The Pelvis and the Perineum

Chapter 4 The Pelvis and the Perineum

I. Bony Pelvis (Figure 4-1) (see also Chapter 5)

A. Overview

1. Composed of paired hip bones, sacrum, and coccyx

2. Oriented in anatomical position so anterior superior iliac spines (ASIS) and pubic tubercles lie in same vertical plane

4-1 Bony pelvis and ligaments, anterior view. The pelvic brim is the boundary between the greater pelvis and lesser pelvis. In the anatomical position, the pubic tubercle and anterior superior iliac spine lie in the same vertical plane.

(From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 353.)

The pelvis has the ASIS and the pubic tubercle in the same vertical plane.

B. Pelvic brim

1. Surrounds superior pelvic aperture or pelvic inlet

2. Formed by sacral promontory, arcuate line of ilium, pecten and crest of pubis, and pubic symphysis

3. Divides bony pelvis into superior greater or false pelvis and inferior lesser or true pelvis

C. Greater pelvis (false pelvis)

1. Expanded portion of bony pelvis superior to pelvic brim: deep in male; shallow in female

2. Lowest part of abdominal cavity with superior part of bony pelvis providing protection to lower abdominal viscera

The greater pelvis is part of the abdominal cavity.

D. Lesser pelvis (true pelvis)

1. Bony pelvis inferior to pelvic brim

2. Open to abdominal cavity superiorly but closed inferiorly by pelvic diaphragm

3. Has inferior part of bony pelvis protecting pelvic organs and providing skeletal framework for perineum

E. Pelvic outlet

• Diamond-shaped area bounded by coccyx, sacrotuberous ligaments, ischial tuberosities, ischiopubic rami, and pubic symphysis

Because the pelvis functions as a rigid ring of bone, traumatic injury frequently causes a fracture in two places: a site where traumatic force is applied and 180° opposite that site. If an individual falls on the greater trochanter or falls from a height and lands on his feet, the head of the femur may be driven through the acetabulum into the pelvic cavity. Pelvic fractures may injure pelvic organs, including the urinary bladder and reproductive organs, and cause hemorrhage from pelvic blood vessels and resultant shock. The majority of bleeding often results from venous plexus injury. A full bladder is more likely to rupture than an empty one, and urethral injuries are more likely in males. During surgical repair, screws must be carefully placed to avoid injuring the internal iliac artery and vein lying against the inner surface of the bone.

Traumatic pelvic fractures often occur in two places with pelvic organ injury and hemorrhage.

Avulsion fractures occur at muscle attachments in skeletally immature patients.

Fetal head rotates 90° during birth as maximum diameter changes from transverse at pelvic inlet to anteroposterior at pelvic outlet.

In skeletally immature individuals, avulsion fractures at the sites of muscle attachments are common. Frequent sites of avulsion fractures include the anterior superior iliac spine (sartorius), anterior inferior iliac spine (rectus femoris), and ischial tuberosity (hamstrings).

The midpelvic diameter is the narrowest point of the birth canal and the point of greatest difficulty during labor.

II. Pelvic Measurements (Figures 4-2 and 4-3)

A. Overview

1. In a female, dimensions of pelvic inlet, midpelvis, and pelvic outlet are important determinants of successful vaginal birth.

2. In a female, pelvic deformities and some individual variations may cause difficult labor (dystocia).

B. Measurements of Obstetrical Significance (Table 4-1)

III. Differences Between Male And Female Bony Pelvis (Table 4-2)

1. Typical funnel shape of male pelvis

2. Heart-shaped pelvic inlet with maximum transverse diameter close to sacrum

B. Gynecoid

1. Typical shape of female pelvis with straight side walls and wide interspinous diameter

2. Oval pelvic inlet with maximum transverse diameter well anterior to sacrum

4-2 Pelvic measurements with obstetrical significance. Obstetrical conjugate is estimated as diagonal conjugate minus 1.5-2.0 cm.

(From Seidel, H M, Ball, J W, Dains, J E, Benedict, G W: Mosby’s Guide to Physical Examination, 6th ed. St. Louis, Mosby Elsevier, 2006, Figure 18-28.)

4-3 Interspinous diameter between ischial spines is narrowest transverse diameter of midpelvis. Measurement is estimated by moving examining fingers in vagina from side to side between spines.

(From Lowdermilk, D L, Perry, S E: Maternity and Women’s Health Care, 8th ed. St. Louis, Mosby, 2004.)

