Embryology of the Genitourinary Tract

CHAPTER 5 Embryology of the Genitourinary Tract

Mark F. Bellinger, MD

For a normal kidney to form, the ureteric bud must unite with what embryonic tissue?

It must join with the metanephric mesenchyme.

Although one theory proposes that the renal vasculature develops in situ during development of the embryonic kidney, the classical teaching is that the renal vessels develop by what mechanism?

They develop as branching vessels from the aorta.

Remnants of the mesonephric duct in females may be seen in the ovarian mesentery. What are these structures called?

The epoophoron and the paroophoron.

What is the name given to the cystic remnants of the mesonephric duct in the anterolateral wall of the vagina?

Gartner duct cysts.

The urorectal septum divides the cloaca into the posterior anorectal canal and what anterior structure?

The urogenital sinus.

To initiate gonadal development, specialized undifferentiated cells must migrate to the location of the future genital ridge. What are these cells called and where do they migrate from?

They are primordial germ cells and migrate from the yolk sac.

What embryological process initiates the development of the prostate?

The outgrowth of solid epithelial cords from urogenital sinus epithelium into the surrounding mesenchyme.

Name the müllerian duct remnants that may persist in males.

The appendix testis and the prostatic utricle.

What is the mesonephric duct remnant that may persist near the inferior pole of the testis?

The paradidymis.

What is the potential significance of finding an upper pole renal cyst on fetal sonography? What else should the sonographer look for?

The upper pole renal cyst may represent a complete ureteral duplication with a ureterocele or upper pole ectopic ureter. The sonographer should look for hydroureter and a ureterocele in the bladder.

Describe the appearance of Type 1 and Type 3 posterior urethral valves.

Type 1 valves are a pair of sail-like leaflets, and Type 3 valves look like an iris diaphragm in configuration.

Name 2 pressure pop-off mechanisms in fetuses with posterior urethral valves that vent pressure from the bladder and may help prevent the development of renal dysplasia.

Two mechanisms are contralateral vesicoureteral reflux and a patent urachus.

What may be one consequence of oligohydramnios?

Pulmonary hypoplasia may be a consequence of oligohydramnios.

Explain the embryological basis for the finding of a bifid scrotum.

Failure of fusion of the labioscrotal folds may produce a bifid scrotum.

Explain the clinical significance of an atypical median presacral dimple.

An atypical presacral dimple may be a cutaneous manifestation of occult spinal dysraphism.

Describe the genetics and transmission of “infantile” polycystic kidney disease (ARPKD). Also describe the pulmonary and liver diseases that may be associated with it.

ARPKD is transmitted as an auto recessive trait. This is a bilateral disease with a variable spectrum of severity. Congenital hepatic fibrosis is associated with the renal disease. Pulmonary hypoplasia may be a consequence of oligohydramnios in severe cases.

Explain why an ectopic ureter in females may be associated with incontinence, whereas in males, normal continence is the rule.

In females, the ectopic ureter may insert into the lower urinary tract or the lower genital tract below the external sphincter (distal to the bladder neck, in the urethra or vagina). In males, the ectopic ureter always inserts above the external sphincter.

Describe the 3 main physical characteristics of the prune belly syndrome. What is the most important pathological aspect of this syndrome in terms of prognosis?

The prune belly (triad) syndrome consists of 3 major physical findings: deficiency of the abdominal musculature, anomalous urinary tract with dilated and tortuous ureters, and bilateral intra-abdominal testes. The degree of renal dysplasia is the most important prognostic factor.

A female infant is found to have unilateral renal agenesis. Ultrasound examination of the contralateral kidney and bladder and pelvis are normal. What concern should lead the urologist to recommend long-term monitoring of this child?

Females with unilateral renal agenesis have a significant incidence of ipsilateral müllerian anomalies, and may present in early adolescence with a pelvic mass indicative of hydrometrocolpos due to any of a spectrum of uterine or vaginal anomalies, commonly uterus didelphys with an obstructed uterine horn.

Ectopic and fused kidneys often have anomalous collecting systems. What is the orientation of the renal pelvis in most anomalous kidneys?

The renal pelvis begins development in an anterior position and the kidneys rotate during ascent so that the pelves come to lie in a medial position. Most kidneys that are anomalous in location display incomplete rotation. The pelves are likely to be located in an anterior position.

A 1-month-old female has a duplex left kidney with hydroureteronephrosis of the lower pole segment, which has a thin cortex. What is the most likely explanation for the hydronephrosis?

In a completely duplicated collecting system, the upper pole is most likely to be hydronephrotic because of ureteral obstruction (ectopic ureter, ureterocele), while hydronephrosis of the lower pole system is most likely caused by vesicoureteric reflux.

