It must be mono: An atypical case of splenic rupture.

Splenic rupture is a rare but life-threatening complication of infectious mononucleosis, typically associated with Epstein-Barr virus. Early diagnosis of infectious mononucleosis is essential for appropriate management but may be delayed by false-negative early testing and atypical presentations. We report an atypical case of infectious mononucleosis in a 17-year-old male who presented with an acute abdomen secondary to atraumatic splenic rupture confirmed on CT. Initial mononucleosis testing was negative, delaying diagnosis, but repeat testing and subsequent laboratory findings strongly supported the diagnosis of infectious mononucleosis. Despite initial conservative management, worsening symptoms and progression of the splenic hematoma necessitated partial splenectomy. This case highlights the importance of maintaining a high index of suspicion for infectious mononucleosis in young patients with atraumatic splenic rupture despite negative initial testing, as early diagnosis may help guide appropriate management.