The kidney arises from the mesoderm. The mesonephros will give rise to the mesonephric ducts, also known as Wolffian ducts. By week 5 of development, the metanephros forms caudal to the mesonephros, in close vicinity to the bladder, in the pelvis. The key step in renal organogenesis is the invasion of the metanephros by the ureteric bud, a derivative of the Wolffian duct. This interaction induces the formation of glomeruli within the metanephros as well as the differentiation of the ureteric bud into the renal collecting system, starting with the collecting ducts and ending with the ureters and trigone of the bladder. Failure in this relationship is responsible for multiple congenital anomalies.

Renal development occurs as the embryo elongates, making the kidneys ascend from the pelvis (S1–S2) into their adult location in the lumbar region. As they ascend, they rotate medially, with the renal pelvis passing from an anterior to a posterior location. Finally, there is a change in blood supply to the kidney. Vessels arising from the abdominal aorta and inferior vena cava substitute the original supply arising from the distal aorta and iliac vessels (Fig. 20.1).

The process of relocation of the kidneys may be arrested at any stage. As the name implies “pelvic” kidneys fail to ascend and rotate medially (the renal pelvis remains in an anterior position). These kidneys also preserve their original blood supply. Due to their flattened shape, they are also called pancake kidneys. As the kidney ascends along the vascular ladder from the pelvis to the perilumbar position, the gonads descend along the same ladder in the vascular axis taking blood vessels from the high lumbar area into the pelvis [1–3].

Horseshoe kidneys are the most common fusion abnormality of the kidneys. They arise from the fusion of the inferior renal poles while they still reside in the pelvis. This union impedes subsequent medial rotation and ascent of the kidneys, as the area of fusion cannot progress cephalad to the inferior mesenteric artery. The lack of medial rotation determines that the ureters remain in an anterior location. Vascular development is also hindered, and horseshoe kidneys often preserve their primitive blood supply arising from the distal aorta and iliac vessels [4].

While up to one third of horseshoe kidneys remain asymptomatic and are discovered incidentally, the abnormal blood supply and ureteral implantation predispose to urinary stasis and reflux, leading to nephrolithiasis and urinary tract infections.

Horseshoe kidneys are more vulnerable to trauma due to their lack of protection by the ribs. In addition, the isthmus may be compressed against the spinal column. There have been reports of tumors arising from horseshoe kidneys, and it is unclear whether horseshoe kidney is a predisposing factor for renal cell carcinoma. Finally, horseshoe kidneys represent an obstacle in the repair of abdominal aortic aneurysms. This obstacle can be circumvented by the use of endovascular or retroperitoneal approaches.

Horseshoe kidneys do not require any specific treatment. Division of the isthmus and attempts at relocation are contraindicated. However, surgery may be undertaken to address urinary reflux and stones [5].

Simple renal cysts are commonly seen as acquired lesions. They are epithelium-lined, urine-containing cavities thought to constitute the diverticula of the distal convoluted or collecting tubules due to an age-related weakening of the basement membrane. They are typical of the elderly population and tend to increase in number and size with time. They are not considered a premalignant lesion and require no specific therapy [6–8].

Adult (autosomal dominant) polycystic kidney disease (PKD) is the most common genetically transmitted renal cystic disease, occurring in 2 per 1,000 live births. It is caused by mutations in the PDK1, PDK2, and PDK3 genes. Although it may become manifest at any age, it is most often detected between the fourth and fifth decades of life, when a multitude of cysts of varying size throughout the renal parenchyma have developed [9].

Patients with adult PKD are at increased risk for developing renal carcinoma. They may also develop hepatic, pancreatic, and splenic cysts. Another noteworthy association is that with cerebral aneurysms, which occur with an 8 % incidence. Hypertension, hematuria, and recurrent urinary tract infections are often present. This disease causes progressive loss of renal mass leading to end-stage renal disease.

Infantile (autosomal recessive) PKD is 40 times less common than the adult variety (1 per 20,000 live births). It is caused by a mutation in the PKDH1 gene. The infantile variety of PDK is consistently associated with hepatic cysts. Thirty percent of affected patients die in the perinatal period due to lung hypoplasia. Survivors develop hypertension, with up to 50 % of cases developing end-stage renal disease by age 15. Cyst morphology is distinct, with multiple, homogeneous dilatations of the collecting ducts, with radial orientation. Liver involvement consists of portal ectasia leading to cirrhosis [10].

The renal arteries are typically single and arise from the abdominal aorta, between L1 and L2, inferior to the superior mesenteric artery. The right renal artery originates slightly more cephalad than the left and follows a downward course behind the inferior vena cava towards the kidney. In contrast, the left renal artery has a more caudal origin and follows a short straight course towards the kidney. Both arteries travel from anterior to posterior to reach the kidney. At the level of the renal hilum, they occupy an intermediate plane, in front of the renal pelvis and ureter, but behind the renal vein. The renal arteries are considered the sole end artery supply of the kidney, although accessory renal arteries may be present in about 2 % of the population. Ligation of the renal artery or an accessory branch will lead to an area of infarction. However, renal veins can be ligated in exceptional traumatic injuries. In this setting, venous drainage occurs through collaterals through the adrenal veins. The renal veins course parallel and slightly inferior and anterior to the renal arteries. These relationships are important as instrumentation of the inferior vena cava and aorta is usually performed below the level of the renal vessels to preserve kidney perfusion and protect the superior mesenteric artery (Fig. 20.2).

At the renal hilum, the renal artery starts branching into progressively smaller vessels becoming the afferent arterioles that supply the glomerulus. The efferent arterioles collect the blood from the glomerular tufts and channel it towards the renal tubules via the vasa recta. In low-perfusion states, renal tubules are particularly vulnerable to acute tubular necrosis because of this arrangement [11, 12] (Fig. 20.3).

Please see discussion for question 6.

A clear knowledge of ureteral anatomy is essential to those operating in the abdomen, retroperitoneum, pelvis, and perineum, where the incidence of injury to these structures ranges from 0.3 to 1.5 %. This high incidence is explained by the presence of hostile surgical conditions as well as to the multiple anatomical variations.

The adult ureters are 25–30 cm in length, with a diameter of 1.5–6 mm. The ureters remain extraperitoneal throughout their course. They course lateral to the lumbar vertebrae and anterior to the psoas muscles as they descend into the pelvis. Through their course, they come in relation with multiple structures.