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Ischiorectal fossa
Lumbosacral plexus
Arteries
Nerves
11/07/2016
BAAB@2016
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The ischiorectal fossa (also called ischioanal fossa) is
the fat-filled space located lateral to the anal canal and
inferior to the pelvic diaphragm.
It is somewhat prismatic or wage shaped, with its base
directed to the surface of the perineum, and its apex at
the line of meeting of the obturator and the anal
fasciae.
Fig: Pelvic organs and spacial arrangement
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Boundaries
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ANTERIOR:
◦ fascia of Colles covering the Transversus perinei superficialis
◦ inferior fascia of the urogenital diaphragm
POSTERIOR:
◦ gluteus maximus
◦ sacrotuberous ligament
LATERAL:
◦ tuberosity of the ischium
◦ obturator internus muscle
◦ obturator fascia
MEDIAL:
◦ levator ani
◦ sphincter ani externus muscle
◦ anal fascia
SUPERIOR:
◦ levator ani
INFERIOR:
◦ skin
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Contents
 The contents include:
- Ischiorectal pad of fat with numerous fibrous bands
extend from side to side allows distension of the anal
canal during defecation
- Inferior rectal nerve and vessels.
- Posterior scrotal / labial nerve and vessels.
- Pudendal canal (Alcock's canal) on the lateral wall and
its contents which are:
 internal pudendal artery
 internal pudendal vein
 pudendal nerve
Perineal branch of fourth sacral nerve.
Perforating cutaneous branch of S2 , S3 nerve .
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Applied Anatomy 1. The two Ischiorectal fossae allow distension of rectum and
anal canal during passage of faeces.
2. [a] Both the Perianal and Ischiorectal spaces are common
site of abscesses. This is due to poor blood supply and coarse
lobulated fat which predispose it for infection.
[b] The Ischiorectal abscess may be the result of spread of
infection from the nearby area - skin, lumen of bowel or
perirectal tissue above the levator ani or through the blood or
lymphatic.
[c]They can be excised fearlessly because of the poor
vascularity of the fossa.
[d]Abscesses in this region are - (i) Perianal abscess (ii)
Ischiorectal abscess (iii) Supra levator abscess (iv) Sub
mucous abscess.
[e]When making incision for drainage of abscesses care must
be taken to avoid injury to inferior rectal neuromuscular
bundle to prevent paralysis of external sphincter.
3. The Ischiorectal fat acts as a cushion like support of rectum and
anal canal. Loss of this fat in debilitating diseases like diarrhea in
children may results in prolapse of the rectum.
4. The occasional gap between the origin of levator ani and the
Obturator fascia is known as the hiatus of Schwalbe. Rarely pelvic
organs may herniate through this gap resulting in an Ischiorectal
hernia.
5. Tension in gluteus maximus as during standing compresses fat of
the fossa around anal canal contributing to fecal continence.
6. Fournier's Gangrene - An uncommon but potentially lethal
complication of Ischiorectal abscess. This is a type of necrotizing
fasciitis usually affecting the perineum. It is commonly occuring in
elderly men, but also in women and children, more likely in diabetes,
alcoholics, or immune compromised cases.
7. Through the inter Sphincteric longitudinal fibers the inter
Sphincteric abscess tracks down and gives rise to Perianal abscess.
8. Pudendal Nerve - (a) Sphincteric Incontinence - Injury
to the inferior rectal branch of the pudendal nerve causes
Sphincteric incontinence.
( b) Pudendal Block - The pudendal nerve is infiltrated with
local anaesthetic solution where it crosses the ischial spine.
The ischial spine is palpated through the vagina / rectum and
the needle is inserted through the perineum, medial to the
ischial tuberosity to anaesthetize the perineum.
Further sensory branches of the perineum are derived from
the ilio inguinal nerve, the perineal branch of the posterior
cutaneous nerve of the thigh and the genital branch of the
genito femoral nerve.
This means that when complete perineal anesthesia is
required an injection of local anaesthetic must be given
around the anus.
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This is plexus of nerves formed from the anterior divisions of
the lumbar nerves, sacral nerves, and coccygeal nerve, the first
lumbar nerve being frequently joined by a branch from the
twelfth thoracic.
For descriptive purposes this plexus is usually divided into
three parts:
◦ lumbar plexus
◦ sacral plexus
◦ pudendal plexus
Fig: Lumbosacral plexus of nerves
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The lumbar plexus is a web of nerves (a nervous plexus) in the lumbar region
of the body which forms part of the larger lumbosacral plexus.
It is formed by the divisions of the first four lumbar nerves (L1-L4) and from
contributions of the subcostal nerve (T12), which is the last thoracic nerve.
Additionally, the ventral rami of the fourth lumbar nerve pass
communicating branches, the lumbosacral trunk, to the sacral plexus.
◦ The lumbosacral trunk comprises the whole of the anterior division of the
fifth and a part of that of the fourth lumbar nerve; it appears at the medial
margin of the psoas major and runs downward over the pelvic brim to join
the first sacral nerve.
The nerves of the lumbar plexus pass in front of the hip joint and mainly
support the anterior part of the thigh.
