The author describes fundamental surgical techniques for treating internal carotid (IC)-posterior communicatory (PO and IC-anterior choroidal (AO artery junction aneurysms. As the blood pressure of the internal carotid artery and its aneurysm is extremely high in the intracranial main trunks of the arteries, premature rupture of such aneurysms_ is a very real danger. Therefore, preservation of the parent artery is initially necessary. Preservation of the PC artery, the AC artery, and the small perforating arteries, and a complete neck clipping of an aneurysm can be achieved by several surgical approaches : a pterional approach and an approach from the opposite side via the prechiasmatic cistern -, and temporary clipping of the parent artery, followed by selecting and installing permanent clips, including fenestrated clips. In Japan, most ruptured aneurysms_ are treated surgically during their early stage, and by neurosurgeons who are relatively young. As the incidence of aneurysms at these sites Is high, knowledge of these fundamental techniques of surgery is necessary to achieve good postsurgical results.

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Surgery for intracranial aneurysms can be divided into two types : (1) surgery for acute-stage ruptured aneurysms ; and (2) delayed surgery for ruptured aneurysms and surgery for non-ruptured aneurysms. The purpose of this paper is to discuss operative techniques for acute-stage anterior communicating artery aneurysms. In approaching the aneurysms, cerebral retraction must be minimized, and on initiating the intradural procedure by aspirating the CSF from the chiasmatic cistern via the narrow gap between the frontal lobe and the skull base, the distended brain is slackened. This thus minimizes frontal lobe retraction. Anterior communicating artery aneurysms present in the narrow space surrounded by five arteries and the brain may be found to adhere to the chiasma or be hidden in the interhemispheric fissure, and the authors discribe operative techniques developed for the anatomical features of such anterior communicating artery aneurysms. In addition to preventing an aneurysmal rerupture by neck clipping, surgery for acute-stage intracranial aneurysms should be directed toward preventing vasospasms and hydrocephalus. For this purpose, extensive washing to eliminate the hematoma filling the subarachnoid space is necessary. The authors stress the usefulness of securing an unobstructed, absorbant pathway for the CSF by opening Liliequist's membrane and the lamina terminalis.

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Middle cerebral aneurysms can develop from a variety of locations but most aneurysms occur at M_1 bifurcation, although the origin of the anterior temporal artery, the lenticulostriate artery, and the area distal to the M_2 segments are also likely sites. There are two major surgical approaches to consider for an aneurysm at the M1 bifurcation : the proximal approach, which proceeds from the internal carotid, the M_1, and the bifurcation : and the distal approach, which proceeds from the M_2 directly to the M_1 bifurcation and the aneurysm. We use both approaches interchangeably, even in one patient, whichever was considered safer and less traumatic to the brain. Body clipping is a major surgical requirement for a wide-necked aneurysm, and a combination of the most suited multiple clips should be used on aneurysms with arterial branching. Temporary clips should be limited to cases of a premature aneurysmal rupture, or if an aneurysm appears imminent, or when puncturing the aneurysm to reduce its mass. In all instances, however, the brain must be protected before applying any temporary clip. Although early removal of the blood clot is the best way to prevent the occurrence of a vasospasm, it is impossible to surgically remove a clot sited deeply in the insular cistern. The intrathecal use of thrombolytic agents seems to be promising procedure, provided that their side effect (bleeding) can be controlled. However, no single drug treatment has been found successful. Thus, a combination of several drugs with different mechanisms of action may have to be used to abolish the vasospasm.

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Based on an angiographic analysis, the author presents a selection of surgical approaches and important technical strategies for treating various basilar aneurysms. A lateral, non-subtracted angiogram was a key film for the selection of the surgical approach. In this angiographic analysis of basilar bifurcation aneurysms, several distinct characteristics were noted : the length and deviation of the ICA, the course of the PCA and the Pcom, the origin of the thalamo-perforators, and the location, direction, and width of the neck of each aneurysm. In patients with a short, laterally deviated ICA of the access side, a pterional approach for the resection of the anterior clinoid process, followed by detachment of the carotid ring, was found to be a useful procedure to enlarge the operational field. The proximity of PCA (Y-shaped PCA) or of the thalamo-perforating arteries to the aneurysm was seen to be a risk factor for clipping, especially for large aneurysms. For basilar trunk aneurysms, the use of the anterior transpetrosal approach was found to be advantageous, since retraction damage to the temporal lobe is reduced. Also, the surgical field was enlarged by opening Meckel's cave to mobilize the Vth nerve, as well as by resecting the petrous apex. This approach is indicated for aneurysms located between the pituitary base level and the internal auditory meatus, especially for aneurysms that project posteriorly.

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The surgical techniques for treating the vertebral artery aneurysms are discussed. In the territory of the vertebral artery, atherosclerotic fusiform aneurysms and dissecting aneurysms account for approximately 40% of all aneurysms. These aneurysms are not clippable with an aneurysm clip and should be treated by alternative methods, such as proximal clip occlusion, entrapment, or wrapping. Aneurysms located on the midline or very high in the posterior fossa (13 mm or more posterior to the clivus) are difficult to treat and lower cranial nerve palsy should be anticipated postoperatively. When treating such cases, the right-handed surgeon is advised to select a prone position for a left-sided lesion and a lateral position for right -sided lesion, for in assuming these positionings, the surgical view and surgeon's right hand are properly aligned in operative field. For higher lesions of the vertebral artery, a subtemporal transpetrous surgical approach might be best, this approach requiring drilling the petrous bone between the 5th and the 7th cranial nerves.

