Abstract
A few reports of posterior inferior cerebellar artery (P.I.C.A.) located more proximal to the superior retrotonsillar segment are recognized. However, non traumatic or non mycotic aneurysms located on the peripheral branch more distal to this segment of P.I.C.A. are very rare.
Clinical and anatomical features of the aneurysms located on the peripheral branch of P.I.C.A. are analized based on four previously reported cases together with four present series.
The average age at the onset was 48 years. All the patients presented classical symptoms of SAH : severe headache followed by nausea and vomiting. All the aneurysms in this category were very small. They were less than 5 mm in diagmeter except for one case which was preveously reported (8 × 4 mm). One of the present series the size was extremely small. It was 2 × 2 mm in size and was only demonstrated by magnified angiogram. Multiple aneurysms were found in 3 cases out of the 8 cases and all of them were arising from the same P.I.C.A. In two of the cases, the multiple aneurysms were complicated with AVM's. In these cases, the aneurysms were located on the proximal portion of the same branch of which AVM's located. In these cases, increased of blood flow caused by the existense of AVM was though to be a main cause which facilitates aneurysm formation. CT finding in the present series was very characteristic. In all the cases, hemorrhage was noted in the fourth ventricle and the subarachnoid space over the cerebellum but no hemorrhage was recognized in the basal cisterns.
In the unknown origin of SAH when CT showed the characteristic appearance one should strongly suspect the presence of ruptured aneurysm of the P.I.C.A. peripheral branch, and all efforts should be made to demonstrate by angiography.
