Diagnosis of pulmonary metastases with helical CT: the effect of imaging techniques

Survival in patients after surgical resection of pulmonary metastases correlates with the complete resection of all metastatic deposits. The purpose of this study was to evaluate the additional value of helical CT to see whether the slice thickness and the reading environment was a factor determining the accuracy of helical scans.

Between 2004 and 2007, 93 patients (62 men, 31 women) underwent complete resection of pulmonary metastases by open thoracotomy. A total of 125 thoracotomies were performed with manual palpation of the involved lung. We retrospectively examined the helical CT findings obtained using a 5-mm slice thickness in a routine preoperative analysis, and within this study a second reading was performed independently, using 3-mm slice thickness image sets. The CT images were evaluated in a consensus between two radiologists.

Computed tomography scanning was performed a median of 12 days before thoracotomy (range 1-121 days). Analysis of helical CT in 5-mm slice thickness detected metastases with a sensitivity of 83.7 % whereas a 3-mm slice thickness had a sensitivity of 88.8 %. There were statistically significantly more lesions using helical CT and a 3-mm slice thickness technique than with the 5-mm slice thickness technique, compared to the surgical results ( P = 0.002). This was also found with regard to nodules which were finally histologically confirmed as lung metastases ( P = 0.014).

We conclude that a reduced slice thickness may have an important positive impact on the treatment and outcome of patients with pulmonary metastases. The use of 3-mm slice thickness helical CT may raise the sensitivity for pulmonary metastases detection compared to 5-mm images, but the rate of false positive results may also increase.