Monospot test was positive. He subsequently had both a CT pulmonary angiogram and a CT angiogram of the aorta to exclude pulmonary embolism and aortic dissection. The CT revealed splenomegaly with a large subdiaphragmatic haematoma secondary to splenic rupture. This had likely caused referred pain through diaphragmatic irritation. He was taken to theatre for urgent splenectomy. The unifying diagnosis was infectious mononucleosis complicated by spontaneous splenic rupture secondary to Epstein-Barr virus infection.