Volume and mass doubling times of persistent pulmonary subsolid nodules detected in patients without known malignancy

To evaluate volume doubling time (VDT) and mass doubling time (MDT) of persistent pulmonary subsolid nodules (SSNs) followed-up with low-dose (LD) computed tomography (CT) in patients without a history of malignancy. This retrospective institutional review board-approved study, with waiver of patient informed consent, included 97 SSNs in 97 patients (45 men, 52 women; median age, 58 years; range, 37-87 years) in whom at least two LD CT scans were obtained, with 3-month or longer follow-up interval and median follow-up of 633 days. SSNs were categorized into pure ground-glass nodules (GGNs) (group A), part-solid GGNs with solid components of 5 mm or smaller (group B), and part-solid GGNs with solid components larger than 5 mm (group C). Three-dimensional manual segmentation for all SSNs was performed on initial and latest follow-up LD CT scans; subsequently, VDTs and MDTs were calculated and were compared among groups by using Kruskal-Wallis test, followed by the Dunn procedure with Bonferroni correction for volume-growing SSNs and mass-growing SSNs. Volume growth was thus: 12 of 63 SSNs (19%), group A; nine of 23 SSNs (39%), group B; and eight of 11 SSNs (73%), group C. Median VDT was thus: 1832.3 days (range, 1230.7-4537.3 days), group A; 1228.5 days (range, 934.7-4617.7 days), group B; and 759.0 days (range, 376.4-941.5 days), group C. Mass growth was thus: 17 of 63 SSNs (27%), group A; 11 of 23 SSNs (48%), group B; and nine of 11 SSNs (82%), group C. Median MDT was 1556.1 days (range, 642.5-3564.5 days) for group A, 1199.9 days (range, 838.6-2578.7 days) for group B, and 627.7 days (range, 340.0-921.2 days) for group C. Median VDTs and MDTs of groups A and B were significantly longer than those of group C (P < .01). Pure GGNs and part-solid GGNs with solid components of 5 mm or smaller show significantly longer VDTs and MDTs than do part-solid GGNs with solid components larger than 5 mm. Online supplemental material is available for this article.