A 21-year-old male patient presents to his family doctor with a two-day history of sore throat, fever, and fatigue. He mentions he started feeling unwell after returning from a hockey tournament last month. Submandibular edema is noted on examination. Laboratory findings reveal leukopenia and an elevated serum amylase concentration. An EBV and strep test are both negative. Which of the following complications is most common in patients with this condition?