurysms of the paraophthalmic region of the internal carotid artery has been considered impossible or very difficult. The authors devised a new technique to facilitate clipping these aneurysm necks with greater ease and safety. The giant aneurysms were collapsed and occluded in such a fashion that the intraaneurysmal blood was aspirated from a catheter placed in the cervical internal carotid artery during trapping of the aneurysm. This technique was applied in four cases. All cases showed good postoperative outcome. This method will aid in successfully clipping the giant carotidophthalmic aneurysms previously considered unclippable.

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Surgical approaches for medially oriented internal carotid artery aneurysms include the ipsilateral pterional approach, the contralateral pterional approach, the interhemispheric approach, and the interhemispheric-subfrontal approach. In the ipsilateral pterional approach, the internal carotid artery obstructs direct visualization of the aneurysmal neck. In the contralateral pterional approach, the aneurysmal dome is exposed before dissection of the aneurysmal neck. In the interhe-mispheric and interhemispheric-subfrontal approaches, the aneurysmal neck can be seen without mobilization of the internal carotid artery or aneurysmal dome. The interhemispheric-subfrontal approach requires too much exposure of the brain to deal with this type of aneurysm microsurgically.
There are two kinds of interhemispheric approaches, i.e., the anterior interhemispheric approach (AIH) and the basal interhemispheric approach (BIH). The basal interhemispheric approach was initially developed as an approach for high-positioned anterior communicating artery aneurysms. Compared with the AIH, the BIH can provide a wider view without additional brain retraction. We applied the BIH to 3 cases of medially oriented internal carotid artery aneurysms.
Two cases of carotid-ophthalmic aneurysms and one case of an aneurysm arising from the origin of the duplicated middle cerebral artery were operated on. All aneurysms were successfully clipped. Postoperative complications included cerebrospinal fluid rhinorrhea (1 case), transient oculomotor palsy (1 case), ipsilateral visual disturbance (1 case) and anosmia (2 cases). The patients were discharged in the state of ADLs 1, 2 and 3.
The advantage of the BIH for medially oriented internal carotid artery aneurysms is direct visualization of the aneurysmal neck, with better anatomical orientation for surrounding structures. With decompression of the optic canal, mobilization of the optic nerve and removal of the sphenoid sinus wall, medially oriented aneurysms arising between the carotid bifurcation and the carotid cave can be clipped completely.
Disadvantages of the BIH are opening of the frontal sinus, injury to the olfactory nerve, and a narrow and deep operative field. In our cases, no serious complications such as meningitis were encountered.
he basal interhemispheric approach is a useful approach for medially oriented internal carotid artery aneurysms, especially those with a small neck.

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Seventeen cases of dorsal internal carotid artery aneurysms were surgically treated, and their operative and angiographic features were reviewed. There were 4 males and 13 females ranging in age from 34 to 61 (average: 47 years). Five cases had multiple aneurysms. All patients presented subarachnoid hemorrhage, caused by rupture of the dorsal internal carotid artery aneurysm in 15 cases and of an associated aneurysm in 2 cases.
Preoperative angiograms were classified into three types according to the operative findings. (1) Ten aneurysms, which projected superiorly in the lateral view and superiorly, slight-medially, or slight-laterally in the anteroposterior view, were found at surgery to be adhered to the basal surface of the frontal lobe, except for one very small aneurysm. (2) Three aneurysms, which were superimposed with the internal carotid artery in the lateral view and projected laterally in the anteroposterior view, were found to be adhered to the medial surface of the temporal lobe. (3) Four aneurysms, which were not seen on the angiogram, had no adhesion. Two of these four aneurysms were incidentally found during approach to an associated ruptured aneurysm. The other two were operated for because the CT scan had shown hematoma in the basal cistern, suggesting rupture of an internal carotid artery aneurysm.
The operative procedures were as follows: clipping in 10 cases, clipping and wrapping in 4, wrapping in 2, and trapping and bypass in 1. Intraoperative rupture occurred in 5 cases, during dissection of the Sylvian fissure in 1 case, just before complete closure of the clip blades in 3, and by slipping-off of the clip in 1.
The above angiographic classification should be useful for preventing premature rupture when retracting the brain and dissecting an aneurysm. As for surgical procedure, the clip should best be placed on the neck parallel to the parent artery, including the neck and part of the parent artery within the clip blades. Complete wrapping with cotton sheet is recommended when clipping is impossible or imcomplete.

