The detection of pulmonary metastases by helical CT: A clinicopathologic study in dogs

Purpose: We sought to determine the accuracy of helical CT in the detection of pulmonary metastases. Method: Four anesthetized dogs with metastatic osteosarcoma underwent helical CT with a collimation of 5 mm, a pitch of 2, and a reconstruction interval of 5 mm. All macroscopically evident metastases were recorded at autopsy. CT images were independently reviewed by 10 radiologists and compared with pathologic results. Alternate slices in the dog with the most metastases were microscopically examined in their entirety. Results: Pathologic examination of the lungs revealed 132 macroscopically evident pulmonary metastases, of which 74 (56%) were detected by at least one reader. Forty-four of the 99 (44%) metastases of ≤5 mm in diameter were detected by at least one reader compared with 30 of 33 (91%) metastases of >5 mm in diameter (p < 0.0001). The 10 readers reported a total of 107 false positives. Complete microscopy of alternate slices in the dog with the most metastases (n = 68) revealed an additional 38 micrometastases of ≤3 mm in diameter. None of the 32 micrometastases of ≤ 1 mm were detected by CT. Conclusion: Helical CT has some limitations in the detection of pulmonary metastases.