LO 1

ON EXAM — SAD PUCKER mnemonic, primary vs secondary retroperitoneal, kidney anatomy (hilum: Vein-Artery-Pelvis anterior to posterior), perirenal fat, Gerota's fascia

SAD PUCKER — name each organ

Suprarenal (adrenal) glands

Aorta & IVC

Duodenum (2nd, 3rd, 4th parts)

Pancreas (except tail — intraperitoneal)

Ureters

Colon (ascending and descending)

Kidneys

Esophagus (thoracic/lower)

Rectum (lower 2/3)

Primary vs secondary retroperitoneal

Category	Definition	Organs
Primary retroperitoneal	Developed and remained outside the peritoneum	Kidneys, ureters, adrenal glands, aorta, IVC, rectum (lower)
Secondary retroperitoneal	Initially intraperitoneal; mesentery fused to post. body wall during development	Pancreas (head/body), duodenum (2nd-4th), ascending & descending colon

Intraperitoneal GI organs (for contrast)

Stomach, liver, gallbladder, spleen, 1st part duodenum, jejunum, ileum, cecum/appendix, transverse colon, sigmoid colon, upper 1/3 rectum

Kidney anatomy — layers outer → inner

Layer 1 (outer)

Pararenal fat (posterior)

Layer 2

Gerota's (renal) fascia

Layer 3

Perirenal (perinephric) fat

Layer 4

Renal capsule (fibrous)

Layer 5 (innermost)

Kidney parenchyma (cortex + medulla)

Renal hilum — anterior to posterior (VAP)

Most anterior

Renal Vein

Middle

Renal Artery

Most posterior

Renal Pelvis / ureter

Vertebral levels

Right kidney — vertebral level

T12–L3 (slightly lower)

Left kidney — vertebral level

T11–L2 (slightly higher)

Why is R kidney lower?

Displaced inferiorly by the liver

Adrenal glands — vertebral level

T12 (both)

Right vs left kidney anterior relations

Side	Anterior relations
Right kidney	Right adrenal, liver, 2nd part duodenum, hepatic flexure of colon
Left kidney	Left adrenal, stomach, spleen, pancreas, jejunum, splenic flexure of colon

Urolithiasis — 3 constriction sites

Ureteropelvic junction (UPJ)

Crossing of common iliac vessels (pelvic brim)

Ureterovesical junction (UVJ) — most common impaction site

🪤 TRAP: The pancreas, duodenum (except 1st part), and ascending/descending colon are SECONDARY retroperitoneal (were once intraperitoneal, fused during development). The rectum is BOTH — upper 1/3 intraperitoneal, lower 2/3 retroperitoneal.

LO 2

ON EXAM — celiac (T12), SMA (L1), IMA (L3), renal arteries (L1–L2), bifurcation at L4. 3 unpaired anterior branches feed GI (foregut/midgut/hindgut). Nutcracker syndrome.

Abdominal aorta — entry and termination

Enters abdomen at (diaphragm level)

T12 — aortic hiatus (behind median arcuate ligament)

Bifurcates at _____ into _____

L4 → right & left common iliac arteries

Unpaired anterior (GI) branches — "3-3-3-1" mnemonic

Branch	Vertebral level	GI region supplied
Celiac trunk	T12	Foregut — distal esophagus, stomach, proximal duodenum (to ampulla), liver, gallbladder, pancreas, spleen
SMA	L1	Midgut — distal duodenum → proximal 2/3 transverse colon
IMA	L3	Hindgut — distal 1/3 transverse colon → upper rectum

Celiac trunk — 3 branches

Branch 1

Left gastric artery → distal esophagus + lesser curvature stomach

Branch 2

Splenic artery → spleen, pancreas (body/tail), stomach (via short gastric + L gastroepiploic)

Branch 3

Common hepatic artery → liver, gallbladder (cystic a.), duodenum/pancreas (gastroduodenal), stomach (R gastric, R gastroepiploic)

SMA branches

Left side branches (jejunoileal)

Jejunal and ileal arteries → vasa recta + arcades to small bowel

Right side branches (colic)

Ileocolic, right colic, middle colic arteries

Inf. pancreaticoduodenal a. supplies

Lower pancreatic head + distal duodenum (midgut); anastomoses with sup. pancreaticoduodenal (celiac/foregut)

