Unilateral agenesis of the internal carotid artery with intercavernous anastomosis combined with an unruptured internal carotid artery aneurysm

Unilateral agenesis of the internal carotid artery (ICA) with intercavernous anastomosis is extremely rare. In addition, of these rare cases, only 4 patients had combined intracranial aneurysms, which were located in the anterior communicating artery and posterior cerebral artery. The onset symptoms of these 4 patients included headache, ischemic stroke and aneurysm rupture, but none of them showed intracerebral hemorrhage at onset. This is the first case of unilateral agenesis of the ICA with intercavernous anastomosis combined with an unruptured aneurysm located in the ICA, which had a spontaneous thalamic hemorrhage as the onset symptom. Based on the digital subtraction angiography (DSA) images of the patient, we speculated that asymmetric distribution of blood flow in the posterior circulation secondary to agenesis of the ICA might be a cause of thalamic hemorrhage. Given the presence of an intact aneurysm and the influence of agenesis of the ICA on cerebral blood perfusion, strict follow-up is critical for these patients.