Prognostic Factors and Imaging Strategies in Unknown Subarachnoid Hemorrhage: A Retrospective Study.

Background Subarachnoid hemorrhage (SAH) without an identifiable vascular lesion on initial angiography, commonly referred to as unknown or angiogram-negative SAH, remains diagnostically and prognostically challenging. Although perimesencephalic patterns tend to be benign, diffuse hemorrhages are associated with worse outcomes. The role of repeat vascular imaging in improving diagnosis and predicting prognosis remains unclear. Objective This study aimed to identify clinical and radiological factors associated with outcomes in patients with unknown SAH and evaluate the diagnostic and prognostic value of repeat angiography. Methods We retrospectively analyzed 26 patients with spontaneous, non-traumatic SAH and negative findings on initial digital subtraction angiography (DSA). Clinical status, hemorrhage patterns, and imaging data were recorded. Outcomes were assessed at discharge using the modified Rankin Scale (mRS). Repeat angiographic modalities and timing were analyzed in relation to prognosis. Results Patients with focal hemorrhage patterns, higher Glasgow Coma Scale (GCS) scores at admission, and absence of hydrocephalus had significantly better outcomes. Repeat DSA was more frequently performed in the good outcome group, although no new vascular lesions were identified.  Conclusion Unknown SAH is generally associated with favorable outcomes, but vigilance is warranted in diffuse SAH cases. Repeat DSA may not always reveal new lesions, but it plays a valuable role in guiding clinical confidence and management decisions. Tailored imaging strategies based on clinical and radiological risk factors are recommended.