Calcification of the Carotid Siphon

CALCIFICATION of the internal carotid artery in the region of the cavernous sinus is an extremely common radiologic finding.' Although it is the only readily available laboratory criterion of cerebrovascular disease its significance has never been determined by combined clinical, radiologic, and pathologic studies. Whether the arterial changes in this region, which we shall refer to as the siphon (after Moniz), correlate with athero-sclerosis locally or of the cerebral arteries or of arteries elsewhere in the body is unknown. Despite the localization of disease within the siphon, occlusive carotid thrombosis is relatively uncommon at this level, originating as a rule in the region of the carotid sinus. Also, bruits appear to arise here infrequently even though stenosis may be demonstrated by carotid angiography. To investigate these matters, a portion of the pathologic material from our study of cerebral atherosclerosis at the Massachusetts General Hospital has been especially examined in regard to the radiologically visible calcification and the corresponding pathologic changes in the carotid siphon. The observations on the atherosclerotic aspects of the study have already been reported.2 In the present study the following arteries were selected for scrutiny: the entire carotid systems from their origin up through the neck and petrous bone to the region distal to the siphon, the entire vertebral systems from their origin up through the transverse foramina of the cervical vertebrae to the level of the fora-