Type III Percheron’s variant in thalamic-mesencephalic infarction The unexpected anastomosis

Introduction. Arterial supply of thalamus is complex and highly variable. In particular, the distribution pattern of thalamoperforating arteries received attention some decades ago, but not in recent years. Methods. We are presenting the case of a 46-year-old patient with wake-up drowsiness, complex oculomotor disorder and dysarthria. The brain CT showed a subacute ischemic stroke in the right anterior thalamus and rostral midbran with a normal CTA. DSA was performed, showing a variant of thalamic supply (Percheron type III), constituted by perforating branches arising from an artery bridging the P1 segments of both PCAs. Discussion. Thalamus has a complex and variable arterial supply, mainly in the paramedian thalamic-mesencephalic arteries. The most reported variant is Percheron type IIb and supplies the paramedian thalami and the rostral midbrain. Type IIb occlusion usually causes a bilateral paramedian thalamic stroke, but rostral midbrain and anterior thalamus are involved in 57% and 19% cases. Type III variant probably prevented the bilateral extension of infarction and involved the territory of tuberothalamic and paramedian perforating arteries. Conclusions. Currently, DSA allows directly imaging variants in thalamic vascularization and better understanding the stroke mechanisms. The use of increasingly efficient angiographic techniques could help define the anatomical and hemodynamic factors involved in causing ischemic lesions in territories previously considered difficult to explore.