Abstract Number: Esoc2026a1956 Low-Grade Dural Arteriovenous Fistula Mimicking a Haemorrhagic Brain Tumour: A Diagnostic Neurovascular Challenge

Abstract Background and aims Dural arteriovenous fistulas (DAVFs) can cause intracranial ischaemic or haemorrhagic lesions and may mimic neoplastic or inflammatory disease on neuroimaging. Even low-grade DAVFs without cortical venous reflux may produce focal venous hypertension when venous outflow is functionally restricted, leading to oedema and haemorrhage. We report a tumour-like presentation caused by a Cognard type I DAVF and outline the underlying pathophysiological mechanism. Methods This is a single observational case. A 71-year-old man with hypertension, dyslipidaemia, and atrial fibrillation on apixaban presented with several days of progressive motor aphasia and right arm weakness. Diagnostic work-up included emergency brain CT, serial contrast-enhanced brain MRI with diffusion-weighted and susceptibility-weighted sequences, whole-body CT, and digital subtraction angiography (DSA). Findings were reviewed in a multidisciplinary setting. Results CT and MRI demonstrated a left frontotemporal–insular lesion with extensive vasogenic oedema, haemorrhagic components, and peripheral enhancement, initially suggesting high-grade glioma versus atypical ischaemic injury. Diffusion-weighted imaging revealed a subtle linear restriction in the left insular region, supporting an ischaemic component. Despite partial radiological improvement after corticosteroid therapy, diagnostic uncertainty persisted. DSA identified a DAVF supplied by transdiploic pterygoid branches from the left maxillary artery, with anterograde drainage into the ipsilateral lateral sinus, consistent with Cognard type I. This venous drainage pattern promotes regional congestion, reduced arteriovenous pressure gradient, and impaired venous outflow, resulting in venous ischaemia and secondary haemorrhagic transformation. Conclusions Low-grade DAVFs may present as haemorrhagic mass-like lesions due to focal venous hypertension. Early cerebral angiography is essential to secure diagnosis, guide management, and avoid unnecessary invasive procedures. Conflict of interest Juan Alberto Aguilera Aguilera: nothing to disclose Figure 1 - belongs to Background and aims Figure 2 - belongs to Methods Figure 3 - belongs to Results Figure 4 - belongs to Conclusions