Regional Anatomy 2

Demonstrate a general understanding of the concept of 'Anatomical Ring' structures.

• Identify main bones, bony features, joints and ligaments of the

pelvic girdle and explain their function.

• Describe the inlet and outlet of the pelvis.

• Discuss the differences in male and female pelvis

• Inlet: Pomontry > Sacral ala > arcuate line > Pectin pubic > pubic crest > pubic symphysis

• Outlet: Sacrum & coccyx > sacrotubrous ligament > pubic arch > ischial tuberosity

• The ring shape of the pelvis is vulnerable to injuries

• High energy force on once side of the ring always > '# or ligament lesion on opposite site (polo mint)

• Low energy forces e.g oestoporotic / stress or avulsion # would usually lead to break at one point only.

  • Avulsion fractures are common in young athletes aged between 11-16, predominantly in males. They usually occur at the insertion of tendons.

3 bones makes up the pelvis

• Right and left innominate/pelvic bone, sacrum & coccyx

Joints

• Right and left sacroiliac joint - posteriorly joins the pelvic bones to sacrum

• pubic symphysis - anteriorly joins 2 pelvic bones

• Male - heart shaped , acute pubic arch, more prominent ischial spine

• Female - oval inlet, wider pubic arch, less prominent ischial spine

• Secondary cartilaginous joint - between 2 pubic bodies

• Articular surfaces covered by hyaline cartilage and linked across midline by fibrocartilage

• Stabilised by 2 ligaments:

  • superior and inferior pubic ligaments

• Plane synovial joint between L shaped articular facets on lateral surface of sacrum & facets on iliac part of pelvic bone

• Joint has irregular contour and interlocks to resist movement

• Becomes fibrous with age & may ossify

• Stablised by 3 ligaments:

  • Anterior sacro-iliac ligament

  • Posterior sacro-iliac ligament

  • Interosseous sacro-iliac ligament

Sacrotuberous ligament

• Broad based ligament - attached to posterior superior iliac spine, posterior sacroiliac ligament, lateral sacral crest, lateral margins of caudal sacrum & crainal coccyx

• Prevents upward tilting of pelvis, resists shear & flexion

Sacrospinous ligaments

• Resists external rotation

• Attached to ischial spine & lateral margins of sacrum & coccyx anterior to sacrotuberous ligament

• Pudental nerve (supplies perineal sensation & external sphincters) - crosses ischial spine > perineum

Group of ligaments important for pelvic ring stability. Strongest ligaments in the body.

• Interosseous sacroiliac ligaments

  • Resists anterior-posterior translation of pelvis

• Posterior sacroiliac

  • Resists cephalad-caudad displacement of pelvis (up-down)

• Iliolumbar

  • Resists rotation and augment posterior SI ligament

> Common iliac veins join together at L5 making IVC

> Iliac vessels originate from the common iliac system beginning near L4 at the bifurcation of abdominal aorta

• EIA courses anteriorly along pelvic brim - emerging as common femoral artery distal to inguinal ligament

• IIA dives posteriorly near sacro-liac joint - divides into posterior (superior gluteal artery) and anterior (obturator artery) division.

• Corona mortis - a connection between obturator & external iliac artery - located in some on the superior pubic ramus

  • Subject to damage during pelvic # (crown of death)

> Venous plexus in posterior pelvis > 90% of bleed associate with pelvic ring injuries

• Superior hypogastric plexus - plexus of nerves at lower 1/3rd of L5 and upper 1/3rd of S1 vertebra

  • it is retro-peritoneal, lies anterior to bifurcation of AA

  • From this plexus, sympathetic fibres are carried into pelvis through R and L hypogastric nerves.

  • Also contains parasympathetic fibres which arise from pelvic splanchnic nerves (S2-S4) and ascends from inferior hypogastric plexus.

OTA classificaton incorporates mechanism of injury, degree of pelvic instability and site of injury

• Type A: stable injuries with intact posterior pelvic ring and pelvic floor

• Type B: complete disruptions of the anterior pelvic ring but incomplete disruption of the posterior ring

• Type C: rotationally and vertically unstable injuries

Isolated stable pelvic # can occur in lower energy mechanism or sports injuries:

• Acetabular #, pubic ramus #, iliac wing and avulsion #

• List the structures present in the pelvic cavity in males

• Describe pelvic fascia & peritoneal spaces related to the organs

• Explain the anatomy of male pelvic viscera

• correlate the anatomy with clinical findings in pathological conditions

• Parts of GI tract - sigmoid colon, rectum & anal canal

  • Sigmoid colon is completely intraperitoneal - connected to posterior abdominal wall by sigmoid mesocolon

  • Rectum is retroperitoneal (transitions at S3 level) - structures below are located anterior to rectum.

