MUSCLES

1. Big Picture: Posterior Abdominal Wall Layout

• Middle:
• Lumbar vertebrae (L1–L5) project forwards → normal lumbar lordosis.
• In front of them: aorta + IVC.
• Sides (paravertebral gutters):
• Floor = psoas (medial) + quadratus lumborum (lateral).
• Below iliac crest → iliacus joins in.
• Kidneys lie high in these gutters.

👉 If you say: “Posterior abdominal wall = vertebrae + big vessels in the middle + psoas/Q.L./iliacus making a muscular gutter with kidneys sitting in it” → that’s exam-safe.

2. Psoas Major – Exam Gold Summary

A. Attachments (Origin → Insertion)

• Origin (continuous strip):
• From lower border of T12 → upper border of L5:
• Vertebral bodies + intervertebral discs.
• Medial ends of all lumbar transverse processes.
• Fibrous arches over the sides of the upper 4 lumbar vertebral bodies.

👉 One long vertical attachment line down the front + side of the lumbar spine.

• Course & insertion:
• Runs down in the paravertebral gutter, along the pelvic brim.
• Passes under the inguinal ligament.
• Inserts via tendon to lesser trochanter of femur.
• Joins iliacus → together called iliopsoas.

💡 One-liner:

T12–L5 bodies/discs + transverse processes → under inguinal ligament → lesser trochanter.

B. Psoas Key Relations (SUPER high-yield)

Think: “Psoas = a nerve sandwich.”

• Inside the muscle:
• Lumbar plexus is embedded within psoas major.
• In front of the muscle:
• Genitofemoral nerve pierces and runs on the anterior surface.
• From lateral border of psoas:
• Iliohypogastric nerve
• Ilioinguinal nerve
• Lateral femoral cutaneous nerve
• Femoral nerve
• From medial border of psoas:
• Obturator nerve
• Lumbosacral trunk
• Behind psoas (in front of transverse processes):
• Part of external vertebral venous plexus.
• Four lumbar arteries & veins → run backwards, medial to the fibrous arches, then laterally behind psoas.

If an MCQ asks “which nerve emerges from the anterior surface of psoas?” → Genitofemoral.

If “from lateral border?” → iliohypogastric, ilioinguinal, LFC, femoral.

If “from medial border?” → obturator + lumbosacral trunk.

C. Psoas Fascia & Medial Arcuate Ligament (Clinical Hook)

• Psoas fascia (part of iliac fascia):
• Strong sheath closely investing psoas.
• Attached to:
• Vertebral bodies
• Fibrous arches
• Transverse processes
• Iliopubic eminence along pelvic brim.
• Not part of lumbar fascia, but lateral edge blends with anterior layer of lumbar fascia over quadratus lumborum.
• Clinical:
• Retains pus → psoas abscess (often from spinal TB) can track along the muscle → present as a cold abscess in the groin.
• Medial arcuate ligament:
• Local thickening of psoas fascia.
• Runs obliquely from body of L1 (or L2) → transverse process of L1.
• Gives origin to diaphragm fibres, continuous with the crus.
• Above this ligament → part of psoas lies in thorax.
• Sympathetic trunk passes from thorax to abdomen beneath this ligament.

💡 MCQ triggers:

• “Psoas abscess → cold abscess in groin” → think psoas fascia.
• “Sympathetic trunk passes under which structure?” → medial arcuate ligament.

D. Nerve Supply & Actions

• Nerve supply:
• First three lumbar nerves (L1–L3), mainly L2.
• Actions:
• On hip joint:
• With iliacus → powerful hip flexor (iliopsoas).
• On lumbar vertebral column:
• Because it attaches to the sides of lumbar vertebrae → lateral flexor (side-bending).
• On trunk (acting from below, with opposite side + iliacus + anterior abdominal wall muscles):
• Helps flex the trunk (e.g., sit up movement).

One-liner:

L1–L3 (mainly L2); flexes hip, laterally bends lumbar spine, helps flex trunk.

3. Psoas Minor (Variant Muscle – but exam favourite)

• Presence:
• Present in only about 2/3 of individuals → absent in 1/3.
• Position:
• Slender muscle lying on surface of psoas major.
• Origin:
• From T12 + L1 vertebrae.
• Insertion:
• Long thin tendon flattens and blends with psoas fascia, attaching to iliopubic eminence.
• Nerve supply:
• L1 nerve.
• Action:
• Weak flexor of lumbar spine.

MCQ style:

• “Absent in 30–40% of people?” → Psoas minor.
• “Attaches to iliopubic eminence via long tendon?” → Psoas minor.

QL

1. Where Is Quadratus Lumborum? (Position)

• Lies in the paravertebral gutter:
• Medially: next to psoas major
• Laterally: next to transversus abdominis
• Lies in the anterior compartment of lumbar fascia (anterior layer covers its front).

👉 Picture: Back wall → vertebrae in middle, psoas on inner side, QL just lateral to psoas, then transversus abdominis more laterally.

2. Attachments — One Clean Sentence

Origin (below):

• Transverse process of L5
• Iliolumbar ligament
• Adjacent iliac crest

Insertion (above):

• Transverse processes of upper four lumbar vertebrae (L1–L4)
• Inferior border of medial half of 12th rib

👉 One-liner:

From L5 TP + iliolumbar ligament + iliac crest → up to L1–L4 TPs + medial ½ of 12th rib.

So it forms a vertical “strap” between iliac crest and 12th rib / upper lumbar TPs.

3. Key Relations & Lateral Arcuate Ligament (High Yield)

• Lateral border of QL:
• Slopes upwards and medially.
• Crosses the iliocostalis (erector spinae part), which goes upwards and laterally.
• Anterior surface:
• Covered by anterior layer of lumbar fascia.
• Lateral arcuate ligament:
• A thickening in front of this fascia.
• Extends from L1 transverse process → 12th rib.
• Diaphragm arises from it in continuity.
• Subcostal neurovascular bundle (vein, artery, nerve – from above downwards) passes:
• From thorax → beneath lateral arcuate ligament
• Then slants down across lumbar fascia.

👉 Exam hooks:

• “Lateral arcuate ligament spans from L1 TP to 12th rib and gives origin to diaphragm fibres.”
• “Subcostal nerve + vessels pass under lateral arcuate ligament, over QL region.”