IMA branches

Branch 1

Left colic artery → descending colon

Branch 2

Sigmoid arteries → sigmoid colon

Branch 3 (terminal)

Superior rectal artery → upper rectum

Arterial anastomoses along colon

Marginal artery of Drummond

Continuous collateral along mesenteric border connecting SMA + IMA; often tenuous at splenic flexure

Arc of Riolan

Meandering mesenteric a. — direct anastomosis between middle colic (SMA) and left colic (IMA)

Watershed areas (2) — ischemia prone

Splenic flexure (SMA/IMA junction) and rectosigmoid junction (IMA/superior rectal)

Paired lateral branches

Middle suprarenal (adrenal)

L1 — one of 3 sources to adrenal

Renal arteries — level

L1–L2 (just below SMA)

Gonadal arteries

L2 — testicular or ovarian

Nutcracker syndrome

What gets compressed?

Left renal vein

Between what 2 structures?

Aorta (posteriorly) and SMA (anteriorly)

Classic symptoms (3)

Left flank pain, hematuria, and left-sided varicocele (men) / pelvic congestion (women)

SMA syndrome

What gets compressed?

3rd (transverse) part of duodenum — between SMA (anteriorly) and aorta (posteriorly)

Classic patient (body habitus)

Severe weight loss (loss of mesenteric fat pad) — anorexia, post-burn, bariatric surgery, spinal brace

Classic symptoms

Post-prandial epigastric pain, early satiety, bilious vomiting, weight loss

🪤 TRAP: Foregut = celiac (distal esophagus to 2nd part duodenum). Midgut = SMA (2nd duodenum to proximal 2/3 transverse colon). Hindgut = IMA (distal 1/3 transverse to upper rectum).

LO 2

ON EXAM — IVC forms at L5 (confluence of common iliacs), pierces diaphragm at T8. Portal vein = SMV + splenic. Portosystemic anastomoses: esophageal varices, caput medusae, anorectal (NOT internal hemorrhoids).

IVC — formation and course

Forms at (level + confluence)

L5 — junction of right and left common iliac veins

Pierces diaphragm at

T8 (caval foramen / vena caval hiatus)

Structures traversing w/ IVC through T8

Right phrenic nerve (and small branches of it)

Asymmetric tributaries — R vs L

Tributary	Right side drains into	Left side drains into
Gonadal vein	Directly into IVC	Left renal vein (at 90°) → IVC
Suprarenal (adrenal) vein	Directly into IVC	Left renal vein → IVC
Renal vein	Short — directly into IVC	Long — crosses aorta beneath SMA to reach IVC

Portal vein formation

Portal vein = ______ + ______

Superior mesenteric vein (SMV) + splenic vein (behind neck of pancreas)

IMV drains into

Splenic vein (most commonly) → then into portal vein

Portal vein enters liver at

Porta hepatis, within the hepatoduodenal ligament (along with hepatic a. and CBD)

Portosystemic anastomoses — 3 classic sites

Site	Portal vein	Systemic vein	Clinical finding
Esophageal	Left gastric vein	Azygos vein (esophageal branches)	Esophageal varices — can rupture → massive upper GI bleed
Umbilical (caput medusae)	Paraumbilical veins (in ligamentum teres)	Superficial epigastric veins (to IVC)	Caput medusae — dilated veins radiating from umbilicus
Anorectal	Superior rectal vein (→ IMV → portal)	Middle and inferior rectal veins (→ internal iliac / pudendal → IVC)	Anorectal varices (separate from hemorrhoids)

Azygos system

Azygos drains into

Superior vena cava (at T4)

Hemiazygos drains into

Azygos (crosses midline at T8-T9)

Function when IVC obstructed

Collateral pathway — azygos system connects IVC tributaries to SVC, bypassing IVC blockage

Lymphatic drainage

Cisterna chyli — location

Upper abdomen at L1–L2, posterior to aorta on right

Thoracic duct — drains into

Junction of left subclavian + left internal jugular veins (left venous angle)

Pre-aortic vs para-aortic nodes

Pre-aortic = drain GI tract (celiac, SMA, IMA nodes); Para-aortic (lumbar) = drain paired lateral structures (kidney, gonads, uterus, testes)

🪤 TRAP: Internal hemorrhoids are NOT a portosystemic anastomosis — they are normal anal cushions (superior rectal v. → portal). External hemorrhoids drain via inferior rectal v. → systemic (IVC). The anastomosis sits between them at the dentate line.

