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Year : 2022  |  Volume : 5  |  Issue : 1  |  Page : 59-66

Significance of too-small-to-characterize (TSTC) pulmonary nodules in known extrapulmonary solid tumors: A retrospective observational study

1 Department of Radiodiagnosis and Imaging, Tata Memorial Hospital, Homi Bhabha National Institute, Mumbai - 400 012, Maharashtra, India
2 Department of Medical Oncology, Tata Memorial Hospital, Homi Bhabha National Institute, Mumbai - 400 012, Maharashtra, India
3 Department of Pathology, Tata Memorial Hospital, Homi Bhabha National Institute, Mumbai - 400 012, Maharashtra, India

Correspondence Address:
Abhishek Mahajan
M.D., Fellowship In Cancer Imaging, MRes (KCL, London), FRCR (UK), Consultant Radiologist, The Clatterbridge Cancer Centre NHS Foundation Trust, Pembroke Place, Liverpool, L7 8YA
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/crst.crst_228_21

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Background: Increased use of chest computed tomography (CT) scanning and greater awareness among general radiologists has led to a rise in lung nodule identification. Nodules less than 1 cm in diameter are considered small, and the morphology of such nodules is difficult to characterize. Objectives: The aim of our study was to determine the significance of pulmonary nodules that are too-small-to-characterize on CT scan in patients with extrapulmonary solid tumors and to determine the characteristics that help in distinguishing malignant from benign pulmonary nodules. Materials and Methods: We conducted a retrospective observational study in the Department of Radiodiagnosis of the Tata Memorial Hospital, Mumbai, India, and included patients with non-pulmonary solid malignancies who had obtained baseline CT/positron emission tomography (PET) scans between January 2010 and December 2014. Demographic information, site of the primary tumor, and histological diagnosis were recorded. Baseline and follow-up CT images were read by two radiologists. The significance of associated risk factors was analyzed using Pearson's Chi-square test. A multivariable logistic regression model was used. Results: Our study included 200 patients and 334 nodules, of which 148 (44.3%) nodules were found to be benign and 127 (38%) were malignant. The remaining 59 (17.7%) nodules in 32 patients were indeterminate. Most nodules located at a distance of less than 10 mm from the pleura were benign, whereas more than 2/3rd of the nodules more than 10 mm away from the pleura were malignant (n = 60/94, 63.8% P = 0.0001). The mean size of the 148 benign nodules (5.3 mm) was smaller than that of the 127 malignant nodules (9.2 mm). Nearly 93% of malignant nodules were solid (P = 0.0001). About 83% of malignant nodules were round, while 7 of 10 linear-shaped nodules were either benign or indeterminate (P = 0.006). Among the nodules associated with poorly differentiated primary neoplasms, 63.6% were malignant, 25% were benign, and 11.4% were indeterminate (P = 0.005). Conclusions: Too-small-to-characterize pulmonary nodules detected on CT are a common clinical problem and are more likely to be benign or indeterminate even in patients with known extrapulmonary neoplasms. Using nodule size, distance from the pleura, and morphological pointers, radiologists can help clinicians decide whether there is a need for biopsy or a short-interval follow-up. We have proposed a Pulmonary Metastases Cancer Imaging and Reporting Data System (PM-CI-RADS).

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