TABLE 4-1 Pelvic Measurements of Obstetrical Significance

Measurement	Distance	Comments
Pelvic Inlet
True conjugate diameter	AP distance between sacral promontory and upper border of pubic symphysis
Diagonal conjugate diameter	AP distance between sacral promontory and lower border of pubic symphysis	Measured during vaginal exam
Transverse diameter	Greatest distance between right and left arcuate lines
Oblique diameter	Distance between one sacroiliac joint and contralateral iliopubic eminence
Midpelvis
Interspinous (midpelvic) diameter	Distance between ischial spines	Narrowest point of birth canal; estimated during vaginal exam
Pelvic Outlet
Anteroposterior diameter	Distance between tip of coccyx and lower border of pubic symphysis
Intertuberous (transverse) diameter	Distance between medial surfaces of ischial tuberosities	Smallest diameter of pelvic outlet

AP, anteroposterior.

TABLE 4-2 Differences between Male and Female Bony Pelvis

Feature	Male	Female
False pelvis	Deep	Shallow
Pelvic inlet	Narrow and heart-shaped	Wide and almost oval
Pelvic cavity	Longer, tapered, cone-shaped	Shorter, cylindrical, roomier
Pelvic outlet	Smaller	Larger because of eversion of ischial tuberosities and wider subpubic angle
Subpubic angle	<70°	>80°
Shape of sacrum	Longer, narrower, and more curved	Shorter, wider, and flatter
Anterior pelvic wall	Longer	Shorter

Sacroiliac joints transfer weight from the axial to the lower-extremity skeleton.

IV. Joints of Pelvis

A. Sacroiliac Joint (see Figure 4-1)

1. Only joint between axial skeleton and pelvic girdle

2. Transfers weight of upper body to lower extremity

Sacroiliac joints and pubic symphysis allow limited mobility, more during pregnancy.

3. Reinforced by strong ligaments and so stable that bone on either side of joint is more likely to fracture than joint is to dislocate

B. Pubic Symphysis

1. Midline joint between bodies of two pubic bones

2. Fibrocartilaginous disc connecting surfaces covered by hyaline cartilage

3. Reinforced by superior pubic and inferior (arcuate) pubic ligaments

4. Relatively immovable except in latter stages of pregnancy, when hormones cause ligaments to loosen

Hormonal changes during pregnancy relax the pelvic ligaments and pubic symphysis, allowing enlargement of the birth canal.

V. Pelvic Cavity

A. Boundaries

1. Pelvic brim

2. Lateral walls: hip bone below pelvic brim, obturator membrane, obturator internus muscle and fascia, sacrotuberous and sacrospinous ligaments

3. Posterior wall: sacrum and coccyx and piriformis muscle

4. Floor: pelvic diaphragm

B. Pelvic Diaphragm (Figure 4-4)

a. Muscular hammock formed by levator ani and coccygeus muscles and their fasciae

b. Supports pelvic organs and raises pelvic floor

c. Incomplete anteriorly at urogenital hiatus to allow passage of urethra in both sexes and vagina in female

d. Pierced posteriorly by anal canal

e. Innervated by anterior rami of S4 spinal nerves and pudendal nerves (S2-4)

4-4 Pelvic diaphragm of male, superior view. The levator ani and coccygeus muscles and their fasciae form the pelvic diaphragm. The urogenital hiatus is an anterior gap between the medial borders of the two levator ani muscles, which is filled by the urogenital diaphragm (including the perineal membrane) except for passage of the urethra in both sexes and the vagina in females.

(From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 358.)

The pelvic diaphragm provides dynamic support for pelvic organs.

2. Coccygeus (ischiococcygeus) muscle

• Parallels and blends inferiorly with sacrospinous ligament

3. Levator ani muscle

(1) Funnel-shaped layer consisting of iliococcygeus and pubococcygeus muscles

(2) Aids in maintaining urinary and fecal continence and preventing prolapse of pelvic organs

(3) Susceptible to damage during childbirth

Levator ani injury during childbirth may cause urinary or fecal incontinence and pelvic organ prolapse.

b. Iliococcygeus muscle

• Arises from tendinous arch of levator ani (arcus tendineus) and ischial spine and inserts into coccyx and anococcygeal ligament

c. Pubococcygeus muscle

(1) Arises from dorsal surface of pubis and fuses posteriorly with opposite muscle at anococcygeal ligament

(2) Anteriorly surrounds base of prostate (puboprostaticus, levator prostatae) or inferior end of vagina (pubovaginalis)

d. Puborectalis muscle

(1) Thicker inferomedial part of pubococcygeus muscle; joins opposite muscle to form sling around anorectal junction, maintaining anorectal (perineal) flexure

(2) Relaxes only during defecation

The puborectalis produces anorectal flexure and maintains anal continence.

