Urogenital triangle pdf - Perineum

312

CHAPTER 8

The Perineum

anal columns

anal valves

11 o’clock

3 o’clock

7 o’clock

tributary of superior rectal vein

internal anal sphincter

internal
hemorrhoid

external
hemorrhoid

inferior
rectal vein

perianal hematoma

skin

mucous
membrane

external anal sphincter

FIGURE 8.9

hemorrhoids as seen through a proctoscope with the patient in the lithotomy position.

Positions of three internal

vein forming the internal hemorrhoid. Dotted lines indicate degrees of severity of condition.

Varicosed tributary of the superior rectal

Normal tributary of the superior rectal vein within the anal column.

Development of the Anal Canal

and that of the inferior half of the anal canal is formed from the

The distal end of the hindgut terminates as a blind sac of ento-

derm called the cloaca (see Fig. 7.8). The cloaca lies in contact

with a shallow ectodermal depression called the proctodeum.

The apposed layers of ectoderm and entoderm form the cloacal
membrane, which separates the cavity of the hindgut from the

surface (see Fig. 7.8). The cloaca becomes divided into anterior

and posterior parts by the urorectal septum; the posterior part

of the cloaca is called the anorectal canal. The anorectal canal

forms the rectum and the upper half of the anal canal. The lining

of the superior half of the anal canal is formed from entoderm,

ectoderm of the proctodeum (see Fig. 7.8). The sphincters of the

anal canal are formed from the surrounding mesenchyme. The

posterior part of the cloacal membrane breaks down so that the

gut opens onto the surface of the embryo.

Imperforate Anus
About 1 child in 4000 is born with imperforate anus caused by an

imperfect fusion of the entodermal cloaca with the proctodeum.

E M B R Y O L O G I C N O T E S

Superficial Fascia

phragm (see Fig. 8.12) and laterally to the margins of the

posteriorly to the posterior border of the urogenital dia

(Colles’ fascia) is attached

membranous layer

The

page 131).

of the scrotal skin (see testicular temperature and fertility,

contracts in response to cold and reduces the surface area

The dartos muscle

dartos muscle.

by smooth muscle, the

cial fascia of the thighs. In the scrotum, the fat is replaced

the fat of the ischiorectal fossa (Fig. 8.12) and the superfi

(fascia of Camper) is continuous with

fatty layer

The

divided into a fatty layer and a membranous layer.

The superficial fascia of the urogenital triangle can be

Basic Anatomy

313

rectum

levator ani

anal columns

anal fissure

pelvirectal
abscess

ischiorectal
abscess

subcutaneous
abscess

pelvirectal
abscess

fistulae

anal valves

external
anal
sphincter

submucous
abscess

FIGURE 8.10

Common positions of perianal fistulae.

Tearing downward of the anal valve to form an anal fissure.

B. Common locations of perianal abscesses.

314

CHAPTER 8

pubic arch. The closed space that is contained between the

Fig. 8.12). Laterally, the layers of fascia are attached to the

layer of the superficial fascia and the perineal body (see

of fascia fuse with each other and with the membranous

gap beneath the symphysis pubis. Posteriorly, the two layers

Anteriorly, the two layers of fascia fuse, leaving a small

perineal membrane.

diaphragm. The inferior layer of fascia is often referred to

a superior and an inferior layer of fascia of the urogenital

transverse perineal muscles, which are enclosed between

8.15). It is formed by the sphincter urethrae and the deep

filling in the gap of the pubic arch (see Figs. 8.12, 8.14, and

diaphragm situated in the anterior part of the perineum,

The urogenital diaphragm is a triangular musculofascial

sexes are described on pages 319 and 322.

The contents of the superficial perineal pouch in both

anterior abdominal muscles.

superficial fascia of the anterior abdominal wall and the

municates freely with the potential space lying between the

pubic arch (Figs. 8.14 and 8.15). Anteriorly, the space com

fascia and the urogenital diaphragm to the margins of the

by the attachment of the membranous layer of superficial

the fusion of its upper and lower walls. Laterally, it is closed

urogenital diaphragm (see Fig. 8.12). It is closed behind by

membranous layer of superficial fascia and above by the

The superficial perineal pouch is bounded below by the

Fig. 8.12).

scrotum (or labia majora), it forms a distinct layer (see

penis (or clitoris) as a tubular sheath (Fig. 8.13). In the

wall (Scarpa’s fascia). The fascia is continued over the

nous layer of superficial fascia of the anterior abdominal

pubic arch; anteriorly it is continuous with the membra

The Perineum

Superficial Perineal Pouch

Urogenital Diaphragm

as the

external os of uterus

prostate

bladder

seminal vesicle

head of baby

anterior lip of cervix

site for episiotomy

FIGURE 8.11

baby’s head is presenting at the vaginal orifice.

Position of the episiotomy incision in a woman during the second stage of labor. The

through the anterior rectal wall.

Rectal examination in the male showing how it is possible to palpate the prostate and the seminal vesicles

rior rectal wall.

Rectal examination in a pregnant woman showing how it is possible to palpate the cervix through the ante

Basic Anatomy

315

fatty layer of superficial fascia

urogenital diaphragm

anal canal

fat of ischiorectal fossa

perineal body

superior fascial layer

of urogenital diaphragm

inferior fascial layer of urogenital

diaphragm (perineal membrane)

scrotum

dartos muscle

Colles' fascia

superficial perineal pouch

deep perineal pouch

membranous layer of superficial fascia (Scarpa's fascia)

FIGURE 8.12

Arrangement of the superficial fascia in the urogenital triangle. Note the superficial and deep perineal pouches.

which covers the distal

glans penis,

expands to form the

and 8.16). At its distal extremity, the corpus spongiosum

spongiosum applied to their ventral surface (see Figs. 8.13

two dorsally placed corpora cavernosa and a single corpus

The erectile tissue is made up of

(Buck’s fascia).

cylinders of erectile tissue enclosed in a tubular sheath of

The body of the penis is essentially composed of three

Body of the Penis

(see Figs. 8.13 and 8.16).

corpora cavernosa

side in the dorsal part of the body of the penis, forming the

The two crura converge anteriorly and come to lie side by

(see Fig. 8.17).

corpus spongiosum

the penis and forms the

The bulb is continued forward into the body of

muscle.

ischiocavernosus

and is covered on its outer surface by the

Each crus is attached to the side of the pubic arch

muscles.

bulbospongiosus

and is covered on its outer surface by the

of the urogenital diaphragm. It is traversed by the urethra

situated in the midline and is attached to the undersurface

(Figs. 8.13, 8.16, and 8.17). The bulb is

crura of the penis

left

right

bulb of the penis

tissue called the

The root of the penis is made up of three masses of erectile

Root of the Penis

(Figs. 8.4 and 8.16).

The penis has a fixed root and a body that hangs free

Location and Description

In the male, the triangle contains the penis and scrotum.

Triangle

are described in subsequent sections.

The contents of the deep perineal pouch in both sexes

(see Figs. 8.12, 8.14, and 8.15).

perineal pouch

deep

superficial and deep layers of fascia is known as the

Contents of the Male Urogenital

Penis

and the

and

fascia