Appearance of pulmonary metastases on high-resolution CT scans: comparison with histopathologic findings from autopsy specimens.

OBJECTIVE: The purpose of this study was to compare the appearance of pulmonary metastases on high-resolution CT scans with the histopathologic findings in lung specimens obtained at autopsy. The factors considered were the appearance of the margins of pulmonary metastases, the location of relatively small nodules in relation to the secondary pulmonary lobules, and the detectability of lymphangitic spread of tumors and intravascular tumor emboli on high-resolution CT scans.
MATERIALS AND METHODS: We studied 14 lungs obtained at autopsy that contained metastatic lesions. We used both microscopy and high-resolution CT to evaluate 87 metastatic nodules 5-20 mm in diameter for the appearance of their margins and to determine the location of 43 nodules that were less than 5 mm in diameter relative to the secondary pulmonary lobules. The detection of histologically confirmed intravascular tumor emboli and lymphangitic spread by high-resolution CT also was evaluated.
RESULTS: On high-resolution CT scans, 38% of the nodules had well-defined, smooth margins, 16% had well-defined, irregular margins, 16% had poorly defined, smooth margins, and 30% had poorly defined, irregular margins. The well-defined, smooth margins on high-resolution CT scans corresponded histologically to an expanding type and to an alveolar space-filling type; the poorly defined margins, to an alveolar cell type; and the irregular margins, to an interstitial proliferative type. Some correlation was found between the histologic type of primary tumor and the CT appearance of the lesion's margins. As for small nodules, 12% were connected with the central bronchovascular bundle, 28% were on the perilobular structures, and 60% were apparently not in contact with these structures. Only two of the 11 lungs with histopathologically confirmed lymphangitic tumor spread and none of the tumor emboli were detected on high-resolution CT scans.
CONCLUSION: The characteristics of the margins of metastatic pulmonary nodules noted on histopathologic examination correlated well with their high-resolution CT findings. Microscopic intravascular tumor emboli and lymphangitic tumor spread were difficult to detect on high-resolution CT scans, indicating a limitation of high-resolution CT in the diagnosis of pulmonary metastatic disease.