Female Urinary Organ Anatomy

The female pelvis is accustomed to a wide range of natural and pathologic conditions that a woman may experience in her life. The uterus significantly enlarges during pregnancy. The ovaries can be subject to various natural and pathologic states ranging from benign cysts to advanced ovarian carcinoma.

From the gross anatomy of the female pelvis to the microscopic anatomy, form follows function and allows for reproductive processes as well the possibility for pathologic conditions. The anatomy of the female genitourinary organs (see the image below) is addressed in the following section, along with certain anatomic variants.

The bony female pelvis is formed by two paired hip bones (each of which is made up of ilium, ischium, and pubis), the sacrum, and the coccyx. The pelvic brim divides the false pelvis above from the true pelvis below. The lumbosacral joint (between L5 and the base of the sacrum), sacroiliac joint, sacrococcygeal joint, and pubic symphysis make up the joints of the pelvis.

The female pelvic diaphragm provides the anatomic support for the pelvic viscera and is formed by the levator ani, coccygeus muscles, and their fascial coverings.[1, 2, 3, 4, 5]

The pelvic viscera are covered by 2 layers of peritoneum. This broad ligament extends from the lateral margin of the uterus to the lateral pelvic wall. It comprises the mesovarium, which supports the ovary with the posterior leaf of the broad ligament; the mesosalpinx, which suspends the uterine tube; and the mesometrium, which is the major part of the broad ligament below the mesosalpinx and mesometrium.

Pelvic organs

The female pelvic organs include the ovaries, uterine (fallopian) tubes, uterus, cervix, urinary bladder, ureters, vagina, and rectum (see the images below).

 

During a woman’s active reproductive life, the ovaries measure approximately 4 × 2.5 × 1.5 cm. They lie on the posterior aspect of the broad ligament and, as a consequence of their location, can often enlarge during pathologic states, such as ovarian cancer, without early detection. Accordingly, patients with ovarian cancer can present with nonspecific symptoms, such as abdominal bloating, back pain, and early satiety.

The uterine tubes connect the uterine cavity to the peritoneal cavity and are further subdivided into the uterine portion (interstitial portion), the isthmus, the ampulla (the largest and widest part), and the infundibulum, which terminates into fimbriae. Fertilization usually takes place at the infundibulum or ampulla. The tubes carry the fertilized or unfertilized oocytes to the uterus by means of ciliary assistance and muscular contraction.

The uterus varies in size, depending on a woman’s age and parity. It is divided into the fundus (the most superior and anterior portion), the body, and the lower uterine segment or isthmus, which connects the body of the uterus with the cervix. The cervix is the narrow inferior aspect of the uterus that projects into the vagina. It contains the internal os (the junction of the cervical canal with the uterine body), the cervical canal, and the external os (the opening of the canal into the vagina).

The ureter enters the pelvis by passing anteriorly to the bifurcation of the common artery. It generally has 3 points of constriction: directly at its origin, the point where it crosses the pelvic brim, and its junction with the bladder. In females, the ureter is crossed by the uterine artery within the pelvis. The uterine artery runs above and anterior to the ureter within the cardinal ligament, a structure composed of connective tissue that lies within the mesometrium of the broad ligament. The ureter also courses approximately 1.5 cm laterally to the cervix.

The urinary bladder has an apex at the anterior end and the fundus as its posteroinferior triangular portion. When completely filled, the bladder can have a capacity of up to 500 mL. The bladder trigone is bounded by the two ureteral orifices and the internal urethral orifice. The bladder neck is where the fundus and the inferolateral surfaces come together, leading into the urethra. At the bladder neck, as opposed to the upper bladder, the detrusor muscle layers--transitional epithelium, lamina propria, and muscularis mucosa--are clearly separable.

In females, the inner longitudinal fibers of the bladder neck converge radially to pass downward as the inner longitudinal layer of the urethra. The bladder and urethra are supported by the pubovesical ligament. The bladder neck (proximal urethra) was believed to be responsible for the continence mechanism. However, as a result of the successful use of midurethral slings to treat patients with stress urinary incontinence, the midurethra is now believed to be responsible for continence.

The main blood supply to the pelvic viscera is from branches of the internal iliac artery. Commonly, the internal iliac is divided into a posterior division, which gives rise to the iliolumbar, lateral sacral, and superior gluteal arteries, and an anterior division, which gives rise to the inferior gluteal, internal pudendal, umbilical, obturator, inferior vesical (male), middle rectal, and uterine and vaginal arteries (female).

The middle sacral artery arises from the aorta just before its bifurcation and supplies the posterior aspect of the rectum. The superior rectal artery is a direct continuation of the inferior mesenteric artery. The ovarian artery arises from the aorta and crosses the proximal end of the external iliac artery to enter the pelvis; it reaches the ovary through the suspensory ligament of the ovary (infundibulopelvic ligament).

