A 78-year-old woman with a prior stroke is not feeling well. Her appetite is poor, and today her family noticed that she is confused so they send her to the emergency room for an assessment. She reports no cough, fever, or sputum production but her CXR reveals a left lower lobe infiltrate. Blood cultures are drawn, and she is started on antibiotics. The next day the cultures are positive for S pneumoniae sensitive to penicillin. Which of the following is the most likely complication of pneumococcal pneumonia?