Pulmonary focal fibrosis associated with microscopic arterio-venous fistula manifesting as focal ground-glass opacity on thin-section CT

We report a case of pulmonary focal fibrosis associated with microscopic arterio-venous fistula (AVF), which showed a focal area of GGO on thin-section CT. The patient was a 58-year-old woman with a GGO on thin-section CT which had increased in size over the period of 2 years. Slightly dilated vessels and thickened interlobular septa were also noted around the GGO. It was diagnosed preoperatively as adenocarcinoma in situ and a partial lung resection by video-assisted thoracic surgery (VATS) was performed. Pathological examination yielded a diagnosis of focal fibrosis associated with microscopic AVF.We speculate that the focal fibrosis was produced by a prolonged congestion due to the AVF and that the dilated vessels and thickening of interlobular septa on thin-section CT related to the AVF. Microscopic AVF may be one of the etiologies of focal fibrosis showing focal GGO on thins-section CT. Dilated vessels and thickened interlobular septa around the GGO might offer a clue to the diagnosis of this disease entity. In addition, it should be noted that focal fibrosis may increase in size.Recently, widespread use of computed tomography (CT) for lung cancer screening allows us to detect many faint peripheral pulmonary lesions. Radiologists have come to encounter focal ground-glass opacity (GGO) more frequently than before. Persistent focal GGO is most commonly seen in atypical adenomatous hyperplasia (AAH) and adenocarcinoma in situ that has recently been renamed from bronchioloalveolar carcinoma (BAC) in the revised classification [1]. Focal GGO may also be seen in various benign conditions, including focal fibrosis, focal inflammation, or hemorrhage [2,3]. Focal fibrosis accounts for approximately 15% of focal pure GGO [4]. However its etiology is still unknown.Herein, we present a case of focal fibrosis associated with microscopic arterio-venous fistula (AVF) manifesting as focal GGO mimicking adenocarcinoma in situ on chest CT, which suggested a pathogenesis of focal