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Between April 1978 and March 1989, 35 patients with 38 distal cerebral artery (DACA) aneurysms were admitted to our hospital. Of the 35 patients, 34 underwent microsurgical operation (clipping of 36 saccular aneurysms and wrapping of one fusiform). This group comprised 5.5% of the 642 patients with intracranial aneurysms managed surgically during this period at Shinsyu University and Aizawa Hospital. Their ages ranged from 28 to 74 years (mean 54 years); 14 were male and 21 were female.
Twenty-seven patients suffered subarachnoid hemorrhage (SAH) and one of these died from rebleeding before surgery. The remaining 8 cases were incidental (6 cases with SAH due to associated aneurysms in other locations, one with cerebral thrombosis and one with thalamic hemorrhage).Thirty-one of the DACA aneurysms (82%) were located at the genu of the corpus callosum. Medium-sized aneurysms (7-14mm) comprised 16 (42%). Ten patients (29%) had multiple aneurysms; Azygos ACA was noted in 6 cases and Triplicated ACA in 2. On the basis of the preoperative CT findings, the 26 cases of ruptured DACA aneurysms were classified into four types: Type 1 (3 cases) with thin SAH detected in anterior interhemispheric fissure, Type 2 (10 cases) with intracerebral hematoma, Type 3 (8 cases) with diffuse SAH extending to the basal cistern, Type 4 (5 cases) with intraventricular hematoma. Types 3 and 4 were associated with poor preoperative condition and unfavorable prognosis. Operative results of 26 cases with ruptured DACA aneurysms were full recovery (excellent and good) in 20, minimal deficits (fair) in 3, moderately disabled (poor) in 1, death in 2; All 8 patients with unruptured DACA aneurysms recovered fully. Two intraoperative premature ruptures occurred; one patient died and the other was disabled. The present paper describes our surgical approach to the DACA aneurysm and stresses the usefulness of tentative clipping of the aneurysm.

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The internal carotid-posterior communicating artery aneurysm is common, and a lot of brief reports have been presented about the classification and surgical approach for this aneurysm. The authors noticed the presence of small redish bulges in this portion, of the artery, which are thought to be the origin of aneurysms. Most of them were observed on the lateral wall of origin of the posterior communicating artery, and others were located on the inferior wall of the internal carotid artery including the infundibular widening of the posterior communicating artery. In this report, judging from these findings, the aneurysms were classified into two types: posterior communicating artery origin type and internal carotid artery origin type. The morphologic charactaristics and basic surgical procedures of these aneurysms were presented in two types respectively.
In some subjects, this classification has similarities to former classificstions, but this one is based on a new concept, as mentioned above. Aneurysm surgery based on the concept of this classification shoud be safer and easier to perform.

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The internal carotid posterior communicating (IC-PC) aneurysm is one of the easiest aneurysms to approach and clip. But, in some cases neck clipping is highly difficult for several reasons. In this report, cause of difficulties of neck clipping and operative complications were analyzed in 54 (34.8%) out of 155 IC-PC aneurysms. The frequent causes of difficulty were 1) large aneurysm, 15 (9.7%), 2) anterior clinoid process covering the proximal side of the neck, 15 (9.7%), 3) posterior communicating artery (P com) arising from the aneurysm itself, 12 (7.7%). Intraoperative troubles were 1) rupture of aneurysm, 18 (11.6%), 2) incomplete clipping with single standard clip requiring multiple or fenestrated clips, 14 (9.0%), 3) removal of the anterior clinoid process required, 13 (8.4%) and 4) slippage of the clip, 5 (3.2%). The distance between the anterior clinoid process and the proximal side of the neck was measured on the lateral view of the preoperative angiogram. This distance was from -3.4mm to +2.0mm, average -0.4mm, in 13 cases of which the anterior clinoid process was removed for clipping, while in 142 cases without clinoid removal the distance averaged +4.8mm. This result suggests that if the proximal side of the neck is located whithin 2mm from the anterior clinoid process, removal of the clinoid would be indicated during surgery. Among 22 patients whose P com was occluded during surgery, 7 (32%) developed some neurological dificits while 15 (68%) remained asymptomatic. Of these seven patients, four developed temporary motor weakness and 3 suffered permanent motor weakness. Mental disturbance such as recent memory disturbance or disorientation was noted in two cases, one temporary, one permanent. Identification of the P com on angiogram was possible in only 6 out of 22 cases with P com occlusion. And, none of the P com was visualized on preoperative angiograms in the symptomatic cases. Although, this study failed to reveal the cases in which P com occlusion was safe. Occlusion of small P com runs the risk of inducing some infarction of the thalamus and other cerebral structures.

