C102 Perianeurysmal cyst following flow-diverter-assisted coiling of a carotid artery aneurysm: a very rare epileptogenic focus

<h3>Introduction</h3> The occurrence of a first epileptic seizure three months after endovascular treatment of an incidental cerebral aneurysm should prompt extended diagnostic evaluation, as illustrated by the following case involving a perianeurysmal cyst (figure 1: A) T2-weighted MRI showing the untreated aneurysm [white arrow] without perianeurysmal cyst; B, C) DSA post-treatment with flow-diverter-assisted coiling). <h3>Case Description</h3> A 59-year-old female presented with suspected focal epileptic seizures characterized by gustatory auras three months after flow-diverter-assisted coiling (p64 HPC and hydro coils) of a 12 mm dorsal wall aneurysm of the right internal carotid artery. MRI revealed a new 15 mm cystic lesion in the right mesial temporal region adjacent to the treated aneurysm, interpreted as an epileptogenic focus (figure 2: A) T2w axial and B) FLAIR coronal with perianeurysmal cyst [black arrow] and treated aneurysm [white arrow]). Time-of-flight MRA showed no aneurysm recurrence. Following corticosteroid therapy, the cyst regressed and FLAIR hyperintensity resolved within four weeks (figure 2: C) T2w axial and D) FLAIR coronal showing resolution [black arrow]). <h3>Conclusions</h3> Perianeurysmal cysts after endovascular treatment of cerebral aneurysms are a rare entity, best detected by MRI, and can represent a structural cause of epilepsy. According to scarce case reports in the literature, perianeurysmal typically are a very rare entity and occur in older patients with large, unruptured, and partially thrombosed aneurysms, often after endovascular treatment. Their pathogenesis remains unclear but may involve inflammatory responses, abnormal perivascular spaces, or blood-brain barrier disruption leading to cytokine release. MRI is the modality of choice for detection. <h3>Conflict of Interest</h3> No