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.