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12 patients with anterior choroidal artery (AchoA) aneurysms were operated on between 1980 and 1987 at Keio University. Seven patients had ruptured AchoA aneurysms. In addition to this group, there were 5 cases of unruptured AchoA aneurysms which were found during procedures for ruptured aneurysms at other locations (2 cases), for brain tumor (2 cases) or for TIA (1 case).
Postoperative occlusion of the AchoA occurred in 3 patients who deteriorated as a result of the surgical procedure. In one case, the AchoA could not be identified during operation and might have been occluded by the clip. In another case. there was delayed occlusion of the AchoA 3 days after the operation. The presumed cause of this complication might be a kinking of the vessel due to displacement or rotation of the clip. In the last case, the clip caused stenosis of the AchoA and subsequently infarction during a period of vasospasm. We believe that the clip should be placed at a short distance from the origin of the AchoA in order to avoid unexpected stenosis or even occlusion.

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Temporary clipping of the parent artery in acute-stage aneurysm surgery was popularized by the late Prof. Jiro Suzuki. However, it is not rare that the internal carotid artery (ICA) proximal to the aneurysm cannot easily be identified even during surgery for ICA aneurysms of the common portion. In addition, the difficulty of identification of the ICA proximal to the aneurysm is not always predicted before the operation.
In this paper, authors emphasize that exposure of the common carotid artery in the neck of patients is highly recommended even in aneurysm surgery of the ICA (excluding the cavernous or opthalmic portion) in the cases shown below;
(1) when a ruptured aneurysm protrude posterioly, is located dorsally, or shows up small or large on the angiogram.
(2) when it is not possible to separate the aneurysm from the posterior communicating or anterior choroidal artery on the angiogram.
(3) when younger neurosurgeons perform the operation.

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It seems that the ordinary approach is best in the direct treatment of middle cerebral artery aneurysms. But, sometimes, it is very dangerous with some special types of aneurysms which project rostrally or laterally and/or are attached to the dura mater. The procedure may cause premature rupture, due to retraction of the frontal lobe and the middle cerebral artery itself.
The distal approach is best suited for such types of aneurysms.
But then, we prefer to use the superior approach, by which we are able to treat the aneurysmal neck easily with safety without any brain damage, to the usual type of aneurysm.
The selection of the approach is based on a lateral view of the CAG. If the aneurysmal shadow is obviously rostral from M₁ and origin of M₂ branches, the distal approach should be selected.
The only indication for the ordinary approach is on aneurysm of early bifurcation of the middle cerebral artery.

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One hundred & ten consecutive cases of aneurysm at the anterior communicating artery have been treated under the microscope since 1976 in Kyushu University Hospital.
The site of the neck of anterior communicating artery aneurysms was classified into three types as follows; Type I: the neck is located at the junction of the larger Al segment and anterior communicating artery (ACoA), with a contralateral hypoplastic Al segment. Type II: the neck is located at the junction of the Al segment and ACoA; both Al segments are equal in size. Type III: the neck is located widely on the ACoA; the Al segments are equal in size. Fifty-seven out of 110 cases (52%) were Type I. Forty-four of 57 cases (79%) had the Al hypoplasia on the right side. Thirteen of 110 cases (12%) had vascular variations of the ACoA associated with the aneurysm. Duplicate or fenestrated ACoA was observed in 8 cases, a combination of fenestrated ACoA and triplicate A₂ in 3 cases, a combination of fenestrated ACoA and fenestrated MCA in one case, and a combination of triplicate ACoA and triplicate A₂ in one case. Preoperative bilateral carotid angiograms were reviewed in 10 of 13 cases and vascular variations of the ACoA associated with the aneurysms could be pointed out on angiograms in 4 cases, retrospectively. Anatomical and radiological aspects associated with anterior communicating artery aneurysms are discussed in this paper.

