What is the role of CT scans in the N classification of lung cancer staging?

Updated: Jan 28, 2019
  • Author: Omar Lababede, MD; Chief Editor: Eugene C Lin, MD  more...
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On CT scans, the short-axis diameter is the most reliable measurement of lymph node size. A short-axis diameter greater than 10 mm is considered abnormal. Nodal enlargement on imaging may indicate nodal metastatic involvement. However, normal-sized nodes may contain metastases, and nodal enlargement can be secondary to a variety of inflammatory causes.

The reported sensitivity and specificity of CT scanning in the detection of mediastinal nodes vary considerably, with ranges of 40-84% and 52-80%, respectively. This variability reflects interobserver variability and differences in the size criterion for abnormal lymph nodes, in patient populations, and in the diagnostic criterion standard. CT scanning is more specific in populations in Europe who have a low incidence of granulomatous disease, than it is in populations in the United States, who have a high incidence of histoplasmosis; rates are 80-90% and 50-70%, respectively.

The negative predictive value of CT scanning is about 85%; as a result, patients with normal mediastinal appearances undergo thoracotomy. Mediastinoscopy or thoracoscopy is required during biopsy of enlarged noncalcified lymph nodes before considering surgery.

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