We reviewed 12 cases of anterior wall aneurysms of internal carotid artery. We classified those aneurysms into two types as follows: 1) “chimame” (blister) type, which has a thin wall and fragile neck; and 2) “non-chimame” type, which has a usual wall and neck. Six cases had “chimame” type aneurysms. All 6 patients were women, ranging in age from 37 to 61 years (mean, 49 years). All aneurysms were the source of subarachnoid hemorrhage (SAH). The size of the aneurysms varied from 1 to 4mm with a mean of 2.8mm. There were also 6 cases with “non-chimame” type aneurysms. Three patients were men and 3 were women, ranging in age from 47 to 68 years (mean, 56 years). Two aneurysms were the source of SAH. The size of aneurysms varied from 5 to 18mm with a mean of 12mm. Intraoperative rupture occurred in 5 of the 6 “chimame” type aneurysms, and in only one of the 6 “non-chimame” type aneurysms. Neck clipping was done in one of the 6 “chimame” type aneurysms, but was done in all of the “non-chimame” type aneurysms. One patient of “chimame” type aneurysm treated by trapping died, but the others had good recovery.
“Chimame” type anterior wall aneurysm is easy to rupture, difficult to clip, and so necessitates special surgical techniques such as wrapping or trapping with bypass. On the other hand, “non-chimame” type anterior wall aneurysm can be clipped relatively safely. However, it is important not to induce intraoperative rupture during dissection and clipping, because the aneurysm is severely adherent to the frontal lobe or temporal lobe.

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1994年に当教室は3例の背側部動脈瘤を経験した.背側部動脈瘤は稀ではあるが, 術中破裂が多いなどの点で特徴的な動脈瘤である.今回急性期の診断, 治療上問題になった点を検討した.全例に急性期手術を施行した.診断上の問題は, 通常の血管撮影では壁の不整が唯一の所見で, 明らかな動脈瘤の所見のない場合があり注意を要する点である.また血管撮影において血管動画像撮影法 (cine angiography) およびその録画は有用であった.一方術前の再破裂は2例に認めたが, いずれも高いリスクの症例であった.手術では迅速にへ到達することが必要であり, クリップを掛ける時にも工夫が必要である.脳内血腫の合併など脳腫脹が強い場合は通常のアプローチにとらわれずに最小限のcerebrotomyを追加することは有効であった.また動脈瘤のドームに癒着したくも膜は剥離すべきでないと考えられた.

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Six patients with aneurysms arising from the anterior wall of the internal carotid artery were reviewed to investigate clinical and radiographic characteristics and operative findings. The role of 3D-CT angiography (3D-CTA) was also analyzed in 3 recent patients to determine clinical usefulness in the diagnosis and surgical management of this lesion. They were all females ranging in age from 25 to 62 years with a mean age of 47.5. Five patients presented with subarachnoid hemorrhage and the remaining had an unruptured aneurysm in association with another ruptured aneurysm. The aneurysms arose from the right carotid artery in 5 patients and from the left in 1 patient. The 3 recent patients underwent 3D-CTA immediately after they were transferred to our hospital following aneurysm rupture.
At surgery 2 of 4 saccular aneurysms, which adhered to and were buried in the frontal lobe, were dissected subpially. Two patients had a blister type of the aneurysms with a wide neck, and the remaining 4 patients had a saccular type of the aneurysms with a narrow and distinct neck. A small, blister-like aneurysm in 1 patient was wrapped with thin sheets of cottonoid together with the parent artery, followed by clip placement. In the remaining 5 patients a variety of angled clips were placed in parallel to the parent artery. The 3D images generated by 3D-CTA were of great value in assessing the exact site of the aneurysms, their growth projection, the shape and the size of the fundus, and their anatomical relationships to the adjacent arteries and other landmarks such as the anterior clinoid process and the optic canals. They were also a great help in surgical planning and simulation for aneurysm dissection and neck clipping.

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Aneurysms of the dorsal (anterior) wall of the internal carotid artery (IC d-ANs) are rare. Although their clinical features are well described, their mechanism of pathogenesis is unknown. We present 6 cases, including an autopsy case, of IC d-AN and the pathogenesis of IC d-ANs on the basis of clinical records, anatomic findings and history. Most IC d-ANs have fragile walls and necks and can be described as “blister like.” In our series, 3 aneurysms were of the blister type and 3 were of the saccular type. Although the operative findings and clinical course differ a little between blister-type and saccular-type IC d-ANs, we could not conclude that these 2 types of aneurysm have different pathogenesis. Moreover, the possibility still remains that some blister-type aneurysms may grow to saccular aneurysms. Some authors report that the blister-type, or fragile wall, aneurysm may be a type of dissecting aneurysm. Intraoperative and pathologic findings suggest that these aneurysms may be pseudoaneurysms caused by a partial- or full-thickness tear through the wall of the artery,but they cannot be defined as dissecting aneurysms because there is no dissecting lumen. Moreover, if there are findings of dissecting aneurysm intraoperatively we should treat it as dissecting aneurysm. IC d-ANs should be defined more clearly on the basis of findings of the aneurysm and the parent artery because IC d-ANs are classified on the basis of intraoperative features, not pathologic findings.

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