Abstract 240: Diagnostic Value of Catheter Angiography and Magnetic Resonance Imaging in Perimesencephalic and Non‐Perimesencephalic Subarachnoid Hemorrhage: A Retrospective Analysis

Introduction/Purpose Spontaneous subarachnoid hemorrhage (SAH) without a structural source can be seen in up to 15% of all spontaneous SAH, which includes diffuse non‐aneurysmal SAH, sulcal SAH and perimesencephalic (PM) SAH. Although catheter angiography is considered the gold standard to exclude a vascular etiology, multiple studies suggest that computed tomography angiography (CTA) is adequate in PMSAH and magnetic resonance imaging (MRI) does not produce additional benefit. Without clear recommendations, practice patterns regarding the diagnostic management of these patients remain variable throughout the country. The aim of this study was to evaluate the diagnostic value of MRI and catheter angiography in perimesencephalic (PM) and nonperimesencephalic (non‐PM) subarachnoid hemorrhage (SAH) of unknown origin. Materials and Methods: We conducted a retrospective study of all patients with spontaneous SAH between January 2021 and July 2023. Included in the study were cases of spontaneous SAH diagnosed with CT with an initial negative digital subtraction angiogram (DSA). Additionally, patients who had a positive finding for a vascular source of hemorrhage such as an aneurysm, arteriovenous malformation (AVM) or dural arteriovenous fistula (dAVF) on DSA with a negative CTA or a CT with a PMSAH bleeding pattern were included for comparison. The number and types of follow‐up imaging studies were recorded. Results 420 patients with spontaneous SAH were screened, in which 101 patients met study criteria. 86 patients were found to have a negative DSA, of which 51 (59.3%) were found to have a PMSAH bleeding pattern. Follow‐up MR performed within one week of presentation demonstrated no source of hemorrhage in any of the patients with PMSAH, however, within the subgroup of diffuse‐non‐aneurysmal SAH, two patients (5.7%) were found to have a cavernoma on MRI (p=0.039). Among the 226 patients (53.8%) who had a positive DSA in the same time period, nine patients (3.9%) had a negative CTA and 10 patients (4.4%) had a PMSAH hemorrhage pattern. Conclusion In spite of a well‐established hemorrhagic pattern for aneurysmal SAH, aneurysms may still present with a perimesencephalic SAH distribution. In light of our institutional experience, CTA is not deemed adequate alone for the exclusion of aneurysms in PMSAH, where catheter angiography should still be considered the gold standard in diagnostic evaluation. Finally, MRI of the brain and craniocervical region did not produce any benefit for the detection of a vascular etiology in PMSAH, however, the utilization of MRI should be considered for rare bleeding sources in non‐PM SAH, particularly when intraparenchymal hemorrhage is also present.