5.17 Pelvic peritoneum, vessels and nerves

Pelvic peritoneum

In male

Never reaches pelvic floor.  Anteriorly runs from abdominal wall ® bladder, roofing in retropubic space.  Rectovesical pouch runs from bladder ® rectum, with Denonvilliers fascia below. 

In female

Similar to male but for uterus which forms vesicouterine pouch anteriorly and rectouterine pouch posteriorly (from which abscesses can be drained by transvaginal incision through posterior fornix).  Broad ligament attaches uterus to pelvic side walls. 

Nerve supply

Visceral layer has no nerve supply.  Parietal layer supplied by obturator nerve (L3).

Pelvic vessels (373-4)

Internal iliac system; veins tend to lie posterior and to R.

Vessels lie within parietal pelvic fascia; only gluteal branches pierce this layer. 

Internal iliac artery

Bifurcates at pelvic brim (opposite SI jts) ® short posterior and larger anterior divisions. 

Posterior division ® 3 branches, all parietal:

Iliolumbar

Lateral sacral

Superior gluteal

Anterior division ® 9 branches.

3 vesical

3 other visceral

3 parietal

Superior vesical

Middle rectal

Obturator

Obliterated umb

Uterine

Internal pudendal

Inferior vesical

Vaginal

Inferior gluteal

Superior vesical (continues as obliterated umbilical) = 1st branch. 

Internal pudendal and inferior gluteal = terminal branches.

-           rest arise at variable levels, some may have common stems

Branches of posterior division

Iliolumbar

Passes out of pelvis deep to psoas anterior to lumbosacral trunk.

-           Lumbar branch = 5th lumbar artery (® psoas and QL)

-           Iliac branch ® iliacus & iliac bone; ® anastomosis around ASIS (w/ circumflex iliacs, ascending br of lat fem cut and upper br of deep division of sup gluteal artery.

Lateral sacral (373)

Runs lateral to anterior sacral foramina ® sacral nerve roots, piriformis.

-           spinal branches ® meninges; pass through posterior foramina ® muscles on back of sacrum

-           takes over segmental supply from lumbar a’s; often multiple (often 2: superior & inferior)

Superior gluteal

Largest branch of internal iliac.  Passes backwards, pierces pelvic fascia between lumbosacral trunk and S1, leaves pelvis through greater sciatic foramen above piriformis. 

Branches of anterior division

Superior vesical

= patent proximal part of foetal umbilical artery (distal part ® medial umbilical ligament)

-           passes across side wall ® medially to reach upper bladder (also ® ureter, ductus)

Inferior vesical

® lower course than superior counterpart ® trigone (& ureter, ductus s.v. + prostatic artery in males).

Middle rectal

Small May be absent in females (replaced by uterine & vaginal arteries) or males (by inferior vesical).

Crosses pelvic floor anterior to lateral ligaments ® branches to enter rectum. 

Uterine

Crosses pelvic floor in base of broad ligament, passing above / superficial to ureter. 

-           at cervix runs up next to uterus in the broad ligament ® lateral to tube to meet ovarian artery

Vaginal

Supplies upper part of vagina (= inferior vesical in males); may branch from uterine.

Obturator

Runs along sidewall, below nerve ® enters obturator foramen ® thigh.

-           Pubic branch to pubic periosteum anastomoses with namesake from inferior epigastric;

-           this connection patent in 30% as accessory obturator artery to replace the obturator.

-           Passes on lateral side of femoral ring; can lie on medial side along edge of lacunar ligament ® vulnerable in femoral hernia repair.

Inferior gluteal

Pierces pelvic fascia, passes below S1 nerve root® leaves pelvis through greater sciatic foramen inferior to piriformis ® buttock.

Internal pudendal

In front of inferior gluteal.  Passes through greater sciatic foramen inferior to piriformis ® loops around sacrospinous ligament to enter ischiorectal fossa  via lesser sciatic foramen ® anal canal, perineum and external genitalia. 

 

Pelvic veins

Internal Iliac

3cm, begins at confluence of gluteal (and others) above greater sciatic notch.

® runs posteromedial to artery; joins external iliac on psoas major ® common.

-           tributaries from rectal, vesical, prostatic, uterine and vaginal plexi (bleed badly in # pelvis)

-           communicates with vertebral venous plexus via lateral sacral veins (no valves, coughing ® drives blood back to heart via spine below diaphragm; attributed as route of spread of carcinoma from pelvic viscera to vertebrae

Pelvic nerves (380-88)

Obturator nerve

Anterior divisions of L2-4 ventral rami; from lumbar plexus ® thigh adductors.