VI. Other Features of Pelvic Walls and Floor

A. Obturator Membrane

1. Closes obturator foramen except superiorly at obturator canal where obturator nerve and vessels pass into thigh

2. Surfaces provide attachment for obturator internus and obturator externus muscles.

B. Sacrotuberous Ligament (see Figure 4-1)

1. Extends from posterior iliac spines, sacrum, and coccyx to ischial tuberosity

2. Forms inferior boundary of lesser sciatic foramen

3. Stabilizes sacroiliac joint

C. Sacrospinous Ligament (see Figure 4-1)

1. Extends from sacrum and coccyx to ischial spine, separating greater and lesser sciatic foramina

2. Stabilizes sacroiliac joint

D. Pelvic Fascia

1. Parietal pelvic fascia lines pelvic walls and is continuous with transversalis and iliopsoas fasciae of the abdomen.

2. Visceral pelvic fascia covers and supports pelvic viscera; condensations form fascial ligaments extending from pelvic walls to viscera.

Pelvic fascial ligaments and the pelvic diaphragm support the pelvic viscera, especially when intraabdominal pressure is increased. Injury to the pelvic floor during childbirth or laxity associated with advancing age causes loss of support with prolapse of pelvic organs, particularly the uterus and rectum. Other risk factors include genetic predisposition, nerve lesions, connective tissue disorders, and chronically increased intraabdominal pressure (e.g., from coughing or strenuous physical activity).

The sacrospinous ligament separates greater and lesser sciatic foramina, and the sacrotuberous ligament forms the inferior boundary of the lesser.

E. Pelvic Ligaments (Figure 4-5)

• Fibrous condensations of pelvic fascia containing variable amounts of smooth muscle

4-5 Female pelvic ligaments, superior view.

Risk factors for pelvic organ prolapse include childbirth, age, obesity, neurogenic dysfunction, and connective tissue disorders.

1. Puboprostatic (male) or pubovesical/pubocervical (female) ligament

a. Condensation of superior fascia of pelvic diaphragm

b. Attaches prostate (male) or neck of bladder and cervix (female) to posterior surface of pubis

2. Transverse cervical ligament (female)

a. Cardinal (Mackenrodt) ligament

b. Fascial condensation with embedded smooth muscle in base of broad ligament

c. Extends from lateral pelvic wall to cervix of uterus and lateral fornix of vagina with uterine artery running medially in it

d. Most important ligament supporting uterus and vagina

3. Sacrogenital ligament

a. Also called rectoprostatic in male; extends from prostate to sacrum

b. Also called uterosacral/rectouterine in female; forms posterior continuation of transverse cervical ligament from cervix and vagina to sacrum

c. Stabilizes and supports pelvic organs

The transverse cervical and uterosacral ligaments passively support the uterus.

VII. Pelvic Organs in Both Male and Female (Figures 4-6 and 4-7)

1. Constricted at ureteropelvic junction, pelvic brim, and entrance into bladder

2. Crosses pelvic brim near bifurcation of common iliac artery

4-6 Male pelvic organs in paramedian and median sagittal sections.

(From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 361.)

4-7 Median sagittal section of female pelvic organs. Note close relationship of rectouterine pouch to posterior fornix of vagina.

(From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 360.)

Obstruction of a ureter by a calculus usually occurs at sites of constriction.

3. In male, crossed superiorly by ductus deferens near bladder

4. In female, crossed anteriorly and superiorly by uterine artery in base of broad ligament

Renal calculi (kidney stones) typically obstruct the ureter at its three sites of constriction. Most calculi are too small to be seen on plain radiographs, so an intravenous pyelogram is required (Figure 4-8).

4-8 Intravenous pyelograms in patient with ureteral calculus. Images taken at 5 minutes and 25 minutes following contrast agent injection in young male with intense right flank pain and hematuria. A, Small calculus is shown at the entrance of the right ureter into the bladder (arrow). B, Delayed image shows right renal collecting system and ureter dilated due to the distal obstruction.