LO 3

ON EXAM — T8 (IVC), T10 (esophagus + vagus), T12 (aorta + thoracic duct + azygos). "I ate 10 eggs at 12" mnemonic. Phrenic nerve C3-4-5. Shoulder pain from diaphragm irritation (C3-5 referred).

Diaphragm origin and insertion

Three muscular origins

Sternal (xiphoid), costal (lower 6 ribs), lumbar (crura + arcuate ligaments from L1–L3)

Insertion

Central tendon

Crura (R vs L) — attach to

Right crus: L1-L3 vertebrae (longer, encircles esophagus). Left crus: L1-L2 only

Three openings — "I 8, 10 Eggs, At 12"

Level	Opening	Structures passing through
T8	Caval foramen (vena caval hiatus) — in central tendon	IVC + right phrenic nerve
T10	Esophageal hiatus — within right crus	Esophagus + vagus nerves (anterior & posterior trunks) + esophageal branches of left gastric a./v.
T12	Aortic hiatus — behind median arcuate ligament (posterior to diaphragm)	Aorta + thoracic duct + azygos vein ("Aortic Duct Azygos" at 12)

Innervation

Motor nerve

Phrenic nerve (entirely — for both hemidiaphragms)

Nerve roots

C3, C4, C5 ("C3-4-5 keeps the diaphragm alive")

Sensory to central diaphragm

Phrenic nerve (C3-C5)

Sensory to peripheral diaphragm

Lower intercostal nerves (T5-T11) and subcostal (T12)

Referred pain

Diaphragmatic irritation — pain referred to

Ipsilateral shoulder / supraclavicular region

Why? (dermatome)

C3-C5 phrenic overlaps with supraclavicular nerves (C3-C4) — same dermatome

Classic examples (2)

Kehr sign (splenic rupture → L shoulder); subphrenic abscess; ectopic pregnancy rupture

Clinical — hiatal hernia

Sliding hernia (Type I)

GE junction slides up into thorax — most common (~95%); axial displacement

Paraesophageal (Type II)

GE junction stays in place; gastric fundus herniates alongside esophagus — risk of strangulation, volvulus

Symptoms

GERD, heartburn, regurgitation, dysphagia; paraesophageal can → strangulation requiring surgery

Median arcuate ligament syndrome (MALS)

What gets compressed?

Celiac trunk — by median arcuate ligament of diaphragm

Classic symptoms

Postprandial epigastric pain, weight loss, abdominal bruit

Classic patient

Thin young woman (20–40 yo)

Phrenic nerve injury / traumatic rupture

CXR finding in phrenic injury

Elevated hemidiaphragm on affected side; paradoxical motion on sniff test/fluoroscopy

Right phrenic vs left — which more commonly injured in trauma?

Left side more commonly ruptured; right often iatrogenically injured in cardiac surgery (longer intrathoracic course)

Why left hemidiaphragm more vulnerable to rupture

Right side is protected by the liver; left side is unprotected → ~3× more common rupture with blunt trauma

⚠️ "C3, 4, 5 keeps the diaphragm alive" — phrenic nerve palsy from cervical spine injury above C4 → diaphragmatic paralysis. Shoulder pain after splenic rupture = Kehr sign (C3-5 referred).

LO 3/4

ON EXAM — psoas major (+ iliacus = iliopsoas, hip flexion, L1-L3), quadratus lumborum (lateral flexion), transversus abdominis (deep). Lumbar plexus nerves through psoas. Positive psoas sign in appendicitis/psoas abscess.

