A 7-year-old girl presents to the emergency department with fever, left ear pain, and swelling behind her ear for the past three days. She had acute otitis media (AOM) one week ago, which was treated with amoxicillin, but her symptoms have worsened. On examination, her left auricle is pushed forward, and there is tenderness, erythema, and swelling over the mastoid process. A CT scan confirms mastoid air cell opacification with bony destruction. Which of the following is the most serious potential complication of her condition?
