Low-density foci in the left kidney suggest the presence of lesions, which may compress the kidney, metastasize to other parts of the body and cause secondary lesions, and whether they are harmful or not mainly depends on the pathological type of the lesion. 1. If the low-density foci are benign diseases with some harm, but relatively mild, such as renal cysts, misshapen tumors or local ischemia, etc., the early stage is usually asymptomatic, and generally does not affect the health of the organism, and it is feasible to observe the conservative treatment, but also feasible to directly remove the surgical treatment, with a better prognosis. However, regular review is necessary to avoid recurrence. 2. If the low-density foci are malignant tumors, they are more harmful, such as renal cancer, in the middle and late stages, there will be serious symptoms such as waist pain, anemia and weakness, and the urine is washed meat and water, etc., and it is necessary to carry out radical resection and peripheral lymph node dissection in time, so as to avoid the disease’s further progress and metastasis. It should be noted that when the benign or malignant nature of the disease can not be determined, it is necessary to go to the hospital in time to consult the doctor and carry out pathological biopsy to clarify the nature of the disease.