Spontaneous regression of unruptured small intracranial aneurysm associated with proximal parent artery stenosis.

Spontaneous thrombosis of intracranial aneurysms is rare. Spontaneous regression of unruptured small saccular aneurysms is even more rare. A 76-year-old woman with a history of hypertension and dyslipidemia was referred for evaluation of an unruptured intracranial aneurysm. Magnetic resonance angiography showed a left internal carotid artery aneurysm with a maximum width of 4.0 mm and a neck diameter of 3.0 mm. She was monitored using annual magnetic resonance angiography. Imaging at the 8.5-year follow-up showed partial aneurysm regression and stenosis in the parent artery proximal to the aneurysm. The next year, it had almost completely regressed. Spontaneous regression can occur even with unruptured small intracranial aneurysms. In our patient, proximal parent artery stenosis may have played a role.