558 CHAPTER 15 Pediatric urology

Cystic kidney disease

Congenital cystic kidney disease can be classified into genetic and nongenetic types.

Genetic

Autosomal recessive polycystic kidney disease (ARPKD)

ARPKD is a disease of infancy and childhood, where renal collecting tubules and ducts become cystically dilated and numerous small cysts form in the renal cortex and medulla. Severe forms present early and have a poor prognosis.

Prenatal US demonstrates oligohydramnios (amniotic fluid <200 mL) and large, “bright” homogeneously hyperechogenic kidneys, which can cause obstructed labor and respiratory problems.

Neonates have large flank masses and limb and facial anomalies. All cases are associated with congenital hepatic fibrosis. Infants develop fatal uremia and respiratory failure; older children present with renal failure, hypertension, and portal hypertension. Most develop end-stage renal failure by adulthood, requiring hemodialysis and renal transplantation.

Autosomal dominant polycystic kidney disease (ADKD)

ADKDA Typically presents in adulthood, although older children can present with complications of hematuria, flank pain, flank mass, UTI, proteinuria, hypertension, and intracerebral bleeds (secondary to berry aneurysm rupture).

It is characterized by multiple expanding cysts of both kidneys that ultimately destroy the intervening parenchyma, and accounts for 10% of all chronic renal failure.

Familial juvenile nephronophthisis

This is an autosomal recessive disorder that develops in early childhood and accounts for up to 20% of pediatric renal failure. Medullary cystic disease is a similar (autosomal dominant) condition that develops in later childhood.

Histology shows interstitial nephritis associated with medullary and corticomedullary cysts. Disease progression causes a reduction in kidney size. Features include polyuria, polydipsia, anemia, growth retardation, and chronic renal failure.

Renal cysts are also a feature of autosomal dominant conditions, including Von–Hippel–Lindau syndrome (cerebellar hemangioblastomas, pheochromocytoma, renal cell carcinoma) and tuberous sclerosis (adenoma sebaceum, epilepsy, learning difficulties).

Nongenetic

Multicystic dysplastic kidney (MCDK)

MCDK is the most common cystic kidney disorder and second most common cause of abdominal mass in newborns (after UPJ obstruction). The cysts of a multicystic kidney are not due to dilatation of renal collecting ducts (as in polycystic disease); instead, the entire kidney is dysplastic, with immature dysplastic stroma and cysts of various sizes. The kidney does

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not have a renoform shape or a calyceal drainage system—the ureter is atretic.

Bilateral disease is incompatible with life. Unilateral disease is often associated with reflux (20–40%) or UPJ obstruction (10%) in the contralateral kidney. Affected kidneys may undergo renal aplasia, where they spontaneously shrink to a tiny remnant.

Ultrasound helps to distinguish this condition (noncommunicating cysts) from hydronephrosis. Renal scanning shows no function.

Most patients can be treated conservatively with close surveillance for the associated risks of hypertension and Wilms’ tumor, which would be indications for surgery. It may involute spontaneously.

Multilocular cystic nephroma

This condition presents in young children, with unilateral flank mass. It is included in a spectrum of diseases that are closely associated with Wilms tumor, so the recommended treatment is partial or full nephrectomy.

There is bimodal distribution—male infants <2 and female adults >40 years of age.

560 CHAPTER 15 Pediatric urology

Exstrophy

Bladder exstrophy results from defective development of the anterior bladder and lower abdominal walls, leaving the posterior bladder wall lying exposed on the abdomen.

Epidemiology

Incidence is 3.3 cases per 100,000 live births, with a male-to-female ratio >2:1. There is and increased risk in offspring of affected patients and with younger maternal age and increased parity.

Embryology

An embryological malformation results in the abnormal overdevelopment of the cloacal membrane, which prevents in-growth of lower abdominal tissues. The cloacal membrane normally perforates to form the urogenital and anal openings, but in exstrophy there is premature rupture, resulting in a triangular defect below the umbilicus.

The timing of this rupture determines the type of defect (bladder exstrophy, cloacal exstrophy, OR epispadias).

Associated anomalies

•Bone defects: diastasis (widening) of the symphysis pubis due to outward rotation of the pelvic bones along the sacroiliac joints (Fig. 15.8)

•Musculofascial defects: umbilical hernias, inguinal hernias, abnormal pelvic floor

•Genital defects: Males have a short, broad epispadiac penis with lateral splaying of the corporal cavernosa, and short urethral plate. Females have a bifid clitoris, stenotic vaginal orifice, short vaginal canal, and vaginal prolase.

•Urinary tract defects: Most patients suffer vescioureteric reflux (VUR) due to lateral displacement of the ureteric orifices.

•GI defects: anteriorly displaced anus, rectal prolapse; abnormal anal sphincter contributes to incontinence.

Investigation

Typical features seen on prenatal ultrasound scan include a lower abdominal wall mass, absent bladder filling, low-set umbilicus, small genitalia, and abnormal iliac crest widening. Diagnosis can help in planning of delivery in a center with facilities to perform early surgical correction.

Management

At birth, cover the bladder with plastic film and irrigate regularly with sterile saline. Trauma to the bladder mucosa can eventually result in squamous metaplasia, cystitis cystica, or adenocarcinoma and squamous cell carcinoma after chronic exposure.

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Selected cases are suitable for one-stage repair, but most require a three-stage procedure:

•Newborn: pelvic osteotomy (cutting bone to correct deformity) with external fixation with closure of bladder, abdominal wall, and posterior urethra

•6–12 months: epispadias repair

•4–5 years: Bladder neck reconstruction (Young–Dees–Leadbetter procedure) and anti-reflux surgery (ureteric reimplantation) are performed when there is adequate bladder capacity and children can participate in voiding protocols. Where bladder capacity is too small, bladder augmentation or urinary diversion is required.

Figure 15.8 KUB from exstrophy patient shows characteristic wide separation of pubes.