13-03-23 - Pelvis: Walls, floor and neurovascular supply

Question 1

Learning outcomes

Answer 1

• Differentiate between the abdomen, the pelvic cavity and the perineum
• Describe the bony and ligamentous anatomy of the pelvis
• Describe the pelvic inlet and outlet
• List the sex differences in the pelvic skeleton
• Describe the musculature forming the lateral pelvic walls and the pelvic floor
• Describe the functions of the pelvic floor musculature
• Describe how somatic and autonomic (sympathetic and parasympathetic) innervation reach the pelvic cavity
• Name some of the branches of the internal iliac artery and the tributaries of the internal iliac vein
• Discuss the clinical implications of the anatomy of the pelvic floor, and pelvic neurovascular supply

Question 2

What 3 bones articulate to form the hup bone?

What 3 bones articular to form the pelvis?

Answer 2

• 3 bones that articulate to form the hip bone:
  1) Ilium
  2) Ischium
  3) Pubis
• 3 bones articulate to form the pelvis:
  1) Hip bones
  2) Sacrum
  3) Coccyx

Question 3

Pelvis diagram

Answer 3

Question 4

What is the abdominopelvic diagram divided into?

What is the pelvis divided into?

What are the boundaries of the greater pelvis?

What are the boundaries of the lesser pelvis?

Answer 4

• Abdominopelvic cavity is divided into abdominal and pelvic cavities
• The pelvis is divided into a greater (false) pelvis and a lesser (true) pelvis, divided by the pelvic brim
• The boundaries of the greater pelvis are the pelvic brim and a transverse line between the iliac crests
• The boundaries of the lesser pelvis are the ischium, pubic, and a small part of the ileum

Question 5

Where does the Sacrotuberous ligament run between?

Where does the Sacrospinous ligament run between?

What do these 2 ligaments form?

Answer 5

• Sacrotuberous ligament: runs from posterior-inferior iliac spine, sacrum and coccyx to ischial tuberosity
• Sacrospinous ligament: runs from sacrum, coccyx and sacrotuberous ligament to the ischial spine
• These 2 ligaments form the greater & lesser sciatic foramina

Question 6

What are pelvic gateways used for?

What are the 4 pelvic gateways?

What structures run through each?

Why is the pudendal nerve unique when it comes to these pelvic gateways?

Answer 6

• Pelvic gateways are used by structures that originate in the pelvis and move outside of it
• The 4 pelvic gateways and structures that run through each:

1) Greater sciatic foramen
* Sciatic nerve
* Superior and inferior gluteal neurovascular bundle
* Pudendal nerve
* Piriformis muscle

2) Lesser sciatic foramen
* Pudendal nerve
* Internal pudendal vessels

3) Deep to inguinal ligament
* Femoral neurovascular bundle
* Iliopsoas muscle

4) Superior aspect of obturator membrane
* Obturator neurovascular bundle

• The pudendal nerve is unique as it exits the pelvic cavity through the greater sciatic foramen, then enters the perineum (bottom region of pelvic cavity) through the lesser sciatic foramen

Question 7

What is the pelvic inlet the boundary between?

What are 3 other names for the pelvic inlet.

What are 5 boundaries of the pelvic inlet?

Answer 7

• The pelvic inlet is the boundary between the greater and lesser pelvis
• 3 other names for the pelvic inlet:
  1) Pelvic brim
  2) Superior pelvic aperture
  3) Linea terminalis
• 5 boundaries of the pelvic inlet:
  1) Pubic symphysis
  2) Pubic crest
  3) Pectineal line
  4) Arcuate line of ilium
  5) Sacral ala & sacral promontory

Question 8

What are the 5 boundaries of the pelvic outlet?

Answer 8

• 5 boundaries of the pelvic outlet:
  1) Pubic symphysis
  2) Ischiopubic ramus
  3) Ischial tuberosity
  4) Sacrotuberous ligament
  5) Sacrum & coccyx

Question 9

What are 3 important differences in the female and male pelvis?

What is the purpose of each?

Answer 9

• 3 important differences in the female and male pelvis:

1) Greater pelvis (false pelvis)
* Females – shallow
* Males – deep
* Wider in females, so allows the baby to develop in utero

2) Pelvic inlet
* Females – oval and rounded; wide
* Males – heart-shaped, narrow

3) Pubic arch and subpubic angle
* Females – wide (more than 80 degrees)
* Males – narrow (less than 70 degrees)
* Wider for females as it allows the passage of baby’s head

Question 10

What are the 3 walls of the true (lesser) pelvis?

