Takamiya S, et al. - Experts conducted a retrospective review of the cases of spinal intra-dural arteriovenous malformations (AVMs), which were identified by three-dimensional digital subtraction angiography (3D-DSA), and estimated the number of feeding arteries. The patients with spinal intra-dural AVMs who underwent 3D-DSA at Hokkaido University Hospital from January 2005 to December 2016 were retrospectively reviewed. As per data, the F/D ratio obtained from 3D-DSA can be used to estimate the number of feeding arteries of spinal intra-dural AVMs. They noted 2.3 to be the average number of feeders, and a significantly positive correlation of the number of feeders with the F/D ratio was noted.