Cerebral Microbleeds: Are They Indicative of a Hemorrhage-Prone Brain?

Introduction

The term “cerebral microbleed” (CMB) is usually used to refer to small, round, dark signal lesions detected by T2*-weighted or gradient-echo (GRE) MR imaging 1. CMBs were only recently discovered due to the development of techniques sensitive to paramagnetic effects. Their clinical significances have been actively investigated, especially in the stroke field and more recently in studies on cognitive impairment and ageing 2. Histological studies have shown that CMBs are focal tiny spots containing hemosiderin-laden macrophages and abnormal microvessels showing fibrohyalinosis 3, 4. Clinical cases with frank symptoms caused by CMBs were uncommon. However, because CMBs are manifestations of the focal extravascular leakages of blood components, it has been suggested that an accumulation of CMBs in individuals with an elevated risk of cerebral hemorrhage reflects a bleeding-prone status. Clinical studies have found strong associations between CMBs and chronic hypertension 5 and low cholesterol levels 6, and between their proximities and volumes and those of subsequent intracerebral hemorrhage (ICH) 7, 8. Furthermore, longitudinal studies have found that CMBs are related to subsequent hemorrhagic stroke in stroke survivors 9, and suggested that they are related to antithrombotic-related hemorrhage 10, 11. In this review, we will discuss the fundamental findings of CMBs and their clinical implications.

Abstract

Cerebral microbleeds (CMBs) are tiny, round, dark signal lesions that are usually detected on gradient-echo MR images. CMBs consist of extravasations of blood components through fragile microvascular walls with lipohyalinosis and surrounding macrophages. The prevalence of CMBs in elderly subjects without a history of cerebrovascular disease is around 5%, but it is much higher in ischemic or hemorrhagic stroke patients. The development of CMBs is closely related to various vascular risk factors, and in particular, lobar CMBs are considered to be associated with cerebral amyloid angiopathy. Because CMBs are tiny spots, their presence has been hypothesized to reflect a cerebral hemorrhage-prone status in patients with a hypertensive status or amyloid microangiopathy. Furthermore, it has been consistently documented that stroke survivors with CMBs have an elevated risk of subsequent hemorrhagic stroke or an antithrombotic-related hemorrhagic complication. However, previous studies have failed to establish a link between hemorrhagic transformation after thrombolytic treatment and CMBs. Therefore, the authors considered that a larger prospective study was required to conclude the clinical significance of CMBs and their applicability as a decision-making index.

Keywords

cerebral microbleeds, stroke, cerebral hemorrhage