Left kidney low-density foci and high-density foci are both CT examination description of lesions in the left kidney, the difference between the two lies in the density of the lesion, the type of lesion, and the treatment program is different. 1. Lesion density: low-density foci indicate that the overall density of the lesion is lower than the renal parenchyma, while high-density foci have a higher overall density than the renal parenchyma. 2. Types of lesions: common types of low-density foci include cysts, lipomas, malignant tumors, and some renal cancers; high-density foci mainly include complex cysts, calcifications, stones, hemorrhages, and tumors with hemorrhages. 3. Treatment plan: low-density lesions need to further enhance the examination, benign lesions can continue to review, suspected malignant lesions, if necessary, combined with clinical surgery; high-density foci, most of which are benign, mainly to review, suspected that the tumor with hemorrhage can be considered for surgery. Abnormal density in the kidney, accompanied by obvious low back pain and hematuria and other symptoms, need to consult a doctor in time for examination and standardized treatment under the guidance of clinicians.