Editing Pediatrics: Anomalies of the Kidneys (section)

== Anomalies of Form and Fusion ==

* '''Horseshoe Kidney'''
** '''Most common of all renal fusion anomalies'''
*** '''Occurs in 0.25% of the population, more commonly in males'''
** Consists of two distinct renal masses lying vertically on either side of the midline and connected at their respective lower poles by a parenchymatous or fibrous isthmus that crosses the midplane of the body
** Insert figure
** '''Embryology'''
*** '''The abnormality occurs between 4-6 weeks’ gestation'''
*** Increased incidence of horseshoe kidneys in children with vertebral and neural tube defects
** '''Description'''
*** The blood supply can be variable
*** '''In 95% of cases, the kidneys join at the lower pole'''
*** '''Migration is usually incomplete and it is thought that the inferior mesenteric artery prevents full ascent'''
*** '''The isthmus of a horseshoe kidney is located adjacent to the L3 and L4 vertebrae'''
*** '''The pelves and ureters of the horseshoe kidney are usually anteriorly placed'''
*** '''The calyces are normal in number'''
*** '''Because the kidney fails to rotate, the calyces point posteriorly,''' and the axis of each pelvis remains in the vertical or obliquely lateral plane.
** '''Associated Anomalies'''
*** '''Frequently found in association with other congenital anomalies'''
**** '''Genitourinary anomalies''' include hypospadias, undescended testes, bicornuate uterus, and a septate vagina
**** Other associated anomalies include duplication of the ureter, ectopic ureterocele, VUR
*** '''The high insertion of the ureter into the renal pelvis, its abnormal course anterior to the isthmus, and the anomalous blood supply to the kidney may individually or collectively contribute to the hydronephrosis'''.
**** UPJ obstruction, causing significant hydronephrosis, occurs in as many as 1/3 of individuals with horseshoe kidneys
**** In the modern era, frequently discovered incidentally, and their apparent hydronephrosis more often shows a non-obstructed pattern on radionuclide scanning.
** Associated clinical conditions
*** Cystic disease and adult polycystic kidney disease
*** Stones
**** Hypovolemia, hypercalciuria, and hypocitraturia were the most common metabolic defects
*** Because a horseshoe kidney is located above the pelvic inlet, it should not adversely affect pregnancy or delivery
*** 60% of patients with horseshoe kidneys remained asymptomatic for an average of 10 years after discovery
*** '''Horseshoe kidney and coarctation of the aorta are seen in patients with Turner syndrome (45,XO).''' Therefore, in these patients, a karyotype should be obtained. Other stigmata of Turner syndrome may include lymphedema, shield chest, low hairline, and webbed neck.
* '''Crossed Renal Ectopia with and without Fusion'''
** '''When a kidney is located on the side opposite that in which its ureter inserts into the bladder, the condition is known as crossed ectopia.'''
** '''90% of crossed ectopic kidneys are fused with their mate'''
*** The superior pole of the ectopic kidney usually joins with the inferior aspect of the normal kidney.
** '''Associated Anomalies'''
*** '''In all the types of fusion anomalies, the ureteral orifice associated with each kidney is usually orthotopic'''
*** The most common genital anomalies are cryptorchidism or absence of the vas deferens and vaginal atresia or a unilateral uterine abnormality
*** The highest incidence of associated anomalies occurs in children with solitary renal ectopia and involves both the skeletal system and genital organs.
** Symptoms
*** Most individuals with crossed ectopic anomalies present no symptoms
*** An asymptomatic abdominal mass is the presenting sign in 1/3 of cases