Background and objectiveLung cancer is prevalent among patients with interstitial pneumonia (IP). HRCT findings mucinous adenocarcinoma in patients with IP have not been described. MethodsIn 112 consecutive patients with 120 surgically resected IP-associated lung cancers, 42 patients had pathologically proven invasive adenocarcinoma (IA). A total of 14 out of 42 patients (10 men, 4 women, mean age, 68.4years) had invasive mucinous adenocarcinoma. We reviewed the patients' medical records and HRCT scans. ResultsInvasive mucinous adenocarcinoma were most commonly associated with idiopathic IP (n=13) affecting the lower lobe adjacent to a fibrocystic changes. In 11 patients with invasive mucinous adenocarcinoma or other types of IA, the tumour was adjacent to a fibrocystic lesion. In invasive mucinous adenocarcinoma, malignant signs included lobulation (n=11), spiculation (n=9), vascular convergence (n=10) and pleural indentation (n=2). Characteristic findings of mucinous adenocarcinoma (i.e. vague margins (n=10), lobular-bounded margins (n=11), air bronchogram (n=11) and bubble-like low attenuation (n=8)) were more common in invasive mucinous adenocarcinoma than in other IA types. All invasive mucinous adenocarcinoma tumours (n=11) were closely associated with fibrosis. ConclusionMixed ground-glass opacity and consolidation adjacent to a fibrocystic lesion with malignant signs and characteristic features of mucinous adenocarcinoma indicate malignancy. This study describes the unique HRCT features of invasive mucinous adenocarcinoma in patients with interstitial pneumonia. Signs of malignancy like lobulation, spiculation, vascular convergence and pleural indentation are together with vague margins, lobular-bounded margins, air bronchogram and bubble-like low attenuation indicative for an invasive mucinous adenocarcinoma.