These diverticula are considered to be congen-

Gonadal Development

ital in origin.

While bladder diverticula can be congenital,

Sexual differentiation in the fetus is bipoten-

they are generally acquired. The majority of

tial. This is true not only for the gonad and

such acquired diverticula are due to some form

the external genitalia which are derived from

of outlet obstruction. In children, posterior

a common primordium but for the ductal

urethral valves and congenital urethral stric-

structures as well, each sex having its own

tures are the most common cause. In adults,

primordium.

benign prostatic hypertrophy and acquired

Formation of the undifferentiated gonad

urethral strictures are the general basis for this

begins during the fifth week of fetal life when the

problem.

proliferation of germinal epithelial cells and the

However, the classical distinction, between an

mesenchyme underlying them produce a prom-

acquired and a congenital diverticulum is that

inence on the medial side of each mesonephros.

the congenital diverticulum displays an adventi-

This prominence is then known as the gonadal

tial, muscular, and mucosal layer whereas the

ridge.While the germinal epithelial cells and the

acquired diverticulum has only an adventitial

underlying mesenchymal tissue continue to pro-

and mucosal layer. Symptomatology is generally

liferate, primordial germ cells migrate into this

related to stasis with complicating infection, cal-

underlying mesenchyme at about the sixth week

culus formation or tumor formation. The treat-

of fetal life and the undifferentiated or bipoten-

ment is surgical if the diverticulum cannot be

tial gonad is formed (see Fig. 1.16).

cystoscoped, does not empty well, or complica-

tions exist.

20

Practical Urology: EssEntial PrinciPlEs and PracticE

Primordial germ cells

Supranenal medulla

Suprarenal cortex

Mesonephric duct

Tubule

Paramesonephric

duct

Medulla

Hindgut

Cortex

Primary sex cord

Y

No

(13th

(Seventh week)

Y

to

Influence

Influence

14th week)

Developing testes

Developing ovaries

Germinal epithelium

(Former primary

sex cord)

Mesovarium

Seminiferous cord

Mesonephric

duct

Mesonephric

tubule

Tunica

Germinal epithelium

Primordial germ cell

Paramesonephric duct

3. The deep portions of the seminiferous tubules

about the ninth week of fetal life, a primary cor-

narrow to form the tubuli recti, and these

tex and medulla form.These structures then give

converge to form the rete testis. The Sertoli

rise to a definitive cortex by the fourteenth week

of life. In ovarian development, the coelemic ger-

cells, seminiferous tubules, tubuli recti, and

minal epithelium gives rise to the primary ovar-

rete testis thus all originate from the coelemic

ian follicles, the underlying mesenchyme to the

epithelium. The Sertoli cells produce

stromal cells, and the primordial germ cells to

Müllerian inhibiting factor (MIF).

the ova. Like the testis, the ovary also gains a

4. The interstitial cells of Leydig differentiate

mesentery known as the mesovarium, and set-

between the seminiferous tubules. They pro-

tles into a more caudal position as the fetus

duce testosterone, which is the androgenic

develops. In addition to this early internal

hormone which influences male genital tract

descent,the ovary also becomes attached through

the gubernaculum to the tissues of the genital

and external genital development and

folds, which form the round ligaments of the

differentiation.

ovary, as well as to the tissues of the uterovaginal

5. As the Wolffian body (Genito-urinary ridge)

canal which form the broad ligament of the

regresses, the rete testes anastomose with the

uterus. A small processus vaginalis also forms

adjacent mesonephric tubules thus establish-

and passes toward the labial swellings, but this

ing the first genito-urinary connection (GU).

structure is usually obliterated at full term.

These connecting mesonephric tubules are

known as the vasa deferentia, and that por-

Gonadal Anomalies

tion of the mesonephric duct into which they

open becomes the epididymis.

Gonadal anomalies can simply be broken down

As the testicle further develops,it increases in size

into anomalies of development and anomalies

and shortens into a more compact organ while

of position.

achieving a more caudal location. Furthermore,

Anomalies of development include anomalies

its broad attachment to the mesonephros is con-

in number such as agenesis or anorchism, hypo-

verted into a gonadal mesentery known as the

genesis, supemumerary gonads or polyorchism,

mesorchium. By the third month of fetal life, the

as well as the extremely rare anomaly of gonadal

testis has descended and is located retroperitone-

fusion or synorchism.

ally in the false pelvis from where it gradually

Anomalies of position include cryptorchidism,

descends to the abdominal end of the inguinal

or imperfect descent of the testis, which is by far

canal. It remains there until the seventh month of

the commonest spermatic tract anomaly. The

fetal life at which time it passes through the ingui-

causeof imperfecttesticulardescentisunknown,

nal canal behind the processus vaginalis to enter

but is usually anatomic or hormonal in origin.

the scrotum by the end of the eighth month.

Testicular ectopy is due to faulty testicular

Caudal migration of the testes is facilitated by

descent along one of the subsidiary strains of

means of the gubenaculum. This fibromuscular

the gubemaculum. In such aberrant descent, the

band extends from the lower pole of the testis

testicle may be interstitial, femoral, penile,

through the developing muscular layers of the

perineal, or transverse in its position.

anterior abdominal wall to terminate in the sub-

Failure of union between the rete testes and

cutaneous tissue of the scrotal swelling. The

mesonephros, that is, the mesonephric tubules,

gubenaculum also has several subsidiary strands

results in a testis separate from the male genital

that extend to adjacent regions (femoral, inter-

ducts.

stitial, penile, etc.) and these explain testicular

maldescent into these regions.

22

Practical Urology: EssEntial PrinciPlEs and PracticE

function are absolutely essential in the devel-

The Müllerian inhibiting factor is secreted by

opment of the male fetus, neither the 46 XX

the Sertoli cells and acts locally (rather than sys-

complement nor the ovaries are necessary, for

temically) to suppress the development of the

female fetal development. It has been experi-

adjacent Müllerian structures in direct contact

mentally shown that if a genetic male fetus is

with the ipsilateral fetal testis. As the testis des-

castrated (no testosterone or MIF) before the

cends it acts sequentially on the adjacent Müllerian

genitalia differentiate, a female phenotype will

structures with the only remnants being the

develop. Thus while testicular influence is abso-

appendix testis at the superior end and the utricle

lutely necessary for male development, ovarian

in the verumontanum at the distal end.

influence is of no significance in female devel-

This action cannot be duplicated by andro-

opment since the natural tendency of the fetus

gens since testosterone, which is secreted by the

is to develop into a female.

Leydig cells, acts systemically rather than locally

As alluded to earlier, for normal male pheno-

and plays the most important role in two other

type development in utero, the testes must not

major facets of male phenotype development.

only differentiate normally but also function

First of all, it permits differentiation of the

normally. Two specific substances which are

mesonephric tubules and ductal structures into

critical to the development of the male pheno-

the epididymis, vas deferens, seminal vesicles,

type must be produced by the testes. The first of

and ejaculatory ducts. Secondly, testosterone

these is the hormone testosterone which is

also acts as a prehormone on the androgen

secreted by the Leydig cells. The second is the

dependent target areas, which include the com-

Müllerian inhibiting factor (MIF) which is

ponents of the urogenital tubercle, the urogeni-

thought to be secreted by the Sertoli cells (see

tal sinus, and that area in the urogenital sinus

Fig. 1.18).

which will eventually develop into the prostate