Perimesencephalic (pretruncal) nonaneurysmal subarachnoid hemorrhage is a subarachnoid hemorrhage (PNSAH) pattern with unknown etiology and a benign outcome. Although they are rarely seen, they comprise 20-68 % of all angiogram-negative subarachnoid hemorrhages. In this study, a patient admitted to our emergency department with a severe headache and a CT image of perimesencephalic bleeding was presented and relevant literature was reviewed. It is important to diagnose PNSAH for the sake of avoidance from unnecessary neuroradiological and surgical procedures.

Keywords: Perimesencephalic, pretruncal, subarachnoid hemorrhage