CT insensitive to mediastinal lymph node metastasis in bronchogenic carcinoma [Classics Series]

1. Computed tomography (CT) of the chest is limited in the ability to detect the presence of mediastinal lymph node involvement in patients with bronchogenic carcinoma.

2. This study helped popularize the use of 1 cm (measured in short axis) as the criteria for abnormally enlarged lymph nodes. The rate of positive mediastinal nodal involvement was increased from 13% to 62% for nodes measuring < 1 cm and ≥2 – 2.9 cm, respectively.

Original Date of Publication: February 1992

This study summary is an excerpt from the book 2 Minute Medicine’s The Classics in Medicine: Summaries of the Landmark Trials, 2e (The Classics Series).

Study Rundown: Lung cancer is the leading cause of cancer-related death worldwide with over 1.2 million deaths in 2012. Accurate evaluation of mediastinal lymphadenopathy is vital in the staging of a patient with lung cancer to provide prognostic information for patients as well as to direct treatment. CT scans of the chest provide visualization of mediastinal lymph nodes not typically accessible by mediastinoscopy or thoracotomy; however, there have been conflicting reports on the sensitivity and specificity of CT chest to identify lymph node metastases in the mediastinum. The purpose of this landmark prospective trial was to determine the accuracy of CT chest to identify mediastinal lymph node metastases in patients with lung cancer.

The trial prospectively followed over 140 patients with bronchogenic carcinoma that underwent CT chest evaluation with surgical staging correlation. CT evidence of mediastinal metastases was defined as any lymph nodes greater than 1 cm in short axis. At the conclusion of the trial, the sensitivity and specificity of CT examinations for mediastinal metastases were found to be 64% and 62%, respectively. Additionally, the sensitivity for individual nodal stations within the mediastinum was lower at 44%. In particular, there were high rates of false-positive lymph nodes within the right paratracheal group and the aorticopulmonary window. Although larger nodes were associated with increased likelihood of mediastinal metastases, over one-third of all lymph nodes over 2 cm were found to be benign and hyperplastic. The results of this study demonstrated the relative insensitivity of CT to identify mediastinal metastases in patients with lung cancer due to confounding conditions such as atelectasis or pneumonitis leading to hyperplastic and reactive lymph node changes. This landmark trial provides strong evidence for the use of CT chest scans in conjunction with mediastinoscopy or thoracotomy to adequately provide staging information for patients with bronchogenic carcinoma.

Please click to read study in Radiology

In-Depth [prospective cohort]: This was a prospective study of 143 patients with pathologically-confirmed, non-small cell lung cancer from a single institution in the United States. Each patient underwent CT examination of the chest followed by pathological staging of the mediastinum either through mediastinoscopy or thoracotomy. Mediastinal lymph nodes were measured in the short axis and considered abnormal if they measured greater than 1 cm in diameter. The primary outcome of interest was the patient-by-patient accuracy rate of the CT findings correlated with the pathological results from surgical staging. Secondary outcomes included the accuracy of each specific mediastinal nodal station, as defined by the American Thoracic Society mapping scheme, to its pathological correlate. At the conclusion of the trial, the CT sensitivity for mediastinal metastases for each individual patient was 64% with a specificity of 62%. The sensitivity and specificity for all nodal stations are 44% and 85%, respectively. In the subgroup analysis of each individual lymph node station, groups 4R, 5, and 10R in the right paratracheal and aorticopulmonary window demonstrated the highest false-positive rate. Increase in lymph node size on CT was associated with an increased likelihood of metastatic disease; however, over 33% of the lymph nodes between 2 and 4 cm in size in this cohort demonstrated a benign hyperplastic reaction rather than metastasis. For lymph nodes < 1 cm in short axis diameter, the prevalence of metastases was 13%; for nodes ≥1 – 1.9 cm, the prevalence of metastases was 25%; for nodes ≥2.0 – 2.9 cm, the prevalence of metastases was 62%.

McLoud TC, Bourgouin PM, Greenberg RW, Kosiuk JP, Templeton PA, Shepard JA, et al. Bronchogenic carcinoma: analysis of staging in the mediastinum with CT by correlative lymph node mapping and sampling. Radiology. 1992 Feb 1;182(2):319–23.

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