A case of the right hypothalamic angioma operated by the contralateral subchoroidal approach is presented. A 31-year-old man presenting with mild hemiparesis and diplopia was admitted for examination in May 1991. He had suffered from a similar attack a few month before and at that time, a small hypothalamic hematoma revealed by MRI was left untreated. The CT and MRI revealed a hematoma in the right thalamus just above the mamillary body, extending from the posterior hypothalamus to the upper cerebral peduncle. Despite this apparent lesion in the right mamillary body, his recent memory function was found to be normal. Four-vessel angiography revealed no vascular abnomalities. T₂-weighted MRI demonstrated a typical picture of cavernous angioma with a mixed intensity core surrounded by a low-intensity hemosiderin ring. Since this was the second hemorrhage, it was decided to undertake a radical operation.
Via the interhemispheric approach, the corpus callosum was divided and the left lateral ventricle was entered. The thalamostriate vein was sacrificed and the third ventricle was opened from above by dividing the tenia choroidea posteriorly. Following section of the massa intermedia, the contralateral wall of the third ventricle could be seen clearly by the above approach. The hematoma was easily found by the discolaration of the wall. On evacuation of the hematoma, angioma-like abnormal vessels were found and resected. The pathological diagnosis was AVM. The postoperative course was uneventful except for recent memory disturbance, which was severe in the first three months and then gradually improved. The patient returned to his previous job 18 months after the operation.
The above case shows that lesions in the vicinity of the third ventricular wall can be safely operated on by the contralateral subchoroidal approach. However, since some damage to the contralateral thalamus due to retraction or venous stasis is unavoidable, this approach is considered to carry a high risk of recent memory disturbance, although if may be transient.

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This paper describes a surgical approach to basilar tip aneurysm. Direct operation for such aneurysms has not been performed at the acute stage due to the restriction on surgical space.
To overcome the narrow surgical space, the lesser wing of the sphenoid bone was removed extradurally. The anterior clinoid process and roof of the optic canal were drilled off by the extradural approach. The dural ring of the internal carotid artery (ICA) in the cavernous sinus was partially opened. By removing the lesser wing of the sphenoid bone, mobilization of the ICA and of the optic nerve was increased. Extensive mobilization of the ICA provided a wide surgical space, which permitted clipping of the basilar tip aneurysm at the acute stage. During retraction of the ICA, the patency of this vessel was maintained and the cerebral blood flow in the ICA territory was preserved as the ICA and optic nerve were not fixed by the lesser wing of the sphenoid bone at the point of entry into the intracranial space.
In conclusion, the lesser wing approach affords better mobilization of the ICA and the optic nerve, and provides a good surgical view for operation on basilar tip aneurysm.

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Thirty-two patients were treated with embolization of brain arteriovenous malformations (AVM's). Of these patients, 16 underwent surgical removal of AVM and 16 radiosurgery following embolization. Embolization caused neurological deficit in six patients (morbidity 18%) and fatal brain swelling in one (mortality 3%). Complication occurred in 6 out of 17 patients with AVM's in the eloquent area (35%) and 1 out of 15 with those in the non-eloquent areas (6%). Although embolization was a valuable procedure in the treatment of brain AVM's combined with surgery or radiosurgery, indication for embolization of AVM should be carefully decided with consideration of therapeutic risk, especially for lesions in the eloquent areas.

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Radiation injury is the most serious complication after gamma knife radiosurgery. To reduce the rate of radiation injury, it is important to minimize the irradiated volume of the surrounding normal brain tissue. Especially, when AVMs are located adjacent to eloquent areas such as the brain stem or optic pathway, sparing the surrounding vital structures is one of the most important factors to minimize the radiation injury. However, the three dimensional shape of the nidus cannot be fully delineated with only angiograms of frontal and lateral views. Morever, it is impossible to determine the accurate dose at surrounding vital structures from angiograms alone. To solve these problems, dose planning using axial MRI combined with angiograms was performed in 40 cases from July 1991 to June 1992. Axial MRI combined with angiograms gave us more information about the shape of the nidus than only angiograms of frontal and lateral views in all cases. Because MRI showed accurate irradiated dose to surrounding vital structures, we were able to minimize the dose irradiated to optic pathways in 7 cases and the brain stem in 9 cases.
To minimize radiation injury, dose planning using axial MRI combined with angiograms should be carried out especially in cases of AVMs located adjacent to the optic pathway and brain stem.

