Influence of Lesion Location on Detection of Lung Adenocarcinoma and Peripheral Squamous Cell Carcinoma

Abstract

Objective: In order to evaluate the influence of normal chest structures on radiologic detection of lung cancers, we examinedthe location of lesions detected by screening.
Methods: The study comprised 132 cases (135 lesions) of lung cancer. They were detected by miniature chest X-rayfilms taken at annual screenings between April 1991 and March 1999, and consisted of 98 adenocarcinomas and 37 peripheralsquamous cell carcinomas. They were separated into groups by stage, tumor size and histological type. The locationof the lesions was plotted on a schematic representation of the posteroanterior (PA) view, and their distribution patternswere compared among groups. The areas where early detection of lung cancer was difficult, and the areas where it waseasy, as well as the areas of intermediate difficulty were represented on the schematic PA view. The borders around difficultareas were drawn with reference to the distribution pattern of lesions more than 3cm in diameter, while thosearound easy areas were based on the distribution pattern of stage I lesions 2cm or less in diameter. The remaining areaswere designated as intermediate areas. The proportion of stage I lung cancers and other indices for three areas were estimatedin order to determine differences among them. The distribution pattern of adenocarcinomas was compared withthat of squamous cell carcinomas. Previously missed lung cancers among the 135 lesions were identified retrospectivelyfrom serial X-ray films. Potentially detectable nodules on previous chest X-ray films were classified as missed lung cancers.The distribution pattern of missed lung cancers is also shown.
Results: Most of the stage IA lung cancers were detected in the area where no large normal structures were superimposedon the nodules. Stage III and stage IV lung cancers showed a wider distribution, and the superimposition of normalstructures such as the heart, great vessels, pulmonary peripheral vessels, diaphragm, ribs surrounding the apex, clavicleand the tip of the first rib on a considerable number of nodules. There were statistically significant differences among thethree areas in the proportion of lesions 2cm or less in diameter. The proportions of stage I lung cancers within the difficult, intermediate, and easy areas were 34%, 57% and 75% respectively. The ratio of squamous cell carcinomas to adenocarcinomaswithin difficult areas was higher than that outside them. There was no statistically significant difference in theproportion of missed lung cancers among the three areas. “Areas where lung cancer lesions were often missed” and “areaswhere early lung cancers could hardly be detected” showed different appearances.
Conclusion: The superimposition of normal chest structures markedly influenced the stage and size of adenocarcinomaand peripheral squamous cell carcinoma as detected by chest X-ray. Gross classification of lung fields was made inrelation to the efficiency of radiologic detection of early lung cancer.