Chapter 21 - The Lower Urinary Tract and Male Genital System
Jonathan I. Epstein MD
The Lower Urinary Tract
Despite differing embryonic origins, the various components of the lower urinary tract come to have many morphologic similarities. The renal pelves, ureters, bladder, and urethra (except
for its terminal portion) are lined by a special form of transitional epithelium (urothelium) that is two to three cells thick in the pelvis, three to five cells thick in the ureters, and three to
seven cells thick in the bladder. The surface layer consists of large, flattened "umbrella cells" that cover several underlying cells. The umbrella cells have a trilaminar asymmetric unit
membrane and possess apical plaques composed of specific proteins called uroplakins. Toward the basal layer, the cells become smaller or more cylindrical (particularly in contracted
bladders), but they are capable of some flattening when the underlying wall is stretched. This epithelium rests on a well-developed basement membrane, beneath which there is a lamina
propria. The lamina propria in the urinary bladder contains wisps of smooth muscle that form a discontinuous muscularis mucosae. It is important to differentiate the muscularis mucosae
from the deeper well-defined larger muscle bundles of the detrusor muscle (muscularis propria), since bladder cancers are staged on the basis of invasion of the latter. The bladder
musculature is capable of great thickening if there is obstruction to the flow of urine.
Several variants of the normal epithelial patterns may be encountered. Nests of urothelium or inbudding of the surface epithelium may be found occasionally in the mucosa lamina propria;
these are referred to as Brunn nests.
The ureters lie throughout their course in a retroperitoneal position. Retroperitoneal tumors or fibrosis may trap the ureters in neoplastic or dense, fibrous tissue, sometimes obstructing
them. As ureters enter the pelvis, they pass anterior to either the common iliac or the external iliac artery. In the female pelvis, they lie close to the uterine arteries and are therefore
vulnerable to injury in operations on the female genital tract. There are three points of slight narrowing: at the ureteropelvic junction, where they enter the bladder, and where they cross the
iliac vessels, all providing loci where renal calculi may become impacted when they pass from the kidney to the bladder. As the ureters enter the bladder, they pursue an oblique course,
terminating in a slitlike orifice. The obliquity of this intramural segment of the ureteral orifice permits the enclosing bladder musculature to act like a sphincteric valve, blocking the
upward reflux of urine even in the presence of marked distention of the urinary bladder. As discussed in Chapter 20 , a defect in the intravesical portion of the ureter leads to vesicoureteral
reflux. The orifices of the ureters demarcate an area at the base of the bladder known as the trigone. In women, the trigone is frequently covered by glycogenated squamous epithelium, a
normal finding, not metaplasia resulting from injury.
The close relationship of the female genital tract to the bladder makes possible the spread of disease from one tract to the other. In middle-aged and elderly women, relaxation of pelvic
support leads to prolapse (descent) of the uterus, pulling with it the floor of the bladder. In this fashion, the bladder protrudes into the vagina, creating a pouch (cystocele) that fails to empty
readily with micturition. In men, the seminal vesicles and prostate have similar close relationships, being situated just posterior and inferior to the neck of the bladder. Thus, enlargement of
the prostate, so common in middle to later life, constitutes an important cause of urinary tract obstruction. In the subsequent sections, we discuss the major pathologic lesions in the ureters,
urinary bladder, and urethra separately. 
Congenital anomalies of the ureters occur in about 2% or 3% of all autopsies. Although most have little clinical significance, certain anomalies may contribute to obstruction to the flow of
urine and thus cause clinical disease. Anomalies of the ureterovesical junction, potentiating reflux, are discussed with pyelonephritis in Chapter 20 .
Double ureters (derived from a double or split ureteral bud) are almost invariably associated either with totally distinct double renal pelves or with the anomalous development of a large
kidney having a partially bifid pelvis terminating in separate ureters. Double ureters may pursue separate courses to the bladder but commonly are joined within the bladder wall and drain
through a single ureteral orifice. The majority of double ureters are unilateral and of no clinical significance.
Ureteropelvic junction obstruction, a congenital disorder, results in hydronephrosis. It usually presents in infants or children, much more commonly in boys, usually in the left ureter.
However, it is bilateral in 20% of cases and may be associated with other congenital anomalies. It is the most common cause of hydronephrosis in infants and children. In adults,
ureteropelvic junction obstruction is more common in women and is most often unilateral. There is agenesis of the kidney on the opposite side in a significant number of cases, probably
resulting from obstructive lesions in utero.
Diverticula, saccular outpouchings of the ureteral wall, are uncommon lesions that are usually asymptomatic and found incidentally on imaging studies. They appear as congenital or
acquired defects and are of importance as pockets of stasis and secondary infections. Dilation (hydroureter), elongation, and tortuosity of the ureters may occur as congenital anomalies or
as acquired defects. Congenital hydroureter is thought to reflect some neurogenic defect in the innervation of the ureteral musculature. Massive enlargement of the ureter is known as
megaloureter and is probably due to a functional defect of ureteral muscle. Hydronephrosis and decreased renal
function results if the lesion goes untreated. These anomalies are sometimes associated with some congenital defect of the kidney.
Ureteritis may develop as one component of urinary tract infections. The morphologic changes are entirely nonspecific. Only infrequently does such ureteritis make a significant
contribution to the clinical problem. Persistence of infection or repeated acute exacerbations may give rise to chronic inflammatory changes within the ureters.
In certain cases of long-standing chronic ureteritis, specialized reaction patterns are sometimes observed. The accumulation or aggregation of lymphocytes in the subepithelial region may
cause slight elevations of the mucosa and produce a fine granular mucosal surface (ureteritis follicularis). At other times, the mucosa may become sprinkled with fine cysts varying in
diameter from 1 to 5 mm (ureteritis cystica). These changes are also found in the bladder (described in greater detail later, in the section on the urinary bladder). The cysts may aggregate
to form small, grapelike clusters ( Fig. 21-1 ). Histologic sections through such cysts demonstrate a lining of modified transitional epithelium with some flattening of the superficial layer of
Date: 2016-04-22; view: 711