Skip metastasis and hidden N2 disease in lung cancer: how successful is mediastinal dissection?

Out of 703 consecutive patients who underwent lung cancer surgery from 1986 to 1994, 562 were studied with an emphasis on lymph node metastasis. Skip metastasis was defined as metastasis to the upper mediastinum without involvement of the carinal, hilar, or intrapulmonary nodes. Twenty-nine patients had skip metastasis, accounting for 17% of the 175 with N2 disease. Except for one patient with a huge tumor, there was no lower-lobe disease. Patients with N2 disease nodes were categorized into the following groups: (1) 32 with false negative N2 that could not be detected macroscopically on the specimen; (2) 64 with true positive N2, detected macroscopically on the specimen; and (3) 79 patients with obvious N2. Positive carinal nodes were found in 12 of 70 N2 patients who underwent upper lobectomy, and in 60 of the (105) remaining N2 patients who had other types of surgery. We conclude that upper mediastinal dissection should be carried out in patients with adenocarcinoma in the upper lobe, because skip and undetectable metastasis are not rare. However, dissection of the carinal nodes with upper-lobe tumors, and of the upper mediastinum with lower-lobe tumors, can be omitted when the gross and frozen section findings are negative in the upper mediastinum and both the carinal and hilar nodes.