Walsh & Hoyt: Pathogenesis

During the development of the blood supply to the brain, the primordial vascular system splits into an inner layer that supplies the brain and the retina and an outer layer that supplies the meninges, choroid, and face. The common derivation of the meningeal, choroidal, and facial vessels accounts for a congenital malformation affecting all three tissues. The leptomeningeal vascular malformation results in impaired cortical venous drainage and excessive emptying into the deeper galenic system. This abnormal drainage is associated with neuronal death and calcification in the middle layers of neurons in the cerebral cortex, subcortical white matter, and local blood vessels.