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In this paper, the authors discuss the angle of projection in the preoperative cerebral angiography most useful for predicting the intraoperative view of the anterior communicating artery aneurysm when the pterional approach is used.
Preoperative cerebral angiograms taken from various angles (AP view: OM-20, -10,0, +15 degrees; contralateral oblieque view: 30, 45, 60 degrees) were compared with the intraoperative findings of the respective anterior communicating artery aneurysm complex. A picture simulation was made to predict the intraoperative view according to the findings of the preoperative angiograms.
The results showed that the preoperative angiogram taken with on AP angle of OM-10 degrees, and a rotative angle of contralateral oblique 45-60 degrees corresponded well to the intraoperative findings of the aneurysm. We adopted the angle of OM-10 degrees, and contralateral oblique 45 degrees as a standard operative view angle of the anterior communicating artery aneurysm because an excessive contralateral rotation often disturbed visualization of the aneurysm by the orbital rimb. This specific angle was useful in predicting the intraoperative finding of the anterior communicating artery aneurysm operated on via the pterional approach. Especially when the angiogram was taken with a stereoscopic view, it offered further information about the intraoperative surgical anatomy around the aneurysm.
On the bases of these results, we classify the aneurysms into 4 types according to the preoperative angiography. Technical difficulties are discussed for each type.

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The degree of difficulty of surgery of an anterior communicating artery aneurysm (A com A aneurysm) depends on the position of the neck, size and projection of the aneurysm and relationship to major vessels.
We have been using the pterional approach for operating on A com A aneurysms and have analyzed 47 cases of our experience with ruptured A com A aneurysms.
The right pterional approach was used in forty-four cases (94%) and the left pterional approach was used in three cases (6%)
Aneurysms were divided into four types: Type A: Aneurysm clipped anterior to bilateral A₂; 19 cases (44%)
Type B: Aneurysm clipped posteriorly between bilateral A₂; 13 cases (30%)
Type C: Aneurysm clipped anteriorly between bilateral A₂; 5 cases (12%)
Type D: Aneurysm clipped posterior to bilateral A₂; 6 cases (14%)
Type A was not difficult to clip, but types B, C and D were more difficult to clip than type A. Neck clipping was complicated in the following cases.
·Aneurysm existed between bilateral A₂
·Aneurysm grew posteriorly to bilateral A₂
·Neck of aneurysm existed at the back of major vessels Lateral angiogram 20°. oblique anteriorly was close to the operative view of the aneurysms and was especially useful for predicting the degree of clipping difficulty.

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The essentials for safe, reliable and prompt ruptured anterior communicating aneurysm surgery through the pterional approach were retrospectively studied by the analysis of preoperative cerebral angiogram (AG) and operative procedure, including topographical microanatomy.
The subjects of the study were 28 patients who had undergone acute neck clipping of aneurysms performed by the same surgeon over the last three years.
As for preoperative AG, left A₁ dominancy was observed in 12 cases (43%), right A₁ dominancy in 7 cases (25%) and no dominancy in 9 cases (32%). The number of cases classified according to the projection of the aneurysm were 19 (68%) for anterior, 7 (25%) for inferior and 2 (7%) for dorsalposterior.
The size of the aneurysm was 4~14mm (mean 7mm), though the height was 2~14mm (mean 7mm). Concerning the antero-posterior relationship of bilateral A₂, segment, there were nine cases (32%) of right A₂ posterior to left and 11 cases (39%) of left A₂ posterior to right. In eight cases (29%) there was no difference.
As regards the essentials of the operative procedure, 15 patients (54%) underwent right craniotomy, while 13 patients (46%) underwent left craniotomy. The area of the craniotomy was extended further to the anterior and the midline in left craniotomy than in right.
Premature rupture happened in 2 cases (7%) with inferior projection. A temporary clip on the dominant A₁ was applied in 7 cases (25%), two of which were cases of premature rupture and five of which were cases of intentional clipping on dissection of the aneurysmal complex. The mean occlusion time was 9 min.. Rectal gyrus was partially removed in only 2 cases (7%).
From these observations, the following conclusions were made. The dominant side of the A₁ segment was basically used as the side for the craniotomy. When no dominancy was seen, the posterior side of the A₂ segment was chosen.
The further extended craniotomy on the left side should be used by right handed surgeons. The advantage of the approach through the same side as the dominant A₁ segment was that surgical procedure was extremely safe because of premature rupture and dissection of the aneurysmal complex. On the other hand, it is a disadvantage when the A₂ segment is situated anteriory to the oposite side. In these cases, oposite A₁ and A₂ could be dissected through the“dorsal A₁-A₂ junction related trangle”. Furthermore, the use of the fenestrated clip was effective.