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We report three cases of the sylvian fissure arteriovenous malformation (sylvian fissure AVM). The sylvian fissure AVM was a circumferential or penetrating type of AVM and many short feeding arteries of less than 1 mm were directly branched from the middle cerebral arteries (M2, M3). Preservation of the parent and transit arteries of the middle cerebral arteries was the most important goal of the operation.

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A case of anterior cerebral artery dissecting aneurysm presenting subarachnoid hemorrhage and cerebral infarction at the same time is reported.
A 62-year-old male suffered from vomiting and speech disturbance. On admission, however his consciousness was clear, mild dysarthria and right hemiparesis were recognized and a CT scan revealed subarachnoid hemorrhage in the interhemispheric fiissure and the left parietal region. A CT scan and MRI taken on the next day demonstrated cerebral infarction in the left anterior cerebral artery perfusion area. The first angiogram showed small dilataion of a part of the left A₂ portion only. Two weeks later the second angiogram showed segmental narrowing of the left A₂ and A₃ portion following the bulbous dilatation of the lumen on the left A₂ portion, which suggested a dissecting aneurysm. We performed side-to-side anastomosis between the bilateral A₃ portion and trapping of the bulbous dilatation to prevent reattack. The postoperative course was not only uneventful, but the right hemiparesis improved remarkably.
The anterior cerebral artery dissecting aneurysm presenting both subarachnoid hemorrhage and cerebral infarction is very rare. It is believed this is the first case which received anastomosis and trapping for anterior cerebral artery dissecting aneurysm.

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Aneurysms arising from the dorsal wall of the intracranial internal carotid artery (DICA) are rare but known as dangerous, easily rupturing aneurysms. We present 17 cases with such aneurysms from 261 cases of internal carotid aneurysm (6.5%). Characteristic clinical features of DICA are as follows: 1) Younger onset of subarachnoid hemorrhage, 2) rapid growth of domes in a relatively short time, 3) fragile wall and neck causing frequent ruptures from its neck during surgery, 4) frequent rebleeding and/or regrowth of the dome after the neck clipping. From these peculiar clinical characteristics, we propose a dissecting aneurysm as a cause of this abnormally thin-walled aneurysm.
The neck clipping cannot be the treatment of the best choice, because obliteration of the entry of dissection solely is capable of stopping rebleeding only if the dissected cavity is not thrombosed yet. Actually both in our series and in reported cases, the neck clipping often failed to obliterate the dome of DICA, especially in case of early surgery. The trapping or proximal ligation of the internal carotid artery brings severe and diffuse damage to the affected hemisphere much more frequently in the acute stage than chronic. We therefore recommend the elective operation for DICA as a first-choice treatment and preoperative balloon-occlusion test as well. To certify the rationality of this hypothesis as to the pathogenesis of DICA, histopathological investigation in the future would be essential.

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To minimize the temporary occlusion time during bypass surgery, continuous absorbable sutures with 9-0 polydioxanone (PDS) were employed in the superficial temporal artery-middle cerebral artery (STA-MCA) anastomoses. Two cases of internal carotid artery occlusion and 4 cases of its stenosis were operated on in the chronic stage, and one case of MCA occlusion in the superacute stage. In all cases, a cold xenon-enhanced CT revealed the reduction of local cerebral blood flow (LCBF) preoperatively. Postoperative courses were uneventful and there were no anastomotic complications. The follow-up period ranged from 6 to 14 months. In 5 of the 6 cases in the chronic stage, all STAs and anastomotic sites grew remarkably in diameter 3 months after the surgery, when PDS had already lost tensile strength, and thereafter gradually increased in size. These changes were correlated with the improvement of LCBF. In the remaining one in the chronic stage, the STA showed less growing due to increased collateral flow via the external carotid artery system. In the case of MCA occlusion, growing of STA did not occur due to the low bypass-flow that resulted from the spontaneous recanalization of the occluded MCA. Previous studies suggested that absorbable PDS does not elicit inflammatory response, wall thickening, hyalinoid degeneration or calcification, which occasionally occur in use of nonabsorbable polypropylene sutures. In conclusion, PDS seems to be suitable for anastomosing small vessels and continuous PDS sutures are available for extracranial-intracranial arterial bypass surgery in which anastomotic sites grow corresponding to the increases of the bypass-flow.