4. Functional Identity

• QL is effectively the innermost muscle layer of the body wall in this region.
• It is in series with:
• Diaphragm above
• Transversus thoracis muscle group in thorax

(That’s more conceptual, but nice for viva / essay.)

5. Nerve Supply

• T12
• Plus upper 3 or 4 lumbar nerves (L1–L3 / sometimes L1–L4)

👉 Safe line:

Supplied by T12 and first 3–4 lumbar nerves.

6. Actions (Extremely Exam-Relevant)

• Main job:
• Fixes 12th rib during inspiration → prevents it being pulled up by diaphragm.
• Helps breathing:
• By depressing 12th rib, it assists the descending diaphragm (helps inspiration by stabilizing lower thorax).
• Spinal action:
• Lateral flexor of lumbar spine (side-bending).

👉 One-liner:

Quadratus lumborum fixes and depresses 12th rib for diaphragm, and laterally flexes lumbar spine.

7. Simple Mental Picture

Imagine:

• A quadrangular muscle strap on each side of the lumbar spine:
• Lower end anchored to iliac crest / iliolumbar ligament / L5 TP.
• Upper end attached to 12th rib + TPs of L1–L4.
• In front of it → anterior lumbar fascia, whose thickening (L1 TP → 12th rib) is the lateral arcuate ligament → diaphragm comes from here.
• Through under that ligament comes subcostal vein, artery, nerve.

If you can see:

“A vertical strap between iliac crest and 12th rib, fixing the rib for diaphragm and bending the spine sideways” → you’ve got the essence.

ILIACUS

1. Where is Iliacus? (Location & Relationship)

• Sits in the iliac fossa on the inside of the hip bone.
• Lies lateral to psoas major.
• Joins psoas → together they form iliopsoas, the main hip flexor.

👉 Picture: inside of the iliac bone = a shallow bowl filled by iliacus, which then flows medially to merge with psoas.

2. Attachments — One Clean Line

Origin

• Upper two-thirds of iliac fossa
• Up to inner lip of iliac crest
• Also from anterior sacroiliac ligament

Insertion

• Fibres converge medially → pass under the lateral part of inguinal ligament
• Insert into:
• Psoas tendon
• Adjacent femur just below lesser trochanter

👉 One-liner to remember:

Upper 2/3 iliac fossa + inner iliac crest + anterior SI ligament → under inguinal ligament → joins psoas tendon → femur below lesser trochanter.

3. Iliac Fascia – Why It Matters

• Iliacus is covered by strong iliac fascia.
• Fascia is attached:
• To bone at the margins of the muscle.
• To the inguinal ligament.
• Continuous with psoas fascia.
• It:
• Helps form the floor of the abdominal cavity.
• Provides attachment for parietal peritoneum.
• Sends a prolongation into the femoral sheath (with vessels) → but does not itself continue as a muscle into the thigh (only as fascia).

👉 High-yield idea:

Iliac fascia + psoas fascia = important fascial floor + part of femoral sheath.

4. Nerve Supply

• Femoral nerve (L2, L3) in the iliac fossa.

Easy line:

Iliacus = femoral nerve, L2–L3.

5. Action

• Works with psoas on the hip joint:
• Together → iliopsoas = powerful hip flexor.
• Functionally:
• Flexes thigh on trunk (e.g. lifting leg while walking).
• If leg fixed, can help flex trunk (like sitting up from lying).

👉 Exam-safety:

Iliacus + psoas = main flexors of the hip → “iliopsoas.”

6. Quick Mental Picture

Imagine:

• Inside of the iliac bone = a triangular fan of muscle (iliacus).
• Its fibres gather medially like a funnel.
• This funnel joins psoas tendon under the inguinal ligament.
• Together they attach to the lesser trochanter area → when they pull, the femur flexes.

If you feel: “Fan in the iliac fossa → funnel under inguinal ligament → join psoas → flex hip” → you’ve got it.

🧠 POSTERIOR ABDOMINAL WALL — COMPLETE MASTER TABLE (ZERO-OMISSION)

🔒 One-Look Exam Lock

• Psoas = nerve sandwich
• QL = rib fixer for diaphragm
• Iliopsoas = strongest hip flexor
• Medial arcuate ligament → sympathetic trunk
• Lateral arcuate ligament → subcostal nerve/vessels
• Cold groin abscess → psoas

FASCIA

1. Big Picture: Why This Fascia Matters

• Posterior abdominal wall muscles (psoas, quadratus lumborum, iliacus) = each wrapped in a dense, unyielding fascia.
• Fasciae of adjacent muscles blend at their margins → a continuous fascial sheet.

👉 Clinically and in exams: they love

• Thoracolumbar fascia
• Compartments it forms
• Origins of abdominal muscles from it

2. Lumbar (Thoracolumbar) Fascia – 3 Layers, 2 Compartments

In the lumbar region, the thoracolumbar fascia has 3 layers:

1. Anterior layer
2. Middle layer
3. Posterior layer

These 3 layers form 2 muscular compartments:

• Anterior compartment → contains quadratus lumborum
• Posterior compartment → contains erector spinae

👉 Super important one-liner:

Quadratus lumborum = in front compartment (between anterior & middle layers). Erector spinae = in back compartment (between middle & posterior layers).

3. Anterior Layer – Over Quadratus Lumborum

What it covers / contains:

• Lies in front of quadratus lumborum → forms the anterior wall of its compartment.

Attachments:

• Below: front of iliolumbar ligament + adjacent iliac crest
• Above: lower border of 12th rib
• Medially: attached to the front of lumbar transverse processes, near where psoas fascia attaches
• Laterally: blends with middle layer along lateral border of quadratus lumborum

👉 VERY high-yield:

At this lateral fusion line, transversus abdominis and internal oblique take origin.

So:

Transversus abdominis + internal oblique arise from thoracolumbar fascia → mainly where anterior + middle layers meet.

4. Middle Layer – Between QL and Erector Spinae

Position:

• Lies behind quadratus lumborum and in front of erector spinae.

