Plasma cell variant of Castlemans disease - associated with HHV-8 infection and HIV infection
Mesenteric lymphadenitis after viral systemic infection (particularly in the GALT in the appendix) can commonly present like appendicitis.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. Tumoral:
Primary: Hodgkin lymphoma and non-Hodgkin lymphoma give lymphadenopathy in all or a few lymph nodes. Secondary: metastasis, Virchows Node, neuroblastoma, and chronic lymphocytic leukemia. Autoimmune: systemic lupus erythematosus and rheumatoid arthritis may have a generalized lymphadenopathy. Immunocompromised: AIDS. Generalized lymphadenopathy is an early sign of infection with human immunodeficiency virus (HIV), the virus that causes acquired immunodeficiency syndrome (AIDS). "Lymphadenopathy syndrome" has been used to describe the first symptomatic stage of HIV progression, preceding a diagnosis of AIDS. Bites from certain venomous snakes such as the pit viper
Unknown: Kikuchi disease, progressive transformation of germinal centers, sarcoidosis, hyaline-vascular variant of Castlemans disease, Rosai-Dorfman disease, Kawasaki disease, Kimura disease

Benign (reactive) lymphadenopathy
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:
Follicular hyperplasia: This is the most common type of reactive lymphadenopathy. Paracortical hyperplasia/Interfollicular hyperplasia: It is seen in viral infections, skin diseases, and nonspecific reactions.
By extent:
Localized lymphadenopathy: due to localized spot of infection e.g., an infected spot on the scalp will cause lymph nodes in the neck on that same side to swell up
Generalized lymphadenopathy: due to a systemic infection of the body e.g., influenza or secondary syphilis
Persistent generalized lymphadenopathy (PGL): persisting for a long time, possibly without an apparent cause
By localization:
Hilar lymphadenopathy. Mediastinal lymphadenopathy
Bilateral hilar lymphadenopathy
Dermatopathic lymphadenopathy: lymphadenopathy associated with skin disease. By malignancy: Benign lymphadenopathy is distinguished from malignant types which mainly refer to lymphomas or lymph node metastasis. Size
By size, where lymphadenopathy in adults is often defined as a short axis of one or more lymph nodes is greater than 10mm. However, there is regional variation as detailed in this table:Lymphadenopathy of the axillary lymph nodes can be defined as solid nodes measuring more than 15 mm without fatty hilum. Axillary lymph nodes may be normal up to 30 mm if consisting largely of fat.In children, a short axis of 8 mm can be used. However, inguinal lymph nodes of up to 15 mm and cervical lymph nodes of up to 20 mm are generally normal in children up to age 8–12.Lymphadenopathy of more than 1.5–2 cm increases the risk of cancer or granulomatous disease as the cause rather than only inflammation or infection. Still, an increasing size and persistence over time are more indicative of cancer. See also
Adenitis
Lymphovascular invasion

References
External links
HPC:13820 on humpath.com (Digital slides)