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

To determine whether short-term (<6 month) follow-up imaging by thoracic CT is necessary to evaluate small (< or =4 mm) noncalcified nodules (NCN) in patients with no history of malignancy or acute lung disease.

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 collimation. Patients were excluded if they had a history of neoplasm, infection, pulmonary fibrosis, or immune deficiency; also excluded if nodule(s) > or =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.

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 > or =5 mm nodules. One hundred twenty-seven patients were lost to follow up within the 1-year period. Eight nodules cleared. None of the < or =4 mm NCNs grew on follow-up imaging within 12 months. Three patients developed lung cancer in other nodules > or =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 < or =4 mm will grow within 3, 6, and 12 months (95% CI) is < or =0.89%, 1.01%, and 1.28%, respectively.

The chance of growth in < or =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 < or =4 mm is not necessary.