Attachments:

• Below: back of iliolumbar ligament + adjacent iliac crest
• Above: 12th rib
• Medially: to tips of lumbar transverse processes
• Laterally: blends with both anterior & posterior layers

This fusion laterally helps form a strong aponeurotic origin area for transversus abdominis/internal oblique/external oblique higher up.

5. Posterior Layer – Big, Strong, Extends Far

Coverage:

• Lies over entire erector spinae mass.

Attachments:

• Medially:
• Spinous processes + supraspinous ligaments of all sacral, lumbar, and thoracic vertebrae.
• Laterally (lumbar region):
• From transverse tubercles of sacrum
• To posterior part of iliac crest
• Then slopes outwards to 12th rib
• Above 12th rib:
• Attaches to angles of all ribs
• Lateral border here slopes up medially over thoracic cage.
• Extent:
• Below: to dorsal surface of sacrum
• Above: gradually thins and fades above 1st rib, over muscles of neck, where it's replaced by splenius.

Important distinction:

• In the thorax → only one (posterior) layer = thoracic part of thoracolumbar fascia.
• The 3-layer arrangement exists only in lumbar region (where there are no ribs).

Thickness:

• Thick & strong over lumbar region because it’s reinforced by aponeurotic origin of latissimus dorsi.
• Becomes thinner over thorax, fades in neck.

👉 One-liner:

Posterior layer = thick lumbar sheet over erector spinae, anchored to spinous processes and iliac crest, reinforced by lat dorsi, continues up as thoracic fascia then fades in neck.

6. Minimal “Exam Memory” Summary

If you can say this confidently, you’re in very good shape:

1. Each posterior abdominal wall muscle (psoas, QL, iliacus) has its own dense fascia, blending with neighbours.
2. Thoracolumbar fascia in lumbar region has 3 layers:
• Anterior + middle + posterior.
3. Compartments:
• Anterior compartment (between anterior & middle) → quadratus lumborum.
• Posterior compartment (between middle & posterior) → erector spinae.
4. Anterior layer attachments:
• Iliolumbar ligament + iliac crest → 12th rib, front of transverse processes → fuses laterally with middle layer → origin for transversus abdominis & internal oblique.
5. Middle layer:
• From back of iliolumbar ligament & iliac crest → 12th rib → tips of L TPs → fuses with both anterior & posterior layers laterally.
6. Posterior layer:
• From spinous processes & supraspinous ligaments (sacrum, lumbar, thoracic) → laterally to sacral transverse tubercles, posterior iliac crest, 12th rib, ribs’ angles → thick in lumbar (lat dorsi aponeurosis), thin in thorax → disappears above 1st rib.

VesselsVESSELS OF THE POSTERIOR ABDOMINAL WALL

VESSELS OF THE POSTERIOR ABDOMINAL WALL

(Complete Concept-by-Concept Expansion)

1️⃣ Central Vascular Arrangement of the Posterior Abdominal Wall

Core concept

• The posterior abdominal wall is organized around two major longitudinal vessels:
• Abdominal aorta
• Inferior vena cava (IVC)

Positional relationship

• The inferior vena cava lies on the RIGHT side of the abdominal aorta.
• This right-sided position is consistent throughout the abdomen and is a fundamental orientation concept for:
• Imaging (CT, ultrasound)
• Surgery
• Trauma assessment

2️⃣ Origin of the Abdominal Aorta (Thoracic → Abdominal Transition)

Core concept

• The thoracic aorta becomes the abdominal aorta when it:
• Passes behind the median arcuate ligament
• Passes between the right and left crura of the diaphragm
• Lies anterior to the body of the T12 vertebra

Importance

• This explains:
• The vertebral level of entry (T12)
• The intimate relationship between the diaphragm and the aorta
• Why diaphragmatic structures can affect aortic flow

3️⃣ Course of the Abdominal Aorta

Direction and position

• The abdominal aorta:
• Descends vertically downwards
• Lies retroperitoneally
• Is positioned anterior to the lumbar vertebral bodies
• Inclines slightly to the LEFT of the midline

Neurovascular relation

• The left sympathetic trunk runs along the left margin of the aorta.
• This reflects the close relationship between:
• Autonomic nervous system
• Major vessels of the posterior abdominal wall

4️⃣ Termination of the Abdominal Aorta

Bifurcation

• The abdominal aorta:
• Divides at the level of the body of the L4 vertebra
• Divides into:
• Right common iliac artery
• Left common iliac artery

Positional asymmetry

• The bifurcation lies to the LEFT of the midline, making:
• The right common iliac artery longer
• The left common iliac artery shorter

5️⃣ Structures Crossing the Abdominal Aorta (Anterior Relations)

Between the coeliac trunk(T12) and superior mesenteric artery(L1)

The aorta is crossed anteriorly by:

• Splenic vein
• Body of the pancreas

Between the superior(L1) and inferior mesenteric arteries(L3)

The aorta is crossed anteriorly by:

• Left renal vein
• Uncinate process of the pancreas
• Third part of the duodenum

Clinical relevance

• These relations explain:
• Compression of the left renal vein
• Duodenal compression
• Surgical risk during pancreatic procedures

6️⃣ Surface Marking of the Abdominal Aorta

Surface anatomy

• The abdominal aorta is surface-marked:
• From 2.5 cm above the transpyloric plane in the midline
• To a point 1–2 cm below and to the LEFT of a normally placed umbilicus
• This corresponds to the highest points of the iliac crests

Application

• Used in:
• Physical examination
• Imaging interpretation
• Interventional access planning

7️⃣ Classification of Abdominal Aortic Branches

Major grouping concept

Branches are classified into four functional groups:

A️⃣ Single ventral arteries (to the gut and derivatives)

• Coeliac trunk
• Superior mesenteric artery
• Inferior mesenteric artery

These supply:

• Foregut
• Midgut
• Hindgut respectively

B️⃣ Paired visceral branches

• Inferior phrenic arteries
• Suprarenal arteries
• Renal arteries
• Gonadal arteries

These supply:

• Solid abdominal organs and endocrine structures

C️⃣ Paired parietal branches

• Lumbar arteries

These supply:

• Abdominal wall
• Paraspinal structures
• Spinal components

D️⃣ Posterior unpaired branch

• Median sacral artery

8️⃣ Median Sacral Artery

Origin and course

• Arises:
• Just above the aortic bifurcation
• Runs:
• In the midline
• Over the sacral promontory
• Into the hollow of the sacrum

