Contents of anal triangle pdf - Perineum

Basic Anatomy

303

natomy

asic

Definition of Perineum

their covering fasciae (see Fig. 8.1). It is incomplete

tores ani muscles and the small coccygeus muscles and

The pelvic diaphragm is formed by the important leva

and laterally by the ischial tuberosities (Fig. 8.2).

by the symphysis pubis, posteriorly by the tip of the coccyx,

the perineum is diamond shaped and is bounded anteriorly

(Fig. 8.1). When seen from below with the thighs abducted,

into the main pelvic cavity above and the perineum below

The cavity of the pelvis is divided by the pelvic diaphragm

Pelvic Diaphragm

anteriorly to allow passage of the urethra in males and

inguinal nodes.

of the skin drain into the medial group of the superficial

the inferior rectal (hemorrhoidal) nerve. The lymph vessels

ischiorectal fossa. The skin around the anus is supplied by

the anal canal, lies in the midline, and on each side is the

or lower opening of

anus,

maximus muscle (Fig. 8.3). The

tuberous ligament, overlapped by the border of the gluteus

cyx and on each side by the ischial tuberosity and the sacro

The anal triangle is bounded behind by the tip of the coc

Contents of Anal Triangle

page 247).

the urethra and the vagina in females (for details see

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C H A P T E R O B J E C T I V E S

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Infections, injuries, and prolapses involving the anal canal, the

urethra, and the female external genitalia are common problems

facing the physician.

■

Urethral obstruction, traumatic rupture of the penile urethra,

and infections of the epididymis and testis are frequently seen

in the male.

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The purpose of this chapter is to cover the significant anatomy

relative to these clinical problems. Because the descent of the

testes and the structure of the scrotum are intimately related

to the development of the inguinal canal, they are dealt with in

detail in Chapter 4.

region of
main pelvic
cavity

linear thickening
of fascia covering
obturator internus
muscle

obturator canal
for obturator
nerve and
vessels

obturator
internus muscle

region of
perineum

levator ani
muscle

coccyx

coccygeus muscle

ischial spine

sacrotuberous
ligament

FIGURE 8.1

vator ani and the coccygeus

Right half of the pelvis showing the muscles forming the pelvic floor. Note that the le

the pelvic diaphragm and the region of the perineum lies below the diaphragm.

muscles and their covering fascia form the pelvic diaphragm. Note also that the region of the main pelvic cavity lies above

304

CHAPTER 8

The Perineum

urogenital

triangle

anal
triangle

FIGURE 8.2

Diamond-shaped perineum divided by a broken

line into the urogenital triangle and the anal triangle.

symphysis pubis

perineal body

ischial tuberosity

inferior rectal artery

anococcygeal body

tip of coccyx

gluteus maximus muscle

subpubic ligament

urethra

inferior ramus of pubis

urogenital diaphragm

external anal sphincter

levator ani

inferior rectal nerve

sacrotuberous ligament

FIGURE 8.3

Anal triangle and urogenital triangle in the male as seen from below.

downward and backward from the rectal ampulla to the

The anal canal is about 1.5 in. (4 cm) long and passes

Location and Description

teric artery (see Fig. 8.6). The venous drainage is mainly

superior rectal artery, a branch of the inferior mesen

The arterial supply is that of the hindgut—namely, the

It is sensitive only to stretch (see Fig. 8.6).

and is derived from the autonomic hypogastric plexuses.

The nerve supply is the same as that for the rectal mucosa

deal membrane) (Figs. 8.5 and 8.7).

(remains of procto

anal valves

semilunar folds called

which are joined together at their lower ends by small

anal columns,

It is thrown into vertical folds called

It is lined by columnar epithelium.

lowing important anatomic features:

is derived from hindgut entoderm (Fig. 8.6). It has the fol

mucous membrane of the upper half of the anal canal

The

Structure

part of the vagina (see Fig. 8.4).

perineal body, the urogenital diaphragm, and the lower

the bulb of the penis (see Fig. 8.4). In the female, the

tal diaphragm, the membranous part of the urethra, and

In the male, the perineal body, the urogeni

Anteriorly:

The fat-filled ischiorectal fossae (Fig. 8.5).

