Search for a primary lung neoplasm in patients with brain metastasis: is the chest radiograph sufficient?

We assessed whether chest CT provided an advantage over chest radiography when diagnosing a primary lung neoplasm in a selected group of patients. From a retrospective evaluation of 925 patients who had a discharge diagnosis of brain metastasis, we identified 32 patients who presented without a known primary tumor site and who were investigated subsequently with both chest radiography and CT. Reports of chest radiographs were classified as showing a primary lung neoplasm (positive), as abnormal but nonspecific, or as negative. Patients were categorized as having negative chest radiograph, negative CT; positive chest radiograph, positive CT; nonspecific chest radiograph, positive CT; or negative chest radiograph, positive CT. Radiographic technique and clinical and lesion characteristics were compared among these categories. We found negative chest radiograph and negative CT in one patient who ultimately proved to have breast cancer. The remaining 31 patients (97%) had primary lung carcinoma. In 19 (59%) of the 32 patients, chest radiographs and CT were positive. Twelve patients (38%) had a nonspecific or negative chest radiograph and positive CT. In the 31 patients with lung carcinoma, the mean diameter of lesions in patients with positive chest radiographs was 4.2 cm, compared with 2.5 cm in patients with normal or nonspecific radiographs (p < .01). Lung cancer is by far the most common cause of a de novo presentation with brain metastasis. Chest CT is valuable to supplement chest radiography in patients with metastatic brain disease in whom a primary lesion is sought. Lesion size appears to be the most important determinant of detectability of a primary tumor on chest radiographs.