Spontaneous thrombosis of unruptured small saccular intracranial aneurysm

Spontaneous thrombosis of unruptured small saccular aneurysms is rare. A 77-year-old woman with a history of multiple cancers was referred to our hospital for management of asymptomatic cerebral infarction detected at another hospital. She had also been diagnosed with unruptured intracranial aneurysms at that hospital 7 years earlier. Magnetic resonance angiography showed unruptured aneurysms at the anterior communicating artery complex (left anterior cerebral artery) and the right middle cerebral artery. The anterior communicating artery aneurysm was a non-thrombosed small saccular aneurysm with a narrow neck, measuring 4.6 mm in maximum diameter and 1.8 mm in neck length. She elected to continue observation at the referring hospital. Two years later, she developed acute cerebral infarction and was admitted to our hospital. Magnetic resonance angiography revealed that the anterior communicating artery aneurysm had almost completely regressed and was considered to have spontaneously thrombosed. This report highlights the potential for spontaneous thrombosis to occur even in unruptured, non-thrombosed small saccular intracranial aneurysms. In our patient, the narrow neck may have played a role.