Background: Only 8% to 22% of cases of subarachnoid hemorrhage (SAH) are of nonaneurysmal origin. Among these, perimesencephalic nonaneurysmal SAH is a distinct clinical and radiologic entity with normal angiographic findings and a good prognosis. In contrast, SAH of nonaneurysmal origin occurring along the cortical convexity is rare and poorly understood. We report 2 cases of subarachnoid hemorrhage along the cortical convexity and discuss their possible etiologies. Methods: In a retrospective analysis of 234 patients with SAH, we identified 2 patients with a typical computed tomographic pattern of convexity SAH that was associated with no known etiology. Results: In these 2 cases, the source of hemorrhage could not be identified with computed tomography, magnetic resonance imaging, or digital subtraction angiography, although neurovascular outcomes were good. The patients reported such incidents as coughing or exertion immediately before headache developed. These incidents may have caused increased intracranial pressure. Conclusion: We suggest the possible involvement of a brief increase in intracranial pressure, such as that accompanying coughing or exertion, in the occurrence of SAH along the cortical convexity.
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