Distribution

• Anastomoses with:
• Lateral sacral arteries
• Gives:
• Small branches to the rectum

9️⃣ Inferior Phrenic Arteries

Origin

• Usually the first branches of the abdominal aorta
• May arise:
• Separately
• Or from a common trunk
• Originate just above the coeliac trunk

Course

• Each artery:
• Slopes upwards
• Crosses the crus of the diaphragm
• Specific relations:
• Left → passes behind the oesophagus
• Right → passes behind the inferior vena cava

Supply

• Supply:
• Diaphragm
• Give off:
• Small suprarenal branches

🔟 Suprarenal (Adrenal) Arteries

Origin

• Arise from the aorta:
• Between:
• Inferior phrenic arteries
• Renal arteries

Course

• Run:
• Laterally
• Across the crus of the diaphragm

Relations

• Right suprarenal artery:
• Passes behind the inferior vena cava
• Left suprarenal artery:
• Passes behind the posterior wall of the lesser sac

Termination

• Supply the suprarenal glands

1️⃣1️⃣ Renal Arteries

Origin

• Large paired arteries
• Arise at:
• Right angles
• From the aorta
• At the level of L2 vertebra

Length difference

• Left renal artery → shorter
• Right renal artery → longer (due to left-sided aorta)

Left renal artery – relations

• Crosses:
• Left crus of diaphragm
• Psoas major
• Lies:
• Behind the left renal vein
• Covered anteriorly by:
• Tail of pancreas
• Splenic vessels

Right renal artery – relations

• Crosses:
• Right crus of diaphragm
• Psoas major
• Passes:
• Behind the inferior vena cava
• Behind the short right renal vein
• These structures separate it from:
• Head of pancreas
• Bile duct
• Second part of duodenum

Renal artery termination

• Each artery:
• Reaches the renal hilum
• Divides into segmental arteries
• Supplies renal segments

Branches

• Each renal artery gives:
• Small suprarenal branches
• Ureteric branches

Accessory renal arteries

• One or two may arise:
• Above or below the main renal artery
• Common anatomical variation

1️⃣2️⃣ Gonadal Arteries (Testicular / Ovarian)

Origin

• Arise from:
• Near the front of the aorta
• Below renal arteries
• Well above inferior mesenteric artery

General course

• Slope:
• Steeply downwards
• Cross:
• Psoas major
• Genitofemoral nerve
• Right artery:
• First crosses the inferior vena cava

Additional relations

• Cross the ureter
• Supply its middle portion
• Are crossed by colic vessels

Right gonadal artery

• Crossed by:
• Third part of duodenum
• Root of mesentery

Left gonadal artery

• Crossed by:
• Inferior mesenteric vein

Pelvic brim relation

• Reach the pelvic brim:
• Halfway between:
• Sacroiliac joint
• Inguinal ligament

Sex-specific course

Testicular artery

• Runs:
• Along pelvic brim
• Above external iliac artery
• Enters:
• Deep inguinal ring
• Continues in:
• Spermatic cord
• Ends in:
• Testis

Ovarian artery

• Crosses:
• Pelvic brim
• External iliac vessels
• Enters:
• Suspensory ligament of ovary
• Supplies:
• Ovary
• Uterine tube

1️⃣3️⃣ Subcostal Arteries

Origin

• Arise from:
• Lowest part of thoracic aorta

Entry into abdomen

• Enter:
• Beneath the lateral arcuate ligament

Course

• Run:
• Between subcostal nerve and vein
• On anterior surface of lumbar fascia
• Over quadratus lumborum
• Behind the kidney

Termination

• Pass laterally into:
• Neurovascular plane of anterior abdominal wall
• Between internal oblique and transversus abdominis

1️⃣4️⃣ Lumbar Arteries

Number and origin

• Four pairs
• Arise opposite:
• Bodies of upper four lumbar vertebrae

Early course

• Hug the vertebral bodies
• Pass behind:
• Lumbar sympathetic trunks
• Fibrous arches in psoas

Right-sided relations

• Inferior vena cava overlies:
• Lower two lumbar arteries
• Right crus overlies:
• Upper two lumbar arteries

Left-sided relations

• Left crus overlies:
• Uppermost left lumbar artery

Branches

• Each artery gives:
• Posterior branches
• Spinal branches

Lateral course

• All pass laterally behind psoas

Upper three lumbar arteries

• Pass behind quadratus lumborum
• Enter neurovascular plane between:
• Transversus abdominis
• Internal oblique

Fourth lumbar artery

• Passes:
• In front of quadratus lumborum
• Along upper margin of iliolumbar ligament

1️⃣5️⃣ Absence of Fifth Lumbar Artery & Iliolumbar Compensation

Concept

• There is no fifth lumbar artery.

Replacement

• Replaced by:
• Lumbar branch of the iliolumbar artery
• Originates from internal iliac artery

Course

• Ascends:
• From pelvis
• In front of lumbosacral trunk
• Passes laterally behind:
• Obturator nerve
• Psoas major

Supply

• Supplies:
• Psoas
• Quadratus lumborum
• Gives spinal branch:
• Enters L5–S1 intervertebral foramen

Iliac branch

• Runs into iliac fossa
• Supplies:
• Iliacus
• Ilium
• Ends in:
• Anastomosis at anterior superior iliac spine

1️⃣6️⃣ Common Iliac Arteries

Formation

• Formed by:
• Bifurcation of aorta
• Level:
• Body of L4 vertebra
• Position:
• Left of midline

Length difference

• Right longer than left

Course

• Each passes:
• To front of sacroiliac joint
• Divides into:
• External iliac artery
• Internal iliac artery

Relations

• Ureter lies in front of:
• The bifurcation
• Or beginning of external iliac artery

Crossings

• Left common iliac crossed by:
• Inferior mesenteric (superior rectal) vessels
• Near ureter
• Behind apex of mesocolon
• Both crossed by:
• Sympathetic contributions to superior hypogastric plexus
• Sympathetic trunk passes behind the artery

1️⃣7️⃣ External Iliac Artery

Course

• Continuation of common iliac
• Runs:
• Along pelvic brim
• On psoas major
• Passes:
• Beneath inguinal ligament
• Becomes:
• Femoral artery (within femoral sheath)