Four key posterior abdominal wall muscles

Muscle	Origin	Insertion	Action
Psoas major	T12-L5 vertebrae (transverse processes + bodies)	Lesser trochanter of femur (joins iliacus)	Primary hip flexor; trunk flexion
Iliacus	Iliac fossa	Lesser trochanter (as iliopsoas)	Hip flexion (with psoas)
Quadratus lumborum	Iliac crest + iliolumbar ligament	12th rib + L1-L4 transverse processes	Lateral trunk flexion; fixes 12th rib during respiration
Transversus abdominis	Lower 6 costal cartilages + thoracolumbar fascia + iliac crest + inguinal ligament	Linea alba via aponeurosis; pubic crest	Compresses abdominal contents; forced expiration

Psoas sign

Test maneuver

Extension of right hip (patient supine, raises straight leg against resistance; or lies on left side and extends right hip)

Positive test indicates

Irritation of psoas muscle by adjacent inflammation

Classic diagnosis

Retrocecal appendicitis or psoas abscess

Psoas abscess — classic triad

Symptom 1

Fever

Symptom 2

Flank/back pain

Symptom 3 (posture)

Limp / hip held flexed (psoas guarding posture)

Lumbar plexus nerves — within/through psoas

Nerve	Roots	Main function
Iliohypogastric	L1	Sensory to suprapubic/gluteal; motor to internal oblique + transversus abdominis
Ilioinguinal	L1	Sensory to upper medial thigh + scrotum/labia majora; motor (small) to abdominal wall
Genitofemoral	L1-L2	Genital branch: cremaster reflex; femoral branch: upper anterior thigh sensation
Lateral femoral cutaneous	L2-L3	Sensory only — lateral thigh (meralgia paresthetica)
Femoral	L2-L4	Motor: quadriceps (knee extension); sensory: anterior thigh + medial leg (saphenous)
Obturator	L2-L4	Motor: thigh adductors; sensory: medial thigh

Adrenal gland

Arterial supply (3 sources)

Superior suprarenal a. (from inferior phrenic), Middle suprarenal a. (directly from aorta at L1), Inferior suprarenal a. (from renal a.)

Venous drainage — right adrenal v.

Short — drains directly into IVC

Venous drainage — left adrenal v.

Drains into left renal vein → then IVC

Zones (outer → inner) + products

Capsule → Zona Glomerulosa (aldosterone) → Zona Fasciculata (cortisol) → Zona Reticularis (androgens) → Medulla (epi/NE — chromaffin cells)

Meralgia paresthetica

Nerve involved

Lateral femoral cutaneous nerve (L2-L3)

Location of entrapment

Under inguinal ligament, near the ASIS

Symptoms (area + quality)

Burning, tingling, numbness over lateral thigh; pure sensory — NO motor deficit

Risk factors

Obesity, tight belts, pregnancy, tool belts/heavy pants, diabetes

LOs 1–4

Q1: Retroperitoneal identification

During an emergency laparotomy for blunt trauma, a surgeon identifies blood behind the posterior peritoneum. Which of the following organs is retroperitoneal?

A) Stomach
B) Spleen
C) Pancreas (body and tail)
D) Transverse colon
E) Jejunum

Correct Answer: C

SAD PUCKER: Suprarenal, Aorta/IVC, Duodenum (2nd-4th), Pancreas (except tail), Ureters, Colon (ascending/descending), Kidneys, Esophagus (lower), Rectum (lower 2/3). Stomach, spleen, jejunum, and transverse colon are intraperitoneal.

Q2: Aortic branch level

A CT angiogram shows an atherosclerotic lesion at the origin of the superior mesenteric artery. At which vertebral level is this lesion located?

A) T8
B) T10
C) T12
D) L1
E) L3

Correct Answer: D

Celiac trunk = T12, SMA = L1 (just below celiac), IMA = L3. Aortic bifurcation = L4. "T12–L1–L3" is the 3-3-3-1 framework.

Q3: Nutcracker syndrome

A 28-year-old thin woman presents with left flank pain and hematuria. Imaging shows compression of the left renal vein between the aorta and superior mesenteric artery. What is the name of this syndrome?

A) SMA syndrome
B) Nutcracker syndrome
C) Median arcuate ligament syndrome
D) May-Thurner syndrome
E) Leriche syndrome

Correct Answer: B

Nutcracker syndrome — left renal vein compressed between aorta (posteriorly) and SMA (anteriorly). Causes L flank pain, hematuria, and varicocele in men (L gonadal v. drains into L renal v.). SMA syndrome = compression of 3rd part duodenum. MALS = celiac trunk compression.

Q4: Portosystemic anastomosis

A cirrhotic patient develops dilated tortuous veins radiating outward from the umbilicus. Which anastomosis is responsible?