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In general, the results of surgery on anterior communicating aneurysms (ACom AN) is worse than that on internal carotid and middle cerebral aneurysms (IC and MC AN), because of technical difficulty due to the deep location and complex anatomical relationships. Some attempts were made in our hospital to reduce the technical difficulty and improve the surgical results of operation for ACom AN. In this paper, the effect of these attempts was analysed in 208 cases. The timing of the operation and clinical grade were as followes: within 3 days: 67 cases, 4-14 days: 41 cases, over 14 days: 100 cases, I-II: 154 cases, III: 38 cases, IV-V: 15 cases. The operation was carried out by the unilateral pterional approach in all cases. In each case, the side of the approach was determined by angiographic findings except for cases with additional AN and significant hematoma. Craniotomy was performed at the side of the dominant Al in cases where the AN projected forward-downward. In the other cases, the operation was carried out at the side of the deep-seated A₂. Use of a temporary clip for a short time and partial removal of gyrus rectus were positively carried out.
Craniotomy was performed at the right side in 93 cases (45%) and at the left side in 115 cases (55%). A temporary clip was used in 106 cases (51%) and was significantly frequent in grade II, III cases and in cases operated on within 14 days after SAH. Partial removal of the gyrus rectus was performed in 61 cases (29%) and was significantly frequent in cases where the AN projected upward, grade III, IV cases and cases operated on within 14 days after SAH. Clipping of the AN was performed in all cases. Operatve mortality plus morbidity rate was as follow; I-II: 7%, III: 20%, IV-V: 25%. The side of the craniotomy, use of a temporary clip and partial removal of the gyrus rectus caused no significant difference in these rates. The results in cases with AN were almost the same as the results with IC and MC AN. From these results, we can conclude that the side of the craniotomy should be determined by angiographic findings in each case, and use of a temporary clip and partial removal of the gyrus rectus should be carried out actively at the time of the operation for ACom AN.

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The pterional approach has become popular in operations for anterior circulation aneurysms. With the conventional pterional approach, however, some aneurysms are difficult to access safely because of the ristricted operative field, in spite of greater brain retraction. In this paper, our experience of 20 cases with the orbitocranial approach are presented. In 12 cases, we have used this approach in the early stage after subarachnoid hemorrhage. The orbitocranial approach comprises of removing the orbital rim, the orbital roof and the sphenoid ridge. This approach is characterized by multidirectional operative views of the skull base lesions with less brain retraction.
In 5 patients, the high position aneurysms of the anterior communicating artery were approached with less rectal gyrus resection and brain retraction than with the pterional approach. In 6 patients, IC giant (1 case), IC ophthalmic (3 cases), MCA giant (1 case) and MCA (1 case) aneurysms were approached through the wide operative field after the removal of the anterior clinoid process. The low and lateral operative view was very useful for the ICPC aneurysms, the dome of which directed posteromedially in the remaining 9 cases. After the single bone flap was replaced, there was no functional, anatomical or cosmetic deficits of the supraorbital nerve and the frontotemporal branch of the peripheral facial nerve.
The orbitocranial approach is recommended as intermediate procedure between the pterional and orbitozygomatic approaches

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The operative field of the anterior interhemispheric approach depends on the frontopolar vein, height of the endofrontal eminence, and the lamina cribrosa. We measured the distances between the frontopolar vein and the nasion (F-N distance) and the frontopolar vein and the lamina cribrosa (F-C distance) in lateral view of both carotid angiograms (subtraction films) in 67 cases. The frontopolar vein drained bilaterally into the superior sagittal sinus at the frontal pole in 59 cases (88%). In the remaining 8 cases, the frontopolar vein entered into the well-developed frontal cortical vein instead of the superior sagittal sinus and drained into the superior sagittal sinus at the rolandic area. These configurations were found in 2 cases with both sides, in 3 with the right and in 3 with the left side. The F-N distance averaged 4.2cm (ranging from 3 to 6cm) and the F-C distance 5.3cm (ranging from 4 to 7cm). Before using the anterior interhemispheric approach, it is very important and necessary to know the relationship between the frontopolar vein and structures (the endofrontal eminence, the lamina cribrosa and nasion) of the anterior cranial fossa

