Discussion

Moyamoya disease often causes acute neuromotor deficits. Ischaemic events are the most common initial presentation. ^{Reference Zhang, Zheng and Epidemiology1} The anterior circulation is predominantly involved while posterior circulation stroke develops in the late stage of moyamoya disease. ^{Reference Kim, Lee and Roh3}

Haemodynamic compromise was the primary mechanism of ischaemic stroke in moyamoya disease ^{Reference Kim, Lee and Roh3} , but recent studies proposed embolism may also play a role. ^{Reference Chen, Duan and Xu4} Microembolic signals detected by transcranial Doppler ultrasonography are associated with ischaemic moyamoya disease. ^{Reference Chen, Duan and Xu4} Indeed, both mechanisms have been assumed to coexist and be complementary in moyamoya disease with ischaemic stroke. Therefore, large artery steno-occlusion increases not only the risk of haemodynamic infarction but also the risk of embolic infarction. ^{Reference Sedlaczek, Caplan and Hennerici5} Cerebral angiography is the gold standard for diagnosing moyamoya disease and evaluating its progression. Surgical revascularisation is effective for ischaemic-type moyamoya disease and antiplatelet agents are recommended as a conservative management, but the risk of bleeding remains. ⁶

Patent foramen ovale is the most common anatomical cause of right-to-left shunt. Previous studies have shown that patent foramen ovale is a risk factor for cryptogenic stroke, and paradoxical embolism is considered to be the main pathogenesis. ^{Reference Thaler, Ruthazer and Weimar7} The brain lesions of patent foramen ovale-associated stroke patients mostly involve the posterior circulation and damage a single vascular area. ^{Reference Sookyung Ryoo, Jong-Won Chung and Mi Ji Lee8} A study found that the vertebrobasilar system receives less adrenergic innervation, is less sensitive to sympathetic stimulation, and has weaker vascular regulation ability. Vertebrobasilar circulation receives less adrenergic innervation, when the sympathetic tone is increased by the Valsalva maneuver, vertebrobasilar circulation, which is less responsive to sympathetic stimuli, increases blood flow. ^{Reference Bum Joon, Hoyon and Byung Joo9} Clinical Risk of Paradoxical Embolism score is commonly used to predict the correlation between cryptogenic stroke and patent foramen ovale. Patients in the high Risk of Paradoxical Embolism score strata are much more likely to have patent foramen ovale-related strokes. ^{Reference Kent, Ruthazer and Weimar10} Among patients with cryptogenic stroke, patent foramen ovale prevalence increased from 23% in those with 0–3 points to 73% in those with 9–10 points, corresponding to the patent foramen ovale attributable fraction estimates of approximately 0–90%. Moreover, stroke recurrence rates after patent foramen ovale closure decrease as the Risk of Paradoxical Embolism score increases. ^{Reference Kent, Ruthazer and Weimar10} Some studies advocate that a Risk of Paradoxical Embolism score > 6 is classified as patent foramen ovale-related strokes. ^{Reference Thaler, Ruthazer and Weimar7} Since microemboli via patent foramen ovale increase the risk of cryptogenic stroke, relevant guidelines recommend patent foramen ovale closure combined with double antiplatelet therapy for secondary prevention of stroke. ^{Reference Pristipino, Sievert and D’Ascenzo2} The brain imaging characteristics of ischaemic-type moyamoya disease and patent foramen ovale-associated stroke are summarised in Table 1. ^{Reference Kim, Lee and Roh3,Reference Sookyung Ryoo, Jong-Won Chung and Mi Ji Lee8,Reference Bum Joon, Hoyon and Byung Joo9,Reference Zhao, Zhang and Wang11}

Table 1. The brain imaging characteristics between ischaemic-type moyamoya disease and patent foramen ovale-associated stroke

MMD=moyamoya disease, PFO=patent foramen ovale.

In our case, the patient presented with headache and his age of onset (25 years old) was not at the bimodal peak of moyamoya disease. MRI showed the cortical infarction of left occipital lobe but the posterior circulation was unobstructed, with low National Institute of Health stroke scale score. Therefore, the intracranial artery disease was difficult to explain this stroke. Contrast transthoracic echocardiography revealed a patent foramen ovale and the Risk of Paradoxical Embolism score was 9 (total score: 10 points). Moreover, the clinical manifestations and infarct location were in line with patent foramen ovale-related stroke (Table 1). Hence, we consider that patent foramen ovale is the main reason for this patient’s stroke. To prevent recurrence of ischaemic stroke, the patient successfully underwent percutaneous patent foramen ovale closure and received antiplatelet therapy. On subsequent follow-ups for 12 months after discharge, the patient’s headache continued to alleviate and did not complain of new focal neurological deficit. There was no right-to-left shunting detected in contrast transthoracic echocardiography, and a re-examination of brain MRI showed no additional stroke events.