• Parts of urinary tract - bladder and urethra

  • Bladder is the most anterior viscera in pelvic cavity

• Reproductive system - prostate, seminal vesicles & ducts

  • Prostate is located inferior to bladder - beginning at neck of urethra which penetrates the prostate > underneath pubic none > penis

    
    

The parietal peritoneum reflects on the superior surface of the bladder > descends into posterior surface > anterior surface of the rectum.

• This reflection forms the Rectovesical pouch

• Either side of the rectum are gutters - these are the pararectal fossae.

Pic: superior view

1. The peritoneum around this area of the abominal wall is attached loosly - this is to allow bladder to expand up when it is full.

2. The peritoneum then reflects to cover superficial surface of the badder creating supravesical fossa around 2

1. It descends posteriorly, then 5. laterally forms folds over the ureters & deferense

1. Refects from bladder & seminal glands > rectum = creates rectovesical pouch.

Membranous fascia and the endopelvic fascia

-> Pelvic fascia forms a CT layer between pelvic viscera (internal organs) & the skeletal muscles forming lateral walls & floor of pelvis.

-> Membranous fascia also divided into:

• Parietal pelvic fascia (covers pelvic muscles of floor & lateral wall) - Obturator fascia (obturator internus), pririformis fascia (piriformis muscle), superior fascia over pelvic diaphragm (levator ani) and presacral fascia (in from of sacrum)

• Visceral pelvic fascia (covers pelvic organs)

-> Endopelvic fascia

• fills the subperitoneal space between the parietal & visceral membranous fascia > stronger condensation that support rectum & urinary bladder in men.

• Condensations can be in the form of ligaments > supports & holds organs to pelvic wall

• Superiorly – urinary bladder

• Inferiorly – deep perineal pouch & external urethral sphincter

• Anteriorly – Pubic symphysis (this is the rectopubic space, containing the vesical venous plexus which drains the bladder, the prostatic venous plexus, draining the prostate and the dorsal vein of penis, draining the penis)

• Posteriorly – seminal vesicle, end of vas deferens, and rectum

• Laterally – levator ani (pelvic diaphragm) + prostatic venous plexus

Note: Prostate is penetrated by urethra & ejaculatory ducts (formed by union of ~30 glands) which pass into prostatic urethra. Within prostatic urethra, there is prostatic utricle which is a rudimentary uterus.

This divides the prostate into number of zones:

• Central zone - located behind the prostatic urethra, pierced by the left and right ejaculatory ducts

• Transitional zone - surrounding the prostatic urethra. Its the site of BPH

• Anterior fibromuscular zone - this zone is devoid of glandular tissue, contains only fibromuscular stroma

• Peripheral zone - constitutes the periphery of the prostate. Its where Ca prostate originates

Blood supply

• Inferior vesicle artery (branch of internal iliac artery) - supplies inferior part of the bladder, prostate & seminal vesicle.

  • Some supply comes from middle & inferial rectal + pudental arteries

• Venous return is via prostatic venous plexus on either side of prostate > drains into inferior vesicle vein > IVC

  • This plexus have communication with bladder & internal vertebral plexus which is located around lumbar vertebrae - 1st mets from prostate Ca goes to lumbar vertebrae due to this communication.

Cavernous nerves

• These nerves are resposible for blood flow necessary for erection

• Inferior hypogastric plexus (pelvic plexus) is a paired autonomic plexus - gives raise to prostatic plexus (male) & uterovaginal plexus (femae)

• The inferior hypogastric plexus lies on the anterior surface of the rectum & gives branches to the prostate, bladder, urethra, seminal glands, rectum, and corpora cavernosa (bodies of the penis) via the cavernous nerves.

  • This plexus is ANS supplying both sympathetic & parasympathetic innervation to pelvic structures

• The cavernous nerves continue downwards, lying posterolateral to the prostate. They may be injured during radical prostatectomy, resulting in impotence

Note: Vas deference start from the tail of epidimis at posterior testicles. It croses above the terminal of the ureter > joins the seminal vesicle (both lie superior to prostate gland) to form ejaculation duct

• Produce an alkaline secretion that forms part of the semen

• This secretion is important in reproduction as it neutralise the acidic environment of the female vagina.

• Acidic evironment can also affect the sperm so it helps to neutralise it.

The seminal vesicles have the following relations:

• Anterior - urinary bladder

  Superomedial - ampulla of vas deferens

  Medial - ejaculatory ducts

  Inferior - prostate gland

  Posterior - rectum, rectovasical fascia

-> There are R & L vesicles, lie lateral to vas deferens.

