CT Findings of Atypical Adenomatous Hyperplasia in the Lung

Objective: The aim of this study was to analyze the computed tomographic (CT) findings of atypical adenomatous hyperplasia (AAH) in the lung. Materials and Methods: The CT findings of AAHs in eight patients were retrospectively reviewed. The CT findings of each AAH lesion were evaluated for multiplicity, location, shape, size and internal density of the lesion, the interface between the normal lung and the lesion, the internal features within the lesion and any change of the lesion on the follow-up CT scans (range: 33 to 540 days; average: 145.3 days). Results: The eight patients consisted of three men and five women (age range: 43-71 years). Six of eight patients were asymptomatic. Four of them (50%) had synchronous malignancies in the lung: adenocarcinoma of the lung (n=3), and metastatic squamous cell carcinoma from the uterus (n=1). We could identify and evaluate eleven AAH nodules in seven patients on the CT scans. Three patients had multiple AAHs. Seven of the 11 lesions (64%) were located in the upper lobe. All the AAHs showed a well-defined oval or round shape and pure ground-glass opacity (GGO) without any solid component (size: $3.9{\times}3mm$ to $19{\times}17mm$ internal attenuation: -467 to -785 HU). All the AAHs showed no change of their size and internal density on the follow-up CT scans. Conclusion: Atypical adenomatous hyperplasia is often associated with malignancy. This tumor is shown on CT as persistent well-defined oval or round nodular GGOs without solid components, and it does not change on the follow-up CT.