A 5-year-old boy has had repeated bouts of earache for 3 years. Each time on examination, the bouts have been accompanied by a red, bulging tympanic membrane, either unilaterally or bilaterally, sometimes with a small amount of yellowish exudate. Laboratory studies have included cultures of Staphylococcus aureus, Pseudomonas aeruginosa, and Moraxella catarrhalis. The most recent examination shows that the right tympanic membrane has perforated. The boy responds to antibiotic therapy. Which of the following complications is most likely to occur as a consequence of these events?