Laterally:

cyx (see Fig. 8.4).

fibrous tissue lying between the anal canal and the coc

which is a mass of

anococcygeal body,

Posteriorly: The

anal sphincters.

are kept in apposition by the levatores ani muscles and the

anus (Fig. 8.4). Except during defecation, its lateral walls

Relations

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Anal Canal

Basic Anatomy

305

penile urethra

fossa terminalis

external urethral orifice

urogenital diaphragm

bulb of penis

lves

bladder

prostate

puborectalis

anococcygeal body

anal canal

anal va

perineal body

prepuce

body of penis

rectouterine pouch

perineal body

vagina

urethra

cervix

bladder

cavity of uterus

sigmoid colon

coil of ileum

uterovesical pouch

urogenital diaphragm

anus

anal canal

anococcygeal body

rectum

peritoneum

FIGURE 8.4

Sagittal sections of the male (

mis (see Fig. 8.6).

gradually merges at the anus with the perianal epider

It is lined by stratified squamous epithelium, which

lowing important features:

is derived from ectoderm of the proctodeum. It has the fol

mucous membrane of the lower half of the anal canal

The

Fig. 8.6).

then eventually to the inferior mesenteric nodes (see

superior rectal artery to the pararectal nodes and

The lymphatic drainage is mainly upward along the

mesenteric vein, and the portal vein (see Fig. 8.5).

by the superior rectal vein, a tributary of the inferior

) pelvis. Sagittal sections of the female (

B) pelvis.

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306

CHAPTER 8

The Perineum

superficial

inferior rectal vein

superior rectal vein

lower transverse fold of rectum

middle rectal vein

obturator internus

levator ani

pudendal canal

puborectalis

deep

external

sphincter

subcutaneous

internal sphincter

anus

anal valve

anal column

fat in ischiorectal fossa

internal

pudendal

vessels

pudendal nerve

rectum

longitudinal muscle

ischium

FIGURE 8.5

Coronal section of the pelvis and the perineum showing venous drainage of the anal canal.

At the junction of the rectum and anal canal

skin (see Fig. 8.5).

into the ischiorectal fossa or are attached to the perianal

membrane of the anal canal, whereas others pass laterally

Some of the longitudinal fibers are attached to the mucous

interval between the internal and external anal sphincters.

tinuous coat around the anal canal and descends in the

continuous above with that of the rectum. It forms a con

The longitudinal smooth muscle of the anal canal is

canal, pulling the two forward at an acute angle (see Fig. 8.6).

and passes around the junction of the rectum and the anal

form a sling, which is attached in front to the pubic bones

8.5, 8.6, and 8.7). The puborectalis fibers of the two sides

blend with the deep part of the external sphincter (see Figs.

fibers of the two levatores ani muscles

puborectalis

The

canal and has no bony attachments

which encircles the upper end of the anal

deep part,

behind and the perineal body in front

which is attached to the coccyx

superficial part,

the anal canal and has no bony attachments

which encircles the lower end of

subcutaneous part,

can be divided into three parts:

external sphincter

The

sphincter (see Figs. 8.5, 8.6, and 8.7).

sheath of striped muscle that forms the voluntary external

of the anal canal. The internal sphincter is enclosed by a

the smooth muscle of the circular coat at the upper end

is formed from a thickening of

internal sphincter

The

voluntary external sphincter.

The anal canal has an involuntary internal sphincter and a

Anal Sphincters

muscle (see Fig. 8.5).

an outer longitudinal and an inner circular layer of smooth

As in the upper parts of the intestinal tract, it is divided into

of the anal canal joins the lower half (see Fig. 8.7).

indicates the level where the upper half

pectinate line

The

superficial inguinal nodes (see Fig. 8.6).

