Urinary obstruction and stasis are important urologic disorders because of their potential to damage the kidney. Ureteral obstruction leads to hydroureteronephrosis, and eventually kidney atrophy that may terminate in renal failure. Furthermore, obstruction often is complicated by infection, which can result in systemic complications and cause additional damage to other organs.
CAUSES, TYPES, CHARACTERISTICS, AND SYMPTOMS
Obstruction may be classified according to cause (congenital or acquired), duration (acute or chronic), degree (partial or complete), and level (upper or lower urinary tract).
Congenital anomalies, more common in the urinary tract than in any other organ system, are generally obstructive. In adult life, many types of acquired obstructions can occur.
The common sites of congenital narrowing are the external meatus in boys (meatal stenosis) or just inside the external urinary meatus in girls, the distal urethra (stenosis), posterior urethral valves, ectopic ureters, ureteroceles, and the ureterovesical and ureteropelvic junctions (Beganović et al, 2007; Tan and Smith, 2004). Another congenital cause of urinary stasis is damage to sacral roots 2–4 as seen in spina bifida and myelomeningocele. Vesicoureteral reflux causes both vesical and renal stasis (see Chapter 13).
Acquired obstructions are numerous and may be primary in the urinary tract or secondary to retroperitoneal lesions that invade or compress the urinary passages. Among the common causes are (1) urethral stricture secondary to infection or injury; (2) benign prostatic hyperplasia or cancer of the prostate; (3) vesical tumor involving the bladder neck or one or both ureteral orifices; (4) local extension of cancer of the prostate or cervix into the base of the bladder, occluding the ureters; (5) compression of the ureters at the pelvic brim by metastatic nodes from cancer of the prostate or cervix; (6) ureteral stone(s); (7) retroperitoneal fibrosis or malignant tumor; and (8) pregnancy.
Neurogenic dysfunction affects principally the bladder. The upper tracts are damaged secondarily by ureterovesical obstruction or reflux and, often, by complicating infection. Severe constipation, especially in children, can cause bilateral hydroureteronephrosis from compression of the lower ureters.
Elongation and kinking of the ureter secondary to vesicoureteral reflux commonly lead to ureteropelvic obstruction and hydronephrosis. Unless a voiding cystourethrogram is obtained in children with this lesion, the primary cause may be missed and improper treatment undertaken.
Pathogenesis and Pathology
Obstruction and neuropathic vesical dysfunction have the same effects on the urinary tract. These changes can best be understood by considering the effects of (1) a severe meatal stricture on the lower tract (distal to the bladder neck), (2) a large obstructing prostate on the midtract (bladder), and (3) an impacted stone in the ureter on the upper tract (ureter and kidney).