Branches

• Only two branches, just above inguinal ligament:
• Inferior epigastric artery
• Deep circumflex iliac artery

1️⃣8️⃣ Surface Marking of Iliac Arteries

Surface line

• Drawn from:
• Aortic bifurcation
• To midpoint between:
• Anterior superior iliac spine
• Pubic symphysis

Distribution along line

• Upper one-third → common iliac artery
• Lower two-thirds → external iliac artery

Bifurcation point

• Common → internal + external iliac:
• 3 cm from midline
• Level with:
• Tubercles of iliac crests
• Intertubercular plane

1️⃣9️⃣ Internal Iliac Arteries

Concept

• Enter the pelvis
• Supply:
• Pelvic viscera
• Pelvic walls
• Perineum
• Described separately due to complexity

IVC

1️⃣ Big picture logic (start here)

• IVC = main venous return from below diaphragm
• Longer and more vertical than the aorta
• Lies to the RIGHT of midline → explains:
• Longer left-sided veins
• Asymmetry of gonadal, renal, suprarenal drainage
• Compression phenomena (May–Thurner)

2️⃣ Formation & vertical course (skeleton first)

Formation

• Level: L5 vertebra
• How: Union of right + left common iliac veins
• Exact relation:

→ Behind the right common iliac artery

Upward course

• Ascends on right side of aorta
• Lies on:
• Bodies of lumbar vertebrae
• Right crus of diaphragm
• Pierces diaphragm:
• Through central tendon
• Level T8
• Ends: Right atrium

👉 Compare:

• Aorta pierces at T12
• Esophagus at T10
• IVC at T8 (most superior opening)

3️⃣ Relations – compartment-wise logic

🔹 Infracolic compartment

(= below transverse colon)

IVC is:

• Retroperitoneal
• Crossed anteriorly by:
• Root of mesentery
• Right gonadal artery
• 3rd part of duodenum

Posterior relations:

• Vertebral bodies
• Right sympathetic trunk (partly overlapped)

🔹 Supracolic compartment

(= above transverse colon)

Sequential anterior relations (inferior → superior):

1. Portal vein
2. Head of pancreas
3. Bile duct
4. Posterior wall of epiploic foramen
5. Bare area of liver

→ IVC excavates a deep groove here

Also partly overlaps:

• Right suprarenal gland
• Coeliac ganglion

4️⃣ Arterial crossings (right-sided logic)

IVC is crossed by:

• Right renal artery
• Right suprarenal artery
• Right inferior phrenic artery

This matters in:

• Retroperitoneal surgery
• Suprarenal procedures

5️⃣ Valves – an important exception

• IVC & most tributaries: ❌ No valves
• Exception:
• Gonadal veins (especially testicular)
• Valves usually at termination
• Ovarian veins → valves may or may not be present

Clinical logic:

• Explains varicoceles
• Explains free venous backflow

6️⃣ Surface anatomy (exam favourite)

• Vertical line
• 2.5 cm right of midline
• From intertubercular plane → 6th costal cartilage

7️⃣ Tributaries – NOT a mirror of aorta (core concept)

🔑 Key principle

• No IVC tributaries corresponding to ventral gut arteries
• Gut → portal vein → liver → hepatic veins → IVC

8️⃣ Tributaries in ascending order (must memorize)

1. Common iliac veins (formation point)
2. Lumbar veins (3rd & 4th) – both sides
3. Right gonadal vein
4. Renal veins (both)
5. Right suprarenal vein
6. Inferior phrenic veins
7. Hepatic veins (highest)

9️⃣ Common iliac veins – asymmetric logic

Formation

• Each formed by:
• Internal iliac vein (pelvis)
• External iliac vein (continuation of femoral vein)

Left common iliac vein

• Longer
• Posteromedial to its artery
• Crosses body of L5
• Joins right vein almost at right angle
• May be compressed by right common iliac artery

→ May–Thurner syndrome

• Usually receives median sacral vein

Right common iliac vein

• Shorter
• Almost vertical
• Lies posterior → then lateral to its artery

Both may receive:

• Iliolumbar veins
• Lateral sacral veins (variable)

🔟 Lumbar veins & azygos system (posterior pathway)

Lumbar veins

• Accompany lumbar arteries
• Drain:
• Posterior abdominal wall
• Lateral abdominal wall

Connections:

• Anterior → epigastric veins
• Posterior → vertebral venous plexus

Drainage pattern

• 3rd & 4th lumbar veins → IVC
• Left ones pass behind aorta
• 1st & 2nd lumbar veins → ascending lumbar vein

Ascending lumbar vein

• Vertical channel
• Connects:
• Common iliac
• Iliolumbar
• Lumbar veins
• Course:
• Behind psoas
• In front of transverse processes

Joins subcostal vein to form:

• Right: Azygos vein (enters thorax via aortic hiatus)
• Left: Hemiazygos vein (pierces left crus)

1️⃣1️⃣ Gonadal veins (classic exam asymmetry)

Course

• Paired venae comitantes
• Unite as they ascend on psoas

Termination

• Right gonadal vein → IVC (acute angle)
• Occasionally → right renal vein
• Left gonadal vein → left renal vein (right angle)

Clinical:

• Explains left-sided varicocele
• Explains pressure differences

1️⃣2️⃣ Renal veins – high-yield

• Lie anterior to renal arteries
• Posterior to pancreas
• Join IVC at L2 level
• Enter at right angles

Left renal vein

• ~7.5 cm (3× longer)
• Crosses anterior to aorta
• Receives:
• Left suprarenal vein
• Left gonadal vein
• Sometimes left inferior phrenic vein

Surgical note:

• Can be ligated safely during AAA repair

→ Only if done to the RIGHT of gonadal + suprarenal entries

Variants:

• Retroaortic vein
• Circumaortic double vein

Right renal vein

• ~2.5 cm
• Usually drains only kidney

1️⃣3️⃣ Suprarenal veins (surgical trap)

• Left suprarenal vein
• Long
• Drains into left renal vein
• Right suprarenal vein
• Very short
• Drains directly into IVC
• Passes behind bare area of liver

