Horseshoe kidney, also known as hoof-shaped kidney, is one of the congenital malformations of the kidney. It manifests as the upper or lower poles of both kidneys fusing with each other before the spine or before the large abdominal vessels, forming a horseshoe shape. In about 90% of cases, the lower poles fuse with each other. The site of fusion becomes the isthmus. The horseshoe kidney occurs in the early embryonic stage as a result of the fusion of the two sides of the kidney embryo by being squeezed tightly between the umbilical arteries. Most of the horseshoe kidneys are poorly developed, low in position, and associated with poor rotation. The kidneys and ureters often face anteriorly, with the ureters crossing the isthmus. It is the squeezed ureter that causes poor urinary drainage and is prone to secondary urinary tract infections. Prolonged and recurrent urinary tract infections can cause infected urinary stones. Since most of the infected bacteria contain ureolytic enzymes, it generates ammonia from the urea in the urine, making the urine alkaline and thus contributing to the supersaturation of magnesium ammonium phosphate and carbonate apatite. In addition, necrotic tissue during infection can also encourage crystals to collect on its surface to form stones. Spongy kidney is a type of congenital medullary cystic lesion, which is less common and is characterized by a cystic dilatation of the medullary collecting ducts. It is usually caused by congenital developmental anomalies and develops mostly at the age of 40 to 50 years, with a good prognosis. The disease is present at birth without infection and normal urinalysis, and is usually not detected until the age of 40 to 50 years due to the development of stones and infectious complications. Long-term urinary storage due to dilated collecting ducts, combined with frequent hypercalciuria, is the cause of stones and infections. The main clinical manifestations are recurrent hematuria, urinary tract infections and kidney stones, which can cause renal colic. The disease is often associated with hyperparathyroidism and hypercalciuria. Kidney stones are mainly located in the medulla or conus and are widely distributed, mainly phosphate stones and, to a lesser extent, calcium oxalate stones. Therefore, the origin of stones in the “horseshoe kidney” and “sponge kidney” is mainly due to the congenital abnormal development of the kidney and poor drainage of urine, which can easily lead to urinary tract infection. Infection can cause kidney stones, and stone obstruction can aggravate the infection, thus making the stones bigger and bigger, creating a vicious circle.