Lymph node enlargement

Lymph node enlargement (rarely lymphadenomegaly) is often used synonymously with lymphadenopathy, which is not strictly correct.

Terminology

Lymphadenopathy (or adenopathy) is, if anything, a broader term, 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 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 (including neck, axilla and groin) should ever be palpable and these should be soft and non-tender.

Pathology

Aetiology

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

• infective (acute suppurative)
• reactive
  • follicular hyperplasia
  • paracortical hyperplasia 
  • sinus histiocytosis
  • granulomatous
• neoplastic
• drug-induced, e.g. cyclosporin, phenytoin, methotrexate
• lipid storage diseases
• IgG4-related sclerosing disease ⁷

Radiographic features

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 diameter
• submental and submandibular: 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 squamous cell carcinoma. When nodes have a ratio of >2 (i.e. long and flat) 95% are benign. When the ratio is less than 2 (i.e. rounder) then a similar proportion are malignant.

Size-independent criteria

• loss of fatty hilum
• focal necrosis
• cystic necrotic nodes

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.

Mesenteric lymph nodes

Mesenteric nodes are increasingly visualised 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: normal mesenteric lymph nodes).

See also

• differential diagnosis of high attenuation lymphadenopathy
• differential diagnosis of low attenuation lymphadenopathy