Spleen enlargement--sometimes referred to as splenomegaly--occurs when a large number of red blood cells and platelets get trapped inside the spleen, causing it to grow to an abnormal size. According to the Merck Manuals Online Medical Library, an enlarged spleen is not a primary disease, but rather is caused by one or more secondary medical factors.
Infection
A variety of infections can cause the spleen to swell. According to the Mayo Clinic, bacterial infections such as endocarditis--infection and inflammation of the lining of the heart--and the sexually transmitted disease syphilis are known causes. Brucellosis--a rare bacterial disease contracted through animals--and psittacosis--a bacterial disease spread through bird droppings--may also cause an enlarged spleen, according to Merck Manuals.
Viral diseases caused by herpes viruses, including cytomegalovirus, Epstein-Barr virus and infectious mononucleosis, and parasitic infections like malaria can also cause the spleen to swell, according to the National Institutes of Health.
Liver Disorders
According to the Mayo Clinic, disorders affecting the liver can subsequently result in enlargement of the spleen. Cirrhosis, or a scarring of the liver due to alcoholism or chronic liver disease, is one type of liver disorder that can affect the spleen. Biliary atresia--a condition in which the ducts that carry bile from the liver to the gallbladder are blocked--and sclerosing cholangitis--a condition involving inflammation and damage to the bile ducts associated with the liver--can also cause the spleen to swell, according to the National Institutes of Health. Disorders that interfere with blood flow to the liver through the hepatic portal vein, including portal hypertension and portal vein obstruction, are also known causes of an enlarged spleen.
Anemias and Blood Disorders
Certain genetically transmitted types of anemia that affect the number or shape of blood cells, including hereditary elliptocytosis, hereditary spherocytosis, sickle cell disease and thalassemia, may all cause spleen enlargement, according to Merck Manuals. Other anemias that can enlarge the spleen include immune hemolytic anemia, idiopathic autoimmune hemolytic anemia and hemolytic anemia caused by a deficiency in the enzyme G6PD, according to the National Institutes of Health. Certain types of blood cancers and bone marrow disorders can affect the spleen, as well, including leukemia, Hodgkin lymphoma and myelofibrosis.
Metabolic Disorders
Metabolic disorders that are characterized by a buildup of toxic fatty substances in the body's vital organs, including the liver, brain and spleen, can also cause the spleen to enlarge. Some of these diseases include Gaucher's disease, Neimann-Pick disease and Wolman disease, according to Merck Manuals.
