Part 2: A pathologic spectrum: Basilar dolichoectasia and vertebral dissection, each with fatal subarachnoid hemorrhage

Dolichoectasia, or the dilation and increased curvature of intracranial vessels, has long been linked to atherosclerosis. Rather than the result of atheromatous alterations of the vessel wall, investigators now believe that the primary lesion is a defect in the internal elastic lamina and the elastic components of the media. Remodeled by shear and stress related to blood flow and turbulence, the thickened intima and lipid deposits are secondary phenomena. In some patients, dissection of the intracerebral vessel wall may be the initial event, and with the passage of time, dolichoectasia may be the final phase. We present two patients to illustrate the spectrum of changes that can involve the posterior circulation. The first patient had dolichoectasia of the basilar artery, and the second patient had dissection of the vertebral artery. Each patient died from diffuse subarachnoid hemorrhage, and each had a postmortem examination. To better understand the genetic mechanisms leading to smooth muscle and elastic fiber defects in dolichoectasia, we can focus on a subgroup of patients with polycystic kidney disease. This cohort of renal patients has an abnormally high frequency of intracranial aneurysms, hemorrhages, and dolichoectasia of intracranial vessels. Polycystin is the protein product of the gene PKD1, which undergoes mutation in autosomal dominant polycystic kidney disease. By studying the relationship between aberrant polycystin expression and vascular phenotype, we may someday understand the vascular abnormalities at the molecular level.