The Perineum
The Perineum
It is the region of
the trunk inferior
to the pelvic
diaphragm
(levator ani &
coccygei)
The Perineum
In anatomical
position it is a narrow
area between the
thighs
When the thighs are
abducted, it is a
diamond-shaped
area extending from
pubic symphysis to
the tip of the coccyx
Boundaries of the Perineum
Perineum is bounded
by:
 Pubic symphysis
 Inferior pubic rami
 Ischial rami
 Ischial tuberosities
 Sacrotuberous
ligaments
 Coccyx
Divisions of the Perineum
For descriptive
purposes, divided by an
imaginary transverse line
joining the anterior ends
of the ischial
tuberosities, into two
unequal triangles:
 Urogenital triangle
anteriorly
 Anal triangle
posteriorly
The Anal Triangle
Bounded:
 Anteriorly: by the
imaginary line
 Behind: by the tip of
coccyx
 On each side: by the
ischial tuberosity and the
sacrotuberous ligament
Overlapped by the border of
the gluteus maximus
muscles
Contains: anal canal,
external anal sphincter &
ischiorectal (ischioanal)
fossa
The Anal Triangle cont’d
The perianal skin is:
 Pigmented
 Has many sweat and
sebaceous glands
 Is thrown into folds
 Is supplied by inferior
rectal nerve and vessels
 Its lymphatics drain into
medial group of
superficial inguinal
lymph nodes
The Anal Canal
About 4cm long
Passes downward and
backward from the rectal
ampulla (at the level of the
sling formed by the
puborectalis) to the anus
Remains contracted and
forms an antero-posterior slit,
except during defecation
The walls are kept in
apposition by the levator ani
muscle and the anal sphincter
The Anal Canal: Relations
Anteriorly:
 Perineal body
 Urogenital diaphragm
 Membranous urethra
& bulb of penis in
male, and lower part
of vagina in female
Posteriorly:
 Anococcygeal body
Laterally:
 Ischiorectal fossa
The Anal Canal: Origin
Embryologically the
anal canal is
developed from two
sources:
• Upper half is derived
from hindgut
• Lower half is derived
from the proctodeum
The junction of the two
parts is indicated by
the pectinate line
The part of anal canal
superior to pectinate line
differs from the part
inferior to pectinate line in
its:
• Epithelial lining
• Arterial supply
• Venous drainage
• Innervation
• Lymph drainage
The white line (below the
pectinate line) indicates
the site of
mucocutaneous jnction
Mucous Membrane
Upper Half
 Lined by columnar
epithelium
 Thrown into vertical folds
called anal columns, which
are joined together at lower
ends by semilunar folds
called anal valves
(semilunar folds are
remnants of the anal
membrane)
Lower Half:
 Lined by stratified
squamous epithelium
 No columns
Muscles
Two distinct layers: outer
longitudinal & inner
circular layer of smooth
muscle
Thickening of the smooth
muscles of the circular
layer at the upper end of
anal canal forms the
involuntary internal
sphincter
The internal sphincter is
enclosed by a sheath of
skeletal muscle that
forms the voluntary
external sphincter
External Anal Sphincter
Voluntary
Composed of skeletal muscle
Surrounds the inferior 2/3rd of
anal canal
Divided into three parts:
 Subcutaneous part:
encircles the lower end of
the anal canal, has no bony
attachment
 Superficial part: attached to
perineal body anteriorly, and
coccyx posteriorly
 Deep part: encircles the
upper end of the anal canal,
has no bony attachment
Anorectal Ring
A distinct muscular ring
formed at the junction
of rectum and anal
canal
Formed by the internal
sphincter, deep part of
the external sphincter
and the puborectalis
Can be felt at rectal
examination
Helps in increasing the
anorectal angle
Blood Supply
Arteries:
Upper half:
superior
rectal artery
(continuation
of the inferior
mesenteric
artery)
Lower half:
inferior rectal
artery
Venous Drainage:
Upper half:
superior rectal
vein drained into
the inferior
mesenteric vein
Lower half:
inferior rectal vein
drained into the
internal pudendal
vein
• Important site of
portal-systemic
anastomosis
Nerve Supply
Mucous membrane
Upper half:
 Sensitive only to
stretching
 Supplied by inferior
hypogastric plexus
Lower half:
 Sensitive to pain,
temperature, touch
and pressure
 Supplied by inferior
rectal nerve
Involuntary internal
sphincter supplied by
inferior hypogastric
plexus (sympathetic)
& pelvic splanchnic
nerves
(parasympathetic)
Voluntary external
