Lymphadenopathy or adenopathy is a disease of the lymph nodes, in which they are abnormal in size or consistency. Lymphadenopathy of an inflammatory type (the most common type) is lymphadenitis, producing swollen or enlarged lymph nodes. In clinical practice, the distinction between lymphadenopathy and lymphadenitis is rarely made and the words are usually treated as synonymous. Inflammation of the lymphatic vessels is known as lymphangitis. Infectious lymphadenitis affecting lymph nodes in the neck is often called scrofula.

Lymphadenopathy is a common and nonspecific sign. Common causes include infections (from minor causes such as the common cold and post-vaccination swelling to serious ones such as HIV/AIDS), autoimmune diseases, and cancer. Lymphadenopathy is frequently idiopathic and self-limiting.

Lymph node enlargement is recognized as a common sign of infectious, autoimmune, or malignant disease. Examples may include:

Infectious causes of lymphadenopathy may include bacterial infections such as cat scratch disease, tularemia, brucellosis, or prevotella, as well as fungal infections such as paracoccidioidomycosis.

Benign lymphadenopathy is a common biopsy finding, and may often be confused with malignant lymphoma. It may be separated into major morphologic patterns, each with its own differential diagnosis with certain types of lymphoma. Most cases of reactive follicular hyperplasia are easy to diagnose, but some cases may be confused with follicular lymphoma. There are seven distinct patterns of benign lymphadenopathy:

These morphological patterns are never pure. Thus, reactive follicular hyperplasia can have a component of paracortical hyperplasia. However, this distinction is important for the differential diagnosis of the cause.

In cervical lymphadenopathy (of the neck), it is routine to perform a throat examination including the use of a mirror and an endoscope.

On ultrasound, B-mode imaging depicts lymph node morphology, whilst power Doppler can assess the vascular pattern. B-mode imaging features that can distinguish metastasis and lymphoma include size, shape, calcification, loss of hilar architecture, as well as intranodal necrosis. Soft tissue edema and nodal matting on B-mode imaging suggests tuberculous cervical lymphadenitis or previous radiation therapy. Serial monitoring of nodal size and vascularity are useful in assessing treatment response.