(From Mettler, F A: Essentials of Radiology, 2nd ed. Philadelphia, Saunders, 2004, Figure 7-12.)

The ureter can be damaged during a hysterectomy or surgical repair of a prolapsed uterus because it lies posterior and inferior to the uterine artery. This relationship, easily remembered as “water flows under the bridge,” is an important one for surgeons.

Uterine artery passes anterior and above ureter (“water flows under the bridge”).

B. Urinary Bladder

1. External features

• Attached to umbilicus by median umbilical ligament, a remnant of the fetal urachus

b. Fundus (base)

(1) Related to seminal vesicles and rectum in male and uterus and vagina in female

(2) Receives ureters; internally features trigone

c. Superior surface

• Completely covered by peritoneum and domes into abdominal cavity as bladder fills

• Surrounds urethra; relatively immobile, especially in male where attached to prostate

The full adult urinary bladder may be palpated through the anterior abdominal wall above the pubic symphysis. The empty adult bladder occupies the lesser pelvis but may be palpated when one hand is placed over the bladder with a finger from the other hand placed in the rectum of the male or in the vagina of the female. In a child, the empty or full bladder can always be palpated because it extends above the pubic symphysis into the abdomen.

A young child’s bladder is always an abdominal organ, but an adult’s empty bladder is pelvic.

2. Muscle of bladder wall

a. Interlacing layers of smooth muscle known as detrusor muscle

b. Surrounds urethra at bladder neck as circularly arranged internal urethral sphincter

3. Internal features of urinary bladder

• Small triangular area of fundus defined by two ureteric orifices and internal urethral orifice where mucosa remains smooth whether bladder is empty or filled

b. Ureteric orifices

• Slitlike openings at superolateral angles of trigone

c. Interureteric fold

• Landmark for introducing catheter into ureter

d. Internal urethral orifice

• Lies at inferior angle of trigone

The uvula is a small elevation in the male at the inferior angle of the trigone, just above the internal urethral orifice. It enlarges with age due to enlargement of the underlying median lobe of the prostate and may inhibit complete bladder emptying. Stagnation of retained urine results in development of urinary tract infections. There also may be hesitancy starting urination, diminished force and size of stream, terminal dribbling, and hematuria.

Obstruction of the oblique course of the ureter through the bladder wall (e.g., due to detrusor muscle hypertrophy, invasion by cervical cancer) or vesicoureteral reflux due to trigonal muscle weakness may cause backup of urine. The result is hydroureter and hydronephrosis. The ureter becomes elongated and tortuous due to smooth muscle that hypertrophies to increase peristaltic force (see Figure 4-8, B).

Ninety percent of bladder cancers are transitional cell carcinomas. They are most common in males over the age of 50. Cigarette smoking is the most important risk factor, although occupational exposure to chemicals such as aniline dyes may account for one-third of cases. Painless hematuria is the most common presenting symptom, but frequency, urgency, and dysuria also may be present.

An enlarging uvula in the lower trigone may inhibit bladder emptying and predispose to infections.

4. Blood supply: superior vesical branches of umbilical arteries; inferior vesical arteries in males and vaginal arteries in females

5. Venous drainage: internal iliac veins by vesical and prostatic venous plexuses; connections with the vertebral venous plexus provide a route for cancer metastases

Drainage from vesical to vertebral venous plexus provides a route for cancer metastasis to the vertebral column and spinal cord.

6. Innervation: vesical and prostatic plexuses

7. Micturition reflex

a. Sympathetic fibers inhibit detrusor muscle and stimulate internal urethral sphincter contraction, inhibiting emptying.

b. Parasympathetic fibers stimulate detrusor muscle contraction and inhibit the internal sphincter, facilitating emptying.

Sympathetic fibers stimulate internal urethral sphincter contraction to prevent retrograde ejaculation in males.

c. Somatic motor fibers (pudendal nerve) cause voluntary relaxation of external urethral sphincter (sphincter urethrae).

8. Retropubic space

Sympathetic nerve fibers inhibit and parasympathetic fibers facilitate micturition, with pudendal nerve providing voluntary control.

