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Hyperintense vessels: An early MRI marker of reversible cerebral vasoconstriction syndrome?

Reversible cerebral vasoconstriction syndrome (RCVS) is an increasingly recognized clinical emergency characterized by acute onset of severe headaches (usually multiple thunderclap headaches) and reversible segmental stenosis of cerebral arteries (1). RCVS is associated with several potentially devastating complications or comorbidities, such as posterior reversible encephalopathy syndrome (PRES) (9%–38%), ischemic stroke (4%–54%), intracerebral hemorrhage (12%–20%), cortical subarachnoid hemorrhage (SAH) (22%–34%), or cervical artery dissection (1%–12%) and even death (2– 7). The prevalence of RCVS is unknown, but it could be higher than that of its most important differential diagnosis—aneurismal SAH when patients complain of thunderclap headaches. Although the clinical features of RCVS are distinct, the diagnosis could sometimes be difficult in the lack of awareness or alertness about the dynamic nature of the disease. This is especially the case in the very early stage of the disease, when cerebral vasoconstrictions might be insignificant on the initial angiographic studies (3,4), and ischemic or hemorrhagic complications might not have occurred. In this issue of Cephalalgia, Kameda et al. report on a case of a 30-year-old woman who developed thunderclap headaches and seizure one week post-partum (8). Magnetic resonance imaging disclosed hyperintense vessel signs and PRES on the initial fluid-attenuated inversion recovery (FLAIR) imaging in the absence of significant vasoconstriction on magnetic resonance angiography (MRA). The hyperintense vessels disappeared one week later, but vasoconstrictions of major cerebral arteries became apparent (8). Although this case is not the first one to report hyperintense vessel sign in patients with RCVS (9,10), the unique finding that hyperintense vessels predated the occurrence of cerebral vasoconstrictions raised several important questions: 1.) Could hyperintense vessel sign help diagnose RCVS in the very early stage of disease? 2.) Does this finding support the centripetal propagation theory? and 3.) How to differentiate hyperintense vessels from cortical SAH, the early complication of RCVS? Hyperintense vessels on FLAIR imaging are hypothesized to be distal branches of the cerebral arteries or their leptomeningeal anastomotic collateral vessels with very low-flow velocities attributed to severe stenosis or occlusion of proximal cerebral arteries (11). In RCVS, FLAIR hyperintense vessels could be noted in up to 22% of patients (10). The presence of hyperintense vessels in RCVS is associated with more severe vasoconstrictions and cerebral hemodynamic derangements, and could herald the occurrence of ischemic stroke or PRES (10). In the case reported by Kameda et al. (8), hyperintense vessels were noted concomitantly with PRES two days after the onset of thunderclap headaches, in the absence of MRA vasoconstrictions. If these FLAIR hyperintense vessels also came from the failure of cerebrospinal fluid (CSF) nulling effect due to stagnant or retrograde flow of distal arterioles or leptomeningeal networks, this rare observation might have serendipitously captured the point when severe vasoconstrictions were still restricted to distal arteries beyond the resolution of routine MRA. In our previous study, MRA vasoconstrictions were not at its worse point until 11–20 days after headache onset (4). In another large series, it was reported that up to 33% of the patients with RCVS had a normal early angiogram (3). In other words, in one-third of the patients,