Cortical superficial siderosis Fine dark lines, harbingers of doom

Cerebral amyloid angiopathy (CAA), characterized by beta-amyloid deposition in the media and adventitia of small- and medium-size cortical and leptomeningeal vessels,(1) results in structural alterations in the vessel wall, rendering them fragile and prone to rupture and hemorrhage. Clinical manifestations of CAA include spontaneous lobar intracerebral hemorrhage (ICH) with high recurrence rate. MRI typically reveals lobar cerebral microbleeds (CMBs)(2) or cortical superficial siderosis (cSS) identified on blood-sensitive sequences. Characterized by a curvilinear low signal lesion along the cerebral convexities (bilinear "track-like" appearance), cSS likely results from extravasation of blood from fragile capillaries into the subarachnoid space.(3) These imaging markers have become essential components of diagnosis and are included in the modified Boston criteria for the diagnosis of CAA.(4) They have an increasingly important role in prognostication and risk stratification, and possess a unique potential as surrogate markers for use in clinical research and practice. However, our understanding of their pathophysiology and natural history remains incomplete. Despite having emerged as a highly specific marker of CAA(3) and being strongly associated with lobar ICH risk,(5) little is known about the course and the clinical relevance of progression of cSS.