5.10 Posterior Abdominal Wall

Overview (246)

5 lumbar vertebra ® lordosis, with IVC and aorta lying on the vertebral bodies

-           Anterior longitudinal ligament runs over this then fuses with periosteum in sacrum.

-           deep paravertebral gutters lie to each side, kidneys lie high up in these.

-           floored by psoas and quadratus, and iliacus below the crests.

Crura and diaphragm are also parts of the posterior abdominal wall.

Muscles

Psoas major (246)

Attaches to discs above 5 lumbar vertebrae + bodies + intervening fibrous arches + medial ends of transverse processes.  Lies in the gutter b/n bodies and transverse processes L1-5.

Inserts: ® passes over pelvic brim, below inguinal ligament ® lesser trochanter.

-           the lumbar plexus is embedded in it; the external vertebral venous plexus is behind, as do the four lumbar arteries and veins.

Psoas fascia invests it anteriorly and contains pus as psoas abscess which may discharge into groin. 

-           attached to vertebral bodies, fibrous arches, transverse processes and iliopubic eminence

Thickening of psoas fascia from body of L1 ® transverse process of L2 = medial arcuate ligament; gives rise to diaphragmatic fibres, sympathetic trunk passes below it.  Hence some psoas = above diaphragm.

Nerves emerging from psoas (250):

GF from anterior aspect.

IH, II, lateral femoral cutaneous, femoral nerves from lateral aspect.

Obturator nerve & lumbosacral trunk from medial border.

Innervation: L2, also L1 & L3. 

Action: flexes hip, lateral flexor of vertebral column, from below flexes trunk (with iliacus & abdo wall muscles).

Psoas minor: only 2/3 people have this; shrimpy muscle on major’s surface; arises T12-L1, long tendon flattens out to blend with psoas fascia, attaches to iliopubic eminence.  Weak flexor.  L1 supply.

 

Quadratus lumborum (246)

Flat muscle deep in paravertebral gutter, edge to edge with psoas medially & transversus abdo laterally.

-           is in the anterior compartment of the lumbar fascia.

Origin: stout transverse process of L5, iliolumbar ligament and iliac crest

Insertion: transverse processes of L1-4 (lat to psoas), inferior border of medial 1/2 of 12th rib.

-           its lateral slope upwards crosses the lateral border of iliocostalis (part of erector spinae grp)

-           fascial thickening from 1st transverse process ® 12th rib = lateral arcuate ligament, from which diaphragmatic fibres arise in continuity; and subcostals emerge beneath onto lumbar fascia.

The muscle is innermost of the 3 abdo wall layers; in continuity with transversus and diaphragm.

Innervation: segmentally T12- L3 or 4

Action: Prevents diaphragm from elevating 12th rib; aids descent of contracting diaphragm.

-           weak abductor of the lumbar spine.

 

Iliacus

From hollow upper 2/3 of iliac fossa & anterior sacroiliac ligament.  ® beneath lateral ing ligament.

Inserts in psoas tendon & femur below lesser trochanter.

Covered by strong iliac fascia attached to bone at margins and to inguinal ligament

Floors the abdominal cavity, attached parietal peritoneum over it.

Innervation: femoral nerve (L2,3)

Action: with psoas to flex hip.

Fascia

Each muscle of posterior abdominal wall covered with dense fascia which provides firm attachment for retroperitoneal organs & peritoneum. 

Psoas fascia and iliac  fascia already as mentioned

Lumbar fascia

Part of thoracolumbar fascia: 3 layers of tissue enclose 2 muscular compartments.

Anterior & middle layers in lumbar region only, posterior layer extends from lower neck to sacrum.

Quadratus lumborum occupies anterior compartment, erector spinae posterior compartment.

Anterior layer extends from iliolumbar ligament & adjoining crest ® lower border of rib 12

-           attaches to transverse processes next to psoas fascia; laterally blends with the middle layer along the lateral border of quadratus lumborum (where transversus and int oblique arise)

Middle layer extends from iliolumbar ligament and crest to 12th rib

-           same lateral attachment as anterior (and posterior); medially to tips of transverse processes.

Posterior layer lies over whole erector spinae mass

-           medially attaches to spinous processes and supraspinous ligaments of all sacral, lumbar and thoracic vertebrae

-           laterally passes up from transverse tubercles of sacrum ® posterior iliac crest ® slopes up to towards 12th rib, then attaches to angles of all ribs, angling medially towards neck, where it fades out over the 1st rib and replaced by splenius.

-           Reinforced by fusion of aponeurotic origin of lat dorsi over the lumbar region.

Abdominal aorta

Enters via aortic hiatus at T12 (behind median arcuate ligament and crura of diaphragm)

® runs down on vertebrae, slightly to L ® bifurcates at L4, 2cm below & to L of umbilicus.

