Sporadic cerebral amyloid angiopathy (CAA) is a common age related cerebral small vessel disease, characterised by progressive deposition of amyloid-b (Ab) in the wall of small to medium sized arteries, arterioles and capillaries of the cerebral cortex and overlying leptomeninges. Previously considered to be a rare neurological curiosity, CAA is now recognised as an important cause of spontaneous intracerebral haemorrhage and cognitive impairment in the elderly, two fundamental challenges in the field of cerebrovascular disease. Our understanding of the pathophysiology and clinical manifestations of CAA continues to evolve rapidly, with the use of transgenic mouse models and advanced structural and/or molecular neuroimaging techniques. Yet, despite remarkable recent interest, CAA remains under-recognised by neurologists and stroke physicians. In this review, a fresh look at key developments in understanding the complex pathophysiology, important clinical and radiological features, diagnostic approaches and prospects for rational therapies for this enigmatic small vessel disorder is provided.

Sporadic cerebral amyloid angiopathy is a common, well-defined small vessel disease and a largely untreatable cause of intracerebral haemorrhage and contributor to age-related cognitive decline. The term 'cerebral amyloid angiopathy' now encompasses not only a specific cerebrovascular pathological finding, but also different clinical syndromes (both acute and progressive), brain parenchymal lesions seen on neuroimaging and a set of diagnostic criteria-the Boston criteria, which have resulted in increasingly detected disease during life. Over the past few years, it has become clear that, at the pathophysiological level, cerebral amyloid angiopathy appears to be in part a protein elimination failure angiopathy and that this dysfunction is a feed-forward process, which potentially leads to worsening vascular amyloid-β accumulation, activation of vascular injury pathways and impaired vascular physiology. From a clinical standpoint, cerebral amyloid angiopathy is characterized by individual focal lesions (microbleeds, cortical superficial siderosis, microinfarcts) and large-scale alterations (white matter hyperintensities, structural connectivity, cortical thickness), both cortical and subcortical. This review provides an interdisciplinary critical outlook on various emerging and changing concepts in the field, illustrating mechanisms associated with amyloid cerebrovascular pathology and neurological dysfunction.

Cortical superficial siderosis describes a distinct pattern of blood-breakdown product deposition limited to cortical sulci over the convexities of the cerebral hemispheres, sparing the brainstem, cerebellum and spinal cord. Although cortical superficial siderosis has many possible causes, it is emerging as a key feature of cerebral amyloid angiopathy, a common and important age-related cerebral small vessel disorder leading to intracerebral haemorrhage and dementia. In cerebral amyloid angiopathy cohorts, cortical superficial siderosis is associated with characteristic clinical symptoms, including transient focal neurological episodes; preliminary data also suggest an association with a high risk of future intracerebral haemorrhage, with potential implications for antithrombotic treatment decisions. Thus, cortical superficial siderosis is of relevance to neurologists working in neurovascular, memory and epilepsy clinics, and neurovascular emergency services, emphasizing the need for appropriate blood-sensitive magnetic resonance sequences to be routinely acquired in these clinical settings. In this review we focus on recent developments in neuroimaging and detection, aetiology, prevalence, pathophysiology and clinical significance of cortical superficial siderosis, with a particular emphasis on cerebral amyloid angiopathy. We also highlight important areas for future investigation and propose standards for evaluating cortical superficial siderosis in research studies.

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IMPORTANCE Cerebral amyloid angiopathy-related inflammation (CAA-ri) is an important diagnosis to reach in clinical practice because many patients with the disease respond to immunosuppressive therapy. Reliable noninvasive diagnostic criteria for CAA-ri would allow some patients to avoid the risk of brain biopsy. OBJECTIVE To test the sensitivity and specificity of clinical and neuroimaging-based criteria for CAA-ri. DESIGN, SETTING, AND PARTICIPANTS We modified the previously proposed clinicoradiological criteria and retrospectively analyzed clinical medical records and magnetic resonance imaging fluid-attenuated inversion recovery and gradient-echo scans obtained from individuals with CAA-ri and noninflammatory CAA.

Different patterns of MRI-visible EPVS provide insights into the dominant underlying microangiopathy type in patients with spontaneous ICH.

MRI-visible perivascular spaces are a neuroimaging marker of cerebral small vessel disease.Their location may relate to the type of underlying small vessel pathology: those in the white matter centrum semi-ovale have been associated with cerebral amyloid angiopathy, whilst those in the basal ganglia have been associated with deep perforating artery arteriolosclerosis.Since cerebral amyloid angiopathy is an almost invariable pathological finding in Alzheimer's disease, we hypothesized that MRI-visible perivascular spaces in the centrum semi-ovale would be associated with a clinical diagnosis of Alzheimer's disease, whereas those in the basal ganglia would be associated with subcortical vascular cognitive impairment. We also hypothesised that MRI-visible perivascular spaces in the centrum semiovale would be associated with brain amyloid burden, as detected by amyloid-PET using subcortical vascular cognitive impairment n=116) with standardised MRI and PiB-PET imaging were included. MRI-visible perivascular spaces were rated using a validated 4-point visual rating scale, and then categorised by severity ("none/mild", "moderate" or "frequent/severe").

Background and purposeSmall vessel disease (mainly hypertensive arteriopathy and cerebral amyloid angiopathy (CAA)) is an important cause of spontaneous intracerebral haemorrhage (ICH), a devastating and still poorly understood stroke type. Enlarged perivascular spaces (EPVS) are a promising neuroimaging marker of small vessel disease. Based on the underlying arteriopathy distributions, we hypothesised that severe centrum semiovale EPVS are more common in lobar ICH attributed to CAA than other ICH. We evaluated EPVS prevalence, severity and distribution, and their clinical–radiological associations.MethodsRetrospective multicentre cohort study of 121 ICH patients. Clinical information was obtained using standardised forms. Basal ganglia and centrum semiovale EPVS on T2-weighted MRI (graded 0–4 (>40 EPVS)), white-matter changes, cerebral microbleeds (CMBs) and lacunes were rated using validated scales.ResultsPatients with probable or possible CAA (n=76) had a higher prevalence of severe (>40) centrum semiovale EPVS compared with other ICH patients (35.5% vs 17.8%; p=0.041). In logistic regression age (OR: 1.43; 95% CI 1.01 to 2.02; p=0.045), deep CMBs (OR: 3.27; 95% CI 1.27 to 8.45; p=0.014) and mean white-matter changes score (OR: 1.29; 95% CI 1.17 to 1.43; p<0.0001) were independently associated with increased basal ganglia EPVS severity; only age was associated with increased centrum semiovale EPVS severity (OR: 1.50; 95% CI 1.08 to 2.10; p=0.017).ConclusionsEPVS are common in ICH. Different mechanisms may account for EPVS according to their anatomical distribution. Severe centrum semiovale EPVS may be secondary to, and indicative of, CAA with value as a new neuroimaging marker. By contrast, basal ganglia EPVS severity is associated with markers of hypertensive arteriopathy.