Splenomegaly is an enlargement of the spleen, which usually lies in the left upper quadrant (LUQ) of the human abdomen. It is one of the four cardinal signs of hypersplenism ( Hypersplenism is a type of disorder which causes the spleen to rapidly and prematurely destroy blood cells ), the other three being cytopenia(s), normal or hyperplastic bone marrow, and a response to splenectomy. Splenomegaly is usually associated with increased workload (such as in hemolytic anemias), which suggests that it is a response to hyperfunction. It is therefore not surprising that splenomegaly is associated with any disease process that involves abnormal red blood cells being destroyed in the spleen. Other common causes include congestion due to portal hypertension and infiltration by leukemias and lymphomas.

The spleen is located in the upper left area of the abdomen. One of this organ's major functions is to remove blood cells from the body's bloodstream. In hypersplenism, its normal function accelerates, and it begins to automatically remove cells that may still be normal in function. Hypersplenism is sometimes referred to as enlarged spleen (splenomegaly). An enlarged spleen is one of the symptoms of hypersplenism.

Hypersplenism may occur as a primary disease, leading to other complications, or as a secondary disease, resulting from an underlying disease or disorder such as chronic malaria, rheumatoid arthritis, tuberculosis, or polycythemia vera, a blood disorder. Spleen disorders in general are almost always secondary in nature. Hypersplenism may also be caused by tumors.

Symptoms of hypersplenism include easy bruising, easy contracting of bacterial diseases, fever, weakness, heart palpitations, and ulcerations of the mouth, legs and feet. Individuals may also bleed unexpectedly and heavily from the nose or other mucous membranes, and from the gastrointestinal or urinary tracts. Most patients will develop an enlarged spleen, anemia, leukopenia, or abnormally low white blood cell counts, or thrombocytopenia, a deficiency of circulating platelets in the blood. Other symptoms may be present that reflect the underlying disease that has caused hypersplenism.
An enlarged spleen can be caused by a variety of diseases, including hemolytic anemia, liver cirrhosis, leukemia, malignant lymphoma and other infections and inflammatory diseases. Splenomegaly occurs in about 10% of systemic lupus erythematosus patients. Sometimes, it is caused by recent viral infection, such as mononucleosis. An enlarged spleen may cause pain in the upper left side of the abdomen and a premature feeling of fullness at meals.

Splenomegaly grouped on the basis of the pathogenic mechanism

Diagnosis of hypersplenism begins with review of symptoms and patient history, and careful feeling (palpation) of the spleen. Sometimes, a physician can feel an enlarged spleen. Ultrasound and computed tomography scan (CT scan), liver function tests,  may help diagnose an enlarged spleen and possible underlying causes, such as tumors. Blood tests indicate decreases in white blood cells, red blood cells, or platelets & presence of young red blood cells.

If the splenomegaly underlies hypersplenism, a splenectomy is indicated and will correct the problem. After splenectomy, however, patients have an increased risk for infectious diseases.
After splenectomy, patients should be vaccinated against Haemophilus influenzae and Streptococcus pneumoniae. They should receive annual influenza vaccinations. Long-term prophylactic antibiotics should be given.
 In secondary hypersplenism, the underlying disease must be treated to prevent further sequestration or destruction of blood cells, and possible spleen enlargement. Those therapies will be tried prior to removal of the spleen (splenectomy), which is avoided if possible. In severe cases, the spleen must be removed. Splenectomy will correct the effects of low blood cell concentrations in the blood. In a recent era of minimally invasive surgery. more & more surgeries are done by laparoscopy.