Clinical and epidemiological comparison between perimesencephalic and non-perimesencephalic, non-aneurysmal subarachnoid hemorrhage: a single-center cohort study from a referral center in a developing country.

Background: Non-aneurysmal subarachnoid hemorrhage (SAH) represents a heterogeneous entity with implications for management and prognosis. Perimesencephalic SAH (PSAH) is associated with a more benign clinical course, lower rates of complications, and favorable outcomes, whereas non-perimesencephalic SAH (NPSAH) tends to present with higher rates of vasospasm, hydrocephalus, and worse neurological outcomes. Recognizing these distinct bleeding patterns is, therefore, essential for clinical management. Objective: The present study aims to analyze a series of patients with nonaneurysmal SAH, since it remains a poorly understood and requires further investigation. Methods: A single-center cohort study was carried out with all hospitalizations for spontaneous SAH. Patients were classified according to the pattern of bleeding at cranial computed tomography (CT), as those with a PSAH pattern and those with an aneurysmal pattern of bleeding (NPSAH). A DSA was performed in all patients, and only those who showed no vascular abnormalities were included for data collection. Clinical, epidemiological and functional data were collected and analyzed, comparing the results between both groups. Results: A total of 550 patients with spontaneous SAH were treated at our center, and 74 were classified as nonaneurysmal and included in the final analysis. The bleeding pattern was classified as PSAH in 20 patients and as NPSAH in 54. The NPSAH was more prevalent in women, and PSAH in men. Rates of hydrocephalus and vasospasm were higher in patients with the NPSAH pattern, and clinical outcomes were worse. Conclusion: The NPSAH pattern had an intermediate clinical behavior between perimesencephalic and aneurysmal bleeding. On the other hand, PSAH had a benign course and excellent prognosis.