Pathology Thread

REACTIVE LYMPHOID HYPERPLASIA is the benign and reversible enlargement of lymphoid tissue secondary to antigen stimulus. The lymph node response to stimuli varies. Follicles can increase in size and number; sinuses can enlarge and fill with histiocytes, or the architecture can be diffusely effaced by sheets of lymphocytes, a few immunoblasts and macrophages. In some cases there is a mixture of follicular, sinus and diffuse patterns.

Each of these morphologically recognizable patterns is associated with certain antigenic stimuli, thus the morphologic type of lymphadenopathy may offer clues as to the etiology of the lymphadenopathy.

FOLLICULAR HYPERPLASIA is characterized by enlargement of lymph nodes by hyperplasia of follicular (germinal) centers. At right, note the variablilty in the size of the follicles and the presence of mantle zones in the reactive node.

In FOLLICULAR HYPERPLASIA, the hyperplastic germinal center contains a normal mixture of varibly sized lymphocytes, plasma cells, and macrophages, as well as a few dendritic reticular cells. No one lymphocyte type predominates as in lymphoma.

In SINUS HYPERPLASIA the sinuses become distended and filled with histiocyte/macrophages and some plasma cells.

In DIFFUSE HYPERPLASIA the lymph node architecture is diffusely effaced by sheets of small lymphocytes, and a few scattered immunoblasts and macrophages.

MIXED HYPERPLASIA is a combination of follicular, sinus and diffuse patterns of hyperplasia.

Morphologic patterns of reactive lymphoid hyperplasia and their associated disorders.

FOLLICULAR

• rheumatoid arthritis
• giant lymph node hyperplasia (Castleman's disease)
• AIDS (persistent generalized lymphadenopathy)*
• idiopathic (most common)

SINUS

• sinus histiocytosis with massive lymphadenopathy
• lymphangiogram effect

* increasingly frequent, 1 differential malignant lymphoma, especially ML,large cell

Morphologic patterns of reactive lymphoid hyperplasia and their associated disorders.

DIFFUSE

• post-vaccinial lymphadenitis
• anticonvulsant therapy
• viral lymphadenitis
• dermatopathic lymphadenopathy

MIXED

• infectious mononucleosis
• toxoplasmosis
• cat scratch disease
• tuberculosis

In addition to the aforementioned hyperplasias other diseases, i.e., histiocytosis X and metastatic carcinoma can involve lymph nodes causing a reactive hyperplasia or mimic a hyperplasia (Histiocytosis X in the sinuses of a lymph node) and thus need to be carefully ruled out on microscopic exam.

Reactive follicular hyperplasia may closely resemble some follicular lymphomas and some diffuse interfollicular viral infections mimic diffuse lymphoma.

Whenever a malignant diagnosis is being considered benign reactive disorders must be ruled out by an experienced pathologist.

This is the final page of the Benign White Cell Disorders. The next page begins the Leukemia section.