What do they each consist of?

Answer 10

• 3 walls of the true (lesser) pelvis:

1) Antero-inferior wall:
* Formed by pubic symphysis, body and rami of the pubis

2) Postero-superior wall
* Sacrum
* Piriformis
* Divides the greater sciatic foramen into suprapiriform and infrapiriform spaces

3) Lateral wall
* Obturator internus, with obturator fascia

Question 11

What is the most inferior region of the abdomino-pelvic cavity?

What are the pelvic side walls and floor in contact with?

What is the perineum?

What is the perineum divided into?

Answer 11

• The pelvic floor/diaphragm is the most inferior region of the abdomino-pelvic cavity
• The pelvic side walls & floor are in contact with the central pelvic organs, forming a hammock
• The perineum (pudendal region) is inferior to the pelvic floor
• It is divided into deep & superficial compartments anteriorly by the perineal membrane

Question 12

What is the pelvic diaphragm formed by?

What are the gaps in the pelvic diaphragm called?

Answer 12

• The pelvic diaphragm is formed by levator ani (iliococcygeus + Pubococcygeus) and coccygeus (a.k.a. ischiococcygeus) muscles with their fasciae covering their superior and inferior surfaces
• The gaps between the medial borders of levator ani are called Urogenital hiatus and anal hiatus

Question 13

What 3 structures is the levator ani subdivided into?

What does the levator ani form part of?

What is the levator ani innervated by?

Answer 13

• 3 structures the levator ani is subdivided into:

1) Puborectalis
* Puborectal sling
* Important in faecal continence

2) Puboperinealis

3) Pubovaginalis (female) or puboprostaticus (male)

• The levator ani forms part of the anococcygeal body
• The levator ani is innervated by S3-4

Question 14

What is the role of the levator ani?

What is the role of the puborectalis?

What 2 other sphincters does the levator ani contribute to?

What can weakness of the levator ani cause?

What might the mother have to do after the birth?

Answer 14

• The role of the levator ani is to support the pelvic organs
• The puborectalis makes the anorectal angle more acute and augments the external anal sphincter, which maintains faecal continence
• 2 other sphincters the levator ani contributes to:

1) Augments the urethral sphincter
* Maintain urinary continence

2) Forms a vaginal sphincter
* Forms a vaginal sphincter
* Actively contracted during coughing, sneezing, forced expiration

• Weakness of the levator ani may cause incontinence or prolapse
• The mother may need to do pelvic floor exercises after birth to avoid this

Question 15

What do Pelvic diaphragm muscles of each side form?

What are these structures important for?

Answer 15

• Pelvic diaphragm muscles of each side meet in the midline to form the anococcygeal body (a.k.a. raphe or ligament) and perineal body (a.k.a. central tendon of perineum)
• These structures are important for faecal continence (especially the perineal body) – meaning people can become incontinent if this area is damaged

Question 16

What 2 structures is the pelvic floor supported by anteriorly?

What is the perineal membrane?

Where does it fill?

Answer 16

• 2 structures the pelvic floor is supported by anteriorly:
  1) The perineal membrane
  2) Muscles in the deep perineal pouch
• The perineal membrane is a thick, triangular fascial sheet that fills the space between the arms of the pubic arch

Question 17

What is the pelvic cavity lined by?

What does the peritoneum not reach in most regions?

What is the lowest point in the pelvic cavity?

Answer 17

• The pelvic cavity is lined by peritoneum continuous with the peritoneum of the abdominal cavity
• In most regions, the peritoneum does not reach the pelvic floor
• The rectouterine (female)/rectovesical (male) pouch is the lowest point in the pelvic cavity

Question 18

What are 3 routes for pelvic pre-sympathetic ganglion?

Answer 18

• 3 routes for pelvic pre-sympathetic ganglion:

1) Synapse at its level
* Postganglionic axons (unmyelinated, grey) pass in the GRC and join T1-L2 Spinal nerves

2) Travel down the chain to synapse in a lumbar/sacral ganglion
* Postganglionic axons pass in the GRC and join lumbar/sacral spinal nerves

3) Preganglionic branches enter the sympathetic trunk
* Pass through or descends without synapsing and exit
* Splanchnic nerves
* Synapse in a prevertebral ganglion
* Supply abdominal and pelvic viscera

Question 19

Synapse at its level diagram

Answer 19

Question 20

Travel down the chain to synapse in a lumbar/sacral ganglion diagram

Answer 20

Question 21

Preganglionic branches enter the sympathetic trunk diagram

Answer 21

Question 22

Where are prevertebral plexuses formed?

