Splenomegaly is a term which refers to enlargement of the spleen. The normal adult splenic length upper limit is usually around 12-15 cm.he causes of splenomegaly are protean, and can be thought of under a number of headings: 1  haematological disease. 2  haemodynamic. 3  infectious. 4  storage diseases/metabolic diseases. 5  neoplastic (non-haematologic).