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Complications due to venous injury are occasionally encountered when bridging veins are divided in an anterior interhemispheric approach for acute aneurysmal surgery. We analyzed the relations between the venous drainage pattern into the superior sagittal sinus and postoperative complications derived from venous injury. The results were as follows: 1) There were no such complications in cases without bridging veins draining in the area of approach 2) Great risks were observed when dividing bridging veins which contained more than three major cortical veins on the lateral surface of the frontal lobe. 3) A bridging vein which drained from less than two major cortical veins could be sacrificed without causing any clinical problems. We conclude that angiographical evaluation of the distribution pattern of the bridging veins is useful for preventing complications due to venous injury in an anterior interhemispheric approach.

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Fourteen cases of unruptured aneurysm of the anterior communicating artery (AcoA) in which a radical operation was performed through an interhemispheric approach were reviewed in order to investigate the microsurgical anatomy around the AcoA.
The aneurysms were classified into 3 types according to the relationship of the aneurysm projection and both A₂ portions of the anterior cerebral artery. In Type 1, the aneurysm projects anteriorly to both A₂ arteries. In Type 2, the aneurysm projects between the two A₂, arteries, and in Type 3, the aneurysm projects posteriorly to both A₂ arteries.
In this series we found the neck of the aneurysm originating not only in the AcoA, but also in the unilateral A₁-A₂ junction, and in some cases, in the bifurcation of the unilateral A₁ when the other was hypoplastic or aplastic.
Thirty-nine perforators were identified on video-tapes recorded during the operative procedure. Nine of these perforators arose from the AcoA, mainly on its posterior or superior surfase. Seventeen recurrent arteries of Heubner could be confirmed, and one third of the total arose from the A₁, one third from the A₂, and one third from the A₁-A₂ junction.
During neck clipping of Type 1 aneurysms, the perforators arising from the AcoA can be con-firmed easily, and rarely, if ever, interfere with clipping. Conversely, in Type 3 and in some cases of Type 2 aneurysms, great care must be taken to spare these perforators during dissection or neck clipping, because many times the visualization of them is poor and insufficient.
The recurrent artery of Heubner does not interfere with clipping in this approach, because it runs out lateraly from the AcoA complex. However in some cases of Type 2 and Type 3 aneurysms, it could be necessary to be aware of the origin and course of this artery and take a side view of the aneurysm, to avoid and preserve it.

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One of the biggest advantages of the interhemispheric approach to the anterior communicating artery aneurysm is the easy handling of topographical orientation, which makes this approach very useful regardless of anatomical variations or sites of the aneurysm. However, the fact that dissection of the interhemispheric fissure is not an easy procedure has been pointed out as a disadvantage. In this report, several key points in performing the interhemispheric fissure dissection are described from the anatomical viewpoint of arachnoid and subarachnoid cisterns relating to the interhemispheric approach. The origin of the A₁ segment of the anterior cerebral artery is located in the carotid cistern, whereas the distal part of the A₁, the anterior communicating artery and the proximal part of the A₂ are located in the lamina terminalis cistern, and the distal A₂ is located in the callosal cistern. Between the cingulate gyrus and the rectal gyrus, which corresponds from the inferior part of the falx to the callosal or the lamina terminalis cisterns, is the most difficult part to dissect. Nevertheless, separation of the right and left cerebral hemispheres is possible without causing any damage by carefully approaching the narrow subarachnoid space around the cortical arteries and by making a sharp dissection where the gyri are closely adhered. On the other hand, the arachnoid around the A₁ segment of the anterior cerebral artery which constitutes the walls of the carotid, the chiasmatic, the olfactory and the lamina terminalis cisterns strongly holds the frontal lobes. Therefore, it should be emphasized that a wide operative field without much brain retraction can be obtained only when such arachnoid is divided.