• Potential space containing extraperitoneal connective tissue separating pubic bones and symphysis from anterior surface of bladder

If a urethral catheter can’t be inserted in a patient with obstruction or to provide drainage in patients with spinal cord injuries, urine can be removed from the bladder without penetrating the peritoneum by inserting a needle or catheter just above the pubic symphysis (suprapubic cystotomy). The catheter passes successively through skin, fatty and membranous layers of superficial abdominal fascia, linea alba, transversalis fascia, extraperitoneal connective tissue, and the wall of the bladder.

Retropubic space allows extraperitoneal access to the urinary bladder and prostate gland.

a. Large intestine connecting sigmoid colon and anal canal

b. Has complete outer longitudinal layer of smooth muscle and therefore lacks teniae coli and haustra; also lacks omental appendices

The rectum lacks teniae coli, haustra, and omental appendices that are characteristic of the rest of the large intestine.

c. Peritoneal covering on anterior and lateral sides in proximal third; anterior surface in middle third; none in distal third

d. Transverse rectal folds (Houston valves) may serve to support fecal matter.

2. Blood supply: superior rectal artery from inferior mesenteric artery with contributions from middle and inferior rectal arteries from internal iliac artery

3. Venous drainage: superior rectal vein (inferior mesenteric vein), which anastomoses with middle and inferior rectal veins (internal iliac vein) in a portocaval anastomosis

4. Innervation: preganglionic parasympathetic innervation from pelvic splanchnic nerves and postganglionic sympathetic innervation from inferior hypogastric plexus

A sigmoidoscope or other rigid object can perforate the wall of the rectum. Any object that penetrates the middle third anteriorly or the upper third anteriorly or laterally enters the peritoneal cavity.

Cancer from midgut and hindgut derivatives metastasizes to the liver through the portal vein.

Carcinoma of the rectum is relatively common. Initially it remains localized, but then it spreads along lymphatic vessels and through the venous system. Because the superior rectal vein is a tributary of the portal vein, metastasis to the liver is common. A tumor may penetrate the rectal wall posteriorly and invade the sacral plexus, producing sciatica. Laterally, the tumor may invade the ureter. Anterior spread may involve the vagina and uterus in the female and the prostate, seminal vesicles, or bladder in the male.

Ulcerative colitis is the most common inflammatory disease of the bowel and is limited to the colon. It is mainly a disease of young adults that begins in the rectum and spreads proximally, involving only the mucosa and submucosa with continuous ulcerations (Figure 4-9). Islands of residual mucosa produce pseudopolyps. The patient experiences recurrent left-sided abdominal cramping with bloody mucoid diarrhea. In the most severe cases, toxic damage to parasympathetic ganglia stops bowel function, and the colon progressively swells and becomes gangrenous (toxic megacolon). Patients have an increased risk of adenocarcinoma.

4-9 Radiograph of ulcerative colitis following double-contrast barium enema showing small irregular, confluent ulcers extending from the rectum to the right colic flexure.

(From Mettler, F A: Essentials of Radiology, 2nd ed. Philadelphia, Saunders, 2004, Figure 6-75.)

Ulcerative colitis is a chronic inflammatory bowel disease that begins in the rectum and spreads proximally.

Ulcerative colitis: continuous mucosal-submucosal ulcerations of the rectum and colon. Crohn disease: transmural inflammation with skip lesions involving ileum ± colon

D. Development of Urinary Bladder, Rectum, and Anal Canal (Figure 4-10)

a. Dilated common chamber of allanois and hindgut that gives rise to urinary bladder, rectum, and anal canal

4-10 A, Orientation view of developing urinary and gastrointestinal systems. B-C, Progressive development of urinary bladder, rectum, and anal canal. Urorectal septum grows toward cloacal membrane to divide cloaca into ventral urogenital sinus (urinary bladder) and dorsal rectum and superior part of anal canal. Perineal body develops at site of fusion of urorectal septum with cloacal membrane (C).

(From Cochard, L: Netter’s Atlas of Human Embryology, Icon Learning Systems. Philadelphia, Saunders, 2002, Figures 7.2 and 7.4.)

The cloaca is the dilated common chamber of the allantois and the embryonic hindgut that is divided into the ventral urinary bladder and the dorsal rectum and anal canal.

b. Contacts surface ectoderm at cloacal membrane

2. Urorectal septum

a. Mesenchymal wedge that divides cloaca into urogenital sinus ventrally and rectum and anal canal dorsally

b. Fuses with cloacal membrane at future site of perineal body

3. Urinary bladder

• Develops mainly from upper, vesical part of urogenital sinus

4. Allantois

a. Initially diverticulum of yolk sac into connecting stalk continuous with cloaca

b. Continuous with vesical part of urogenital sinus but constricts into fibrous urachus, extending to umbilicus

Usually the embryonic allantois is obliterated to form the fibrous urachus connecting the apex of the bladder to the umbilicus. In the adult it is known as the median umbilical ligament. If the lumen remains patent in a newborn (urachal fistula), this connection causes urine to leak from the umbilicus. Midline urachal cysts also may occur.