A) Left gastric ↔ esophageal veins
B) Paraumbilical ↔ superficial epigastric veins
C) Superior rectal ↔ middle/inferior rectal
D) Splenic ↔ left renal
E) Retroperitoneal (of Retzius)

Correct Answer: B

Caput medusae = paraumbilical veins (portal) ↔ superficial epigastric veins (systemic). Esophageal varices = left gastric (portal) ↔ azygos. Anorectal varices = superior rectal (portal) ↔ middle/inferior rectal (systemic). These represent internal rectal varices — separate entity from hemorrhoids.

Q5: Diaphragm opening

The esophagus passes through the diaphragm alongside which other structure?

A) Thoracic duct
B) Azygos vein
C) IVC
D) Vagus nerves (anterior + posterior trunks)
E) Aorta

Correct Answer: D

T8 = IVC + right phrenic nerve. T10 = Esophagus + vagus nerves (anterior + posterior). T12 = Aorta + thoracic duct + azygos vein. "I 8 10 Eggs At 12."

Q6: Kehr sign

A 22-year-old man with blunt abdominal trauma complains of left shoulder tip pain. Vital signs are deteriorating. What is the most likely source of the shoulder pain?

A) Cardiac ischemia
B) Diaphragmatic irritation from splenic rupture
C) Rotator cuff tear
D) Clavicular fracture
E) Cervical nerve root impingement

Correct Answer: B

Kehr sign = referred shoulder pain from diaphragmatic irritation, classically from splenic rupture causing hemoperitoneum. Phrenic nerve (C3-5) shares dermatomal overlap with supraclavicular nerves → pain perceived at shoulder.

Q7: Psoas sign

A 19-year-old man with RLQ pain has worsened pain when his right hip is extended. What does this suggest?

A) Obturator hernia
B) Retrocecal appendicitis or psoas abscess
C) Ureteral stone
D) Crohn disease flare
E) Inguinal hernia

Correct Answer: B

Psoas sign = hip extension stretches the psoas, worsening pain if there is adjacent inflammation (classic retrocecal appendix, psoas abscess, or ileal pathology). Obturator sign (internal rotation of flexed hip) suggests pelvic/obturator pathology.

Q8: Left gonadal vein drainage

A 35-year-old man presents with a left-sided varicocele that does not reduce when supine. What diagnosis must be ruled out?

A) Bladder cancer
B) Renal cell carcinoma invading left renal vein
C) Testicular torsion
D) Lymphoma
E) Epididymitis

Correct Answer: B

Left gonadal (testicular) vein drains into the LEFT RENAL vein (at 90°) before reaching the IVC. A non-reducing left varicocele in an older man raises concern for RCC obstructing the left renal vein. Right gonadal v. drains directly into IVC. Nutcracker syndrome is another cause.

Q9: Diaphragmatic rupture

A patient involved in a motor vehicle collision has a chest X-ray showing bowel loops in the left chest cavity. Why is the left hemidiaphragm more commonly ruptured than the right?

A) The left diaphragm has thinner muscle fibers
B) The liver protects the right hemidiaphragm
C) The left diaphragm is congenitally weaker
D) The left phrenic nerve is shorter
E) The left crus is more mobile

Correct Answer: B

The liver cushions the right hemidiaphragm from trauma; the left is unprotected, making left-sided rupture ~3× more common. Stomach and bowel herniate into the left chest, mimicking a pneumothorax or pleural effusion on CXR.

Q10: Meralgia paresthetica

An obese patient who wears a tight belt reports burning numbness on the lateral aspect of the thigh. Which nerve is entrapped, and where?

A) Femoral nerve at the inguinal ligament
B) Lateral femoral cutaneous nerve at the inguinal ligament / ASIS
C) Obturator nerve in the obturator canal
D) Sciatic nerve at the piriformis
E) Genitofemoral nerve at the deep inguinal ring

Correct Answer: B

Meralgia paresthetica = lateral femoral cutaneous nerve (L2-L3) entrapment as it passes under the inguinal ligament near the ASIS. Causes pure sensory symptoms (pain, burning, numbness) on the lateral thigh. No motor deficits. Associated with obesity, tight belts, pregnancy, tool belts.

Retroperitoneum & Posterior Abdominal Wall — Answer Key