The plexus is formed lateral to the intervertebral foramina and passes through
psoas major. Its smaller motor branches are distributed directly to psoas
major, while the larger branches leave the muscle at various sites to run
obliquely down through the pelvis to leave under the inguinal ligament, with
the exception of the obturator nerve which exits the pelvis through the
obturator foramen.
Fig: This is a lumbar plexus
Distribution of the lumbar plexus
 lumbar plexus gives out the
◦ iliohypogastric giving the
 lateral cutaneous branch
 anterior cutaneous branch
◦ ilioinguinal giving the
 anterior scrotal ♂/labial ♀
◦ genitofemoral giving the
 femoral branch
 genital branch
◦ lateral cutaneous giving the
 patellar
◦ obturator giving the
 anterior branch which also gives cutaneous
 posterior
 accessory
◦ Femoral giving the
 anterior cutaneous branches
 Saphenous giving infrapatellar and medial crural cutaneous
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The Sacral plexus is a nerve plexus which
provides motor and sensory nerves for the
posterior thigh, most of the lower leg and foot,
and part of the pelvis. It is part of the
lumbosacral plexus and emerges from the
lumbar vertebrae and sacral vertebrae (L4-S4).
A sacral plexopathy is a disorder affecting the
nerves of the sacral plexus, usually caused by
trauma, nerve compression, vascular disease, or
infection. Symptoms may include pain, loss of
motor control, and sensory deficits.
◦ Plexopathy is a disorder affecting a network of nerves,
blood vessels, or lymph vessels. The region of nerves it
affects are at the brachial or lumbosacral plexus.
Fig: sacral and pudendal plexuses
Distribution of the sacral plexus
 Sacral plexus gives out the
◦ Sciatic
 common peroneal
 lateral sural cutaneous
 communicating branch
 deep peroneal
 lateral terminal branch
 medial terminal branch
 dorsal digital
 superficial peroneal
 medial dorsal cutaneous
 intermediate dorsal cutaneous
 dorsal digital
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Sacral plexus
◦ Tibial
 medial sural cutaneous
 medial calcaneal
 medial plantar
 common plantar digital nerves
 proper plantar digital
 lateral plantar
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◦ Sural
deep branch
superficial branch
common plantar digital
proper plantar digital
 lateral dorsal cutaneous
 lateral calcaneal
◦ Other
 Muscular
 lateral rotator group
 to quadratus femoris
 to obturator internus
 to the piriformis
 cutaneous:
 posterior cutaneous of thigh
 inferior cluneal
 perineal branches
 perforating cutaneous
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Fig: Schematic diagram of the sacral plexus
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The Pudendal or coccygeal plexus originates from
S4, S5, and Cx1 spinal nerves. It is interconnected
with the lower part of sacral plexus. The only
nerve of the plexus is the anococcygeal nerve,
which serves sensory innervation of the skin in
the coccygeal region (tail and around the anus)
Distribution of the Pudendal plexus
◦ Pudendal
 Inferior branch
 Anal branch
◦ Perineal
 Deep scrotal/labial
 Posterior scrotal/labial
◦ Dorsal nerve of the penis/clitoris
◦ Anococcygeal cutenous of the lower limb.
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Vessels, and Nerves of the pelvis.
Oxygenated blood begins its course down the chest
through the thoracic aorta, then it becomes the abdominal
aorta in the abdomen then in the pelvis, the abdominal
aorta forks into two branches called common iliac
arteries. These travel down each leg, where they branch
into internal and external iliac arteries.
A pair of internal iliac arteries , superior rectal arteries ,
ovarian arteries and un paired median sacral artery,
supply the pelvic region.
Ovarian arteries from abdominal aorta, supply blood to
the reproductive organs, such as the ovaries, fallopian
tubes, and uterus.
Internal iliac arteries through their anterior and posterior
branches supply blood to the pelvic viscera, perineum,
pelvic wall, and the buttocks
superior rectal arteries are direct continuations of the
inferior mesenteric arteries supply the mucosa of the
rectum and upper half of the anal canal
median sacral artery arises at the birfucation of the aorta.
It descends over the anterior surface of the sacrum and
the coccyx.
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Veins typically follow the same path as arteries.
Similar to the arteries in the pelvis, veins form
plexuses within the legs. As blood returns to the
heart the tributaries -- the internal and external
iliac veins -- the common iliac vein -- the
inferior vena cava, the large vessel that runs
parallel to the abdominal aorta.
Common iliac vein also receives inferior
epigastric and the deep circumflex iliac veins.
Nerves branch from the spinal cord. There are
three types of nerves:
◦ Autonomic nerves: These control involuntary or partially
voluntary actions such as heartbeat.
◦ Motor nerves: These signal muscles to move.
◦ Sensory nerves: These relay information from the skin and
muscles, such as heat and pain.
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In the pelvis, the vertebral column ends in the
sacrum, (five fused vertebral bones) that form
the back of the pelvis. Behind it is the sacral
plexus, a collection of nerves that serve the
pelvic area, genitals, buttocks, and parts of
the legs and feet.
The sciatic nerve is the largest nerve, and
originates from the sacral plexus. This large
nerve fiber begins in the lower back at the
vertebral column, runs through the buttocks
(beneath the gluteus maximus muscle), and
extends down the back of the thigh.
There is one sciatic nerve in each leg, and
each is about one inch wide in the pelvis.