Pial collateral shift after unilateral bypass in bilateral moyamoya disease: illustrative cases.

BACKGROUND

Bilateral revascularization surgery is commonly performed in patients with bilateral moyamoya disease (MMD), even when ischemic symptoms or strokes are confined to one hemisphere. However, in select cases, a unilateral bypass may suffice to revascularize both hemispheres due to the development of post-revascularization pial collateral shift. This report aims to introduce the concept of pial collateral shift and presents 3 cases of bilateral MMD in which unilateral revascularization alone was deemed sufficient.

OBSERVATIONS

Three adult patients with ischemic MMD exhibited bilateral type III vascular insufficiency on single-photon emission CT (SPECT) imaging after Diamox challenge. Each underwent unilateral revascularization of the symptomatic hemisphere. Postoperatively, cerebral angiography and SPECT with Diamox were performed. The angiograms revealed a phenomenon the authors term "pial collateral shift," an adaptive redistribution of pial collateral flow following cerebral revascularization, specifically an increase in pial collateral flow toward the non-bypassed hemisphere in those 3 cases. Postoperative SPECT with Diamox demonstrated normalization of cerebrovascular reserve in both hemispheres, eliminating the need for contralateral revascularization.

LESSONS

Pial collateral shift observed on the postoperative angiogram suggests a fully augmentative bypass. Patients with bilateral MMD should be reassessed after the initial bypass, as bilateral revascularization may not be necessary in all cases. https://thejns.org/doi/10.3171/CASE25229.