-> Their ducts joins the terminal part of vas deferencs & pierces the posterior aspect of prostate to form 2 ejaculatory ducts

-> Blood supply (same as prostate) is by inferior vesicle artery, nerve supply by inferior hypogastric plexus.

-> Seminal vesicles produce fructose (energy source) & prostaglandin (regulate smooth muscles) - these help the spermatozoa advance.

-> Function - production / contribution to seminal fluid

Beningn prostatic hyperplasia

• Enlargement of glandular tissues of prostate mostly in the transitional zone > compress the prostatic urethra > difficulty / frequency micturation, incomplete emptying of bladder > urgency, dribbling & nocturnia

• Occurs in older men. DRE -> firm & smooth

• Rx: TuRP by inserting cystoscopy via prostatic urethra, incision made, tissue removed to relieve compression

Prostate cancer

• Usually arises from peripheral zone (Adenocarcinoma )= urinary Sx occurs later stage as this zone is far from urethra.

• Sx pelvic or back pain (mets to lumbar spine)

• DRE -> hard, irregular. Bloods -> raised PSA

• Rx: staging, bipsy > radical prostectomy

1. Bladder

2. Vas deference

3. Ejaculating duct

4. Prostate

5. Seminal vesicle

6. 
   

• Both are terminal part of the GIT

• Rectum located in most posterior compartment of pelvis

• It is retroperitoneal = only anterior surface is covered by peritoneum

  • Upper part is covered anterior & laterally, middle is covered anteriorly only by the peritoneum

• Anteriorly it is separated from bladder by seminal vesicles

• Posteriorly it follows the curvature of sacral bone - then it angulate posteriorly to become anal canal forming ano-rectal junction (important for fecal incontinence).

Coronal section of rectum shows number of important features:

• Anorectal line = marks the end of rectum & beginning of anal canal

• The pectinate (dentate) line = marks the anatomical junction between superior part of anal canal (originate from hind gut endoderm) and inferior part (originate from ectoderm)

  • Any pathology above the line is painless, but below the line is painful. Neurovascular supply also differs

• The transverse folds show the 3 lateral curvatures (superior, middle & inferior rectal flexures) of the rectum.

• The Anocutaneous line = marks the junction between the mucosal lining of the anal canal and the stratified keratinised squamous epithelial covering of the skin

The Anal canal has 2 sphincters:

• The internal anal sphincter - deep to the mucosa, surrounds upper 2/3rd anal canal, involuntary

• The external anal sphincter is far superficial and forms part of the pelvic diaphragm

  • Surrounds lower 2/3rd of anal canal, made of skeletal muscles = voluntary control..

-> Anal fissure = tear in the mucosa of the anal canal due to chronic constipation > painful defectation (occurs below dentate line). It is Rx by incision of anal sphincter muscles or relaxation by anaesthetic.

Blood supply comes from 3 rectal arteries:

• Superior anorectal artery - branch of the inferior mesenteric artery

• Middle anorectal artery - branch of the internal iliac artery

• Inferior anorectal artery - branch of the internal pudendal artery

The drainage follows the same pattern, there are 3 veins:

• Superior rectal vein - drains into inferior mesenteric vein which drain into splenic vein and into portal circulation.

  • This makes rectal vein a site of portosystemic anastomosis = get engorged in portal HTN

• Middle rectal vein - drains into internal iliac vein

• Inferior rectal vein - drains into inferior pudendal vein

Lymphatic drainage - follows the blood supply

• Inferior mesenteric lymph nodes

• Internal iliac lymph nodes

• Pararectal lymph nodes

• Makes it a site of portosystemic anastomosis

• These venous plexus are visible at 3, 7 & 9 o’clock during examination when pt lies supine

• The veins get engorged in portal HTN > external haemorrhoids (painful as below dentate line)

• In severe cases, the weight of the engorged venal pleux > partial prolapse of the mucosa throgh the anal cavity > rupture of the veins

• Internal haem results from straining in constipation, pregnancy, straining > increase venous pressure.

  • Internal Haem occurs above the dentate line = painless

• Rx - incision of the mucosa at 3, 7, 9 o’clock & ligation of the veins

Note

• Describe the boundaries and divisions of the perineum in female and male.

• Describe the anatomy of the fascia and spaces in the urogenital triangle.

• Describe the anatomy of the ischio-anal fossa and explain its clinical significance in relation to abscesses and fistulas.

• Describe the origin, course and distribution of the pudendal nerve and sites of pudendal nerve block.