-           crossed by splenic vein and body of pancreas b/n CA and SMA

-           crossed by L renal vein, uncinate of pancreas and D3 b/n SMA and IMA

Surface marking: 2.5cm above transpyloric plane to 1-2cm below and left of umbilicus (iliac crest level)

3 groups of branches:

(1) Ventral midline branches to gut & its derivatives (coeliac, SMA, IMA)

-           these have been considered already.

(2) Paired visceral branches to paired viscera (to kidneys, adrenals & gonads)

(3) Paired lateral branches to abdominal wall (inferior phrenics and lumbars)

Median sacral artery

Runs on down into hollow of sacrum, anastomoses with lateral sacral arteries

-           tiny branch given to the rectum

Paired visceral branches to paired viscera

Inferior phrenic artery (314)

Leaves aorta in diaphragmatic orifice ® slopes across & supplies crus ® gives off branches to adrenal. 

-           L passes behind oesophagus; R passes behind IVC.

Suprarenal arteries (314)

Arise b/n inferior phrenics and suprarenal. Run across crus ® enter gland after branching. 

-           L passes behind posterior wall of lesser sac; R passes behind IVC

Renal arteries (314)

Arise at L2; R longer than L. Each gives off suprarenal and ureteric branches.

-           L crosses left crus and psoas ( both behind veins), covered by pancreas tail and splenic vessels

-           R crosses right crus and psoas, covered by tail of pancreas, splenic vessels & IVC, these separate it from further anterior structures: D2, bile duct, head of pancreas.

1-2 accessory renal arteries often arise below or above the main artery.

Gonadal arteries (314)

Arise near front of aorta, below renal arteries (but well above IMA) ® slope down over psoas & GF nerve ® cross (and supply) ureters ® reach pelvic brim 1/2way between SIJ and ing ligament. Then:

-           (R artery is also crossed by D3 and mesentery root; L by IMV)

Males: run along pelvic brim above external iliac artery ® enters deep ring & run in spermatic cord. 

Females: crosses pelvic brim, runs down lateral pelvic wall ® passes to ovary via suspensory ligament. 

Paired branches to abdominal wall

Subcostal arteries

Arises from aorta just above diaphragm ® passes below lateral arcuate ligament ® runs over QL to pass into neurovascular plane of abdominal wall.

Lumbar arteries (247)

4; arise opposite bodies of upper four vertebrae

Pass beneath sympathetic trunks and arches of psoas.  R arteries pass beneath IVC.

1-3 pass posterior to QL into neurovascular plane, 4 passes anterior to QL into neurovascular plane (as for subcostal artery – see 247).

No 5th lumbar artery; iliolumbar from posterior division of internal iliac is equivalent.

-           this ascends in front of lumbosacral trunk, passes behind obturator & psoas

-           ® lumbar branch; supplies psoas and QL & spinal branch which enters at L5-S1

-           ® iliac branch (see 247); runs around iliac crest to iliac fossa, anastomoses at ASIS.

Common iliac arteries

Pass to SIJ’s before bifurcating.  R longer than L (since bifurcation is to L of midline).  Crossed by ureters, sympathetic branches to superior hypogastric plexus (trunk itself is behind), IMA on L. 

External iliac arteries

Continues along pelvic brim on psoas ® pass below inguinal ligament to enter femoral sheath.

2 branches (just above ligament): inferior epigastric and deep circumflex iliac.

-           surface markings from bifurcation ® midpoint b/n ASIS and pubic symphysis

-           common iliac is upper 1/3 and external lower 2/3 of this line

-           bifurcation of common iliac is 3cm from midline, level with iliac crest tubercles.

Inferior Vena Cava (248)

Longer than abdominal aorta; commences at L5 behind R common iliac (cf L4) ® pierces diaphragm at T8 (cf T12).

Lies on bodies of lumbar vertebrae and R sympathetic trunk (plus part of coeliac ganglion); crosses R renal, suprarenal and inferior phrenic arteries and R crus.

-           in the infracolic compartment, is crossed by root of mesentery, right gonadal artery and D3

-           in the supracolic, behind portal vein, head of pancreas, bile duct, and epiploic foramen.

Does not have valves, except for gonadals (esp testicular)

Tributaries

Note adrenals and gonads only tributaries with asymmetric drainage; directly into IVC on R, into L renal vein on L. 

The portal system replaces the anterior gut trunks, reach IVC only after liver via high hepatic veins.

In ascending order:

Iliac veins

Enters abdomen medial to artery ® runs along pelvic brim behind artery; joined by internal iliac vein at SIJ.   CIV’s unite to form IVC behind R common iliac artery. 

