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Lymph node enlargement

Lymph node enlargement is often used synonymously with lymphadenopathy, which is not strictly correct. Lymphadenopathy is, if anything, a broader term, referring to any pathology of lymph nodes, not necessarily resulting in increased size. Indeed abnormal number of nodes, or derangement of internal architecture (e.g. cystic necrotic nodes). In addition, increase in size is not always pathologic; some nodes are bigger than other normally (e.g compare jugulodigastric nodes, to 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 in the neck, axilla and groin should ever be palpable and these should be soft and non-tender.

There are many (many) causes of lymph node enlargement which include :

  • infective (acute suppurative)
  • reactive :
    • follicular hyperplasia
    • paracortical hyperplasia 
    • sinus histiocytosis
    • granulomatous
  • neoplastic
  • drugs : e.g. Cyclosporin, Phenytoin , Methotrexate
  • lipid storage diseases

By region

The upper limit in size of a normal node varies with location, and of course the size cut off used depends on the desired sensitivity and specificity. 

Cervical lymph nodes
Size criteria
  • most nodes : 10 mm in short-axis except...
  • sub-mental & sub-mandibular : 15 mm
  • retropharyngeal : 8 mm

There is an error rate of  ≈  10 - 20% if using size criteria alone.

The long to short axis ratio has also been proposed 2 to help evaluate enlarged nodes in the setting of head and neck SCC. When nodes have a ratio of >2 (ie long and flat) 95% are benign. When the ratio is less than 2 (i.e. rounder) then a similar proportion where malignant.

Size-independent criteria
Mediastinal lymph nodes

In general 10 mm is considered the upper limit for normal nodes (short transverse 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.

Mesenteric lymph nodes

Mesenteric nodes are increasingly visualised as a result of multidetector volume acquisition and are most easily seen on coronal reformats. 

Although 3mm had been used as the upper limit for the short axis diameter or mesenteric lymph nodes, up to 39% of healthy normal patients have larger nodes than this. As such a figure of 5mm is considered normal 6. (see normal mesenteric lymph nodes)

See also

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