The veins of the pelvis commonly correspond to the arteries. The usual exception is that the left ovarian vein empties into the left renal vein, whereas the right ovarian vein leads directly to the inferior vena cava. The blood supply to the bladder comes via the superior vesicular arteries from the umbilical artery and the inferior vesicular arteries from the vaginal artery. The venous drainage is from a plexus that drains into the internal iliac veins.

Lymphatic drainage parallels the course of venous blood supply. However, with respect to female cancers in the pelvis, lymphatic metastasis can obstruct flow and lead to retrograde metastasis, which can skip regional lymphatic chains. It is important to note that lymphatic drainage of the ovaries follows the suspensory ligaments of the ovary; thus, ovarian cancers can have isolated lateral aortic lymph node metastasis.

The nerve supply to the pelvis is made of the sacral plexus and autonomic nerves. Great care is taken by pelvic surgeons to avoid sacral nerve injuries. Femoral nerve injury results in decreased hip flexion and leg extension. Excessive traction or strain on the lower limbs imposed by the stirrups used for the dorsal lithotomy position during surgery is a cause of femoral nerve injury.

 

The sympathetic trunk and the hypogastric nerves are responsible for the sympathetic innervation of the pelvis. The pelvic splanchnic nerves (S2-S4) control the parasympathetic innervations of the pelvis and control micturition and defecation.

The parasympathetics stimulate detrusor muscle contraction along with relaxation of the internal urethral sphincter, which facilitates bladder emptying. Alternately, the sympathetic nerves relax the detrusor and contract the urethral sphincter. Often, radical pelvic surgery, such as radical hysterectomy for cervical cancer, can compromise parasympathetic innervation and thereby lead to postoperative urinary retention.

Anatomic spaces

Surgeons who operate on the female pelvis should be comfortable with several anatomic spaces. These spaces are often dissected during various gynecologic, urologic, and oncologic procedures, as follows.

The paravesical space is lateral to the bladder and is opened by dissection underneath the round ligament insertion; it is bounded by the superior pubic ramus and medially by the bladder and vagina. The lateral wall is made up of the external iliac vessels and obturator fossa. The posterior border is the cardinal ligament, which also divides the paravesical from the pararectal space.

The pararectal space is bounded by the sacrum posteriorly, the cardinal ligament anteriorly, the ureter laterally, and the origin of the internal iliac artery laterally.

The prevesical space (space of Retzius) is defined anatomically as the area between the bladder and the pubic bone.

The obturator canal contains the obturator vessels, nerves, and lymphatics. The vessels and nerves of this canal are at risk for injury during placement of transobturator slings placed for urinary stress incontinence.

Pelvic support

The downward descent of the uterus, vagina, cervix, bladder, and rectum relative to the vaginal vault is defined as pelvic organ prolapse. Cystocele (prolapse of the urinary bladder) and rectocele (prolapse of the rectum into the vaginal tissue) are due to central defects of the pubovesical and rectouterine tissue. DeLancey described 3 levels of uterovaginal support by the deep endopelvic fascia, as follows[6] :

• Level I - Proximal suspension of ligaments to the paravaginal tissue; damage to this support causes enterocele, posthysterectomy vaginal prolapse, and uterovaginal prolapse

• Level II - Lateral support of the pelvic fascia to the side walls; damage leads to paravaginal and pararectal defects

• Level III - Fusion of the sphincter urethrae and pelvic diaphragm (formerly called urogenital diaphragm) anteriorly and the proximal perineum posteriorly' compromise leads to urinary incontinence

In the examination of patients for pelvic organ prolapse, the Baden-Walker halfway system and subsequently, the pelvic organ prolapse-quantification system (POP-Q) have been used so that the reconstructive surgeon has a means of objectively evaluating and documenting these patients.

The ovary is divided into a cortex and a medulla. Follicles in varying stages (according to the menstrual cycle) are found within the outer cortex. With each cycle, 1 follicle develops into a Graafian follicle, leading to ovulation. After ovulation, this follicle becomes the corpus luteum. Corpora lutea of varying stages, as well as corpora albicantia, are present in the ovarian cortex.

The medulla of the ovary is generally made up of loosely arranged mesenchymal tissue, along with small clusters of round to polygonal epithelial-appearing cells around vessels and nerves, which are also steroid-producing. The uterine tube consists of epithelium containing ciliated columnar cells, nonciliated cells, and columnar secretory cells.

The endometrium during the menstrual cycle is under the influence of ovarian hormones, specifically follicle-stimulating hormone and luteinizing hormone. The hypothalamic-pituitary-ovarian axis drives the menstrual cycle.

