“…15,16) Histological evaluation of dissecting aneurysms of the cerebral arteries has suggested that defects in the IEL or media, or degeneration of the media induce intimal changes, and rupture of the intima results in dissection of the arterial wall. 1,4,6,7,15,[17][18][19][20][21] Other dissections were attributed to rupture of the vasa vasorum or a newly formed vessel in the vascular wall associated with degeneration of the media. 5,28) The intima and IEL at the opening of a dissection are washed away by blood, so preventing histological investigation.…”