To determine the risk of epileptic seizures due to a brain arteriovenous malformation (AVM) or cavernous malformation (CM). In a prospective population-based study of new diagnoses of AVMs (n = 229) or CMs (n = 139) in adults in Scotland in 1999-2003, we used annual medical records surveillance, general practitioner follow-up, and patient questionnaires to quantify the risk of seizures between clinical presentation and AVM/CM treatment, last follow-up, or death. The 5-year risk of first-ever seizure after presentation was higher for AVMs presenting with intracranial hemorrhage or focal neurologic deficit (ICH/FND: n = 119; 23%, 95% confidence interval [CI] 9%-37%) than for incidental AVMs (n = 40; 8%, 95% CI 0%-20%), CMs presenting with ICH/FND (n = 38; 6%, 95% CI 0%-14%), or incidental CMs (n = 57; 4%, 95% CI 0%-10%). For adults who had never experienced ICH/FND, the 5-year risk of epilepsy after first-ever seizure was higher for CMs (n = 23; 94%, 95% CI 84%-100%) than AVMs (n = 37; 58%, 95% CI 40%-76%; p = 0.02). Among adults who never experienced ICH/FND and presented with or developed epilepsy, there was no difference in the proportions achieving 2-year seizure freedom over 5 years between AVMs (n = 43; 45%, 95% CI 20%-70%) and CMs (n = 35; 47%, 95% CI 27%-67%). AVM-related ICH confers a significantly higher risk of a first-ever seizure compared to CMs or incidental AVMs. Adults with a CM have a high risk of epilepsy after a first-ever seizure but achieve seizure freedom as frequently as those with epilepsy due to an AVM.
