Pathophysiology Middle cerebral artery aneurysm Mrs S suffered a grade-IV SAH as a consequence of a ruptured MCA aneurysm. This is a poor-grade SAH and is associated with raised intracranial pressure (ICP) andtherefore potential for reduction in cerebral perfusion pressure . explained that the main cause of SAH is ruptured saccular aneurysm (70-90% of cases), but other causes include trauma and, less commonly, tumours and lesions. Saccular aneurysms often occur at sites of artery bifurcation, where turbulent blood flow and increased shearing forces cause weakness in the muscular layers of the vessel and result in bulging sac-like protrusions ). Aneurysms in the MCA are common . The MCA is the largest branch of the internal carotid artery; it supplies blood to part of the frontal lobe and the lateral surface of the temporal and parietal lobes . Lack of blood supply and damage to these areas of the brain may cause long-term damage to the speech centre and to the primary motor and sensory areas. This may have implications for recovery, rehabilitation and independence; however, the extent of disability cannot be predicted in the acute phase. When an aneurysm ruptures, blood passes into the subarachnoid space at high pressure, spreading into the cerebral fissures and basal cistern and across the surface of the brain . At the site of haemorrhage, irritation and inflammation occur and the extrinsic clotting cascade is activated as brain tissue becomes damaged. Pressure from the surrounding tissue stops the bleeding by tamponading the aneurysm, and fibrin and platelets form a plug at the site of bleeding .