Whether the condition of low density foci in the left kidney is serious or not needs to be diagnosed by a specialist and judged according to different individuals, different conditions and different causes. Patients should not judge and take medication without authorization, so as not to delay treatment and aggravate the condition. Generally the left kidney low density foci may be caused by renal cyst, renal vascular smooth muscle lipoma, renal malignant tumor and other diseases. 1. Renal cysts may cause low density foci in the left kidney. If it is caused by simple renal cysts, it is usually not serious and regular review under the guidance of doctor is enough. If the diameter of the cyst is more than 5cm, you need to go to the hospital in time for examination and treatment under the guidance of a professional doctor. 2. Renal vascular smooth muscle lipoma can also cause low-density foci in the examination, due to the low-density adipose tissue in it, usually there is a low-density fat shadow in it under the CT enhancement. However, it is considered a benign lesion, and further examination is needed to determine the specifics. 3. Left kidney hypodense foci caused by renal malignant tumors, this malignant tumor needs to attract enough attention, patients should go to regular hospitals to do further CT examination and take appropriate treatment measures. The cause of left kidney hypodense foci is complicated, patients are advised to go to regular hospitals for examination and treatment in time.