Almost pure primary intraventricular haemorrhage is seen on the initial non-contrast scan. There is only a small amount of blood in the cerebellopontine cistern. There is no blood elsewhere.
On CTA, the cause was identified - a small, 3.5 mm wide, left PICA aneurysm (or possibly pseudoaneurysm, the patient unfortunately expired prior to DSA) in its supratonsillar segment, which manifested itself as a pure intraventricular haemorrhage.