• Interpret standard diagnostic images of the pelvis and perineum andrecognise common abnormalities.

A diamond-shaped region below the true pelvis. It is inferior to the pelvic floor/outlet, between the thighs and buttocks.

• Pelvic floor = Group of muscles and ligaments along with the CT forming base of pelvis.

• Pelvic diaphragm = central part of pelvic floor, muscle sling that separates pelvis from perineum mostly consits of levator ani & coccygeus muscles.

Anatomically, perinuem is divided into - anterior urogenital triangle and the posterior anal triangle.

Boundaries of the Perineum:

• Anterior - Pubic Symphysis 

• Anterolateral - Ischiopubic rami 

• Lateral - Ischial tuberosities

• Posterolateral - Sacrotuberous ligament

• Posterior - Tip of the coccyx

An imaginary line between the ischial tuberosities.

• The ischial tuberosities are palpable on each side as large bony masses near the crease of the skin known as the gluteal folds which are located between the thigh and gluteal region.

• There are different structures in these triangles between male & female. In the anal traingle, both have anal aperture

The pelvic diaphragm.

• Function of pelvic floor - support pelvic organs

• It is supported by perineal membrane & muscles in deep perineal pouch

The levator ani and coccygeus muscles.

The perineal membrane.

The urethra and vagina.

Bulbospongiosus, ischiocavernosus, and superficial transverse perineal muscles.

It helps maintain erections by compressing venous outflow.

They are in the superficial perineal pouch and secrete mucus to lubricate the vaginal opening.

They are in the deep perineal pouch and secrete mucus that lubricates the urethra and helps neutralise acidity before ejaculation.

Part of the urethra, the external urethral sphincter, and deep transverse perineal muscles; it also contains sex-specific structures.

The anal opening, external anal sphincter, and ischioanal fossae.

Fat, which acts as an elastic cushion.

The pudendal nerve and its branches, internal pudendal artery, and internal pudendal vein.

A midline aggregation of fibromuscular tissue where the two triangles meet; it provides attachment for muscles that support the pelvic floor.

Descent of vaginal tissue and/or the uterus into the vaginal canal; it can result from weakness or injury to pelvic floor muscles and connective tissue.

The internal pudendal artery.

Mainly S3–S5, except the anterior region, which often receives L1 innervation.

To numb the pudendal nerve for pain relief during childbirth or for gynaecological and anorectal procedures.

• Micturition means passing urine.

• The detrusor is the smooth muscle forming most of the bladder wall; when it contracts, it raises pressure inside the bladder and helps expel urine.

• Reflex - an unlearned, automatic, repeatable response to a specific stimulus that does not require the brain to be intact

The bladder has a

• Body - stores urine

  • Supplied by ANS (symp & parasymp), it is not under voluntary control so all its activities are operated via reflex pathway of spinal cord

• Trigone - where the ureteric openings and internal urethral opening form the corners of a triangle

• Neck - connects the bladder to the urethra. (lies between internal urethral sphincter and external urethral sphincter)

Note: in babies, ballder is located in the abdomen & it doesnt descend into levis until around puberty.

The bladder’s control involves:

• sympathetic, parasympathetic, and somatic nerves.

• In terms of autonomic innervation, bladder continously receives dual innervation by both SNS & PNS at all time.

• The somatic nervous system controls the external urethral sphincter (doesnt supply the bladder itself), while the autonomic branches act on the bladder.

• Bladder is an autonomic effector muscular organ without any activity on its own = all its activity is determined by nervous system.

  • Without the nervous innervation, it ceases to function

• Its activity switches between either storing or voiding urine

• Detrusor urinae muscle (a smooth muslce but has no myogenic electrical activity) - forms the body of bladder.

  • Electrical activity from innervation increases intramuscular pressure > exertion of pressure on fluid stored > which leaves through the internal urethral sphincter into the urethra > through the external urethral sphincter

• Internal urethral sphincter (physiological - it cannot be differentiated histologically and is simply composed of flaps of the bladder wall collapsed on one another to form a seal, without any activity)

• External urethral sphincter- formed by the pelvic floor muscles.

  • Supplied by somatic nervous system = under voluntary control from cerebral cortex via spinal cord

Layers from inside to out :-

• Urothelium > lamina propria - together = mucosa

• Submucosa

• Detrusor muscle

  • Lined iwth transitional epithelium which is characterised by presence of umbrella cells which prevent leakage from urinary bladder as vol of urine increases

  • It is found in the true (lesser) pelvis in adults

• Adventitia

• Sympathetic activity relaxes the detrusor and contracts the internal urethral opening and narrows urethral opening -> supporting storage.

