Pediatric urology

Embryology: urinary tract 538

Undescended testes 540

Urinary tract infection (UTI) 542

Vesicoureteric reflux (VUR) 544

Ectopic ureter 546

Ureterocele 548

Ureteropelvic junction (UPJ) obstruction 549

Hypospadias 550

Normal sexual differentiation 552

Abnormal sexual differentiation 554

Cystic kidney disease 558

Exstrophy 560

Epispadias 562

Posterior urethral valves 564

Non-neurogenic voiding dysfunction 566

Nocturnal enuresis 568

538 CHAPTER 15 Pediatric urology

Embryology: urinary tract

Following fertilization, a blastocyte (sphere of cells) is created, which implants into the uterine endometrium on day 6. The early embryonic disc of tissue develops a yolk sac and amniotic cavity, from which are derived ectoderm, endoderm, and mesoderm.

Organ formation occurs between 3 and 10 weeks’ gestation. Most of the genitourinary tract is derived from mesoderm.

Upper urinary tract

The pronephros (precursor kidney; pro = (Gk) before), derived from an intermediate plate of mesoderm, is present at weeks 1–4. It then regresses.

The mesonephros (meso = (Gk) middle) functions at weeks 4–8 and is also associated with two duct systems—the mesonephric duct and, adjacent to this, the paramesonephric duct (para = (Gk) beside) (Fig. 15.1).

The mesonephric (Wolffian) ducts develop laterally and advance downward to fuse with the primitive cloaca (hindgut). By week 5, a ureteric bud grows from the distal part of the mesonephric ducts and induces formation of the metanephros in the overlying mesoderm (permanent kidney; meta = (Gk) after).

Branching of the ureteric bud forms the renal pelvis, calyces, and collecting ducts. Glomeruli and nephrons are created from metanephric mesenchyme.

During weeks 6–10, the caudal end of the fetus grows rapidly and the fetal kidney effectively moves up the posterior abdominal wall to the lumbar region. Urine production starts at week 10.

Thus, in both males and females, the mesonephric duct forms the ureters and renal collecting system. The paramesonephric essentially forms the female genital system (fallopian tubes, uterus, upper vagina); in males, it regresses. The mesonephric duct forms the male genital duct system (epididymis, vas deferens, seminal vesicles, central zone of prostate); in the female, it regresses.

Lower urinary tract

The mesonephric ducts and ureters drain into the cloaca (Latin = sewer), which is later subdivided into the urogenital sinus (anteriorly) and the anorectal canal (posteriorly) during weeks 4–6 (see Fig. 15.1).

The bladder is formed by the upper part of the urogenital sinus. The lower part forms the urethra in females. In males, the mesonephric ducts form the posterior urethra, and closure of the urogenital groove creates the anterior urethra.

540 CHAPTER 15 Pediatric urology

Undescended testes

The testes descend into the scrotum in the third trimester (passing through the inguinal canal at 24–28 weeks). Failure of testicular descent results in cryptorchidism (or undescended testes).

Incidence

Incidence is 3% at birth (unilateral > bilateral). Approximately 80% will spontaneously descend by 3 months. The incidence at 1 year is 1%.

Classification

•Retractile: an intermittent active cremasteric reflex causes the testis to retract up and out of the scrotum.

•Ectopic (<5%): abnormal testis migration below the external ring of the inguinal canal (to perineum, base of penis, or femoral areas)

•Incomplete descent (~95%): testis may be intra-abdominal, inguinal, or prescrotal

•Atrophic/absent

Risk factors

These include preterm infants, low birth weight, small for gestational age, and twins.

Etiology

This includes abnormal testis or gubernaculum (tissue that guides the testis into the scrotum during development); endocrine abnormalities (low level of androgens, human chorionic gonadotrophin [hCG], luteinizing hormone (LH), calcitonin gene–related peptide); and decreased intraabdominal pressure (prune-belly syndrome, gastroschisis).

Pathology

There is degeneration of Sertoli cells, loss of Leydig cells, and atrophy and abnormal spermatogenesis.

Long-term complications

•Relative risk of cancer is 40-fold higher in the undescended testis. Most are seminomas; carcinoma in situ represents a small percentage (~2%). There is a slightly increased risk of cancer in the contralateral, normally descended testis.

•Reduced fertility

•Increased risk of testicular torsion

•Increased risk of direct inguinal hernias (due to a patent processus vaginalis)

Management

Full examination is required to elucidate if the testis is palpable and to identify location. Assess for associated congenital defects. If neither testis is palpable, consider chromosome analysis (to exclude an androgenized female) and hormone testing (high LH and FSH with a low testosterone indicates anorchia).

UNDESCENDED TESTES 541

Treatment should be performed within the first year. Hormone therapy (hCG, LHRH) stimulates testosterone production. Surgery consists of inguinal exploration, mobilization of spermatic cord, ligation of processus vaginalis, and securing the testis into a dartos pouch in the scrotal wall (orchidopexy). Laparoscopy can be used in planning surgery and for treatment.

Intra-abdominal testes may require division of spermatic vessels to provide extra length (Fowler-Stevens procedure, relying on collateral blood flow from vas), two-stage procedures, or microvascular autotransplantation.