Table 2.

Variable branching patterns and origin of the TPAs, emerged unilaterally or bilaterally from the P1 arterial segment.

Type I (Park 38.5%)
TPAs bilaterally, multiple	TPAs bilaterally, multiple
Type II (Park 26.9%)
TPA unilateral, single	TPAs contralateral, multiple
Type III (Park 19.2%; Percheron 40%)
TPA single	TPA single
Type IV (variant IIb, AOP) (Park 11.5%; Percheron 33%)	Contralateral P1 segment: present/ absent (full FPCA) / hypoplastic
TPA arises unilaterally (from one P1, as a single unpaired trunk, AOP)	−
Type V (variant IIa) (Park 3.8%; Percheron 7%)	Contralateral P1 segment: present/ absent (full FPCA)/hypoplastic
TPAs arise unilaterally (from one P1, as multiple branches)	−
Percheron's  variant III (C): an arterial arcade is bridging P1 segments of both PCAs; the perforating branches arise from this arterial shunt.

TPAs, thalamoperforating arteries. P1, proximal arterial segment of the PCA (from the top of the basilar artery, to the PCoA). IIa and IIb, arterial variants of vascularization of the thalamus and midbrain described by Percheron. In brackets Park's [13] and Percheron's [7, 8] data are mentioned, respectively.