Most subpleural nodules are benign nodules and are usually not dangerous. Subpleural nodules that are malignant are more dangerous because they are prone to invasion and metastasis. The pleura is divided into the dirty pleura and the mural pleura. The dirty pleura is a thin layer of structure on the outside of the lung tissue, and usually the two layers are fitted together and lubricated by only a small amount of fluid. Subpleural nodules generally refer to nodules under the dirty pleura, but it is not possible to differentiate between the dirty pleura and the mural pleura on CT images, so a subpleural nodule is a nodule on the side of the lung tissue near the pleura. Most subpleural nodules are benign, and benign nodules are not dangerous and can be made smaller or even disappear with treatment. However, if the subpleural nodule is malignant, it is more dangerous because it is close to the pleura, so it is easy to spread and metastasize through the pleura.