A:

The spleen sits underneath the rib cage in the left upper part of the abdominal cavity. Normally it is slightly less than 5 inches long and 3 inches wide.

The spleen is a curious organ. It filters our blood by removing older or misshapen cells. Also it’s part of our immune system and helps fight certain infections.

Even though it performs some important functions, the spleen is not an essential organ. It can be surgically removed without affecting other vital body functions.

There are many possible reasons for an enlarged spleen. Your situation is quite common. A person has a CAT scan or ultrasound of the abdomen and the spleen is noted to be larger than normal. This finding may be unrelated to why the imaging procedure was ordered. If no cause is found, it is called "idiopathic splenomegaly" and has no special significance.

The broad categories of conditions that enlarge the spleen include:

• Infection, such as mononucleosis.
• Immune disorders, such as lupus and rheumatoid arthritis.
• Hemolytic anemia. A low red blood cell count caused by rapid breakdown of red blood cells in the circulation.
• Cirrhosis of the liver. Scarring of the liver impairs blood flow through the portal veins (the veins going into the liver). The blood backs up into the spleen and enlarges it.
• Lymphoma. But rarely is just the spleen enlarged. Usually the lymph nodes swell, and there are other signs.