The lymph drainage is downward to the medial group of

iliac vein (see Figs. 8.5 and 8.6).

internal pudendal vein, which drains into the internal

drainage is by the inferior rectal vein, a tributary of the

of the internal pudendal artery (see Fig. 8.3). The venous

The arterial supply is the inferior rectal artery, a branch

and pressure (see Figs. 8.3 and 8.6).

nerve; it is thus sensitive to pain, temperature, touch,

The nerve supply is from the somatic inferior rectal

anal columns (see Fig. 8.7).

There are

■

Muscle Coat

■

(see Fig.

rnal sphincter, the deep part of the

8.6), the inte

on rectal examination.

which can be felt

anorectal ring,

distinct ring, called the

external sphincter, and the puborectalis muscles form a

Basic Anatomy

307

columnar epithelium

sensitive to stretch

entoderm

sensitive to pain,

touch, and temperature

stratified squamous epithelium

superior rectal artery

inferior rectal artery

superior rectal vein

inferior rectal vein

pararectal lymph nodes

along superior

rectal artery

superficial inguinal

lymph nodes

rectum

deep

coccyx

anococcygeal body

superficial

subcutaneous

anal canal

perineal body

puborectalis

ectoderm

anus

FIGURE 8.6

wing their embryologic origin and lining epithelium (

Upper and lower halves of the anal canal sho

muscle and different parts of the external anal sphincter (

). Arrangement of the muscle fibers of the puborectalis

), their venous drainage (

A), their arterial

supply (B

C), and their lymph drainage (D

E).

308

CHAPTER 8

The Perineum

anal column

anal sinus

anal canal
(1.5 in. long)

anal valve

pectinate line

pecten
or transitional
zone

internal
sphincter
of anal canal

intersphincteric
plane

superficial part

of external

sphincter of

anal canal

deep part of

external sphincter

of anal canal

puborectalis

levator ani
muscle

longitudinal muscle of
rectum

circular muscle of rectum

rectal ampulla

subcutaneous part

of external

sphincter of

anal canal

FIGURE 8.7

Coronal section of the anal canal showing the detailed anatomy of the mucous membrane and the arrangement

“pecten” (the transitional zone between the skin and the mucous membrane) are sometimes used by clinicians.

of the internal and external anal sphincters. Note that the terms “pectinate line” (the line at the level of the anal valves) and

pudendal nerve

greater sciatic foramen

lesser sciatic foramen

inferior rectal nerve

dorsal nerve
of penis

perineal nerve

scrotal nerves

sacrospinous ligament

FIGURE 8.8

Course and branches of the pudendal nerve in

internal sphincter is supplied by sympathetic fibers from

innervated by the inferior rectal nerves. The involuntary

sitive to pain, temperature, touch, and pressure and is

through the hypogastric plexuses. The lower half is sen

stretch and is innervated by sensory fibers that ascend

The mucous membrane of the upper half is sensitive to

Nerve Supply

nodes (see Fig. 8.6).

half drains into the medial group of superficial inguinal

nodes and then the inferior mesenteric nodes. The lower

The upper half of the anal canal drains into the pararectal

Lymph Drainage

vein.

by the inferior rectal vein into the internal pudendal

the inferior mesenteric vein, and the lower half is drained

The upper half is drained by the superior rectal vein into

Veins

artery supplies the lower half (see Fig. 8.6).

The superior artery supplies the upper half and the inferior

Arteries

the male.

Blood Supply

Basic Anatomy

309

the inferior hypogastric plexuses. The voluntary external

arch and laterally by the ischial tuberosities (see Fig. 8.3).

The urogenital triangle is bounded in front by the pubic

Urogenital Triangle

spond to the branches of the internal pudendal artery.

The internal pudendal vein receives tributaries that corre

Internal Pudendal Vein

in the female.

clitoris

to the labia and

Branches to the penis

anal canal (see Fig. 8.3).