⚠️ Makes right adrenal surgery difficult

1️⃣4️⃣ Inferior phrenic veins

• Accompany arteries on diaphragm undersurface
• Usually → IVC
• Left side variants:
• To left renal vein
• To suprarenal vein
• May be double

1️⃣5️⃣ Hepatic veins (final entry)

• Right, middle, left + accessory veins
• Drain directly into IVC
• Enter while IVC lies in hepatic groove
• No valves
• Final venous gateway before right atrium

1️⃣6️⃣ Lymphatic drainage – arterial rule

Fundamental rule

• Lymph follows arteries back to aorta

Node groups

• Pre-aortic nodes:
• Along coeliac, SMA, IMA
• Drain gut, liver, spleen, pancreas
• Para-aortic nodes:
• Along paired aortic branches
• Drain kidneys, gonads, posterior wall
• Pelvic viscera:
• Internal iliac → common iliac → para-aortic
• Lower limb:
• Inguinal → external iliac → common iliac → para-aortic

1️⃣7️⃣ Cisterna chyli & thoracic duct

• Formed by:
• Intestinal lymph trunks
• Lumbar lymph trunks
• Location:
• In front of L1–L2
• Under cover of right crus
• Between aorta and azygos vein
• Shape:
• Elongated sac
• Often replaced by a plexus
• Continues as thoracic duct

Fat absorption logic

• Some lipids → portal vein → liver
• Chylomicrons → lacteals → lymph
• Milky lymph → cisterna chyli → thoracic duct → venous system

🔚 One-line master summary (exam recall)

IVC forms at L5, ascends right of aorta, pierces diaphragm at T8, receives asymmetric tributaries (gonadal, renal, suprarenal), lacks valves, grooves liver, and is the final venous highway below the diaphragm.

Nerves

Posterior Abdominal Wall Nerves (Somatic + Autonomic)

1) The big wiring plan (what goes where)

• Upper 4 lumbar anterior rami (L1–L4): immediately enter psoas major after exiting the intervertebral foramina.
• Inside psoas they:
• Give segmental motor branches to psoas major and quadratus lumborum
• Split into anterior + posterior divisions
• Then reunite to form the named lumbar plexus branches within psoas
• Functional split
• Body wall (anterior abdominal wall): mainly T12 + L1
• Lower limb (thigh nerves): mainly L2–L4 via lumbar plexus
• Link to sacral plexus: part of L4 + all L5 → lumbosacral trunk → sacral plexus

SOMATIC NERVES

2) Segmental continuity from thorax

• Segmental outflow continues in series with intercostals:
• T12 (subcostal) + L1–L5 emerge serially
• But only T12 + L1 actually supply the anterior abdominal wall
• L2–L4: after giving branches to psoas + quadratus lumborum → join lumbar plexus → thigh nerves

3) “Who supplies the thigh?” (exam map)

• Obturator nerve → adductor compartment (noted as derivative of flexor compartment)
• Femoral nerve + lateral femoral cutaneous nerve → extensor compartment
• L4 contribution + L5 → lumbosacral trunk → sacral plexus → lower limb

A) Nerves that CROSS quadratus lumborum anteriorly (Anterior abdominal wall set)

4) The three nerves on the front of quadratus lumborum

These are the anterior abdominal wall nerves that cross the anterior surface of quadratus lumborum:

1. Subcostal (T12)
2. Iliohypogastric (L1)
3. Ilioinguinal (L1)

4.1 Subcostal nerve (T12) — pathway + supply

Course logic

• Leaves thorax behind lateral arcuate ligament
• Lies below the vein and artery there (as per text)
• Neurovascular bundle slopes down parallel to the 12th rib
• Crosses anterior layer of lumbar fascia behind kidney
• Passes through transversus abdominis → enters neurovascular plane
• Continues around anterior abdominal wall supplying its muscles

Supply

• Motor: anterior abdominal wall muscles; ends by supplying:
• lower part of rectus abdominis
• pyramidalis
• Sensory:
• Skin over those muscles
• Branches:
• Collateral (muscular) branch
• Lateral cutaneous branch:
• Pierces obliques
• Descends over iliac crest
• Supplies anterior buttock skin between iliac crest and greater trochanter

4.2 Iliohypogastric + ilioinguinal (both L1) — relationship

• Both arise from anterior ramus of L1
• Ilioinguinal = collateral branch of iliohypogastric (key exam line)
• Emerge from lateral border of psoas major
• As common stem then divides OR as separate nerves
• Slope across quadratus lumborum behind kidney
• Pierce anterior layer of lumbar fascia
• Pass through transversus abdominis
• Travel above iliac crest in the neurovascular plane, going downward + forward

Iliohypogastric — key branches and exit points

• Gives lateral cutaneous branch
• Pierces obliques above iliac crest
• Supplies upper buttock skin, behind the area supplied by subcostal nerve
• Main trunk:
• Continues in neurovascular plane
• Pierces internal oblique above ASIS
• Pierces external oblique aponeurosis about 2.5 cm above superficial inguinal ring
• Ends as sensory supply to suprapubic skin

Ilioinguinal — key “inguinal canal” identity

• Runs parallel but lower
• Pierces lower border of internal oblique
• Enters inguinal canal
• Emerges via superficial inguinal ring
• Covered by external spermatic fascia, which it pierces → becomes subcutaneous

Sensory supply

• Anterior 1/3 of scrotum
• (In females) mons pubis + labium majus
• Root of penis (clitoris)
• Upper + medial groin

Motor supply (high-yield detail)

• Before perforating lower border of internal oblique, it gives motor branches to:
• Those fibres of internal oblique + transversus inserted into the conjoint tendon
• Why this matters:
• These fibres help maintain integrity of the inguinal canal

B) Nerves emerging from the LATERAL border of psoas (major lateral group)

5) Lateral femoral cutaneous nerve (L2–L3, posterior divisions)

Formation

• Union of fibres from posterior divisions of anterior rami L2 + L3

Course

• Emerges from lateral border of psoas major
• Crosses iliac fossa on surface of iliacus
• Lies deep to iliac fascia
• Relations:
• Posterior to caecum on right
• Posterior to descending colon on left
• Enters thigh:
• Passes below or perforates inguinal ligament
• About 1 cm from ASIS

