Enlarged spleen. Ultrasound scan of an enlarged spleen (dark grey, upper frame), a condition known as splenomegaly. The spleen is a mixture of white and red pulp, storing red and white blood cells. It is situated behind the stomach. Its largest dimension is normally 12 centimetres. This spleen is 15.8 centimetres across. Splenomegaly may be caused by malaria and other parasitic infections, bacterial & viral infections, and blood disorders. Treatment is of the underlying cause. Ultrasound scans use reflected high-frequency sound waves to construct a picture of internal body organs.