Beyond Trauma: Splenic Rupture While Surfing Revealing Occult Infectious Mononucleosis

When a young patient collapses with haemoperitoneum after physical activity, trauma is the presumptive diagnosis; Epstein-Barr virus (EBV) infectious mononucleosis (IM) is easily overlooked. However, IM carries a rare but potentially fatal complication: splenic rupture, occurring in approximately 0.1-0.5% of symptomatic cases. We report the case of a previously healthy 21-year-old man who presented with sudden-onset abdominal pain and presyncope while surfing, without any fall or direct abdominal impact. Over the subsequent two hours, he developed progressive haemodynamic instability. A focused assessment with sonography for trauma (FAST) was positive for free intraperitoneal fluid. Following initial resuscitation, contrast-enhanced computed tomography demonstrated a grade V splenic injury, splenomegaly, and massive haemoperitoneum, prompting emergency splenectomy. Intraoperatively, the spleen was markedly enlarged, approximately three times the expected normal weight, friable, and extensively lacerated. The initial diagnosis was traumatic splenic rupture. However, on postoperative day three, persistent fever prompted investigation for an infectious cause. Serology confirmed acute EBV infection. This case highlights that severe splenic rupture occurring during ordinary physical activity, particularly when accompanied by splenomegaly disproportionate to the reported mechanism, should prompt postoperative evaluation for EBV infection, even in the absence of classic symptoms of IM. Earlier recognition of the underlying diagnosis might also help avoid unnecessary investigations and treatments during the postoperative period.