Extra point

• Supplies parietal peritoneum of iliac fossa (often forgotten)

6) Femoral nerve (L2–L4, posterior divisions)

Formation

• Within psoas: union of branches from posterior divisions L2–L4

Course

• Emerges from lateral border of psoas into iliac fossa
• Runs deep in gutter between psoas + iliacus, behind iliac fascia
• Gives branches to iliacus (L2–L3)
• Leaves pelvis:
• Passes beneath inguinal ligament
• To lateral side of femoral sheath
• Lies on iliacus

C) The “different pathway” nerves (NOT lateral border)

7) Genitofemoral nerve (L1–L2) — anterior surface of psoas

Formation

• In substance of psoas by union of branches from L1 + L2

Course

• Emerges on anterior surface of psoas major
• Runs down on psoas deep to psoas fascia
• Structures overlying it (important relations)
• Left side: ureter, gonadal vessels, ascending branch of left colic artery, inferior mesenteric vein
• Right side: ureter, gonadal vessels, ileocolic artery, root of mesentery of small intestine
• Just above inguinal ligament:
• Perforates psoas fascia
• Divides into genital + femoral branches
• Fibre note: genital branch = L2 fibres, femoral branch = L1 fibres

Branches

• Genital branch
• Enters inguinal canal via deep ring
• Motor: cremaster
• Sensory: spermatic fasciae, tunica vaginalis, small scrotal skin area (male)
• Female: mons pubis + labium majus
• Femoral branch
• Passes under inguinal ligament with femoral artery
• Pierces femoral sheath + fascia lata
• Supplies skin over upper femoral triangle

8) Medial border of psoas → pelvis entry

• Obturator nerve and lumbosacral trunk
• Emerge from medial border of psoas
• Enter pelvis (then continue to their pelvic/thigh distributions)

AUTONOMIC NERVES (abdominal overview)

9) One-liner framework

• Abdomen receives:
• Sympathetic (two components)
1. Lumbar sympathetic trunk
2. Coeliac plexus (receives fibres from thoracic sympathetic trunk)
• Parasympathetic
• Vagus from above
• Pelvic splanchnics from below
• Visceral vs mixed:
• Coeliac plexus = wholly visceral (supplies all abdominal organs, including gonads)
• Lumbar sympathetic trunk:
• Gives somatic branches for lower abdominal wall + lower limb
• Visceral branches supply pelvic organs only
• Parasympathetic is described as wholly visceral
• Vagus → branch to coeliac plexus
• Pelvic splanchnics → join inferior hypogastric plexus

SYMPATHETIC NERVES — lumbar sympathetic trunk + plexuses

10) Lumbar sympathetic trunk: where it runs

Inputs

• Brings preganglionic fibres descending from lower thoracic trunk
• Receives additional preganglionic fibres (white rami) from L1 + L2 spinal nerves

Entry into abdomen

• Passes behind medial arcuate ligament
• Lies on front of psoas major

Course

• Runs down behind peritoneum on vertebral bodies along medial margin of psoas
• Lies in front of segmental vessels (lumbar arteries + veins)
• BUT: some lumbar veins may pass in front of trunk (clinical trap)

Side relations

• Left lumbar trunk: beside left margin of aorta; para-aortic lymph nodes in front
• Right lumbar trunk: behind IVC

Ganglia

• Usually 4 lumbar ganglia
• Fusion may reduce number

11) White rami vs grey rami (how fibres distribute)

• White rami communicantes (preganglionic) from L1 + L2 join trunk and relay in lumbar + sacral ganglia
• Grey rami communicantes (postganglionic) from lumbar ganglia:
• accompany lumbar arteries around vertebral bodies
• pass medial to fibrous arches
• join anterior rami of lumbar nerves
• then distribute to body wall + lower limb via branches of lumbar plexus
• Key applied point:
• Vasoconstrictor fibres for femoral artery + branches travel in femoral nerve

12) Lumbar splanchnic nerves → superior hypogastric plexus (presacral region)

• Lumbar splanchnic nerves arise from all lumbar ganglia
• From 1st + 2nd ganglia → to plexuses in front of aorta
• From 3rd + 4th:
• pass respectively in front of and behind the common iliac arteries
• They join with each other + fibres from aortic plexuses → form superior hypogastric plexus
• Contains pre- and postganglionic sympathetic fibres

Where the superior hypogastric plexus lies (must-know anatomy)

• Anterior to aortic bifurcation
• Anterior to left common iliac vein
• Between common iliac arteries
• In front of L5 vertebral body and sacral promontory
• Often slightly left of midline
• Close to apex of attachment of sigmoid mesocolon

Important naming correction

• Previously called “presacral nerve”
• Misnomer because it is:
• prelumbar, not presacral
• a plexus, not a single nerve

Surgical plane

• Lies behind parietal peritoneum
• Peritoneum can be stripped off anterior aspect because:
• avascular areolar tissue plane lies between

Division

• Splits like an inverted Y into right + left hypogastric nerves
• may be bundles rather than single nerves
• These descend into pelvis → join inferior hypogastric plexuses
• Cellular content detail:
• Only few ganglion cells in superior hypogastric plexus
• Preganglionic white fibres in hypogastric nerves pass through to relay in inferior hypogastric plexus ganglia

13) Coeliac plexus + splanchnic nerves (upper abdominal sympathetic hub)

Location

• Around origin of coeliac trunk
• Above upper border of pancreas

Inputs

• Greater + lesser splanchnic nerves:
• pierce crura of diaphragm
• enter two large coeliac ganglia
• Right ganglion: in front of crura, behind IVC
• Left ganglion: in front of crura, behind splenic artery
• Splanchnic nerves are almost all preganglionic (white)
• many relay in coeliac ganglia
• Least splanchnic nerve:
• relays in small renal ganglion behind renal artery
• described as an offshoot of main coeliac ganglion
• Separated ganglion masses may lie on aorta at:
• superior mesenteric origin
• even inferior mesenteric origin

