Which mediastinal lymph nodes should be examined during operation for diagnosing N0 or N1 disease in bronchogenic carcinoma?

We retrospectively reviewed the patterns of mediastinal metastasis in relation to the location of the, primary lung cancer in 55 p-N2 patients who underwent resection of the primary lesion and standard mediastinal lymphadenectomy. All (17/17, 100%) were diagnosed as N2 disease based on investigation of nodes 2, 3 and 4 in right upper lobe cancers, 91% (20/22)by examination of nodes 3,7 and 8 in right lower lobe cancers, 91% (10/11) by examination of nodes 4, 5 and 7 in left upper lobe cancers and 100% (5/5) by examination of nodes 4, 7, and 8 in left lower lobe cancers. As a prospective study, these 3 levels were investigated pathologically during operation by selecting one lymph node, which was most strongly suspected to be metastatic, from each level in 61 patients. The N status diagnosed by the frozen sections (f-N) was compared with the N status diagnosed by the permanent sections (p- N) obtained after the standard mediastinal dissection. The f-N was consistent with the p-N in 39 patients with N0 or N1 and in 16 patients with N2 or more. The f-N resulted in under-diagnosis in six patients, four of whom had a micrometastasis at one of the 3 levels. We concluded that the pathological examination of the 3 levels for each lobe during operation is useful to diagnose mediastinal N status and that limited mediastinal lymphadenectomy consisting of the 3 levels can be indicated for patients with negative f-N.