Background. We report the natural history of the carotid artery contra
lateral to the ipsilateral endarterectomized carotid artery. Methods.
The incidence of new symptoms and disease progression of the patent co
ntralateral side after unilateral carotid endarterectomy (CE) was stud
ied by clinical follow-up and serial duplex scanning in 127 patients.
Results. During a mean follow-up of 44 months, new hemispheric events
occurred in nine (7%) and significant progression was recorded in 27 (
21%) patients. In 97 patients with initial stenosis of less than 50% (
group I), contralateral progression to greater than 50% was noted in 2
2% and new symptoms (one transient ischemic attack and one cerebrovasc
ular accident) in 2% of patients; three patients underwent CE. In 30 p
atients with initial stenosis between 50% and 99% (group II), new symp
toms (all transient ischemic attacks) occurred in seven (23%) (group I
I vs group I; p < 0.003) and nine underwent CE (group II vs group I; p
< 0.001). Progression in 26 patients with 50% to 79% stenosis within
group II to greater than 80% was noted in 19% of patients (difference
not significant compared with group I). Conclusions. Overall, new symp
toms occurred in 7% and significant contralateral disease progression
in 21% of patients; subsequent CE was performed in 9.4% of patients. I
nitial presence of greater than 50% contralateral stenosis is a predic
tor of future hemispheric symptoms, which are likely to be transient i
schemic attacks. New symptoms did not necessarily correlate with disea
se progression. Because disease progression was observed in patients w
ith varying degrees of initial contralateral stenosis, serial clinical
and duplex scanning in all patients undergoing unilateral CE is recom
mended.