Extensive subarachnoid blood is demonstrated within the suprasellar, ambient, and quadrigeminal plate cisterns and the sylvian fissures bilaterally. Large volume of blood also fills prepontine cistern and extends through foramen magnum. Intraventricular blood demonstrated within the lateral, third and fourth ventricles. Periventricular hypodensity likely related to chronic microvascular ischaemia.
A complex, multiple aneurysm arises from the right posterior inferior cerebellar artery (PICA) approximately 12mm beyond its origin, with both fusiform and saccular components. A high grade stenosis in the more proximal PICA supports a diagnosis of dissecting aneurysm.
Conclusion: Large volume subarachnoid haemorrhage (largest volume posterior fossa) with
intraventricular blood and hydrocephalus, with a large right PICA aneurysm.