Mediastinal lymph node enlargement can occur from a wide range of pathologies, either by its own or in association with other lung pathology. Historically, a size cut-off of 10 mm short-axis diameter was used.
Although mediastinal lymphadenopathy is used interchangeably - by some - with "mediastinal lymph node enlargement", they are not synonymous entities, and it is important to be cognizant of this. Many enlarged mediastinal nodes will be pathological, however not all, and conversely, some mediastinal lymphadenopathy will be found in non-enlarged nodes.
The diagnostic waters are muddied further as some pathologies produce nodal enlargement via reactive change, and not because the pathology is actually infiltrating the node itself, eg. bacterial pneumonia is associated with reactive enlargement of the mediastinal nodes, but the organism is not generally infecting the node itself. In tuberculosis, however, the mycobacterium is actually infiltrating and infecting the lymph node.
Some radiologists make a point of differentiating between reactive nodal enlargement and pathological nodal enlargement, reserving lymphadenopathy for the latter etiologies only.
The spectrum of conditions that can result in mediastinal lymphadenopathy is extremely diverse and includes:
- sarcoidosis (see: pulmonary manifestations of sarcoidosis)
- primary lung cancer
- metastatic malignancies to the mediastinum from other sites
- mediastinal lymphoma
- Kaposi sarcoma
- certain non-lymphomatous pulmonary lymphoid disorders
- infective etiology
- occupational lung disease
- mediastinal lymphadenopathy in interstitial lung disease
- pulmonary manifestation of rheumatoid arthritis (rare) 5
- scleroderma / CREST syndrome 10,11
- related to congestive cardiac failure 7,8
- thoracic amyloidosis 12
- medication-related, e.g. phenytoin, methotrexate 6
If incidentally detected, the ACR committee white paper in 2018 suggests clinical consultation, further workup with CT-PET +/- follow up CT chest in 3-6 months if short-axis diameter over 15 mm and if there is no explicable disease 9. Interval size increase on follow up dictates the need for biopsy.
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