Lower Urinary Tract Obstruction: Pathophysiology, Prenatal Assessment, and In Utero Intervention

Abstract

Congenital renal and urinary tract anomalies are common, accounting for up to 21% of all congenital abnormalities [1]. The reported incidence is approximately 1:250-1:1000 pregnancies [2] and the routine use of prenatal ultrasonography allows relatively early detection, particularly for the obstructive uropathies, which account for the majority. According to the latest UK renal registry report in 2015, ‘obstructive uropathy’ was the second leading cause (19%) of chronic renal failure in children under 16 years of age after renal dysplasia +/- reflux [3]. The obstructions may occur within the upper or lower urinary tract, and their prognosis varies significantly, with obstructions at the level of the bladder neck being associated with the majority of neonatal mortality and renal failure. In untreated cases, perinatal mortality is high (up to 45%, often because of associated severe oligohydramnios and pulmonary hypoplasia) [4], and 30% of the survivors suffer from end-stage renal failure (ESRF) requiring dialysis and renal transplantation before the age of 5 [5]. The overall chance of survival in childhood is lowest if renal support therapy or transplantation is commenced before 2 years old when compared with starting at 12-16 years old (hazard ratio [HR] of 4.1, 95% confidence interval [CI] 1.7-9.9, P = 0.002) [3]. Therefore, in utero intervention, by the insertion of a vesicoamniotic shunt, or therapeutic treatment by fetal cystoscopy and valvular ablation, has been attempted to attenuate in utero progression of these pathologies (and their consequences) and to alter the natural history of congenital bladder neck obstruction in childhood. In this chapter, we discuss the etiology, pathophysiology, prenatal presentation and diagnosis of congenital bladder neck obstruction. Suggested algorithms for screening and the prenatal prognostic evaluation in selecting candidates for in utero therapy will be discussed.