Mammary nodules as incidental findings on chest computed tomography: a retrospective analysis on their frequency and predictive value

Purpose: To evaluate the frequency of mammary nodules as incidental findings on chest CT scans and to determine a correlation between semiological features and mammographic and histopathological outcomes. Methods: A total of 42,864 chest CT scans performed on patients with breast-unrelated working diagnoses by the Radiology Department at AOU Maggiore della Carità, between 1st January 2016 and 30th April 2022, were analysed. Sixty-eight patients (3 males and 65 females) with mammary nodule CT detection were selected and subjected to mammography, mammary ultrasound and, eventually, biopsy. Results: Thirty-five of the 68 patients received a histopathological confirmation of malignancy. According to Pearson's Chi-square test, the CT features most likely associated with BI-RADS 5 following mammography were post-contrast enhancement (p = 0.001), margin irregularity (p = 0.0001), nipple retraction (p = 0.001), skin thickening (p = 0.024), and the presence of structurally atypical lymph nodes suspicious for metastatic involvement (p = 0.0001). The CT features predictive of a biopsy positive for malignancy were post-contrast enhancement (p = 0.0001), margin irregularity (p = 0.0001), and the presence of suspicious lymph nodes (p = 0.011). Finally, 63.4% of patients with a working diagnosis related to cancer were diagnosed with breast cancer. Conclusion: Chest CT incidental findings of mammary nodules had a 0.21% incidence rate. The accurate description of some CT scan features, such as post-contrast enhancement, margin irregularity, nipple retraction, skin thickening and the presence of structurally atypical lymph nodes, may help to establish a radiological suspicion of malignancy, especially if these characteristics are supported by a working diagnosis of cancer.