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From March, 1973 through December, 1991, the authors have surgically treated 885 cases of intracranial aneurysms. Among these cases there were large intracranial aneurysms, which are sometimes difficult to treat, and the authors discuss their results in treating 36 giant aneurysms, greater than 2.5 cm, and 39 big aneurysms, greater than 2 cm. For 6 early aneurysm cases, ligation of the ICA with a STA-MCA anastomosis was performed. Clipping was done for 59 cases, trapping for 6 cases, coating for 2 cases, and an aneurysmectomy for 2 cases, one of these latter cases also requiring an M_1-M_2 anastomosis. Fifteen acute-stage operation cases required immediate surgery, and a good recovery was achieved in 4 cases. The remaining 11 cases, however, developed complications due to the severe grade of their SAH. In contrast, out of 60 cases of delayed stage operation cases of aneurysms, the rusults in 43 cases were excellent and a further 12 cases developed only a temporary postoperative complication, so that a total of 55 cases (92%) ultimately had a good recovery, and 5 cases resulted in a permanent neurological deficit. Based on these results, whenever possible, delayed stage operations are recommended. As for operational techniques, if temporary clips are to be used, the maintenance of the peripheral blood flow must be ensured, and so the authors use short-time temporary clipping with brain-protecting drugs, or they perform bypass surgery prior to the temporary clipping. They recommend, however, tentative clipping rather than temporary clipping. The term tentative clipping means the use or an aneurysm dome clip or a neck clip, such clipping sometimes including the arterial branches. This tentative clipping method has been found useful for avoiding an aneurysmal rupture, and for easy dissection of the aneurysmal site, making a fine and safe dissection of the aneurysm possible. Finally, the selection of the proper clip is important, and they have found fenestrated clips useful in reconstructing the artery with clips.

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The authors report three cases of a chondrosarcoma that arose from the skull base and invaded the paranasal sinuses, and discuss the treatment modality. All the patients underwent a partial removal of the tumor and received postoperative radiation therapy with a dose between 5,000 to 7,000 rads. Although these tumors did not change in size after radiation therapy, in each case calcification developed within the entire tumor, including the soft-tissue elements. Further, in all three cases, tumoral growth was controlled for two to ten years. Chondrosarcomas of the skull base are likely to have extensive spread by the time of diagnosis, and are often beyond the curative surgical removal. However, some reports maintain that radiation of advanced cases does have an effect on the chondrosarcoma. As in these 3 cases, although radiation therapy may not shrink the chondrosarcoma, tumoral regrowth is often controlled. Based on our experiences and a review of literatures, the authors thus feel that radiation therapy of postoperative residual tumors is a reasonable procedure.

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A thorough understanding of the microanatomy of the basilar artery and its perforators is important for the surgical treatment of basilar trunk aneurysms. Therefore, 25 cadaver brains were dissected and their anatomies were observed under an operating microscope. The findings are given below. On the average, 20.5 (±3.1) small branches, consisting of 12 (±2.2)) median branches and 8.4 (±1.9) circumferential branches, originated from the basilar artery. The median branches were distributed rather evenly, whereas the distribution (and number) of the circumferential branches varied, depending on how the anterior inferior cerebellar artery (AICA) and the superior cerebellar artery (SCA) had developed. In clinical cases that showed a poorly developed AICA and SCA on angiography, the blood supplying the brain stem was found to depend on the circumferential branches, so that when surgically treating such cases, particular attention should be paid to preserving the circumferential branches. Further, fenestration of the basilar artery was seen in two specimens, and since the number of perforators from the fenestrated portion of the basilar artery was found to be the same in brains without this anomaly, trapping of the fenestrated portion should be preferably avoided so as to preserve the perforators.

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The authors describe a huge arteriovenous malformation (AVM) in the right temporo-parieto-occipital lobes that was successfully removed after a multi-staged embolization of the feeding arteries. The patient, a 54-year-old housewife, had presented uncontrolable epilepsy, progressive dementia, hemianopsia, hemiparesis, and hemisensory impairment of the left side. Angiography revealed a huge AVM mainly being nourished by the following sources : the parieto-occipital arteries of the posterior cerebra] artery, the temporal branches of the middle cerebral artery and dura] branches from the external carotid and vertebral arteries. Further, the cortical draining veins over the entire hemisphere were markedly, dilated, and the superior sagittal and straight sinuses visualized poorly, probably due to the congestion in the venous circulation caused by the arteriovenous shunt. CT scans also revealed multiple, club-like calcification in the parietal and frontal subcortical regions, indicating chronic brain ischemia caused by the remarkable arterial s_teal and/or venous hypertension. . Preoperative super-selective embolization was done in four sessions, using newly developed, low-friction, high -torque guide wires. and this resulted in a dramatic neurological improvement, especially with regard to the dementia. Then, following intraoperative embolization of the remaining feeding arteries, the AVM was success-fully removed. The patient tolerated these procedures well without hemodynamic complications, and after a few months of rehabilitation, she resumed her normal life.

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The authors report an uncommon case of cerebral nocardiosis in a 62-year-old man, who was admitted to hospital because of general fatigue, cough, and fever. The diagnosis was right lobar pneumonia of an unknown etiology. Chemotherapy with imipenem resulted in decreasing the size of a lesion in the right lung. However, two months after admission, convulsions and a right hemiparesis were manifested, and a subsequent brain CT scan and MRI showed what appeared to be cerebral abscesses in the left frontal and left occipital lobes. Thus, a craniotomy with aspiration was performed and Nocardia, which was isolated from aspirated pus, was found. Further, postoperatively, additional Nocardia was found in the sputum. Thus, an intensive chemotherapy that combined sulfamethoxazole-trimethoprim and imipenem was initiated and resulted in decrease in the cerebral abscesses. Cerebral nocardiosis is a life-threatening disease, and this case was successfully treated by an aspiration of the abscesses and adequate postoperative antibiotic chemotherapy.

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