[Evaluation of the "N" factor in nonsmall cell lung cancer. Correlation between computerized tomography and...

To evaluate the role of CT in identifying other morphological signs of metastatic lymph node involvement from non small cell bronchogenic carcinoma. This is done to improve N staging, a critical step in this disease. In fact, since diameter is the only criterion used to distinguish normal form abnormal lymph nodes, medistinal CT only has 80% diagnostic accuracy.

137 patients with known or suspected lung cancer were examined with Helical CT during early and late arterial phases (2 min delay, 3 mm thickness, 5 mm interslice gap) to depict node characteristics. Mediastinal lymph nodes, located according to the American Thoracic Society mapping, were considered normal when they were not visible or, if visible, less than 1 cm in diameter and of homogeneous density; lymph nodes over 1 cm in diameter and homogeneous density were considered reactive. A lymph node was considered metastatic when, independent of size, the following signs were found: central hypodensity; hyperdense thin/thick rim, with nodules within; hyperdense strands or diffuse hyperdensity in perinodal adipose tissue. The tumor site was also considered.

Seventy patients were excluded because they were inoperable. Sixty-five of the remaining 67 patients were operated on, 1 underwent mediastinoscopy and another one mediastinoscopy followed by surgery. Based on the above CT signs, 46 patients were staged as N0, 61 as N1 and 15 as N2. In 44/46 N0 patients there was agreement between anatomical and pathologic findings; 3 of the 44 patients had lymph nodes over 1 cm in diameter and with homogeneous density. Micrometastases to mediastinal lymph nodes (N2) were found at histology in 2/46 patients (CT false negatives). In the 6 N1 and the 15 N2 patients there was complete agreement between anatomical and pathologic findings; in particular, 9 N2 patients had lymph nodes less than 1 cm in diameter with signs of metastasis and 4 had lymph nodes over 1 cm in diameter with signs of metastasis and 2 had lymph nodes either over or less than 1 cm. In all N2 patients the tumor histotype and the mediastinal location were also considered relative to the lesion site.

A closer correlation was found with node morphology and density than with size. Indeed, CT sensitivity, specificity and diagnostic accuracy were 97, 100 and 97%, respectively, for the former versus 52, 93 and 77% for the latter. Adenocarcinoma was the predominant histotype (70.5%) in N2 patients. Metastases to node region 4 were predominant in right upper lobe carcinomas while node region 5 was predominant in left upper lobe lesions.

Other criteria can be associated with size to improve CT diagnostic accuracy in N staging. Technique optimization plays a major role particularly in the late, thin slice, examination phase.