sphincter supplied by
inferior rectal nerve
(branch of internal
pudendal nerve) and
peineal branch of the
S4 nerve
Lymphatic Drainage
Upper half: pararectal
nodes & then to
inferior mesenteric
lymph nodes
Lower half: medial
group of the
superficial lymph
nodes
The Ischiorectal Fossa
Ischiorectal Fossa
A large fascia-lined
wedge-shaped
space on each side
of the anal canal
Located between
the skin of the anal
region and the
pelvic diaphragm
The two fossae are
communicated with
each other behind
the anal canal
Ischiorectal Fossa: Boundaries
Base of the wedge is
superficial and formed of
skin and fascia
Apex lies superiorly, at the
junction of medial and
lateral walls
Medial wall is formed by
sloping levator ani muscle
and the anal canal
Lateral wall is formed by
ischial tuberosity and the
lower part of obturator
internus muscle and its
fascia
Ischiorectal Fossa: Contents
Dense fat
Pudendal canal and
its contents (internal
pudendal vessels &
nerves)
Inferior rectal vessels
& nerve
Perforating branches
of S2-S3
Perineal branch of S4
Pudendal Canal
A fascial canal formed
by the splitting of the
obturator fascia
Located on the lateral
wall of the ischiorectal
fossa, on the medial
side of the ischial
tuberosity
Contains pudendal
nerve and internal
pudendal vessels
Pudendal Nerve
Branch of sacral plexus
Leaves pelvic cavity
through the greater sciatic
foramen
Enters perineum through
the lesser sciatic foramen
Passes forward in the
pudendal canal
Gives branches:
 Inferior rectal nerve
 Dorsal nerve of penis or
clitorus
 Perineal nerve
Internal Pudendal Artery
Branch of Internal iliac artery
Leaves pelvic cavity through
the greater sciatic foramen
Enters perineum through the
lesser sciatic foramen
Passes forward in the
pudendal canal
Gives branches:
 Inferior rectal artery
 Branches to penis or to
clitorus and to labia
Accompanied veins are
tributaries of the internal
pudendal vein
CLINICAL NOTES
Pudendal Block
Pudendal nerve as it
runs in the pudendal
canal, is blocked by an
anaesthetic to produce
analgesia of the
perineum in forceps
delivery
The anaesthetic can be
injected around the
nerve by:
 Transvaginal method
 Perineal method
Rectal Prolapse
Normally, the rectum is securely
attached to the pelvis with the
help of ligaments and muscles.
This attachment firmly holds the
rectum in place.
Various factors (age, long-term
constipation, the stress of
childbirth) may cause these
ligaments and muscles to
weaken.
This causes the rectum to
prolapse (it slips or falls out of
place)
May be
A. incomplete (mucosal)
B. complete involving the rectal wall
Hemorrhoids
A condition in which the
veins around the anus or
lower rectum are swollen
and inflamed.
May result from straining
to move stool, chronic
constipation or diarrhea,
pregnancy, aging
Hemorrhoids are either
inside the anus (internal)
or under the skin around
the anus (external).
Internal Hemorrhoids
Varicosities of the tributaries
of superior rectal vein
covered by mucous
membrane
Tributaries which lie in anal
columns at 3, 7, 11 o’clock
position are more prone to
become varicosed.
3 degrees:
– 1st degree: contained
within the anal canal
– 2nd degree: protrude out
of anal canal during
defecation but return back
after it
– 3rd degree: protrude in
defecation and remain
outside
External Hemorrhoids
Varicosities of the
tributaries of inferior
rectal vein covered by
skin
Varicosed tributaries
may rupture due to
coughing or straining
and form a perianal
hematoma in the
subcutaneous tissue
around anus
Anal Fissure
It is an elongated ulcer
produced by tearing of anal
valves due to passage of
hard fecal mass
Occurs most commonly in
the midline posteriorly or
anteriorly
Is extremely painful condition
and is usually examined
under anaesthesia
Anal fissure in the lower part
of anal canal results in reflex
spasm of external anal
sphincter
Perianal abcesses
Produced by fecal
trauma to anal mucosa
May be:




Submucosal
Subcutaneous
Pelvirectal
Ischiorectal
Spread or inadequate
treatment of abscess
may lead to the
formation of anal fistula
and anal sinus
Ischiorectal Abscess
Fossa is filled with fat
Is poorly vascularized
Is vulnerable to
infection from anal
canal
Abscess of one side
may spread to opposite
fossa across the
midline behind the anal
canal