Lymph node enlargement
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Lymph node enlargement (rarely lymphadenomegaly) is often used synonymously with lymphadenopathy, which is not strictly correct.
Lymphadenopathy (or adenopathy) is, if anything, a broader term than lymph node enlargement, referring to any pathology of lymph nodes, not necessarily resulting in increased size; this includes abnormal number of nodes or derangement of internal architecture (e.g. cystic or necrotic nodes). In addition, increase in size is not always pathologic; some nodes are bigger than others normally (e.g. cf. jugulodigastric nodes with mesenteric nodes), and reactive nodes are a healthy response and do not imply pathology of the node itself.
There are approximately 600 lymph nodes, of which only some are available to direct palpation. Only some nodes (including neck, axilla and groin) should ever be normally palpable, and when they are, they should be soft and non-tender.
There are many causes of lymph node enlargement which include:
infective (acute suppurative)
drug-induced: e.g. cyclosporine, phenytoin, methotrexate
HIV related: HIV lymphadenopathy 8
The upper limit in size of a normal node varies with location, and the size cut-off used depends on the desired sensitivity and specificity.
Measuring short axis diameter best represents the size of the lymph node in CT imaging 9.
Cervical lymph nodes
See the article: cervical lymph node metastasis (radiologic criteria).
Mediastinal lymph nodes
In general 10 mm is considered the upper limit for normal nodes (short axis diameter) 3-5. This does not, of course, take into consideration the fact that all nodal metastases must start at microscopic size, and thus using only size criteria will miss micrometastases. In the setting of lung cancer staging a sensitivity of 0.83 and a specificity of 0.82 are quoted for CT 5.
See the article: mediastinal lymph node enlargement.
Mesenteric lymph nodes
Mesenteric nodes are increasingly visualized as a result of multidetector volume acquisition and are most easily seen on coronal reformats.
Although 3 mm has previously been used as the upper limit for the short axis diameter of mesenteric lymph nodes, up to 39% of healthy normal patients have larger nodes than this. As such a figure of 5 mm is considered normal 6.
See the article: normal mesenteric lymph nodes.
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