A 2-month-old male is found to have a right ureteral duplication with upper pole hydroureteronephrosis and a cystic mass in the bladder. What is the first logical therapeutic intervention to consider?

The child’s most likely diagnosis is ureteral duplication with a ureterocele subtending the upper pole ureter. In most cases, transurethral incision of the ureterocele is an appropriate first therapeutic intervention.

A 7-year-old boy is found to have a complete right ureteral duplication with hydroureteronephrosis of the upper pole system during evaluation for nocturnal enuresis. Is this anomaly likely to be a cause of his incontinence?

No. Ectopic ureters in males insert into the lower genitourinary tract above the external sphincter, including insertion into the Wolffian duct system (vas, seminal vesicle).

An infant is found to have a right multicystic dysplastic kidney. What studies should be done to evaluate the left kidney?

An ultrasound should be done to rule out hydronephrosis, and a voiding cystourethrogram should be performed since there is greater than 30% incidence of contralateral vesicoureteric reflux.

An infant has drainage of clear fluid from the umbilicus. A small catheter is placed into the umbilical sinus and contrast injected is seen to pass into the gastrointestinal tract. What is the diagnosis?

The child has persistence of the omphalomesenteric (vitelline) duct that connects with the terminal ileum at the site at which a Meckel diverticulum would be found.

Early rupture of the cloacal membrane may result in a spectrum of urological anomalies. List them.

Cloacal exstrophy, exstrophy of the bladder, and epispadias.

Horseshoe kidneys have an incidence of hydronephrosis that in some cases is caused by anomalous renal vasculature. Why is the incidence of this type of ureteral obstruction so high?

Horseshoe kidneys take their vascular supply from a ladder of vessels that alternately appear and involute as the kidneys ascend toward the flank. Persistence of such “anomalous” vessels may result in ureteral obstruction, most commonly at the ureteropelvic junction (UPJ) obstruction.

In cases of unilateral renal agenesis, is ipsilateral adrenal agenesis likely to occur?

No. Ipsilateral adrenal agenesis occurs in less than 10% of cases.

In crossed renal ectopia, are the kidneys more likely to be fused or nonfused?

Fused renal ectopia is more common.

In cross-fused renal ectopia, where does the ureter of the crossed kidney usually enter the bladder?

The ureter draining the ectopic kidney usually crosses the midline to enter the contralateral trigone.

Explain the Meyer–Weigert law in relation to ureteral duplication.

The law states that in complete ureteral duplication, the orifice to the lower pole ureter inserts into the bladder in a more lateral and cranial position, while the ureter to the upper pole inserts in a more caudal and medial position.

A 14-year-old male is found to have right ureteral obstruction secondary to retrocaval ureter. What is the embryologic explanation for this anomaly?

Retrocaval ureter is a result of persistence of (failure of involution of) the right subcardinal vein.

The fetal testis produces 2 hormones that are essential for the development of the internal genitalia. Name these hormones and indicate what effect they have on the developing genital structures.

Testosterone supports the development of the Wolffian duct structures (seminal vesicles, vas, etc). Müllerian-inhibiting substance acts ipsilaterally to suppress the development of the müllerian structures (fallopian tube, uterus, and upper vagina).

A 1-month-old male is found to have a left flank mass. What are the 2 most likely diagnoses and what would be your first imaging study in this case.

The most likely diagnoses are hydronephrosis and multicystic renal dysplasia. The primary imaging technique for infants with abdominal masses should be ultrasound.

A female neonate has a midline pelvic abdominal mass and a bulging interlabial mass. What is the most likely diagnosis?

The most likely diagnosis is hydrometrocolpos secondary to imperforate hymen.

A 12-year-old male presents with terminal hematuria and is found to have a polyp in his posterior urethra arising from the verumontanum. What is the cause of this polyp and the most likely pathologic diagnosis? Where else in the urinary tract are similar lesions occasionally found?

The polyp is most likely a benign fibroepitheliomatous polyp of congenital origin. Similar polyps may be found in the ureter and renal pelvis.

A 15-year-old male with dysuria is found to have a cystic lesion in the bulbous urethra. What is its most likely embryologic origin?

This is most likely a Cowper duct cyst.

A 12-year-old boy with dysuria and bloody urethral spotting is found to have a small diverticulum on the roof of the distal urethra in the fossa navicularis. What is the correct term for this diverticulum?

This lesion is known as a lacuna magna.

A 1-month-old female is found to have a cystic mass prolapsing through the urethral meatus, and ultrasound of the abdomen shows hydronephrosis of the upper pole of the left kidney. What is the most likely diagnosis?