Congenital bilateral ureteral stenosis and hydronephrosis in a neonatal puppy.

Three days after an uneventful parturition, a Brittany spaniel/beagle puppy (Canis familiaris) was nursing but not gaining weight as rapidly as were its littermates. Although its diet was supplemented, the puppy died 10 days after birth. The renal pelves were enlarged and filled with urine. Both ureters were thin throughout their length, and urine could not be expressed from either kidney into its respective ureter. The bladder contained no urine and was firmly embedded in the umbilicus. Histologically, both kidneys were hydronephrotic and contained hypoplastic collecting tubules. The diameter of the right (0.55 mm) and left (0.57 mm) ureters at the uteropelvic junction were narrower than those of an age-matched control of the same breed (1.03 mm and 1.02 mm) and were lined by hypoplastic urothelium. Trichrome staining of the ureters revealed excessive collagen and disorganized smooth muscle fibers; in contrast, the control had predominantly circular smooth muscle fibers and less fibrous tissue. Although neither blood nor aqueous humor could be evaluated for urea nitrogen, we suspect that the puppy died from uremia. The congenital bilateral ureteral stenosis and hydronephrosis of the described puppy is similar to a form of uteropelvic obstruction in humans.