Lymph Node Abnormalities

Reactive Lymph Nodes

Lymph nodes demonstrate hyperplasia as an immunological response to antigens; cells proliferate in the cortex of the node and germinal centre activity results in multiplication of cells in the thymus-dependent area (paracortex). Newly formed plasma cells accumulate in the medullary cords and macroscopically a bulging white cortex is seen which may almost obliterate the medulla

Lymphadenitis

This term refers to true inflammation of the lymph node, which can be enlarged due to congestion, oedema or leukocyte (neutrophil) accumulation. Pyogenic organisms can cause abscessation, and necrosis within the node.

Lymphangitis refers to an inflammation of the lymphatic vessels.

Haemal Lymph Nodes

These occur in ruminants only and their functional significance unclear. They are small dark red/brown nodes that develop during foetal life when the lymph node primordia lose their lymph vessels; as they receive all cells and antigen from the BLOOD their function may be to respond to blood-borne antigens.

Other Lymphadenopathies

These would include:

Lymph node pigmentation

This occurs in the lungs for a variety of reasons including:

• anthracosis
• carbon derived from soot finds its way to the local nodes in macrophages

Skin

• dermatopathic lymphadenopathy or melanic reticulosis
• in pigmented animals, especially black dogs
• chronic inflammatory skin conditions lead to melanin deposition in hyperplastic nodules
• also occurs in nodes draining skin melanomas where the pigment may be the result of skin ulceration or secondary tumour deposit
• these two should not be confused since the prognosis is very different following surgery

Emphysema

Interstitial emphysema can occur in the respiratory lymph nodes and is common in cases of dyspnoea. This condition is seen most commonly in the bovine lung which, due to the well developed pulmonary lobulation and extensive loose interstitial lung tissue permits a collection of gas bubbles in the bronchial and mediastinal lymph nodes. Gas travels to these nodes after gaining entry to the many lymphatic vessels present in the interstitial tissue

Neoplasia

Primary lymph node tumours include lymphosarcoma (lymphoma) which affect lymphoid cells with lymph node enlargement. The nodes become smooth, pale and hemogenous but may have areas of necrosis; this condition may cause pseudo-hyperparathyroidism.

Secondary tumours; the lymph nodes are often involved in the spread of tumours by extension or metastasis and are usually carcinomas