Lymphadenopathy - Most lymph nodes in the body can't be felt easily unless they become swollen or enlarged. Lymphadenopathy is an increase in the size of a lymph node or nodes, most often as the result of a nearby infection (for example, lymphadenopathy in the neck might be the result of an infection of the throat). Less commonly (particularly in children), swelling of the lymph nodes can be due to an infiltration of cancerous cells. If lymphadenopathy is generalized (meaning that the swelling is present in several lymph node groups throughout the body), it usually indicates that the person has a systemic disease.
Lymphadenitis, or adenitis - is an inflammation (swelling, tenderness, and sometimes redness and warmth of the overlying skin) of the lymph node due to an infection of the tissue in the node itself. In children, this condition most commonly involves the lymph nodes of the neck.
Lymphomas - A group of cancers that arise from the lymph nodes, these diseases result when lymphocytes undergo changes and start to multiply out of control. The involved lymph nodes enlarge, and the cancer cells crowd out healthy cells and may form tumors (solid growths) in other parts of the body.
Splenomegaly (enlarged spleen) - the spleen is usually small enough that it can't be felt by pressing on the abdomen, but the spleen can enlarge to several times its normal size with certain diseases. There are many possible reasons for this including various blood diseases and cancers, but the most common cause is infection (particularly viral infections). Infectious mononucleosis, a condition usually caused by the Epstein-Barr virus (EBV), is one of many viral infections associated with an enlarged spleen. People with an enlarged spleen should avoid contact sports because they can have a life-threatening loss of blood if their spleen is ruptured.
Tonsillitis - An extremely common condition, particularly in children, tonsillitis occurs when the tonsils, the collections of lymphoid tissue in the back of the mouth at the top of the throat, are involved in a bacterial or viral infection that causes them to become swollen and inflamed. The tonsils normally help to filter out bacteria and other microorganisms to aid the body in fighting infection. Symptoms include sore throat, high fever, and difficulty swallowing. The infection may also spread to the throat and surrounding areas, causing pain and inflammation.