Vertebrobasilar dilatative arteriopathy (dolichoectasia).

Dolichoectasia (dilatative arteriopathy) describes marked elongation, widening, and tortuosity of arteries. The intracranial vertebral and basilar arteries are preferentially involved. Dolichoectatic arteries usually have an abnormally large external diameter and a thin arterial wall, with degeneration of the internal elastic lamina, multiple gaps in the internal elastica, thinning of the media secondary to reticular fiber deficiency, and smooth muscle atrophy. The most important clinical presentations of dilatative arteriopathy include acute brain ischemia; a progressive course related to compression of cranial nerves, the brain stem, or the third ventricle; and catastrophic outcome caused by vascular rupture. Flow in dilated arteries can become bidirectional, resulting in reduced antegrade flow and thrombus formation. Elongation and angulation of arteries can stretch and distort the orifices of arterial branches, leading to decreased blood flow, especially in penetrating branches.