Fenestration of the internal carotid artery (ICA) is extremely rare on clinical settings. Six cases of fenestration in intracranial and 8 in extracracranial ICA have ever been reported in literature. Authors describe two cases of fenestration at the extracranial ICA that were initially suspected of the dissection of ICA on MRA/I. Both angiography and CT angiography (CTA) disclosed the fenestration, which located at C2 vertebral levels. To confirm the fenestration at extracranial ICA is important in such an occasion that mimic the dissection of ICA, especially in patients who complain of cervical pain, mass and other related symptoms. Differences in the fenestration, the dissection and atherosclerosis on imaging, were reviewed and discussed.