Reasons for Surgery

The most common reason for removing the spleen is injury to the organ. This can occur from any blunt or penetrating trauma. Although efforts are made to preserve the spleen, this is not always possible.

Diseases that affect the spleen

These include certain types of anemia, thrombocytopenia and tumors and cysts. 
More about these diseases

Hypersplenism

Another reason for removing the spleen is hypersplenism. Hypersplenism is the condition in which one or more components of blood are reduced and the spleen is enlarged. The reduction of blood elements is the result of increased clearance of these blood cells by the spleen. Examples include Felty's syndrome, hairy cell leukemia, and cirrhosis. Many of the diseases noted previously, such as hemolytic anemia and hereditary elliptocytosis are also examples of hypersplenism.

Diagnosis

The spleen may be removed to stage an illness, such as Hodgkin's disease.