Your spleen is an organ located just below your rib cage on your left side. A number of conditions - from infections to liver disease and some cancers - can cause an enlarged spleen, also known as splenomegaly. Most people don't have symptoms with an enlarged spleen. The problem is often discovered during a routine physical exam. Your doctor can't feel a normal-sized spleen in adults - unless you're very slender - but can feel an enlarged spleen. If you have an enlarged spleen, your doctor will likely request imaging and blood tests to help identify the cause. Treatment for an enlarged spleen focuses on relieving the underlying condition. Surgically removing an enlarged spleen isn't usually the first treatment, but it may be recommended in certain situations.
 
What are the causes of an enlarged spleen?
Blood disorders:
The spleen will enlarge when it performs more of its duties to filter blood or to manufacture blood cells. Therefore, any disease or condition that damages red blood cells, and requires them to be filtered and removed from the blood stream, will cause the spleen to become larger.

Conditions such as hemolytic anemia, where red blood cells are damaged and broken down (hemolyzed) can cause the spleen to enlarge. Misshapen red blood cells, like those found in sickle cell disease, Thalassemia, and spherocytosis, may be damaged when they try to squeeze through small capillary blood vessels. These damaged red blood cells need to be culled from the bloodstream and are filtered out by the spleen.

Decreased blood flow:
The spleen will enlarge if there is a decrease in blood flow through the splenic vein. This may cause spleen congestion and enlargement. This situation may be associated with liver disease and portal hypertension. Damage to liver cells makes it difficult for blood to flow normally, and as blood backs up in the portal vein system, it may also affect pressure in the splenic vein. The decreased ability of blood to drain from the spleen causes it to become congested and grow larger. People with congestive heart failure may have an enlarged liver and spleen because of poor blood flow to and from the heart.

Cancer:
Leukemia and lymphoma may be associated with abnormal white cells that can invade the spleen and increase its size.

What are other signs and symptoms of an enlarged spleen?
Often, it is not the enlarged spleen itself that causes symptoms, but rather it is the symptoms of the underlying illness that causes splenomegaly.
Due to anemia, individuals may develop weakness, fatigue and shortness of breath.