-           L is longer than the right, & has to bulge over the body of L5. R CIA may compress it.

-           Each CIV receives iliolumbar, and perhaps lateral sacral veins, & median sacral on L.

Lumbar veins

Accompany arteries; drain lateral & posterior abdominal walls; anastomose with epigastrics anteriorly and vertebral venous plexus posteriorly.

-           3rd & 4th ® IVC cf 1st & 2nd ® ascending lumbar vein; this connects: common iliacs, iliolumbar, lumbar, subcostals to the azygos and hemiazygos system; passes behind psoas and in front of lumbar transverse processes; R through aortic opening; L perforates left crus.

-           on L lower 2 lumbar veins pass behind aorta; all 4 pass behind sympathetic trunk. 

Gonadal veins

Paired on entering abdomen ® unite to 1 vein on psoas. 

Renal veins

Emerge from kidney hilum as 5-6 tribs anterior to branches of artery.  L vein 3x longer than R (2.5cm). 

Lie behind pancreas, join IVC at right angles at L2. 

-           the R usually only drains its own kidney.

-           the L collects left gonadal, left suprarenal, and possibly inferior phrenic.

-           the L is not uncommonly divided in AAA surgery (lateral to gonadal entry); kidney ® ok.

-           rarely there are 2 L veins, ant and post to aorta; or occasionally just one post vein.

Suprarenal veins

R enters IVC behind bare area of liver (complicates R gland surgery).

L runs down medially to L renal vein.

Hepatic veins

R; middle and L usually form single trunk.

Inferior phrenic veins

Accompany arteries on lower surface of diaphragm ® join IVC below liver, though L vessel may join the left renal or suprarenal vein (or be doubled).

Development of veins

Sinus venosus receives blood from 3 sources:

(1) placenta via umbilical veins

(2) yolk sac via R & L vitelline veins (which become portal system)

(3) embryonic body tissues via R & L cardinal veins (which become caval system)   

In each system veins of one side disappear & blood is returned from that side to the other by cross channels. 

Umbilical veins

R disappears early; L persists until birth & joins L branch of portal vein.

Continuation of R umbilical vein, the ductus venosus carries blood to R cardinal vein bypassing liver. 

Vitelline veins

SMV is remnant of L vitelline vein.  Portal vein formed by remnants of R & L vitelline veins. 

Cardinal veins

Discussed in chapter 1

Lymph nodes  (249)

The lymph of any viscera flows along its vessels to the aorta.

Preaortic nodes

Drain alimentary canal, liver, pancreas, spleen. (ie viscera supplied by single ventral arteries) 

Para-aortic nodes

Drain paired structures both somatic and viscera.

Includes lymph from some pelvic viscera which flow through nodes along internal iliacs ® common iliacs; which also receive lymph from inguinal and external iliac nodes.

Cisterna chyli

Variable number of intestinal and lumbar lymph trunks join to form cisterna, 5-7.5cm long sac lying between aorta and hemiazygos vein under R crus, in front of L1 and L2. ® thoracic duct.

-           this lymph can look milky as some digested fats pass directly to circulation via it.

Nerves (250)

Anterior rami of lumbar spinal nerves pass into substance of psoas (giving it & QL segmental supply) and forming the lumbar plexus within it.

-           only T12 & L1 give supply to anterior abdominal wall muscles; these cross anterior QL.

-           L2,3,4 give a posterior wall branch, but mostly ® thigh nerves: obturator (adductor but flexor derivative ie the anterior division), femoral and lat fem cutaneous nerve (posterior divisions). 

-           Part of L4 and all of L5 pass as lumbosacral trunk to lower limb.

Lumbar plexus

From anterior rami of upper 4 lumbar nerves.  Most supply is to muscles of lower limb; anterior divisions ® flexor compartment, posterior divisions ® extensors.  Summarised later.

Subcostal nerve (250)

Passes under lateral arcuate ligament (ÝVAN) ® slopes under rib across lumbar fascia behind kidney ® abdominal wall neurovascular plane. Ends in bottom of rectus, supplies it, pyramidalis & skin over.

-           Lateral cutaneous branch ® pierces oblique muscles ® skin of anterior buttock.

Iliohypogastric & Ilioinguinal nerves

Arise from common stem; I-I = collateral branch of I-H (divide at lateral border of psoas).  Run over QL behind anterior lumbar fascia (IH Higher than II).  Then ® neurovascular plan.

I-H ® runs in neurovascular plane, pierces IO above ASIS ® pierces EOA 2.5cm above superficial ring ® suprapubic skin: ant cutaneous branch (see 250).

-           lateral cutaneous branch ® pierces obliques ® skin of upper buttock.

