The 12mm low density nodule on the left kidney is a descriptive statement of CT imaging, which may refer to the adrenal gland or the upper pole of the kidney, suggesting that the patient may have adrenal adenoma, renal cysts, adrenal lymphangioma and other diseases, the patient should bring the report in time for follow-up, further examination to determine the condition. Adrenal adenoma is a common low-density adrenal gland nodule in clinic, and patients with functional adenoma may also have manifestations of centripetal obesity, full-moon face, buffalo back, and purple lines on the skin, etc. Patients without functional adenomas can be followed up and observed in general. Renal cysts will appear low density nodule shadow in CT examination, the nodule surface is smooth, protruding from the body surface, can exist in the renal parenchyma, belongs to benign lesions. If the cyst is smaller than 4cm, follow-up examination is usually enough, but if the cyst is larger and affects the patient’s normal life, surgical treatment is needed. Patients with adrenal lymphangioma may have no obvious symptoms in the early stage, and some patients may have calcification of the cyst wall caused by hemorrhage, infection, mechanization and other factors. There are many other causes of low-density nodules on the left kidney, and it is recommended that patients go to regular hospitals in time for standardized examination and treatment under the guidance of physicians.