What 3 structures are prevertebral plexuses formed by?

How do prevertebral plexuses form?

What are the 5 prevertebral plexuses?

Which prevertebral plexuses form the aortic plexus?

Answer 22

• The prevertebral (pre-aortic) plexuses are formed around the abdominal aorta
• 3 structures are prevertebral plexuses formed by:

1) Preganglionic and postganglionic sympathetic fibres (T1-L2 (3))

2) Preganglionic parasympathetic fibres (vagus or S2-4)

3) Visceral afferent fibres

• Prevertebral plexuses condense around the origins of the branches of abdominal aorta
• 5 prevertebral plexuses:
  1) Coeliac plexus
  2) Renal plexus
  3) Superior mesenteric plexus
  4) Inferior mesenteric plexus
  5) Superior hypogastric plexus
• The super and inferior mesenteric plexuses form the aortic plexus

Question 23

Where are cell bodies of postganglionic sympathetic fibres located?

What can these cell bodies be organised into?

Where are ganglia clustered around?

Where do efferents from these ganglia go?

Answer 23

• Cell bodies of postganglionic sympathetic fibres are scattered throughout the prevertebral plexus
• Some of these cell bodies are organized into ganglia, while others are more randomly distributed
• Ganglia are clustered around the roots of the major branches of the abdominal aorta
• Efferents from these ganglia are distributed along the branches of the corresponding arteries

Question 24

What type of nerves and sacral and lumbar nerves?

What type of nerves are pelvic splanchnic nerves?

What will be the sympathetic and parasympathetic supply of abdominopelvic organs?

Answer 24

• Sacral and lumbar nerves are sympathetic
• Pelvic splanchnic nerves are parasympathetic
• Abdominopelvic organs will receive their sympathetic supply from lumbar/sacral nerves, and will receive their parasympathetic supply from the vagus nerve or pelvic/splanchnic nerves S2-S4

Question 25

What do sacral sympathetic trunks consist of?

What type of nerves do lumbar and sacral splanchnic nerves consist of?

What are the Parasympathetic fibres from S2-4 spinal segments?

What type of fibres do they contain?

What are the 2 hypogastric plexuses?

Which is the most important for pelvic organs?

What 3 type of fibres do periarterial plexuses supply to the arteries?

What are 3 examples of arteries supplied by pareiarterial plexuses?

Describe how primary and secondary plexuses form?

Answer 25

• Sacral sympathetic trunks consist of 4 pairs of sacral sympathetic ganglia + ganglion impar (meeting point of the two sides of the pelvic sympathetic nerves)
• Lumbar and sacral splanchnic nerves consist of both sympathetic and sensory fibres
• Parasympathetic fibres from S2-4 spinal segments are nerve erigentes (Pelvic splanchnic nerves) and contain both visceromotor and sensory fibres
• 2 hypogastric plexuses:
  1) Superior hypogastric plexus
  2) Inferior hypogastric plexus (most important for pelvic organs)
• 3 type of fibres periarterial plexuses supply to the arteries:
  1) Postsynaptic
  2) Sympathetic
  3) Vasomotor
• 3 examples of arteries supplied by pareiarterial plexuses:
  1) Superior rectal
  2) Ovarian
  3) Internal iliac arteries
• How primary and secondary plexuses form:
• Primary plexuses are around the branches of the aorta e.g superior mesenteric plexuses around the superior mesenteric artery
• Some fibres from these plexuses are both sympathetic and parasympathetic, and will pass through these primary plexuses to form secondary plexuses distributed to different parts supplied by the artery of the primary plexus nerve (e.g in this case arteries supplied by the superior mesenteric artery)
• This leads to plexuses being formed such as the ovarian and testicular plexuses, which are named after what they innervate

Question 26

Where is the superior hypogastric plexus found?

What is it formed as a continuation of?

What sympathetic and parasympathetic fibres does the superior hypogastric plexus consist of?

Answer 26

• The superior hypogastric plexus lies in front of the inferior part of the abdominal aorta and its bifurcation (promontory of the sacrum)
• It is formed as a continuation of the aortic plexus
• The hypogastric plexus consists of:
• Sympathetic fibres from L3 and L4 sympathetic ganglia
• Parasympathetic fibres from the pelvic splanchnic nerves

Question 27

Where is the inferior hypogastric (pelvic) plexus found?