During the follicular phase, as a single ovum develops, estrogen production by the dominant follicle increases over the first 2 weeks of the 28-day menstrual cycle. The estrogen level peaks just before ovulation and then declines. During the luteal phase, progesterone is made by the corpus luteum; the progesterone level rises during the last half of the cycle and then falls to a basal level just before menstruation.

The endometrium is made up of glands that are straight tubular structures lined by regular, tall pseudostratified columnar cells and stroma that are compact spindle cells.Its basal third is not hormonally responsive; the remaining endometrium (both glands and stroma) undergoes rapid growth during the proliferative phase of the menstrual cycle. The glands have numerous mitotic figures. The secretory phase is notable for subnuclear vacuoles, predecidual changes, and finally stromal breakdown and the onset of menses.

The external os of the cervix is covered by stratified nonkeratinizing squamous epithelium. The internal os is lined by columnar, mucus-secreting epithelium, which dips down into the stroma to produce endocervical glands. The point at which the squamous and glandular epithelium meet is the squamocolumnar junction.

A combination of ingrowth of the squamous epithelium and metaplasia transforms this area into squamous epithelium and forms the transformation zone. It is in the transformation zone, including the squamocolumnar junction, that precancerous cervical lesions leading to squamous cell carcinoma of the cervix develop, often in the absence of routine Papanicolaou (Pap) screening.

The ureters, bladder, and urethra are lined by transitional epithelium (urothelium). The bladder has bundles of smooth muscle fibers that collectively form the detrusor muscle.

Congenital uterine abnormalities

Congenital uterine abnormalities can lead to infertility and recurrent pregnancy loss. The incidence ranges from 3-4% for fertile and infertile women, 5-10% for women with recurrent miscarriages, and more than 25% of women with late miscarriages and preterm deliveries. Uterine abnormalities can originate from failure of midline fusion of embryologic (Mullerian) structures. Some examples are as follows:

• Septate uterus (most common) - A septum divides the uterus into 2 halves

• Unicornuate uterus - 1 communicating and usually 1 noncommunicating contralateral horn (often with ipsilateral renal agenesis)

• Bicornuate uterus - 2 separate uterine cavities share a common lower segment and a single cervix

• Arcuate uterus - This is a heart-shaped uterus

• Uterus didelphys (didelphic uterus) - The paramesonephric (Mullerian) ducts completely lack fusion, often with 2 compete uterine cavities and 2 cervices

• Vaginal septum - This is usually a longitudinal band of tissue, often found in uterus didelphys

Congenital ureteral abnormalities

Congenital ureteral abnormalities are as follows:

• Bifid ureters - The upper pole and lower pole ureters join proximal to the bladder

• Double ureters - The upper pole ureter and lower pole ureter empty separately into the bladder

• Ectopic ureter - Rarely, a ureter can insert into the bladder at some other location besides the trigone; the ectopic ureter usually enters caudally and can enter the urethra or even some point outside the urinary tract (eg, the distal third of the vagina)

• Pelvic kidney - This is lower-than-normal positioning of the kidney; patients with an ectopic kidney have an approximately 15% incidence of other genital abnormalities

• Ureterocele - This is a congenital defect in which the distal ureter balloons at its opening in the bladder; it is often associated with a duplicated urinary system

One of the most common pathophysiologic conditions within the lower female reproductive tract is uterine fibroids (myomas, leiomyomata uteri). Fibroids are benign smooth muscle tumors whose incidence is approximately 25% in the general population and can be even higher in the black population.

Symptomatic fibroids are a common indication for hysterectomy in the United States. They can be intramural (within the myometrium), submucosal (beneath the endometrium), or subserosal (beneath the serosa). Small subserosal fibroids can be surgically managed by means of hysteroscopic resection. Fibroids can be asymptomatic, or patients can present with menorrhagia, pelvic pressure, bowel symptoms, or urinary symptoms. Fibroids (especially submucosal) can be a cause of female infertility.

Endometriosis is the presence of ectopic endometrial glands and stroma. The exact incidence is unknown, because the only reliable method to diagnose the condition is direct visualization at the time of surgery (usually diagnostic laparoscopy). Endometriosis can lead to pelvic pain, dysmenorrhea, and infertility. Endometriosis implants can be found anywhere in the pelvis, and even extrapelvic implants have been reported.

Commonly, implants can be found on the ovaries, uterosacral ligaments, uterine serosa, and rectovaginal septum. The classic implant is blue-black in appearance, containing hemosiderin deposits (from trapped old blood). Frequently, however, the implants are nonspecific but atypical appearing. Treatment includes surgical ablation and medical management aimed at eliminating cyclic menstruation, such as oral contraceptives and gonadotropin-releasing hormone agonists.