This supplies the lower half of the

Inferior rectal artery:

Branches

sciatic foramen.

sciatic foramen and enters the perineum through the lesser

iliac artery and passes from the pelvis through the greater

The internal pudendal artery is a branch of the internal

Internal Pudendal Artery

surface of the scrotum (or labia majora).

ital triangle (see Fig. 8.8) and the skin on the posterior

This supplies the muscles in the urogen

Perineal nerve:

uted to the penis (or clitoris) (see Fig. 8.8).

This is distrib

Dorsal nerve of the penis (or clitoris):

canal, and the perianal skin (see Fig. 8.3).

ter, the mucous membrane of the lower half of the anal

ischiorectal fossa and supplies the external anal sphinc

This runs medially across the

Inferior rectal nerve:

Branches

anal sphincter and the muscles and skin of the perineum.

canal and, by means of its branches, supplies the external

atic foramen. The nerve then passes forward in the pudendal

the lower limb, it enters the perineum through the lesser sci

men (see Fig. 8.8). After a brief course in the gluteal region of

leaves the main pelvic cavity through the greater sciatic fora

The pudendal nerve is a branch of the sacral plexus and

Pudendal Nerve

vessels and nerve cross the fossa to reach the anal canal.

the ischial tuberosity (Figs. 8.5 and 8.8). The inferior rectal

lateral wall of the ischiorectal fossa, on the medial side of

on the

pudendal canal,

embedded in a fascial canal, the

tion. The pudendal nerve and internal pudendal vessels are

ports the anal canal and allows it to distend during defeca

The ischiorectal fossa is filled with dense fat, which sup

Contents of Fossa

muscle, covered with pelvic fascia.

wall is formed by the lower part of the obturator internus

sloping levator ani muscle and the anal canal. The lateral

medial and lateral walls. The medial wall is formed by the

The edge of the wedge is formed by the junction of the

The base of the wedge is superficial and formed by the skin.

space located on each side of the anal canal (see Fig. 8.5).

The ischiorectal fossa (ischioanal fossa) is a wedge-shaped

now closed by the tonic contraction of the anal sphincters.

puborectalis muscle. The empty lumen of the anal canal is

the anal walls and the contraction and upward pull of the

to the anal canal by the tone of the longitudinal fibers of

fecal mass. At the end of the act, the mucosa is returned

of the anal canal is extruded through the anus ahead of the

submucous coat, the mucous membrane of the lower part

ated through the anal canal. Depending on the laxity of the

cles, is now voluntarily inhibited, and the feces are evacu

external anal sphincters, including the puborectalis mus

abdominal wall. The tonic contraction of the internal and

about by contraction of the muscles of the anterior

It is assisted by a rise in intra-abdominal pressure brought

descending colon, sigmoid colon, rectum, and anal canal.

a coordinated reflex that results in the emptying of the

ence of feces in the lumen. The act of defecation involves

stretch receptors in the wall of the rectum by the pres

The desire to defecate is initiated by stimulation of the

once in several days.

eral times a day, and some perfectly normal people defecate

habit. Some adults defecate once a day, some defecate sev

The time, place, and frequency of defecation are a matter of

of the fourth sacral nerve.

of the pudendal nerve (see Fig. 8.3), and the perineal branch

sphincter is supplied by the inferior rectal nerve, a branch

Defecation

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Ischiorectal Fossa

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in the male and

Portal–Systemic Anastomosis

anal columns at the 3-, 7-, and 11-o’clock positions when the

membrane (Fig. 8.9). The tributaries of the vein, which lie in the

superior rectal (hemorrhoidal) vein and are covered by mucous

Internal hemorrhoids are varicosities of the tributaries of the

The rectal veins form an important portal–systemic anastomo-

sis because the superior rectal vein drains ultimately into the

portal vein and the inferior rectal vein drains into the systemic

system.

Internal Hemorrhoids (Piles)

C L I N I C A L N O T E S

(continued)