<prompt>  A patient with suspected subarachnoid haemorrhage presents with blood isolated in the fourth ventricle on a CT scan. Aneurysmal rupture is likely to have resulted from -Posterior Inferior Cerebellar Artery AneurysmAnterior Communicating Artery AneurysmPosterior Communicating Artery AneurysmBasilar Artery Tip Aneurysm 