Victor J. Del Brutto, MD
Intracranial arterial dolicheoctasia (IADE) is an intriguing arteriopathy. Cerebral ischemia, compression of neural structures and intracranial hemorrhage are common complications of abnormally dilated vessels. The underlying pathology of IADE is unknown. With the exception of few cases associated with an underlying hereditary condition (i.e., Fabry’s disease and late-onset Pompe’s disease), IADE had been historically thought to be secondary to underlying atherosclerosis. On the other hand, several studies show a link between IADE and small vessel disease (SVD) and suggest an underlying vascular process other than atherosclerosis. The study of Zhai and colleagues aims to address this controversy by exploring vascular risk factors associated with IADE and intracranial atherosclerotic stenosis (ICAS), as well as the association of these arteriopathies with different imaging markers of SVD.
The current issue presents a cross-sectional analysis using data from an ongoing community-based cohort in China. The study included 1,237 individuals aged 35 or older that underwent brain MRI. Abnormal arterial dilation was defined by a diameter ≥2DS of either internal carotid artery or the basilar artery after adjusting for total intracranial volume (TIV); basilar artery dolichoectasia (BADE) was defined based on Smoker’s criteria and ICAS by any degree of stenosis of intracranial vessels on MRA. The authors failed to find an association between IADE and traditional vascular risk factors such as higher systolic blood pressure, diabetes mellitus, higher LDL-C and lower HDL-C, whereas ICAS was strongly associated with aforementioned conditions. When the different imaging markers of SVD were analyzed, IADE correlated mainly with enlarged perivascular spaces (E-PVS), as well as lacunar infarcts (LI) and cerebral microbleeds (CMBs) to a lesser extent. ICAS was associated with LI and white matter hyperintensities (WMH), but not with CMBs or E-PVS.
The findings of Zhai and colleagues suggest that IADE is a distinct arteriopathy other than atherosclerosis. As pointed out by the authors, microscopically IADE is characterized by the fragmentation of the elastic lamina in the tunica media, whereas atherosclerotic plaques involve damage to the endothelium and lipid infiltration on arterial intima. Moreover, different phenotypes of SVD associated with these distinct arteriopathies differentiate the mechanism of vascular injury. The association of dilative arteriopathy with E-PVS and CMBs could be explained by pathological changes in cerebral small vessels similar to what happens in large intracranial vessels. In other words, rarefaction of the tunica media at the level of the microvasculature can result in formation of microaneurysms (i.e., CMBs) and dilation of spaces around small penetrating arteries (E-PVS). On the other hand, the co-occurrence of LI and IADE may be explained by several mechanisms, including obliteration of small penetration vessels at the ostium (site of arterial tortuosity), micro-emboli due to sluggish blood flow, and coexistence with lipohyalinosis of small vessels.
Due to better recognition and known physiopathology, ICAS is a better-understood arteriopathy. Small brain infarctions and ICAS can happen due to occlusion of small vessels due to plaque formation or co-existence of vascular risk factors, while the link between ICAS and WMH can be explained by accumulation of small infarcts or hypoperfusion by hemodynamic significant stenosis.
To recognize IADE as an independent arteriopathy from atherosclerosis is essential in clinical practice to implement appropriate preventive strategies for potential complications such as ischemic strokes, brainstem compression and brain hemorrhages. Besides aging, no particular risk factor driving the progression of IADE has been identified, and to the present, idiopathic dilatative arteriopathy seems an appropriate term. Pathological and clinical studies to further elucidate the natural history of IADE are required.