Abstract
Anomalous systemic arterial supply to the basal lung segments is relatively rare. A 39-year-old Japanese man was found to have high serum carbohydrate antigen 19-9 levels during a routine medical examination. He had no medical history and no symptoms. Although his serum carbohydrate antigen 19-9 level was high at 571 U/mL, his abdominal computed tomography (CT), gastrointestinal endoscopy, and abdominal ultrasonography findings were not abnormal. However, his chest CT scan revealed anomalous systemic arterial supply to the basal lung segment of the left lower lobe. He underwent partial resection of the left lung and stapling of the abnormal artery. After surgery, his serum carbohydrate antigen 19-9 level normalized. We consider that bronchiectasis of the basal left lung was involved in carbohydrate antigen 19-9 production and increase in its serum level. It is important to remain aware that various benign lung diseases can cause high serum carbohydrate antigen 19-9 levels.