Certain lung nodules may form small protrusions at their edges, which is known as burr sign. Burr sign is a common manifestation of lung cancer CT, but it does not necessarily mean that burr nodules are lung cancer. In lung cancer, burrs are mostly formed in the form of short spines with high density. The reason for their formation is that the tumor has the phenomenon of vascular proliferation, and capillaries and lymphatic vessels are generated at the edge of the tumor and supply blood supply and nutrition to the tumor. Therefore, when burrs are formed around lung nodules, the degree of benignity and malignancy should be judged in combination with other signs such as follicular disease, lobulation, pleural depression and nodule enhancement, etc. If necessary, pathological biopsy of lung tissue should be performed to further clarify the diagnosis.