Causes of Splenomegaly: Etiology and pathology

Enlargement of the size of the spleen beyond its normal shape and size and position is defined as splenomegaly. The normal anatomy of spleen is defined as a structure of 1inch x 3 inch x 5 inch, with weight of 7 ounces (~150-200g) in size and spans across 9-11 ribs in the left upper quadrant of the abdominal cavity. This is the rule of odd number in spleen (1, 3, 5, 7, 9, and 11).

Etiological Causes of Splenomegaly

The size of the spleen has to increase by at least 500g to called splenomegaly and has to be more than 1000g to define as massive splenomegaly. It is not necessary that every enlarged spleen will be palpable by clinical examination. The size of the spleen has to increase by 3-5 folds to be appreciated clinically. In terms of size it has to be greater than 10-11 cm in its greatest diameter to be defined as moderate splenomegaly and more than 20 cm in its largest dimension to be called as massive splenomegaly.

The cause of splenomegaly can be classified as either etiological causes or pathological cause.

Dividing the causes of splenomegaly etiologically, it could either be infective, hematological, metabolic, collagen vascular disease or other various causes. The most important one are obviously the infective and the hematological causes.

Infective causes of splenomegaly

Bacteria such as salmonella typhi/paratyphi, scrub typhus, mycobacterium tuberculosis, pneumococcal splenic abscess and septicemia by any organism can cause splenomegaly. HIV and EBV (infectious mononucleosis) are the viral causes of splenomegaly. Malaria and Schistosomiasis are few tropical protozoal disease to cause splenomegaly. Parasites like Leshmania donovani (kalazar) and echinococcus (hydatid cyst) are other causes. Syphilis and Weils (Leptospirosis) disease are some spirochetal conditions associated with splenomegaly.

Hematological causes of splenomegaly

Hematological causes may be related to RBC, WBC or platelet. The condition where there is massive RBC destruction or massive extra medullary hemopoeisis is associated with splenomegaly. Most of the hemolytic causes of anemia such as hereditary spherocytosis, autoimmune hemolytic anemia, thalassemia, sickle cell disease, erythroblastosis fetalis have splenomegaly. Similarly faulty RBC synthesis in pernicious anemia leads to increased load in spleen to cause hemolysis. The polycythemia is associated with increased extra hemopoeitic synthesis of RBC. The Leukemia including  CML, ALL, AML, CLL will have splenomegaly. ITP also has splenomegaly.

Splenomegaly Causes other than infection and blood related

Metabolic causes such as rickets, Gaucher’s, porphyria, amyloidosis present with enlarged spleen clinically.  Infarction of spleen, portal hypertension associated with pancreatic carcinoma and splenic vein thrombosis are some of the circulatory or vascular causes. Collagen vascular diseases as Still's disease and Felty syndrome are other causes.  Non paracytic cyst either congenital or acquired cause splenomegaly.

Angioma , primary fibrosacroma, Hogdkins lymphoma, myelofibrosis are other lymphomas are the neoplastic causes of the condition.