[A case of small-sized lung adenocarcinoma, 4 mm in diameter, detected by CT].

A 67-year-old woman presented to our hospital because of an abnormal shadow on her chest X-ray film. The film showed a well-circumscribed nodule, 15 mm in diameter, in her left lower lung field. Compared with her prior film of 1.5 years ago, the size of the nodule had not changed, suggesting the possibility of a benign lung tumor. Chest CT with 10 mm-thick collimation demonstrated another small round opacity near the nodule in the left lower lobe; this small opacity was not detectable on plain chest films. For further analysis of the small opacity, high resolution CT was carried out. High resolution CT with 1.5 mm collimation showed a 4 mm nodule with an ill-defined margin and relatively low internal density, and probable involvement of a peripheral branch of the pulmonary vein. These features suggested the possibility of malignant characteristics of this small opacity. The patient underwent thoracotomy and pathologic examination revealed that the large well-circumscribed nodule was a hamartoma and the small nodule was a papillary adenocarcinoma lesion. High resolution CT is prerequisite to diagnosing the characteristics of small pulmonary nodules.