ABSTRACT NUMBER: ESOC2026A577 HIDDEN CAUSES IN LOBAR INTRACEREBRAL HEMORRHAGE: DIAGNOSTIC YIELD OF DELAYED INVESTIGATIONS IN INITIALLY CRYPTOGENIC CASES

Abstract Background and aims Lobar intracerebral hemorrhage (ICH) is frequently associated with identifiable etiologies, including cerebral amyloid angiopathy, hypertension, anticoagulation, vascular malformations, or neoplastic disease. However, in a subset of patients no cause is identified. Data on the diagnostic yield of delayed investigations in lobar ICH of unknown origin are limited. We aimed to describe the frequency, clinical characteristics, and results of deferred etiological work-up in patients with initially cryptogenic lobar ICH Methods We retrospectively analyzed consecutive lobar ICH admissions between January 2023 and October 2025. Patients with cerebral amyloid angiopathy, anticoagulation-related hemorrhage, or hypertension-related ICH were excluded. Severity was assessed using NIHSS; functional outcome at 3 months with mRS. Lobar ICH was considered cryptogenic when no etiology was identified after standard acute-phase evaluation. Results of delayed investigations during follow-up were reviewed Results Among 46 lobar ICH patients, 17 (37%) were cryptogenic initially (mean age 61.8 years; 58.8% male; median NIHSS 4.5). Deferred investigations identified a definite etiology in 7/17 (41.2%): cerebral arteriovenous malformations (n=3) diagnosed after repeat angiography and brain metastases (n=4) detected on delayed MRI. At 3 months, 9 patients achieved excellent outcome (mRS 0), while 2 died (mRS 6) Conclusions In lobar ICH patients without common etiologies, delayed diagnostic investigations reveal hidden underlying causes in a substantial proportion of cases. Repeat vascular imaging and additional delayed MRI play a key role in uncovering vascular malformations and neoplastic disease, supporting systematic follow-up evaluation in patients with initially cryptogenic lobar ICH, even when clinical presentation is mild Conflict of interest nothing to disclose