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With regard to neurosurgical techniques, the cavernous sinus (CS) is one of the most inaccessible areas. Ten adult cadaveric cavernous sinus were examined in detail to evaluate the surgically important relationships of the blood vessels and cranial nerves in the cavernous sinus.
Cranial nerves (CN) III, IV & V_1,2 were embedded in a deep dural layer of the CS and were supplied by the two main branches of the internal carotid artery. The meningohypophyseal artery gave branches to the CN VI in Dorello's canal and the CN V at the dural entrance area. The inferolateral trunk supplied the CN III, IV & V. The capsular artery did not take part in the blood supply to the CN.
In the rectangular space between the CN III and posterior clinoid process after the removal of the anterior clinoid gave access to the C₃ & C₄ portion of the intracavernous carotid artery without sacrificing cranial nerves. In the lateral wall, the size of the triangular space between the CN III, IV & V varied. The intracavernous carotid artery and some of its branches through the lateral wall had a potential risk of injury to the CN III, IV & VI.
The importance of each of these neurovascular structures in various surgical approaches to the cavernous sinus are discussed in this paper.

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In this paper, operative indications, especially as regards the selection of surgical approach for anterior communicating artery aneurysms (ACAA) are discussed with precise and detailed analyses of angiographical anatomy of the aneurysm and the surrounding arteries in 120 surgical cases.
Aneurysms originating in the anterior communicating artery itself were much less frequently observed (18.3%), and the majority have their origins on the A₁-A₂ junction (81.7%). Fifty percent of the A₁ segments of the anterior cerebral arteries were dominant on the left side. The right-dominant and the equi-A, type comprised 25% each. In 60% of the cases, the left A₂ was anterior to the right one, in 25% vice versa and only in 15% both A, were running in parallel. These inequalities of the arteries surrounding the ACAA seemingly affect the incidence of aneurysmal type. That is, about one third (31.7%) of the ACAA projected laterally from the origin on the A₁-A₂ junction, and for this lateral-type aneurysm the most suitable surgical approach is the interhemispheric (IH), among numbers of access methods.
The location of the neck of the aneurysm, the direction of its dome and the side of the dominant A₁ segment of the anterior cerebral artery are important factors in deciding what type of surgical approach is to be done. Though the anteriority of the A, segment is a factor that cannot be disregarded in the pterional (PT) approach, the authors believe that it is not essential in considering the IH approach because this approach can be used for any type of ACAA. At the same time, surgeons should not stick to a single method, especially in the acute stage of subarachnoid hemorrhage because, in this situation, they must try to accomplish the operation as safely, quickly and, of course, completely as possible. In the authors' series, the pterional approach was used in 66 cases (55.0%), the interhemispheric approach in 47 (39.2%), and the bilateral subfrontal and trans-hematoma access were chosen for 4 and 3 cases respectively. And there were 11 cases in which the IH approach with an additional PT approach was used for securing the Al segment which was hidden behind the dome of the aneurysm from the IH surgical view and/or for removal of diffuse and thick subarachnoid clots.

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The exposure of the petrous segment internal carotid artery (ICA) is detailed in this paper. It was found that there was a 10~15 mm length of the horizontal segment of the petrous ICA that could be exposed. To avoid injury to the cochlea, drilling of the petrous bone must be started in the Glasscock triangle just behind the foramen ovale. And to preserve the facial nerve function, the greater superficial petrosal nerve must be cut first so as not to tract the geniculate ganglion. The exposure was useful for obtaining proxymal control of the cavernous ICA and for making a working space for petrous to supraclinoid carotid saphenous vein graft.
This surgical technique can be recommended in the management of patients with intracavernous vascular or neoplastic lesions, with basilar aneurysms, and with clival tumors.

