Morphometric study of the anterior thalamoperforating arteries. Schematic view and cadaveric specimen showing the segments of posterior communicating artery (PCoA) according to the crowding pattern of anterior thalamoperforating arteries. Black arrows mean the length of each segment occupying the PCoA. Red arrows indicate the interval between each segment. Red circles indicate the perforator-free zone from the internal carotid (ICA) and the posterior cerebral arteries (PCA), respectively.