A 25-year-old male with no history of trauma or use of vasoactive substances presented with recurrent migrainous headaches associated with alternating right or left hemiparesis or hemianaesthesia. An MRI scan showed a chronic right cerebral watershed infarct with loss of the normal bright vascular signal in the distal extracranial and intracranial portions of the right internal carotid artery (ICA) on T1-weighted Magnetized Prepared Rapid Gradient Echo images interpreted as chronic ICA occlusion (Fig. 1a). Duplex carotid ultrasound scan four weeks later reported patent ICAs bilaterally, with elevated peak systolic velocities and broadening of the spectral waveform with a “beaded” appearance to the distal right ICA, consistent with bilateral stenoses, right 50%–69%, left 70%–79% (Fig. 1b). Computed tomography angiography (CTA) a week later demonstrated a focal critical stenosis in the mid-cervical left ICA (Fig. 1c), with no contralateral abnormality. To investigate other potential sites of arterial pathology, we performed CTA with aortography six weeks later. There was no evidence of fibromuscular dysplasia or other vasculitis. The stenosis of the left ICA had completely resolved with diffuse narrowing of both ICAs in their intracranial course (Fig. 1d).

Figure 1: (a) MRI of the brain demonstrating a chronic right cerebral watershed infarct on fluid-attenuated inversion recovery images [black arrow] and loss of the normal bright vascular signal in the right ICA on T1-MPRAGE images [white arrow]. (b) Right carotid ultrasound four weeks later showed broadening of the spectral waveform and “beading” of the distal right ICA. (c) CTA after another week revealed a focal critical stenosis of the left ICA with a normal-appearing ICA on the right. (d) Resolution of left ICA stenosis on repeat CTA after six weeks, with diffuse narrowing of both ICAs.

Reversible idiopathic extracranial internal carotid vasospasm (IEICAV) is a rare cause of stroke in adolescents and young adults. ^{Reference Moeller, Hilz and Blinzler1–Reference Wöpking, Kastrup, Lentschig and Brunner6} Segmental filiform narrowing of one or the other cervical ICA spontaneously resolves in 24–72 hours. ^{Reference Huisa and Roy7} Due to the dynamic nature of the process, diagnosis often depends on serendipitously-timed imaging studies, ^{Reference Moeller, Hilz and Blinzler1,Reference Wöpking, Kastrup, Lentschig and Brunner6,Reference Huisa and Roy7} and the demonstration of alternating and spontaneously-resolving ICA stenosis differentiates IEICAV from fibromuscular dysplasia, ICA dissection and atheromatous disease. ^{Reference Hirayama, Hirayama and Tahara4} Unlike reversible cerebral vasoconstriction syndrome which affects the intracranial ICA and its branches, patients with IEICAV have recurrent episodes of vasospasm over years and do not experience thunderclap headaches. ^{Reference Moeller, Hilz and Blinzler1,Reference Graham, Orjuela, Poisson and Biller3,Reference Wöpking, Kastrup, Lentschig and Brunner6} Yokoyama et al reported worsening of focal neurological symptoms when standing, reflecting the role of flow limitation from vasospasm in the development of cerebral ischaemia. ^{Reference Yokoyama, Yoneda and Abe8}

This condition is analogous to other vasospastic conditions including Raynaud’s phenomenon and Prinzmetal’s variant angina. ^{Reference Graham, Orjuela, Poisson and Biller3} Migraine, coronary events and smoking may be risk factors for IEICAV. ^{Reference Hirayama, Hirayama and Tahara4,Reference Kaneko, Tateoka and Kanemaru5} Kaneko and colleagues postulated ICA sensitivity to head rotation, ^{Reference Kaneko, Tateoka and Kanemaru5} while Moeller et al suggested adrenergic overactivity affecting the cervical ICAs and demonstrated that metronomic deep breathing, presumably increasing parasympathetic outflow and the alpha-adrenergic antagonist prazosin alleviated vasospasm. ^{Reference Moeller, Hilz and Blinzler1} Stellate ganglion block produced only temporary amelioration of attack severity. ^{Reference Yokoyama, Yoneda and Abe8} Antithrombotics, gabapentin, corticosteroids, balloon angioplasty and stenting, intra-arterial vasodilators and calcium channel blockers have also been used with variable results, but no definitive treatment guidelines exist. ^{Reference Graham, Orjuela, Poisson and Biller3,Reference Wöpking, Kastrup, Lentschig and Brunner6,Reference Huisa and Roy7}