Letter by Mugikura and Takahashi regarding article, "Perfusion characteristics of moyamoya disease: an anatomically and clinically oriented analysis and comparison".

We completely agree with the findings by Schubert et al1: cerebrovascular reserve capacity was exhausted in the large area, including the middle cerebral artery (MCA) territory and its adjacent anterior and posterior watershed areas with resultant decreased cerebral blood flow (CBF), whereas cerebrovascular reserve capacity in the pericallosal area was not with relatively preserved CBF. In their patients without posterior cerebral artery (PCA) involvement, deep leptomeningeal collaterals through the posterior pericallosal artery (Fisher’s anastomosis) from the proximal PCA as well as superficial leptomeningeal collaterals from the more distal PCA branches presumably developed to compensate for the reduced blood flow in the anterior circulation.2,3 In that case, the deep collaterals mainly perfuse the medial part of the …