Unique combination of hyperintense vessel sign on initial FLAIR and delayed vasoconstriction on MRA in reversible cerebral vasoconstriction syndrome: A case report

Introduction

Reversible cerebral vasoconstriction syndrome (RCVS) is a condition with clinical and radiological features characterized by sudden-onset severe thunderclap headache and reversible multifocal segmental constriction of cerebral arteries, with or without focal neurological deficits (1). Conventional cerebral angiography and magnetic resonance angiography (MRA) are used for the diagnosis and follow-up of vasoconstriction (1,2). Magnetic resonance imaging (MRI) of cerebral vasoconstriction shows various abnormalities such as non-aneurysmal cortical subarachnoid hemorrhage, intracerebral hemorrhages, cerebral intraparenchymal T2-hyperintense lesions compatible with posterior reversible encephalopathy syndrome, or border-zone cerebral infarctions (1,3). Additionally, hyperintense vessel sign (HVS) on fluid-attenuated inversion recovery (FLAIR) images has been reported in some cases of cerebral vasoconstriction (4–6). HVS is observed as hyperintense signals along the cerebral cortical surfaces, and mainly has been observed in acute stroke patients associated with large-vessel occlusion or severe stenosis (7). Chen et al. have reported in their large series that HVS has been observed in one-fifth of patients with RCVS and associated with severe vasoconstriction (8). However, they have not described the difference in timing between HVS and vasoconstriction on MRA. We report a patient with RCVS, showing HVS on initial FLAIR despite the absence of vasoconstriction on initial MRA.

Case report

A 30-year-old woman presented to an emergency room, reporting her worst-ever headache. The headache began as a throbbing pain at the bilateral temples and reached a peak within a few minutes. Her past medical history included migraine without aura. Seven days before onset, the patient had delivered a healthy infant. She had no signs of hypertension or proteinuria during the perinatal period. Clinical examination, cerebrospinal fluid examination and head computed tomography were normal. That night, she again developed a severe headache. Sumatriptan administration only slightly ameliorated the headache. The following morning, she was found by her mother in a confused state, and a few minutes later developed generalized tonic-clonic convulsions. She was immediately admitted to our hospital. She complained of a severe headache, nausea and blurred vision, and was disoriented to time and place. Her systolic blood pressure was 120–150 mmHg, her pulse rate was 100 beats per minute and temperature was 37.2℃. Her pupils were isocoric with 3 mm diameters and reactive to light. She presented with bilateral blindness. Her strength, sensation and tendon reflexes were all intact. Babinski sign and meningeal signs were absent. Routine hematological and biochemical test findings were normal except for a high level of plasma D-dimer (29.4 µg/ml). The anticardiolipin and antinuclear antibodies were negative. Brain magnetic resonance imaging (MRI) T2-weighted and FLAIR images showed multiple hyperintense areas in the bilateral cerebellum, occipital lobes and right frontal lobes. The lesions were isointense on diffusion-weighted images and hyperintense on apparent diffusion coefficient value maps, indicating vasogenic edema. FLAIR imaging also revealed HVS within the subarachnoid space along the cortical surfaces in the bilateral middle cerebral artery territory. Her brain MRA was normal at this time (Figure 1(a) and (b)). OPEN IN VIEWER

Intravenous nicardipine, phenytoin and glycerol infusion rapidly and dramatically improved the patient’s mental status and visual function with the severe headache almost disappearing. Follow-up MRI performed on day 7 of admission revealed complete resolution of HVS as well as the cerebrocerebellar intraparenchymal hyperintense areas, but MRA revealed multifocal segmental stenosis of the basilar, posterior and anterior cerebral arteries (Figure 1(c) and (d)). She was clinically diagnosed with RCVS because MRA on day 16 showed normalization of the arterial vasoconstriction.

Discussion

Our patient developed thunderclap headache in the postpartum period and subsequently generalized tonic-clonic seizure, which may have been triggered by the vasoactive drug sumatriptan. FLAIR sequence of the initial MRI showed posterior reversible encephalopathy syndrome (PRES) and HVS, while the initial MRA was apparently normal. Thus, we were not able to diagnose her condition at first. Because the follow-up MRA revealed reversible cerebral arterial vasoconstriction, we later diagnosed her condition as RCVS-PRES overlap syndrome according to the typical clinical and radiological features.

It is noteworthy that the first MRA did not show significant vasoconstriction. Ghia et al. reported a patient with RCVS who showed delayed vasoconstriction despite resolution of the headache (9). In a recent case series of 67 patients with RCVS, the first MRA did not detect arterial vasoconstriction in 14/67 (21%) patients (3). In this case series, cortical subarachnoid hemorrhage, intracerebral hemorrhages, seizures and posterior reversible encephalopathy syndrome associated with distal arteries, which cannot be detected by MRA (for example, distal cortical branches or pial arteries), were mainly observed during the first week after onset, and border-zone cerebral infarction, probably attributed to large arteries, mainly occurred during the second week (3). To explain these findings, the authors hypothesized that the initial arterial changes might start from distal small arteries and progress toward proximal large arteries. In contrast to MRA, HVS was observed in the FLAIR sequence of only the first MRI in our patient. Some previous reports have similarly described HVS appearing in the early stage of RCVS accompanied by multiple sites of vasoconstriction on MRA (4–6). HVS is indicated by dot-shaped or linear hyperintense signals within the subarachnoid space along the cortical surfaces, and was first described in acute stroke patients associated with proximal large-vessel occlusion or severe stenosis (8). HVS was also observed in patients with multiple cerebral arterial stenoses, including cerebral vasoconstriction in distal small arteries (3). The exact mechanisms of HVS remain unclear. One study suggested that the retrograde leptomeningeal collateral flows might be the origin of HVS (10), while another study indicated that HVS might reflect extremely dilated pial vasculature (11). In either hypothesis, HVS is likely to reflect slow blood flow within distal small arteries dilated to compensate for the hypoperfusion resulting from severe arterial stenosis. Thus, even when MRA indicates that proximal arteries are normal, HVS might suggest the result of more distal vasoconstriction.

In conclusion, the unique radiological findings in our case suggest that vasoconstriction in RCVS may progress from distal small to proximal large arteries. Importantly, HVS on initial FLAIR may be useful for an early diagnosis of RCVS. When HVS is detected in a patient with thunderclap headache, even if initial MRA is normal, RCVS should be considered among the probable differential diagnoses.

Clinical implications

Hyperintense vessel sign on initial fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI) is useful for an early diagnosis of reversible cerebral vasoconstriction syndrome (RCVS).