Pathological Consideration of a "Blister-like" Aneurysm at the Superior Wall of the Internal Carotid Artery: Case Report

OBJECTIVE AND IMPORTANCE: Although the incidence is low, a very small aneurysm with a thin wall and no neck arises at the superior wall of the supraclinoid portion of the internal carotid artery and is called a "blister-like" aneurysm. However, the pathogenesis of such a vascular lesion remains uncertain. CLINICAL PRESENTATION: A 57-year-old man developed a fatal subarachnoid hemorrhage caused by the rupture of a blister-like aneurysm at the superior wall of the internal carotid artery. An autopsy was performed, and the lesion was pathologically examined. RESULTS: The internal elastic lamina and media had disappeared at the border between the eccentrically sclerotic and normal carotid wall. The gap in the internal elastica was covered with normal adventitia and fibrinous tissue. This portion was not composed of collagenous tissue as ordinarily seen in an aneurysmal wall. Neither infiltration of inflammatory cells nor dissection of the artery were observed. CONCLUSION: The blister-like aneurysm appeared to be a laceration of the carotid wall based on degeneration of the internal elastic lamina.