Chapter 12. Urinary Obstruction & Stasis

Because of their potential damage on renal function, urinary obstruction and stasis are important urologic disorders. Ureteral obstruction leads to hydronephrosis, kidney atrophy that may terminate in renal failure. Furthermore, obstruction often is complicated by infection, which causes additional damage to the organs involved.

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).

Etiology

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.

Congenital

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 (Beganovic´ 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

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; (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 given.

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).

Lower Tract (eg, Urethral Stricture)

Hydrostatic pressure proximal to the obstruction causes dilation of the urethra. The wall of the urethra may become thin, ...