A 0.4 x 0.4 mm nodule that constitutes the inferior lingual segment of the upper lobe of the lung may be due to chronic inflammation or a tumor in the lung and requires further examination and monitoring. With improved imaging techniques, chest CT can clearly visualize lung lesions. In general, a single tiny nodule in the lung may be a chronic inflammatory nodule, such as those caused by long-term smoking, exposure to dust or air pollution, or a nodule caused by a previous lung infection that has not resolved. In addition, a single microscopic lung nodule may be a primary or metastatic tumor, which is more dangerous than a benign inflammatory lesion. The presence of lung nodules requires active medical attention to clarify the nature of the nodule and to provide targeted treatment.