Background: Nonaneurysmal perimesencephalic subarachnoid hemorrhage (NAPH) is a form of subarachnoid hemorrhage (SAH) occurring predominantly in the perimesencephalic region, in the absence of an aneurysm or other source of bleeding on diagnostic angiography. The underlying cause of NAPH remains unclear. Case report: Herein, we describe three patients who developed NAPH during strenuous activity in the absence of trauma after traveling to an altitude of approximately 7,500 feet. The patients were treated conservatively without any residual neurological deficits. Conclusions This case series suggests that hypoxia and vigorous exercise could be risk factors for NAPH. Patients traveling to higher altitudes should be counseled to increase their exercise intensity gradually.

Background: Nonaneurysmal perimesencephalic subarachnoid hemorrhage (NAPH) is a form of subarachnoid hemorrhage (SAH) occurring predominantly in the perimesencephalic region, in the absence of an aneurysm or other source of bleeding on diagnostic angiography. The underlying cause of NAPH remains unclear. Case report: Herein, we describe three patients who developed NAPH during strenuous activity in the absence of trauma after traveling to an altitude of approximately 7,500 feet. The patients were treated conservatively without any residual neurological deficits. Conclusions This case series suggests that hypoxia and vigorous exercise could be risk factors for NAPH. Patients traveling to higher altitudes should be counseled to increase their exercise intensity gradually.

Background: Nonaneurysmal perimesencephalic subarachnoid hemorrhage (NAPH) is a form of subarachnoid hemorrhage (SAH) occurring predominantly in the perimesencephalic region, in the absence of an aneurysm or other source of bleeding on diagnostic angiography. The underlying cause of NAPH remains unclear. Case report: Herein, we describe three patients who developed NAPH during strenuous activity in the absence of trauma after traveling to an altitude of approximately 7,500 feet. The patients were treated conservatively without any residual neurological deficits. Conclusions This case series suggests that hypoxia and vigorous exercise could be risk factors for NAPH. Patients traveling to higher altitudes should be counseled to increase their exercise intensity gradually.