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A digital subtraction angiographic (DSA) apparatus has been installed in one of our operating rooms since April 1987. We performed intraoperative DSA in 42 aneurysmal surgeries in 38 patients and balloon temporary occlusion in 33 surgeries. The aneurysm was on an internal carotid artery in 26 cases and on the vertebro-basilar system in 16. A heparin-coated catheter (Anthron, Toray, Tokyo), 6 french in diameter, was inserted transfemorally and was put in a parent artery under general anesthesia. A balloon catheter was coaxially introduced into the proximal portion of the aneurysm. The balloon was temporarily inflated to determine inflation volume. The balloon catheter was soon deflated and was drawn back into the introducing catheter to avoid developing microembolus. The patients were not systemically heparinized but the introducing catheters were slowly flushed with heparinized saline during operation. Then a craniotomy was carried out. Next DSA was performed when temporary occlusion or confirmation of clipping was necessary.
In cases of balloon temporary occlusion, the operating field was not obstructed as it is when a temporary clip is used, despite adequate flow reduction of the parent artery. After DSA for confirmation of clipping adjustment of it was performed in 12 cases out of 42. No complications occurred due to use of an introducing or a balloon catheter. We conclude that combined intravascular and neurosurgical approach, particularly for the large aneurysms with the difficulty of proximal control, can be a useful method of treatment.

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We have been employing preoperative embolization prior to microsurgical removal of cerebral arteriovenous malformations (AVMs) since 1988. In the present study, we analyzed the effects of preoperative embolization in a consecutive series of 24 cases of high-flow, large AVMs (>4cm in maximum diameter) treated between 1985 and 1991. We have chosen to use polyflilament polyester threads as an embolization material, because they cause minimal inflammatory reactions and no risks of venous occlusion. The threads were 200 micron in diameter and 5-10mm in length. We embolized 1 or 2 feeders each time until the mean feeder pressure rose to 70-90mmHg. This was repeated several times with an interval of 1-2 weeks. Microsurgical removal was performed within 1-2 weeks after the final embolization. In five cases, we encountered headache, deterioration of impaired consciousness or hemiparesis after embolization. However, all of these were transient. There was no major difference in location, age or initial symptoms between the group treated by microsurgical removal alone, and the group treated by combination of microsurgery and embolization. However, the AVMs operated after embolization were larger in volume than those treated by microsurgery alone. A classification of Spetzler and Martin also indicated that more difficult AVMs were treated by microsurgery with preoperative embolization. The total amount of blood loss was significantly small in cases operated after embolization in the group of very large AVMs (>20ml). Consequently, the operation time tended to be shorter in cases operated with embolization. Hyperemic complications were significantly less frequent in cases operated after embolization. Although there was no significant difference in overall outcome between these 2 groups, new deficits produced by microsurgical removal were significantly less frequent in cases operated after embolization. Earlier surgery after embolization appeared to be important to avoid recruitment and enlargement of small deep penetrating feeders. Polyfilament polyester threads are useful as an embolization material to make earlier surgery easier because of minimal inflammatory reactions and no risks of venous occlusion.

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A case of a true posterior communicating artery aneurysm is presented. A 51-year-old woman was admitted to our hospital with sudden severe headache. Subarachnoid hemorrhage in the left Sylvian fissure was recognized on CT scan and an aneurysm, 4×5mm in size, was revealed by angiography on the left posterior communicating artery (P co A) itself 5 mm distal from the origin of P co A. During the surgery, the aneurysm was found projecting toward out of upward on the curved portion of P co A, 5mm distal from the carotid artery. The neck of the aneurysm was narrow, but since a few perforating arteries were found very close to the neck, the neck clipping sparing them was very difficult. The patient was discharged from the hospital without neurological deficit.
The incidence of true P co A aneurysm is rare with reports of 0-3.3% among all intracranial aneurysms. As the surgical treatment of this aneurysm, proximal ligation of the carotid artery or the posterior communicating artery is not effective to prevent the rerupture of the aneurysm because rich collateral blood flow comes from the circle of Willis. In saccular aneurysms, neck clipping is performed with relative ease, but careful attention must be paid not to injure the perforating arteries from P co A close to the neck, which feed the thalamus, hypothalamus, internal capsule, etc. In some cases, trapping of aneurysm must be performed for unavoidable reasons such as broad aneurysmal neck or fusiform aneurysm. However, since the blood flow of perforating arteries is interrupted by this procedure, the appearance of severe neurological deficits is not rare.

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