Ureteral reflux is more common in females postnatally. Primary vesicoureteral reflux is usually due to congenital shortening and loss of longitudinal muscle of the intravesicular ureter. Secondary vesicoureteral reflux can be caused by anatomic and functional causes. Reflux and ureteropelvic junction (UPJ) obstruction are both congenital, and both may present as hydronephrosis.

Reflux may cause recurrent urinary tract infection and renal scarring and may lead to renal failure, especially in the pediatric population. UPJ obstruction can be caused by crossing vessels or nonperistalsis segments. Patients need an appropriate workup. Some patients with mild disease need no surgical intervention; others need intervention (such as nephrostomy, ureteral stent, or urinary diversion) to prevent loss of renal function.

Urethral caruncle and urethral diverticulum are 2 uncommon genitourinary pathologic variants. Urethral caruncle is a soft, fleshy protruding mass from the urethral opening. It is more common in prepubescent girls and elderly women but overall is a rare condition. Patients with a urethral caruncle present with bleeding and dysuria.

Urethral diverticulum is an outpouching that forms next to the urethra. Because of increased use of radiologic imaging, the overall incidence of diverticula has increased; however, the exact incidence is not known. Urethral diverticulum has a preponderance for females, usually those 40-70 years of age. Patients with a diverticulum tend to present with recurrent urinary tract infections and obstruction of the periurethral glands.

Ureteral injury

An increased risk for ureteral injury exists during female pelvic surgery. If the ureter is damaged at the pelvic brim, then a primary ureteroureterostomy can be performed. This type of injury can result from clamping and incising the suspensory ligament of the ovary. Additionally, when pelvic anatomy is distorted, iatrogenic midureteral injury can occur--for example, in cases of ovarian cancer debulking surgeries or salpingo-oophorectomies in which pelvic adhesions or endometriosis exist.

If the ureteral injury is lower or more proximal to the bladder, as when the uterine arteries are clamped and incised during hysterectomy, then ureteroneocystostomy can be performed. The ureter is reimplanted into the bladder or a flap of bladder is made into a tube that can be anastomosed to the ureter. A so-called psoas hitch can be performed, in which the tube of bladder is sutured to the iliopsoas fascia above the iliac vessels. In this way, the ureter can be anastomosed to the bladder with less tension.

This approach is often required when the distal ureteral segment is transected and compromised, and it has a success rate of 95-100%. If the injury is to the lower two thirds of the ureter and the bladder cannot be brought up in the psoas hitch procedure, then a Boari flap or transureteroureterostomy can be performed. A pedicle of bladder is swung upward and used to bridge the gap to the injured ureter.

Pelvic hemorrhage

Pelvic hemorrhage can result from uterine atony after delivery, from trauma, or from vessel injury during surgical procedures. During cesarean section, several surgical methods can be used to control hemorrhage from uterine atony: uterine compression sutures (B-lynch sutures), uterine artery ligation, internal iliac artery ligation, and intrauterine tamponade balloons.

An important point regarding internal iliac artery (hypogastric artery) ligation is that ligation of the anterior division of the internal iliac artery is needed to control pelvic hemorrhage. Inadvertent ligation of the posterior division in part results in necrosis of the gluteal muscles.

Another method for controlling pelvic hemorrhage is uterine artery embolization, in which a catheter is advanced via the femoral artery, the bleeding point is identified with contrast imaging, and the branch of the uterine artery involved is embolized with an absorbable material.

In certain cases of hemorrhage, the ovarian vessels may intentionally or unintentionally become embolized. To embolize ovarian vessels, a catheter must be placed above the level of the renal artery and then advanced to the ovarian vessels; the mesenteric artery must be identified beforehand to prevent ischemic damage to the bowel.

Fistula

Vesicovaginal fistula is an abnormal communication between the bladder and the vagina.Ureterovaginal fistula is an abnormal communication between the ureter and the vagina.Rectovaginal fistula is an abnormal communication between the rectosigmoid or anal canal and the vagina.Most female genitourinary fistulae are due to gynecologic surgery--specifically, urogynecologic procedures, total abdominal hysterectomy, childbirth complications, or (infrequently) radiation therapy for cancer.

Patients often present with dribbling of urine. They may have fever and recurrent urinary infections. Patients can be managed conservatively with urinary diversion (eg, a Foley catheter) before surgical repair is initiated.

Rectovaginal fistula is often caused by obstetrical trauma and is occasionally due to radiation-induced injury. High rectovaginal injuries can be due to diverticular abscess or to inflammatory bowel disease. Patients present with stool or gas per vagina, along with foul-smelling vaginal discharge. Generally speaking, surgical management consists of vaginal repair for lower defects and (usually) colostomy for upper defects.