False alarm: Perifissural nodules on CT are likely benign

Despite growth that typically represents malignancy, pulmonary perifissural nodules (PFNs) are almost certainly benign and likely represent lymph nodes, according to a study published in the November issue of Radiology.

By recognizing PFNs—classified as fissure-attached homogenous solid nodules with a lentiform or triangular shape—the number of follow-up CT scans for screen-detected nodules can be reduced, according to Bartjan de Hoop, MD, PhD, of Rijnstate Hospital, Arnhem, the Netherlands, and colleagues.

“Our results show that…even rapidly growing PFNs are still very likely to be benign in a population without known cancer,” they wrote.

To assess the malignancy rate of PFNs in asymptomatic smokers, de Hoop and colleagues looked at data from the Dutch-Belgian Randomised Lung Cancer Multi-Slice Screening Trial. A total of 2,994 current or former heavy smokers, aged 50-74, underwent CT screening for lung cancer. CT was repeated after one and three years, with additional follow-up to 5.5 years conducted if necessary.

At baseline, 4,026 nodules were detected in 1,729 participants, according to the authors, with 19.7 percent of the nodules classified as PFNs. Mean size of PFNs was 4.4 mm, and mean volume was 43 mm3.

de Hoop and colleagues reported that none of the PFNs were found to be malignant during follow-up, even though more than 15 percent were found to have grown. A volume doubling time of less than 400 days—a common indicator of malignancy—was even demonstrated by 8.3 percent of the benign PFNs. One was resected and was found to be a lymph node.

“Based on evidence that includes the similarities to morphologic features on CT scans, growth rate, and the resected PFN, it is likely that the majority of PFNs indeed represent lymph nodes,” wrote the authors.

Since volume doubling times of less than 400 days are not entirely uncommon in this type of nodule, the authors suggested growth should not be a predictor of malignancy. By being more selective in determining the types of nodules that require follow-up CT scans, physicians can reduce patient anxiety, costs and radiation exposure inherent with follow-up studies.