Jiaying (Jayne) Zhang, MD

Cerebral microbleeds (CMBs) are small perivascular hemorrhages seen on MR susceptibility sequences. They are markers of microangiopathic disease mainly classified into two general patterns: deep CMBs signifying hypertensive arteriopathy; and strictly lobar CMBs signifying Cerebral Amyloid Angiopathy (CAA). CMBs are increasingly recognized as a hallmark of small vessel pathology. The rationale for studying CMBs and its correlation to cognitive dysfunction stems from the putative relationships between cerebral small vessel disease, vascular cognitive impairment (VCI), and Alzheimer’s disease (AD). Studies have shown the synergistic effect of cerebrovascular disease and neurodegenerative pathology in producing more severe cognitive dysfunction.

Although the association between CMB and cognitive function has been explored in the past with large population studies, the nature of this link in the stroke population is obscure. As such, in a study by Werring et al, the authors investigated this relationship in a cohort of patients with known ischemic strokes or TIA who had undergone MRI (including GRE T2*-weighted and FLAIR sequences), and complete neuropsychological testing in multiple cognitive domains. The study also looked at what location of CMB is most associated with cognitive dysfunction. Of the 320 patients included, at least one CMB was identified in 72 patients (22.5%). Thirty patients (42%) had strictly lobar CMBs. Impairment in executive functions, but not other cognitive domains, was more prevalent in patients with CMBs regardless of the location. Moreover, the presence and number of strictly lobar CMBs (≥1 or ≥5) was independently associated with increased likelihood executive impairment.

The results of this study bring several points to mind. First, whether there is a direct cause and effect between CMBs and cognitive impairment remains unclear. Second, this study gives added evidence that strictly lobar CMBs may reflect cognitive impairment associated with CAA. Finally, while Gradient-echo is widely used as a standard sequence for detecting hemosiderin on MRI, newer MRI techniques such as T2*-weighted angiography (SWAN) and Susceptibility-weighted imaging (SWI) will be even more sensitive at uncovering the presence of CMBs. As the authors suggested, ascertaining the exact nature of the co-existence and interaction between neurodegenerative and cerebrovascular processes may have important implications for the treatment and prevention of cognitive impairment in stroke patients.