[Spontaneous partial thrombosis of an unruptured peripheral, superior cerebellar artery aneurysm: a case report].

A 52-year-old female suddenly developed headache and dizziness. On admission she complained of gait disturbance with dizziness but cranial nerve palsy could not be detected. CT scan revealed a mild high density lesion in the right ambient cistern and the density of the lesion had become much higher 5 days after admission. MRI revealed a homogeneous iso-intense lesion on T1WI, T2WI 2 days after admission and the lesion had changed to homogeneous high. The lesion was suspected to be a fresh thrombus. Right vertebral angiography showed a part of aneurysm arising from the ambient segment of the right superior cerebellar artery and we diagnosed the lesion as a partially thrombosed superior cerebellar artery aneurysm. About forty cases of peripheral superior cerebellar artery aneurysm have been described in the literature, but cases of spontaneous thrombosis of the aneurysms have been very rare. Spontaneous thrombosis of aneurysms was usually thought to occur in large aneurysms, but the aneurysm in our case was not large. We suspected that in our case spontaneous thrombosis may have been caused by occlusion of the parent artery of the aneurysm.