What 2 structures is the inferior hypogastric plexus formed by?

What 3 structures the secondary plexuses of the inferior hypogastric plexus innervate?

What is the inferior hypogastric plexus susceptible to?

What does it play a key role in?

Answer 27

• The inferior hypogastric (pelvic) plexus lies on each side of the rectum, the base of the bladder and the vagina
• 2 structures the inferior hypogastric plexus is formed by:
  1) Sympathetic fibres from hypogastric nerves (from the superior hypogastric plexus)
  2) Parasympathetic fibres from the pelvic splanchnic nerves
• 3 structures the secondary plexuses of the inferior hypogastric plexus innervate (most organs in the pelvic cavity):
  1) Distal ureter to bladder
  2) Ductus deferens to penis
  3) Ovaries to vagina
• The inferior hypogastric plexus is susceptible to injury during surgical operations
• It plays a key role incontinence and sexual function

Question 28

Pelvic visceral afferents. What do pelvic visceral afferent fibres travel with?

What do visceral afferent fibres conducting unconscious (reflexive) sensation travel with?

What do visceral afferent fibres conducting pain travel with?

Where 2 locations mark to pelvic line?

What do visceral afferent fibres conducting pain travel with above and below the pelvic line?

Answer 28

• Pelvic visceral afferents
• Pelvic visceral afferent fibres travel with autonomic nerves
• All visceral afferent fibres conducting unconscious (reflexive e.g stretching of ureter/ovarian tubes) sensation travel with parasympathetic fibres
• Visceral afferent fibres conducting pain travel with sympathetics or parasympathetics, depending on the pelvic pain line
• 2 locations mark to pelvic line:
  1) Inferior limit of the peritoneum
  2) Middle of the sigmoid colon posteriorly

o Visceral afferents carrying pain impulses from organs (or part of an organ) superior to the pain line accompany sympathetic fibres
* Visceral afferents carrying pain impulses from organs (or part of an organ) inferior to the pain line accompany parasympathetic fibres

Question 29

Somatic innervation: pudendal nerve.

What roots make up the pudendal nerve?

Describe the 3 movements of the pudendal nerve.

What 6 structures does the pudendal nerve supply?

Answer 29

• The pudendal nerve is made up of roots S2-S4
• 3 movements of the pudendal nerve:
  1) Passes through the greater sciatic foramen
  2) Curves posterior to the ischial spine and sacro-spinous ligament
  3) Runs forwards into the perineum inferior to levator ani
• 6 structures the pudendal nerve supplies:
  1) External urethral sphincter
  2) External anal sphincter
  3) Levator ani (striated voluntary muscle)
  4) Ischiocavernous
  5) Bulbospongios
  6) Transverse perineal muscles

Question 30

Describe the common iliac artery division in the pelvis.

What 4 structures do the anterior and posterior trunks of the internal iliac artery supply.

Where is the trochanteric anastomoses formed?

Answer 30

• Common iliac artery division in the pelvis:
• The common iliac artery forms the internal iliac artery opposite the sacroiliac joint at the level of the L5 disc
• The internal iliac artery divides into anterior & posterior trunks
• 4 structures do the anterior and posterior trunks of the internal iliac artery supply:
  1) Supplies buttock & medial thigh
  2) Posterior pelvic & abdominal walls
  3) Pelvic viscera
  4) Oerineum
• The trochanteric anastomosis is between lateral and medial circumflex femoral and superior and inferior gluteal arteries

Question 31

What do most of the pelvic viscera have in terms of venous drainage?

Where does the internal iliac vein drain.

Where do the internal and external iliac vein join?

Answer 31

• Most pelvic viscera have an extensive venous plexus that drains into the internal iliac or internal pudendal vein
• The internal iliac vein drains equivalent areas to the artery
• The internal iliac vein joins the external iliac vein to form the common iliac vein that meets its opposite to form the inferior vena cava at the level of L5

Question 32

How does lymphatic drainage of the pelvis compare with the venous drainage?

What are the 4 types of pelvic lymph nodes.

How are they linked?

Answer 32

• The lymphatic drainage of the pelvis tends to parallel the venous drainage, with exceptions
• 4 types of pelvic lymph nodes:
  1) Common
  2) External
  3) Internal iliac
  4) Sacral lymph nodes
• All of these are very interconnecting