I-I enters inguinal canal from side ® exits superficial ring covered by external spermatic fascia ® pierces external spermatic fascia below superficial ring to become cutaneous

-           ® anterior 1/3 of scrotum, root of penis/clitoris, superomedial groin.

-           motor branches to fibres of IO and TA inserting into conjoint tendon (maintain integrity). 

Lateral femoral cutaneous nerve L2, 3

From posterior divisions of anterior rami L2,3.  Exits laterally to psoas, curves around iliac fossa deep to iliac fascia (and caecum) ® passes below or through inguinal lig to enter thigh.

-           also supplies the parietal peritoneum of the iliac fossa.

Femoral nerve L2,3,4

From posterior divisions of anterior rami L2,3,4.  Emerges lateral to psoas (low – see 250). Runs deep to iliac fascia in gutter b/n iliacus and psoas.  Passes below inguinal ligament lateral to femoral sheath. 

Genitofemoral nerve L1,2

Emerges from anterior surface of psoas ® runs down deep to psoas fascia. 

-           L nerve overlaid by ureter, gonadal vessels, ascending br of left colic artery & IMV

-           R overlaid by ureter, gonadal vessels, ileocolic artery, mesentery root.

Perforates psoas fascia and divides just above the ing lig.

-           genital branch (L2) passes through transversalis fascia ® enters spermatic cord to supply cremaster, tunica vaginalis.

-           femoral branch (L1) passes anterior to femoral artery ® supplies skin of groin below mid part of inguinal ligament. 

Obturator nerve & lumbosacral trunk

Emerge from medial border ® enter pelvis.  

Autonomic nerves (250)

Sympathetic nerves

Twofold supply: lumbar part of sympathetic trunk & coeliac plexus (latter from thoracic segments).

-           coeliac is wholly visceral;  supplies all abdominal organs including gonads

-           lumbar trunk is somatic to lower abdo wall and lower limb, and visceral to pelvis only.

 

Coeliac ganglion

Lies around origin of coeliac trunk above pancreas. From greater and lesser splanchnic nerves.

-           2 large ganglia: L lies behind splenic artery on crus; R behind IVC.

-           splanchnic nerves are almost all preganglionic, and most relay in the coeliac ganglia.

-           the least splanchnic instead relays in a small renal ganglion behind renal artery. 

Postganglionic fibres from coeliac ganglia and preganglionic splanchnic fibres form a tangle around coeliac, SM plexus, intermesenteric plexus, IM plexus.

-           anyway, get to arteries of viscera; (vasomotor, motor to sphincters, inhibit peristalsis, carry sensory fibres from all viscera)

-           special preganglionics from greater splanchnic pass directly to suprarenal medulla, which also has a postganglionic supply from the regular relay in the coeliac ganglion.

 

Lumbar part of sympathetic trunk

Preganglionic fibres descending from thoracic segments, and L1-L2 white rami.

Passes behind medial arcuate ligament ® lies on vertebral bodies just touching psoas.

-           and ends by passing behind common iliacs to become the sacral part of the trunk.

-           runs inside vessels (lumbar arteries & veins); though in fact a couple may run in front which is important in lumbar sympathectomy.

-           L trunk lies beside L aortic margin behind para-aortic nodes; R lie behind IVC.

4 ganglia ® somatic branches ® all 5 lumbar nerves (L1-2 sparse) ® body wall & lower limb. 

and ® visceral branches ® coeliac, aortic and superior hypogastric plexuses:

-           those from first 2 ganglia ® aortic plexus

-           L3 & L4 fibres pass behind and in front of common iliacs respectively, then join and meet aortic plexus fibres to form superior hypogastric plexus (pre and post-ganglionic, lies in front of aortic bifurcation, L5, sacral promontory; behind peritoneum, close to apex of attachment of pelvic mesocolon – see 381).

-           divides into ® R & L hypogastric nerves run down pelvis ® inferior hypogastric plexus; most preganglionic cells in the superior plexus relay here instead of in the first plexus. 

 

Lumbar sympathectomy

Removal of 3rd and 4th ganglia, approached extra-peritoneally through flank or anteriorly.

-           ie peritoneum stripped from deep transversus and posterior wall to vertebral column.

-           Carefully retract the IVC to get to the right trunk

-           The left (beside aorta) is easier.

Can just inject them with phenol.

 

Parasympathetic nerves

Twofold supply: vagus from above, pelvic splanchnics below.  Wholly visceral.

i)                       vagus ® coeliac plexus; without relay ® accompany arteries to supply gut as far as transverse colon, kidney.  (motor and secretomotor to gut, inhibit pyloric sphincter)

ii)                     pelvic splanchnics ® (from sacral segments 2,3,4) ® inferior hypogastric plexus ® pelvic viscera and colon as far back as splenic flexure. 

Both contain some sensory fibres.