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Figure 14.1 Normal lymph node. A, The anatomic structure and functional zones of a lymph node. B, Maturation of lymphoid cells in the follicle. CHAPTER 14

REACTIVE LYMPHADENITIS phils. The lymphoid follicles are prominent with presence
Lymph nodes undergo reactive changes in response to a wide of many mitoses and phagocytosis. In more severe cases,
variety of stimuli which include microbial infections, drugs, necrosis may occur and neutrophil abscesses may form.
environmental pollutants, tissue injury, immune-complexes
and malignant neoplasms. However, the most common Chronic Nonspecific Lymphadenitis
causes of lymph node enlargement are inflammatory and Chronic nonspecific lymphadenitis, commonly called reactive
immune reactions, aside from primary malignant neoplasms lymphoid hyperplasia, is a common form of inflammatory
and metastatic tumour deposits. Those due to primary reaction of draining lymph nodes as a response to antigenic
inflammatory reaction are termed reactive lymphadenitis, and stimuli such as repeated attacks of acute lymphadenitis and
those due to primary immune reactions are referred to as lymph from malignant tumours.
lymphadenopathy. Depending upon the pattern in chronic nonspecific
Reactive lymphadenitis is a nonspecific response and is lymphadenitis, three types are distinguished, each having
categorised into acute and chronic types, each with a few its own set of causes. These are: follicular hyperplasia,
variant forms. paracortical hyperplasia and sinus histiocytosis. However, mixed Disorders of Leucocytes and Lymphoreticular Tissues
patterns may also be seen in which case one of the patterns
Acute Nonspecific Lymphadenitis
predominates over the others.
All kinds of acute inflammations may cause acute nonspecific
lymphadenitis in the nodes draining the area of inflamed MORPHOLOGIC FEATURES. Grossly, the affected
tissue. Most common causes are microbiologic infections or lymph nodes are usually enlarged, firm and non-tender.
their breakdown products, and foreign bodies in the wound Microscopically, the features of 3 patterns of reactive
or into the circulation etc. Most frequently involved lymph lymphoid hyperplasia are as under:
nodes are: cervical (due to infections in the oral cavity), axillary 1. Follicular hyperplasia is the most frequent pattern,
(due to infection in the arm), inguinal (due to infection in the particularly encountered in children. Besides nonspecific
lower extremities), and mesenteric (due to acute appendicitis, stimulation, a few specific causes are: rheumatoid arthritis,
acute enteritis etc). toxoplasmosis, syphilis and AIDS. The microscopic
Acute lymphadenitis is usually mild and transient but features are as follows (Fig. 14.2):
occasionally it may be more severe. Acutely inflamed nodes i) There is marked enlargement and prominence of the
are enlarged, tender, and if extensively involved, may be germinal centres of lymphoid follicles (proliferation of B-
fluctuant. The overlying skin is red and hot. After control of cell areas) due to the presence of numerous mitotically
infection, majority of cases heal completely without leaving active lymphocytes and proliferation of phagocytic cells
any scar. If the inflammation does not subside, acute containing phagocytosed material.
lymphadenitis changes into chronic lymphadenitis. ii) Parafollicular and medullary regions are more cellular
and contain plasma cells, histiocytes, and some
MORPHOLOGIC FEATURES. Grossly, the affected
lymph nodes are enlarged 2-3 times their normal size and neutrophils and eosinophils.
may show abscess formation if the involvement is iii) There is hyperplasia of mononuclear phagocytic cells
extensive. lining the lymphatic sinuses in the lymph node.
Microscopically, the sinusoids are congested, widely Angiofollicular lymphoid hyperplasia or Castleman’s
dilated and oedematous and contain numerous neutro- disease is a clinicopathologic variant of follicular