Rectal cancer: Incidence of pulmonary metastases on thoracic CT and correlation with T staging

Purpose: The aim of the study was to evaluate the incidence of pulmonary metastases detected on thoracic computed tomography in patients with rectal cancer and assess the association between the incidence of pulmonary metastases and the stage of the rectal tumor. Materials and Methods: Fifty-six consecutive patients who were diagnosed with rectal cancer over a 22-month period were included in the study. These patients had local tumor staging with a pelvic magnetic resonance imaging and staging computed tomographic scan of the chest and upper abdomen immediately after the magnetic resonance imaging. Two radiologists retrospectively reviewed all the thoracic imaging performed on these patients for the presence of metastases. The presence of a parenchymal lung nodule (greater than or equal to 1 cm if single and 0.5 cm if multiple) with a soft tissue component without calcification on lung and mediastinal window settings was considered positive for the presence of metastasis. All other patients were considered as not having any lung metastases. Results: Of the 56 patients, 10 (17.9%) had evidence of pulmonary metastases on computed tomography. Of the 56 patients, there were 3 patients with stage T1, 24 with T2, 26 with T3, and 3 with stage T4 tumors. Of these 10 patients, 1 had a stage T2 tumor, 7 had T3, and 2 had stage T4 tumors. Statistical analysis using exact logistic regression showed the odds of getting lung metastases is an increasing function of tumor grade. Conclusions: There is a high incidence of lung metastases in patients with rectal cancer, and thoracic computed tomographic scanning should be performed as part of a staging protocol in all patients before any form of treatment is planned. There is a higher incidence of lung metastases with higher T stage.