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Nine cases of cavernous portion aneurysm (AN) were treated by direct surgery.
One AN was a persistent trigeminal artery AN at the C_4-5 portion, five ANs were located at the C₃ portion and the other three were ophthalmic ANs of the subchiasmal type at the C₂ portion.
In four cases, subarachnoid hemorrhage occurred as a result of a saccular aneurysm located at the C₂ portion (three cases) and at Acom accompanied by a C₃ portion AN (one case). In two cases, epistaxis occurred as a result of a saccular aneurysm located at the C₃ portion. In one case, ophthalmoplegia occurred suddenly. And in two other cases, aneurysms were incidentally discovered by angiography.
Operation was performed under normotensive, normothermic anesthesia in a half sitting position with the head lifted up by approximately 35°. In this position, it was easy to control venous bleeding from the cavernous sinus owing to reduction of venous pressure. Intraoperative monitoring was performed to evaluate cerebral blood flow (CBF), somatosensory evoked potential (SEP) and visual evoked potential (VEP).
The subtemportal approach was used for a C_4-5 AN and the pterional approach was used for C_2-3 ANs with the removal of the anterior clinoid process. Bleeding from the opened cavernous sinus was controlled with Oxycel packing. Doppler sonography was useful for checking on the patency of the internal carotid artery.
All nine aneurysms were clipped with no stenosis of the carotid artery. There was no major ischemic complication, but ipsilateral blindness (2 cases), ophthalmoplegia (1 case), transient oculomotor palsy (1 case) and transient CSF rhinorrhea (1 case) were observed.
Details of direct surgery on the nine cases of cavernous portion aneurysms are reported in this paper.

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Detachable balloons were used for proximal occlusion of the internal carotid artery in 5 patients with intracavernous giant aneurysms. As a result, decrease in size of the aneurysm was observed in all patients on follow-up CT and MRI. Moreover, improved neurological symptoms were noted in 2 patients in whom treatment had been completed within 2 months after the onset of symptoms.
Before performing proximal occlusion, it is important to conduct a balloon occlusion test so as to accurately evaluate the availability of the occlusion of the internal carotid artery. In these patients who underwent simultaneous STA-MCA bypass surgery, none of them showed any late cerebral ischemic symptoms during follow-up observation up to 27 months.
Thus, the above procedure is considered to be a useful method of treatment for intracavernous giant aneurysms because it is a safe and easy method for reducing the size of aneurysms and for improving neurological symptoms.

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Due to the location, there are many surgical problems and pitfalls in the treatment of infraclinoid internal carotid artery (ICA) aneurysms. It is impossible to evaluate exactly from the preoperative angiogram whether the aneurysm is located in the cavernous sinus (CS), in the carotid cave, or around the dural ring. Therefore, cervical internal carotid artery (ICA) or petrous ICA has been exposed to control bleeding from aneurysms during surgery. The cavernous ICA should be exposed not only in order to accurately perform aneurysmal neck clipping but also to be prepared for possible premature bleeding. In this paper, we report on the surgical technique for accurate clipping of infraclinoid aneurysms called the transcavernous approach. The surgical technique is as foliows: (1) Semisitting position to decrease venous bleeding from the cavernous sinus.
(2) Combined epi- and subdural approach to remove the anterior clinoid process and to open the optic cannal. At the final stage of this approach, drilling of bony structures should be done subdurally so as not to injure the ICA.
(3)It is necessary to cut the falciform ligament and to open the optic dural sheath.
(4) The C₄ segment of the ICA is exposed for temporary clipping of the ICA before cutting the dural ring.
(5)Bleeding from the CS is controlled by packing with Biobond-soaked Oxycel.
(6)The Sugita curved blade“L”shaped fenestrated clip is useful. During the last 12 years, 39 infraclinoid aneurysms were treated by this approach. Thirty four aneurysms were clipped, whereas one was trapped and four were trapped and the cavernous ICA was reconstructed using a saphenous vein interposition graft. Thirty three patients (92%) recovered and returned to the preveous jobs. One remained vegetative because of vasospasm. Two patients died from vasospasm and agranulocytosis.

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A series of 5 patients with a carotid-ophthalmic artery aneurysm were treated surgically. In two patients the aneurysms were large, and two had ruptured. The combined extra- and intradural direct approach seemed to provide a better and safer exposure of the central segment of the internal carotid artery. However, a finding of anterosuperior or superolateral direction of the aneurysm in cerebral angiography indicated danger of rupture of the aneurysm during extradural drilling. In this anatomical situation, intradural removal of the anterior clinoid process makes it safer to state in contact with the wall of aneurysm. In two of the five patients these aneurysms were clipped by removing the anterior clinoid process intradurally. The angiographical direction of the aneurysm dictates the selection of approach for removing the anterior clinoid process and unroofing the optic canal.

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