Small incidental pulmonary nodules - How useful is short-term interval CT follow-up?

Purpose: To determine whether short-term (<6 month) follow-up imaging by thoracic CT is necessary to evaluate small (less than or equal to4 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-min collimation. Patients were excluded if they had a history of neoplasm, infection, pulmonary fibrosis, or immune deficiency; also excluded if nodule(s) greater than or equal to5 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 greater than or equal to5 mm nodules. One hundred twenty-seven patients were lost to follow up within the 1-year period. Eight nodules cleared. None of the less than or equal to4 mm NCNs grew on follow-up imaging within 12 months. Three patients developed lung cancer in other nodules greater than or equal to5 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 less than or equal to4 mm will grow within 3, 6, and 12 months (95% CI) is less than or equal to0.89%, 1.01%, and 1.28%, respectively. Conclusion: The chance of growth in less than or equal to4 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-Lip imaging (<12 month) for nodules less than or equal to4 mm is not necessary.