Magnetic Resonance Imaging Yield in Perimesencephalic versus Non-Perimesencephalic Nonaneurysmal Subarachnoid...

Catheter angiography remains the gold standard to exclude vascular causes of hemorrhage in nonaneurysmal subarachnoid hemorrhage (NASAH), though further diagnostic evaluation varies. This study assessed the diagnostic value of magnetic resonance imaging (MRI) in NASAH and described clinical outcomes.

We retrospectively reviewed patients with spontaneous subarachnoid hemorrhage between January 2021 and December 2024. Patients with subarachnoid hemorrhage initially identified by noncontrast computed tomography and confirmed by negative digital subtraction angiography were included. Clinical and radiographic characteristics were compared between perimesencephalic and non-perimesencephalic NASAH.

Of 121 patients, 69 (57%) had perimesencephalic NASAH, and 52 (43%) had non-perimesencephalic NASAH. Follow-up MRI of the brain and/or spine within 1 week showed no vascular source in perimesencephalic NASAH. Four patients (7.7%) with diffuse non-perimesencephalic NASAH had positive MRI findings (P = 0.030). Compared with perimesencephalic NASAH, patients with diffuse non-perimesencephalic NASAH more often required treatment for hydrocephalus, hyponatremia, and symptomatic vasospasm; had longer hospitalizations; and demonstrated worse functional outcomes at last follow-up (P < 0.01).

MRI of the brain and craniocervical region did not identify vascular pathology in perimesencephalic NASAH, suggesting low diagnostic yield in this subgroup. However, MRI may aid in detecting rare bleeding sources, especially in non-perimesencephalic NASAH. Perimesencephalic NASAH generally follows a benign course with favorable outcomes, raising questions about the necessity and cost-effectiveness of intensive monitoring and prolonged hospitalization.