Delayed Diagnosis of Vertebrobasilar Artery Stenosis Developed During Follow-Up of Two Patients With Pediatric-Onset Moyamoya Disease.

Moyamoya disease is characterized by bilateral stenosis of the terminal portions of the internal carotid arteries, whereas stenotic lesions in vertebrobasilar artery stenosis are reported less frequently. Moreover, de novo stenosis in these vessels during follow-up is exceptionally uncommon and rarely reported in the literature. Herein, we report two patients with pediatric-onset moyamoya disease who developed vertebrobasilar artery stenosis during follow-up after initial surgery. The first patient received initial surgery at the age of four years and demonstrated progression of bilateral vertebral artery stenosis at age 10 that eventually led to postoperative cerebellar ischemic stroke. The second case was diagnosed as moyamoya disease at the age of 15 years and developed basilar artery stenosis with shrinkage of the outer diameter at age 28. Vertebrobasilar stenosis of both patients was undiagnosed when it first appeared, and their diagnosis was delayed for years. The first patient carried the  p.R4810K variant, the susceptibility variant of moyamoya disease in the Asian population, but the second patient did not have any variant in this gene. These cases suggested that, although rare, vertebrobasilar artery stenosis can develop or progress during follow-up in patients with moyamoya disease, so careful assessment of the vertebrobasilar arteries, as well as the arteries of the circle of Willis, is recommended during follow-up. While variants in are known to affect vascular structure and clinical prognosis, the inconsistent results of the  gene variant in our patient suggested that this gene variant is not sufficient to explain vertebrobasilar artery stenosis in this disease. Further accumulation of cases is required to unravel the pathophysiology of this rare condition.