ORIGINAL ARTICLE Small Incidental Pulmonary Nodules How Useful is Short-Term Interval CT Follow-Up? Nitra Piyavisetpat, MD,* Suzanne L. Aquino, MD,† Peter F. Hahn, MD, PhD,† Elkan F. Halpern, PhD,† and James H. Thrall, MD† Purpose: To determine whether short-term (,6 month) follow-up imaging by thoracic CT is necessary to evaluate small (#4 mm) noncalcified nodules (NCN) in patients with no history of malignancy or acute lung disease. Materials and Methods: We reviewed serial thoracic helical CT scans between 1999–2000 obtained for the evaluation or follow-up imaging of small NCNs. CT scans were performed at 5-mm colli- mation. Patients were excluded if they had a history of neoplasm, infection, pulmonary fibrosis, or immune deficiency; also excluded if nodule(s) $5 mm at intake, or no follow-up scan within 1 year. NCNs were evaluated for number, size, configuration, and change in size over time. Exact 95% Confidence Intervals were used to estimate chances of nodule growth in 3-, 6-, and 12- month intervals. Results: A total of 1826 patients received a CT for NCNs. Four hundred fourteen patients met inclusion criteria (221 women, 193 men; mean age, 65.6 years). Eighty-five patients had a single NCN, 329 had multiple NCNs. One hundred seventy-three patients had additional $5 mm nodules. One hundred twenty-seven patients were lost to follow up within the 1-year period. Eight nodules cleared. None of the #4 mm NCNs grew on follow-up imaging within 12 months. Three patients developed lung cancer in other nodules $5 mm (5–10 mm). These nodules grew on follow up intervals of 3–13 months. One patient had a 19 mm benign hamartoma that grew in 9 months. The calculated chance that a NCN #4 mm will grow within 3, 6, and 12 months (95% CI) is #0.89%, 1.01%, and 1.28%, respectively. Conclusion: The chance of growth in #4 mm NCNs in a 3- to 6- month period in patients with no previous history of malignancy or immune disorder is small; therefore, short-term follow-up imaging (,12 month) for nodules #4 mm is not necessary. Key Words: pulmonary coin lesion, lung neoplasms, X-ray com- puted tomography, follow-up studies, diagnosis (J Thorac Imaging 2005;20:5–9) C T scanning is the most sensitive imaging modality for the detection of pulmonary nodules. 1 The advancement of CT technology detects not only more numerous nodules but also increasingly smaller ones. 1,2 CT imaging techniques have been described that may better characterize pulmonary nodules and help distinguish whether they are benign or malignant. These techniques include 1–3 mm thin collimation non- contrast imaging throughout the nodule identifying fat or calcification that suggests benignity 3 and thin section dynamic contrast enhanced imaging in which poorly enhancing nodules are considered benign. 4 However, these techniques have limited utility for nodules that are less than 5 mm in size. 3,4 Positron emission tomography (PET) with fluorodeoxyglucose (FDG) is highly sensitive and specific for differentiating malignant from benign nodules. 5,6 However, the sensitivity decreases with nodules less than 1 cm in size. 6 Relatively poor spatial resolution, partial volume effect, and a relative paucity of tumor cells within small lesions all serve to limit the capability of FDG-PET to detect and therefore to characterize small lesions. 6,7 For nodules #4 mm in size, follow-up CT scan imaging has become the management of choice. 8 Although a minimum 2-year follow-up is widely accepted for follow-up imaging to ensure a benign etiology, the interval for early follow-up imaging, that is, whether it should be a 3-, 6-, or 12-month period has been controversial. The aim of our study is to determine the value of short-term (,6 month) follow-up CT to evaluate incidental small (#4 mm) noncalcified nodules found on non-screening thoracic CT studies of patients who have no previous history of malignancy or acute lung disease. MATERIALS AND METHODS Patient Selection and Population This study was approved by our institution’s Human Research Committee. We searched our department’s comput- erized clinical database for all thoracic CT scans performed for the stated purpose of evaluating pulmonary nodule(s) from January 1, 1999, through December 31, 2000. An additional search was performed for each patient to capture the initial CT examination in which the nodule(s) were initially and From the *Department of Radiology, King Chulalongkorn Memorial Hospital, Chulalongkorn University, Bangkok, Thailand; and †Department of Radiology, Massachusetts General Hospital and Harvard Medical School Boston, MA. The two lead authors have each made substantial contributions to the design and analysis of this work and the writing of the manuscript. Each of the lead authors is equally responsible for the integrity of all data in the manuscript and for the correctness of the analysis and conclusions supported by those data. Reprints: Suzanne L. Aquino, Massachusetts General Hospital, Department of Radiology, FND 202, 55 Fruit Street, Boston, MA (e-mail: saquino@ partners.org). Copyright Ó 2005 by Lippincott Williams & Wilkins J Thorac Imaging  Volume 20, Number 1, February 2005 5