Output distribution

• Postganglionic fibres from coeliac ganglia + preganglionic splanchnic fibres form networks on aorta:
• Coeliac plexus
• Superior mesenteric plexus
• Intermesenteric (abdominal aortic) plexus
• Inferior mesenteric plexus
• Fibres reach viscera by streaming along visceral branches of aorta
• Kidney route:
• fibres to kidney pick up renal ganglion branches → form renal plexus behind renal artery
• Gonads:
• testis/ovary supplied by sympathetic plexus accompanying each gonadal artery

Sympathetic functions (exam list)

• Vasomotor
• Motor to sphincters (example given: pyloric)
• Inhibitory to peristalsis
• Carry visceral sensory fibres from all viscera supplied

14) Special case: suprarenal medulla (direct preganglionic drive)

• Preganglionic fibres from greater splanchnic nerve can pass without relay to suprarenal medulla cells
• Suprarenal medulla cells share neural crest origin with sympathetic ganglion cell bodies
• These preganglionic fibres stimulate adrenaline release
• Vasomotor supply to suprarenal gland also arrives via postganglionic fibres relayed in coeliac ganglion

15) Lumbar sympathectomy — applied surgical anatomy (what to avoid, what’s hard)

Targets

• Surgical removal of 3rd and 4th lumbar ganglia

Approach

• Extraperitoneal
• Through transverse muscle-cutting incision in anterior abdominal wall OR flank on that side
• Intact peritoneum is stripped off deep surface of transversus abdominis + posterior abdominal wall to vertebral column

Structures to avoid damaging (explicit list)

• Gonadal vessels
• Ureter
• Genitofemoral nerve (overlying psoas major)

Right vs left difficulty

• Right sympathetic trunk exposure requires careful retraction of IVC (lies in front)
• Left trunk lies beside aorta → easier access

Vessels relation trap

• Lumbar vessels usually behind trunks
• Some lumbar veins may pass in front of trunks

Non-surgical option

• Lumbar ganglia can be destroyed by phenol injection
• Posterior paravertebral approach
• Under radiographic or ultrasonic guidance

Ultra-quick exam recall grid (one glance)

Somatic: relation to psoas

• Lateral border of psoas: lateral femoral cutaneous, femoral, iliohypogastric/ilioinguinal (after emerging), + others in general
• Anterior surface of psoas: genitofemoral
• Medial border of psoas: obturator + lumbosacral trunk

Abdominal wall nerves crossing quadratus lumborum

• T12 (subcostal) + L1 (iliohypogastric, ilioinguinal)

Key inguinal ring facts

• Iliohypogastric: pierces EO aponeurosis 2.5 cm above superficial ring
• Ilioinguinal: emerges through superficial ring
• Genitofemoral genital branch: enters canal via deep ring

🧠

Parasympathetic Nerves to Abdomen & Pelvis — One Continuous System

1️⃣ Fundamental Logic (Big Picture)

Parasympathetic supply to the gut and pelvic viscera comes from TWO sources only:

👉 No overlap in origin, but continuous overlap in function at the splenic flexure.

2️⃣ VAGUS NERVE — Parasympathetic to Foregut & Midgut

🔹 Origin (Cell bodies)

• Dorsal motor nucleus of vagus (medulla)
• Fibres are preganglionic parasympathetic

🔹 Course (Abdominal entry)

• Right & left vagi → form vagal trunks
• Enter abdomen via oesophageal hiatus (T10)

🔹 Plexus Distribution (Key Concept)

• Vagal fibres do NOT synapse in the coeliac plexus
• They:
• Pass through coeliac plexus
• Mix with sympathetic postganglionic fibres
• Travel together to organs

👉 Parasympathetic ganglia are in the organ wall, not in the plexus.

🔹 Areas Supplied

• Gut:
• Oesophagus
• Stomach
• Duodenum
• Jejunum
• Ileum
• Caecum
• Ascending colon
• Proximal 2/3 of transverse colon
• Accessory organs:
• Liver
• Gallbladder
• Pancreas
• Kidney:
• Via renal plexus (minor functional role)

🔹 Functions (EXAM GOLD)

• Motor → increases peristalsis
• Secretomotor → stimulates glands
• Sphincter effect:
• Inhibitory to pyloric sphincter
• Sensory fibres present
• Physiological reflexes (distension, secretion)

3️⃣ PELVIC SPLANCHNIC NERVES — Parasympathetic to Hindgut & Pelvis

🔹 Origin (CRITICAL DETAIL)

• Cell bodies in lateral horn of S2–S4 spinal segments
• Fibres exit via:
• Anterior rami
• Distal to anterior sacral foramina

⚠️ Only parasympathetic nerves arising from spinal nerves

🔹 Entry into Autonomic Plexus

• Join inferior hypogastric (pelvic) plexus
• Distribute to pelvic viscera

🔹 Ascending Fibres (Commonly Missed Exam Point)

Some fibres:

• Leave pelvis
• Ascend retroperitoneally
• Usually:
• Pass to the left of superior hypogastric plexus
• Occasionally through it
• Confirm parasympathetic supply to hindgut

🔹 Areas Supplied

Hindgut

• Distal 1/3 of transverse colon
• Descending colon
• Sigmoid colon
• Rectum

Pelvic organs

• Bladder (detrusor contraction)
• Uterus
• Vagina
• Erectile tissues
• Distal ureter

🔹 Functions

• Motor → peristalsis of hindgut
• Secretomotor → mucosal secretion
• Bladder:
• Detrusor contraction
• Internal sphincter relaxation
• Sexual function:
• Vasodilation → erection

Mnemonic:

“S2–4 keeps the floor”

(Bowel, bladder, erection)

4️⃣ SPLENIC FLEXURE — The Transition Zone (HIGH-YIELD)

📌 This is the parasympathetic watershed of the gut

📌 Corresponds to midgut–hindgut junction

5️⃣ Sensory Fibres — Clarified Logic

👉 Parasympathetic sensory ≠ pain

6️⃣ Clinical Correlation (Exam Integration)

🔹 Vagotomy

• ↓ gastric acid
• ↓ motility
• Risk of gastric stasis

🔹 Pelvic surgery (e.g. hysterectomy, rectal surgery)

• Damage to pelvic splanchnics →
• Urinary retention
• Constipation
• Sexual dysfunction

🔹 Spinal cord injury

• Above S2–4:
• Reflex bowel/bladder preserved
• At S2–4:
• Areflexic bowel/bladder