Use of lateral position test and perfusion lung scan in predicting mediastinal metastases

The lateral position test (LPT) accurately measures differential ventilation of the lungs when the mediastinum is mobile. The quantitative perfusion lung scan (PLS) also correlates well with differential ventilation but is not dependent on mediastinal movement. If tumor metastasis to mediastinal lymph nodes (MLN) inhibits mediastinal movement, then the PLS may give discordant values for differential ventilation from that of the LPT. Before mediastinoscopy or thoracotomy or both, 14 cases of lung cancer were prospectively evaluated by comparing the relative ventilation of the involved lung as determined by LPT and PLS. Seven patients who had no evidence of MLN involvement had nearly equal ventilation by the two techniques (r = .94), and the absolute difference was always less than 12 percent (mean, 4.4 percent). Seven patients with MLN involvement had unequal ventilation as determined by LPT and PLS (r = 0.07), and between the two techniques there was a difference of at least 13 percent (mean, 27.3 percent). We conclude that the LPT used in combination with the PLS is an accurate, economical, and noninvasive technique for suggesting MLN metastasis and, thus, tentatively staging carcinoma of the lung. Those patients with discordant values should probably undergo mediastinoscopy before thoracotomy.