A urachal fistula causes urine to leak from the neonatal umbilicus.

5. Rectum and anal canal above pectinate line

a. Develop from endoderm of hindgut

b. Supplied by superior rectal artery and drained by superior rectal vein and by lymphatic vessels to inferior mesenteric and internal iliac lymph nodes

c. Innervated by visceral afferent fibers

The hepatic portal and inferior vena caval systems anastomose at the pectinate line.

6. Anal canal below pectinate line

a. Develops from ectoderm of proctodeum

b. Supplied by inferior rectal arteries and drained by inferior rectal veins and by lymphatic vessels to superficial inguinal lymph nodes

The anal canal below the pectinate line drains to the superficial inguinal lymph nodes.

c. Innervated by somatic afferent fibers of pudendal nerve

VIII. Male Pelvic Structures (Figure 4-11; see also Figures 4-6 and 4-12)

A. Seminal Vesicle

1. Coiled, blind-ending tube posterior to fundus of bladder, lateral to ampulla of ductus deferens, and anterior to rectum, through which it normally can be palpated

2. Joins ductus deferens near base of prostate to form ejaculatory duct

3. Produces seminal fluid but does not store spermatozoa

B. Ductus Deferens

1. Thick-walled muscular tube that begins as continuation of epididymis and carries sperm to ejaculatory duct

2. Traverses inguinal canal as part of spermatic cord

3. Becomes dilated posterior to bladder to form ampulla

C. Ejaculatory Duct

1. Formed by union of ductus deferens and duct of seminal vesicle

2. Passes through prostate to open into prostatic urethra

D. Prostate Gland

a. Pyramidal gland surrounding prostatic urethra with its base at neck of bladder and its apex resting on superior fascia of urogenital diaphragm

b. Enclosed by fibrous capsule that is separated from visceral pelvic fascia (prostatic sheath) by prostatic venous plexus

4-11 Urinary bladder and pelvic organs unique to male, posterior view. Note formation of ejaculatory ducts, position of lateral and middle lobes of prostate, and relationship of ureter to ductus deferens.

(From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 384.)

The prostatic venous plexus is a potential source of hemorrhage during prostate surgery.

c. Supported laterally by pubococcygeus muscles and bound anteriorly to pubic bones by puboprostatic ligaments

2. Internal features of prostatic urethra (Figure 4-12)

a. Urethral crest

• Longitudinal ridge in posterior wall

b. Seminal colliculus (verumontanum)

• Enlargement of urethral crest that receives openings of paired ejaculatory ducts and median prostatic utricle

c. Prostatic utricle

(1) Blind pouch opening at summit of seminal colliculus

(2) Homologue of uterus and proximal vagina because it is considered remnant of fused paramesonephric (müllerian) ducts

d. Prostatic sinus

• Depression on each side of urethral crest that receives openings of prostatic ducts

3. Lobes of prostate gland

a. Anterior lobe

4-12 Sections through prostate gland and urethra. A, Frontal section showing posterior wall of prostatic, membranous, and proximal spongy urethra. Note seminal colliculus with prostatic utricle and openings of ejaculatory ducts. B, Median sagittal section through bladder, prostate, and proximal penis.

(From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 384.)

Benign prostatic hyperplasia usually involves the median lobe, and prostate cancer involves the posterior lobe.

• Anterior to urethra and consists of fibromuscular tissue

b. Posterior lobe

• Posterior to urethra and inferior to plane of ejaculatory ducts; referred to clinically as peripheral zone

Prostate cancer usually begins in the periphery of the gland in a region that corresponds to the anatomical posterior lobe (Figure 4-13), so early stages are often asymptomatic. Later, in advanced disease, prostate cancer can occlude the prostatic urethra, causing obstruction. After age 50, primary methods of detection include an annual digital rectal examination (Figure 4-14) and blood tests for prostate-specific antigen (PSA).

4-13

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Tags: Rapid Review Gross and Developmental Anatomy

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