• Parasympathetic activity contracts the detrusor and relaxes the internal sphincter, promoting voiding.

• Sympathetic outflow arises from spinal levels T12–L2 of sympathetic chain.

  • These are pre-ganglionic sympathetic fibres, makes up the superior hypogastric plexus.

  • This plexus has no ganglia & is located in bifurcation of aorta at L5 & sacrum.

  • The firbres from this plexus synapse with inferior hypogastric plexus as hypogatric nerve

• Parasympathetic outflow comes from S2–S4 via the pelvic splanchnic nerves .

Superior hypogastric plexus (SHP):

• Aka hypogastric plexus - Has no ganglia, situated in bifurcation of aorta on L5 body & sacrum

• Its a collection of Sympathetic pre-gangilonic fibres. Joined to inferior hypogastric plexus by hypogastric nerve

Inferior hypogastric plexus

• known as pelvic plexus, its mixed functionally = receives sympathetic & parasympathetic innervation directed towards detrusor muscle of bladder.

• Formed at the latearl pelvic wall from 2 systems of nerves:

  • Hypogastric nerves - orginate from SHP, sympathetic

  • Pelvic splanchnic nerves (aka Nervi Erigentes)- S2-S4 neural values (cell bodies in lateral horns), parasympathetic.

Efferent (autonomic)

-> Sympathetic T12-L2= hypogastric nerve -> Stores urine

-> Parasympathetic S2-S4 = pelvic splanchninc nerve -> void

Somatic supply (voluntary)

-> Originates from ventral horn of spinal cord S2-S4 (Nucleus of Onuff). Leads to EUS contraction during continence & relaxation of EUS during micturation phase

• Sensory free nerve endings (affferent) in the bladder wall detect stretch as urine accumulates.

• Signals travel mainly through S2–S4 pathways and convey the feeling of fullness to the nervous system.

  
  

• As the bladder fills, wall stretch activates sensory nerves.

• These afferents trigger a spinal reflex that increases parasympathetic activity, causing the detrusor to contract, raising bladder pressure and creating the urge to urinate.

• The bladder receives symp & parasymp outflow at all time simultanously - bias towards particular branch at particular time determines the dominent influence

• The cortex and pontine micturition centre coordinate whether to store or release urine.

• If it is not an appropriate time to urinate, the cortex can inhibit the pontine centre and delay voiding.

Normal reflex function requires bladder sensation, intact parasympathetic output, voluntary control of the external sphincter, and an intact sacral spinal cord.

• Detrusor-sphincter dyssynergia occurs when the detrusor and external urethral sphincter contracts simultanously.

• Failure of coordination between parasympathetic & somatic

• This prevents effective emptying and can cause urinary retention.

• An autonomous bladder is flaccid, has little or no tone, and has reduced or absent reflex activity.

• Bilateral damage to the sacral spinal cord at S2–S4 -> loss of Sensory afferent from the bladder and parasympathetic (efferent) output to the bladder

• CNS won’t receive afferent information about the state of bladder fullness > bladder fills to capacity > overflow incontinence due to retention

• So the bladder has LMN sings = flaccid paralysis, atonia & areflexia

• Damage above S2–S4 -> loss of descending voluntary control while leaving spinal reflex circuits active.

• The spinal reflex circuits take over the control to both fill & void the bladder.

• The bladder may then fill and empty automatically in cycles, without normal conscious control. e.g like baby bladder

-> Bladder exibits UMN signs = spastic paralysis, hyper-reflexia and hypertonia

• Detrusor instability is increased, unopposed detrusor activity that can make the bladder’s capacity very small and cause frequent dribbling or incontinence.

• Caused by bilateral spinal cord damage around lumbar region T12–L2 that removes sympathetic drive to bladder.

• This lead to - unopposed, constant, parasympathetic innervation of the bladder > increased basal electrical activity of detrusor muscle

• Rx trial of botox

During storage, somatic nerves keep the external urethral sphincter contracted to help maintain continence. During voiding, it relaxes so urine can pass through the urethra.

Umbrella cells are specialised cells in the bladder’s transitional lining. They help prevent urine from leaking through the lining as the bladder expands.

The internal urethral sphincter is a functional seal at the bladder outlet, rather than a distinct muscle that can be identified histologically. It is formed by folds of the bladder wall lying against one another.

Parasympathetic activity contracts the detrusor and relaxes the internal urethral sphincter. The external urethral sphincter also relaxes, allowing urine to pass through the urethra.

The bladder may lose its ability to sense fullness and contract effectively. It can become enlarged as it fills, with retention and eventual overflow incontinence, where urine leaks in drips.