-           pierces medial psoas ® crosses pelvic brim medial to SIJ ® passes behind angle between internal iliac vessels and fascia on obturator internus, running posterior to pelvic peritoneum (thus separated from ovary; pain from ovary may ® medial thigh)

Converges with artery in obturator foramen, nerve lies highest and divides into anterior & posterior divisions.  

-           anterior ® anterior to upper border of obturator externus

-           posterior ® pierces obturator externus ® branch to that muscle

Accessory Obturator

Sometimes present; emerges medial to psoas passes over pubic ramus to thigh, pectineus.

Sacral plexus 463-465

Most of L4 and all L5 join to form lumbosacral trunk ® joins ventral rami of S1-4 = sacral plexus.

SP is triangular in shape & lies on piriformis covered anteriorly by pelvic fascia.

Lateral sacral vessels overlie (& supply) the plexus.  S1 (& sometimes S2) separates superior from inferior gluteal arteries. (Ureter in front of internal iliacs \ well anterior.

Sacral nerves give off branches then divide into anterior (® flexor compartment) and posterior (® extensor compartment) divisions. 

-           receive grey rami communicantes from SNS via sacral sympathetic ganglia.

12 branches, 6 before main nerves divide and 6 from divisions (3 from anterior & 3 from posterior).

Branches from sacral nerves only  (All start with P)

From posteriorly:

Nerve to piriformis

(S1, S2)

Perforating cutaneous nerve: pierces sacrotuberous lig ® curves around glut max ® buttock skin

(S2, S3)

Posterior femoral cutaneous nerve: (S1,2 but also joined by anterior division S2-3): pass below piriformis behind sciatic ® enters gluteal region.

(S1-S3)
 
From anteriorly:

Pelvic splanchnics

(S2,3 / S3,4)

®inferior hypogastric plexuses ® cloacal derivatives

Pudendal nerve

(S2-4)

Passes back between piriformis & coccygeus; curls around sacrospinous ligament ® ischiorectal fossa ® EAS &

® muscular branches (S3,4) ® levator ani & coccygeus

Perineal branch

of S4

® levators, perianal skin, not EAS

Branches from anterior lumbosacral divisions

Tibial part of sciatic nerve

Large.  From branches of all 5 anterior divisions.  Joins common peroneal part (below) in pelvis to form sciatic nerve, which, leaves pelvis via gr sciatic foramen inferior to piriformis

Nerve to obturator internus (L5, S1,2): below piriformis, lateral to pudendals, also ® superior gemellus.
Nerve to quadratus femoris (L5, S1,2): lies in front of sciatic nerve, also ® inferior gemellus & hip jt.

Branches from posterior lumbosacral divisions

Common peroneal part of sciatic (L4,5 S1,2)

-           if parts do not join in pelvis, common peroneal part usually pierces lower border of piriformis

Superior gluteal nerve (L4,5 S1): Passes above piriformis.
Inferior gluteal nerve (L5, S1,2): Passes below piriformis.

Sacral sympathetic trunks

Cross pelvic brim behind CI vessels and pass medial to anterior sacral foramina.

Unite anterior to coccyx at ganglion impar.

Somatic branches ® sacral nerves; visceral branches ® inferior hypogastric plexus. 

Inferior hypogastric plexuses

On side wall of pelvis within parietal pelvic fascia.

-           lateral to rectum, seminal vesicle, prostate and posterior bladder (in males)

-           lateral to rectum, cervix, vaginal fornix and posterior bladder (in females)

 Large mesh 5x2cm.  Branches entirely visceral. 

Sympathetic components from:

(1) Superior hypogastric plexus through R & L hypogastric nerves

(2) Sacral sympathetic trunks.

Parasympathetic components from:

Pelvic splanchnic nerves (S2,3 or S3,4).

Half nerves are myelinated (preganglionic) ® relay in ganglia of inferior hypogastric plexus

-           remainder pass without relay (including all parasympathetics) ® viscera walls

Innervation of viscera

Accompany visceral branches of internal iliac artery and vein.

-           run together in ‘ligaments’ of pelvis, eg lateral ligaments of bladder, cervix, rectum

Bladder and rectum: parasympathetic; pelvic splanchnic nerves

Internal urethral sphincter: sympathetic; superior hypogastric plexus.

IAS: sympathetic; branches of sacral ganglia.

Distension of these organs: via pelvic splanchnic nerves; pain with both.

-           note that pelvic splanchnics supply colon up to splenic flexure.

Control of viscera

Parasympathetics: dump excretions (motor to bladder and sigmoid/rectum, secretory motor to gut)

Sympathetics: hold on to excretions (motor to visceral muscle of bladder neck and anal sphincter)

-           also motor to ductus deferens, seminal vesicles, prostate (hence sympathetic = sex)

Coccygeal Plexus

From S4,5 branch and coccygeal nerve ® postanal skin over coccyx.