Neural Tube Defects

Neural tube defects, resulting from failure of the neural tube to close spontaneously between the 3rd and 4th wk in utero, result in abnormalities of the vertebral column that affect spinal cord function, including myelomeningocele and meningocele (Chapter 585). A few medical centers in the USA have been performing antenatal myelomeningocele closure, but follow-up studies of the urinary tract have not shown a definite improvement in lower urinary tract function.

Clinical Manifestations and Diagnosis

The most important urologic consequences of neuropathic bladder dysfunction associated with neural tube defects are urinary incontinence (Chapter 537), urinary tract infections (UTIs; Chapter 532), and hydronephrosis from vesicoureteral reflux or detrusor-sphincter dyssynergia. Pyelonephritis (Chapter 532) and renal functional deterioration (see Chapter 529) are common causes of premature death of affected patients.

In the neonate, renal ultrasonography, assessment of postvoid residual urine volumes, and a voiding cystourethrogram are performed after closure of the myelomeningocele. About 10-15% of patients have hydronephrosis, and renal malformations are common; 25% have vesicoureteral reflux. A urodynamic study also should be performed. This study involves filling the bladder with saline, measuring the bladder volume and pressure, and assessing sphincter tone. During bladder filling, the bladder might show uninhibited (premature) contractions at low volumes, normal bladder volume with contraction at an appropriate volume, or atonia (lack of bladder contraction). Bladder compliance or elasticity also may be reduced. The sphincter can show normal tone with relaxation during bladder contraction, reduced or absent tone, or normal or increased tone that increases during bladder contraction (termed detrusor-sphincter dyssynergia) (Fig. 536-1).

Figure 536-1 Grouping of neurogenic bladder dysfunction according to the innervation, tonicity, and coordination of the detrusor and sphincters described by Guzman. This grouping is based on data from imaging studies, cystometrography, and electromyography of the sphincters. Patients in group B are at risk of developing reflux and hydronephrosis. For guidance in the treatment of incontinence, group A benefits from procedures that increase outlet resistance, group B from anticholinergics or bladder augmentation surgery, and group C from intermittent catheterization. Group D requires both increased outlet resistance and pharmacologic or surgical bladder enlargement. Most patients require intermittent catheterization to empty.

(Modified from Gonzalez R: Urinary incontinence. In Kelalis PK, King LR, Belman AB, editors: Clinical pediatric urology, Philadelphia, 1992, WB Saunders, p 387.)

Renal Damage

Renal damage usually results from failure of the sphincter to relax during a spontaneous bladder contraction. This dyssynergia results in functional obstruction of the bladder outlet, leading to high intravesical pressure, bladder muscle hypertrophy and trabeculation, and transmission of the high pressure into the upper urinary tracts, causing hydronephrosis (Fig. 536-2). Vesicoureteral reflux and UTI compound the problem. Treatment includes reduction of bladder pressure with anticholinergic drugs (oxybutynin, 0.2 mg/kg/24 hr in 2 or 3 divided doses) and clean intermittent catheterization every 3-4 hr. If there is vesicoureteral reflux or UTI, antimicrobial prophylaxis also is prescribed.

Figure 536-2 Voiding cystourethrogram in an infant with myelodysplasia shows a severely trabeculated bladder with multiple diverticula and grade V (out of V) right vesicoureteral reflux. Evaluation showed severe detrusor-sphincter dyssynergia.

Temporary urinary diversion by cutaneous vesicostomy is an alternative in the newborn or infant with severe reflux, if intermittent catheterization is difficult or anticholinergic medications are not well tolerated. Another option to treat the severely trabeculated bladder is transurethral injection of botulinum toxin (Botox) into the detrusor muscle, which reduces bladder hypertonicity for approximately 6 mo. A different approach in these children is to temporarily inactivate the tight sphincter by urethral overdilation or transurethral injection of botulinum toxin into the sphincter.

Clean intermittent catheterization and anticholinergic therapy cure the reflux in up to 80% of children with grade I or II reflux. In children with upper tract changes, continuous overnight bladder drainage allows significant bladder relaxation and can reduce bladder wall thickening and reduce hydronephrosis.

Children with more severe reflux often require endoscopic reflux correction or open antireflux surgery followed by intermittent catheterization and anticholinergic drugs. In older children with myelomeningocele with high-grade reflux, UTI, and hydronephrosis, augmentation enterocystoplasty with intermittent catheterization may be necessary.

Urinary Incontinence

Incontinence in the child with neuropathic bladder can result from total or partial denervation of the sphincter, bladder hyperreflexia, poor bladder compliance, chronic urinary retention, or a combination of these factors.

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