Frequency, severity, and physiologic importance of carotid siphon lesions.

Atherosclerotic stenosis of the intracranial portion of the internal carotid artery (SIPHON) may be the cause of neurologic symptoms. The frequency and severity of these lesions were studied in 226 vessels subjected to conventional two-plane carotid angiography, and the impact of sequential or tandem lesions on cerebral flow was assessed in the 167 arteries from this group that also underwent Gee oculoplethysmography (OPG-Gee), a commonly accepted indicator of the physiologic importance of internal carotid stenosis. Atherosclerotic involvement of the SIPHON was present in 46% (103/226) of the vessels studied, including six total occlusions, 11 severe stenoses (severe, 80% to 99% area reduction [AR]), 27 moderate stenoses (moderate, 50% to 79% AR), 40 mild stenoses (mild, 10% to 49% AR), and 19 instances of mural disease (MUR). This was compared with a 73% rate (166 of 226) of proximal internal carotid artery (PICA) stenosis in the neck, including six to 43 severe, 29 moderate, 50 mild, and 38 MUR. There was little correlation (r = 0.33) between the degree of angiographic stenosis in the PICA and the SIPHON. All of the totally occluded arteries had a positive OPG-Gee, whereas a positive study was noted in only 6% (7 of 109) of the arteries with less than moderate stenosis in the PICA. Twenty-one vessels had moderate stenosis of the PICA. Eight of these arteries had an associated moderate or severe lesion in the SIPHON, and seven of eight (88%) had a positive OPG-Gee. The remaining 13 of this subset had had a normal or mildly diseased SIPHON, and 12 of 13 (92%) had a normal OPG-Gee.(ABSTRACT TRUNCATED AT 250 WORDS)