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; this includes 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 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 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)
- follicular hyperplasia
- paracortical hyperplasia
- sinus histiocytosis
- drug induced, e.g. cyclosporin, phenytoin, methotrexate
- lipid storage diseases
- IgG4-related sclerosing disease 7
The upper limit in size of a normal node varies with location, and of course the size cutoff used depends on the desired sensitivity and specificity.
Cervical lymph nodes
- most nodes: 10 mm in short-axis
- sub-mental and 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 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.
- 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 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 3 mm 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 5 mm is considered normal 6 (see: normal mesenteric lymph nodes).
- 1. Steinkamp HJ, Cornehl M, Hosten N et-al. Cervical lymphadenopathy: ratio of long- to short-axis diameter as a predictor of malignancy. Br J Radiol. 1995;68 (807): 266-70. doi:10.1259/0007-1285-68-807-266 - Pubmed citation
- 2. Harnsberger HR. Head and neck imaging. Year Book Medical Pub. (1990) ISBN:0815142854. Read it at Google Books - Find it at Amazon
- 3. Kiyono K, Sone S, Sakai F et-al. The number and size of normal mediastinal lymph nodes: a postmortem study. AJR Am J Roentgenol. 1988;150 (4): 771-6. AJR Am J Roentgenol (abstract) - Pubmed citation
- 4. Libshitz HI, Mckenna RJ. Mediastinal lymph node size in lung cancer. AJR Am J Roentgenol. 1984;143 (4): 715-8. AJR Am J Roentgenol (abstract) - Pubmed citation
- 5. Kramer Henk and Harry J.M. Groen. “Current Concepts in the Mediastinal Lymph Node Staging of Nonsmall Cell Lung Cancer.” Annals of Surgery 238, no. 2 (August 2003): 180–188. doi:10.1097/01.SLA.0000081086.37779.1a.
- 6. Lucey BC, Stuhlfaut JW, Soto JA. Mesenteric lymph nodes: detection and significance on MDCT. AJR Am J Roentgenol. 2005;184 (1): 41-4. AJR Am J Roentgenol (full text) - Pubmed citation
- 7. Horger M, Lamprecht HG, Bares R et-al. Systemic IgG4-related sclerosing disease: spectrum of imaging findings and differential diagnosis. AJR Am J Roentgenol. 2012;199 (3): W276-82. doi:10.2214/AJR.11.8321 - Pubmed citation