Built from GI Lecture 29 (LOs 1–4). Close notes. Fill from memory. Reveal only after a genuine attempt.

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

Primary vs secondary retroperitoneal

Category	Definition	Organs
Primary retroperitoneal
Secondary retroperitoneal

Intraperitoneal GI organs (for contrast)

Kidney anatomy — layers outer → inner

Layer 1 (outer)

Layer 2

Layer 3

Layer 4

Layer 5 (innermost)

Renal hilum — anterior to posterior (VAP)

Most anterior

Middle

Most posterior

Vertebral levels

Right kidney — vertebral level

Left kidney — vertebral level

Why is R kidney lower?

Adrenal glands — vertebral level

Right vs left kidney anterior relations

Side	Anterior relations
Right kidney
Left kidney

Urolithiasis — 3 constriction sites

🪤 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)

Bifurcates at _____ into _____

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

Branch	Vertebral level	GI region supplied
Celiac trunk
SMA
IMA

Celiac trunk — 3 branches

Branch 1

Branch 2

Branch 3

SMA branches

Left side branches (jejunoileal)

Right side branches (colic)

Inf. pancreaticoduodenal a. supplies

IMA branches

Branch 1

Branch 2

Branch 3 (terminal)

Arterial anastomoses along colon

Marginal artery of Drummond

Arc of Riolan

Watershed areas (2) — ischemia prone

Paired lateral branches

Middle suprarenal (adrenal)

Renal arteries — level

Gonadal arteries

Nutcracker syndrome

What gets compressed?

Between what 2 structures?

Classic symptoms (3)

SMA syndrome

What gets compressed?

Classic patient (body habitus)

Classic symptoms

🪤 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)

Pierces diaphragm at

Structures traversing w/ IVC through T8

Asymmetric tributaries — R vs L

Tributary	Right side drains into	Left side drains into
Gonadal vein
Suprarenal (adrenal) vein
Renal vein

Portal vein formation

Portal vein = ______ + ______

IMV drains into

Portal vein enters liver at

Portosystemic anastomoses — 3 classic sites

Site	Portal vein	Systemic vein	Clinical finding
Esophageal
Umbilical (caput medusae)
Anorectal

Azygos system

Azygos drains into

Hemiazygos drains into

Function when IVC obstructed

Lymphatic drainage

Cisterna chyli — location

Thoracic duct — drains into

Pre-aortic vs para-aortic nodes

🪤 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

Insertion

Crura (R vs L) — attach to

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

Level	Opening	Structures passing through
T8
T10
T12

Innervation

Motor nerve

Nerve roots

Sensory to central diaphragm

Sensory to peripheral diaphragm

Referred pain

Diaphragmatic irritation — pain referred to

Why? (dermatome)

Classic examples (2)

Clinical — hiatal hernia

Sliding hernia (Type I)

Paraesophageal (Type II)

Symptoms

Median arcuate ligament syndrome (MALS)

What gets compressed?

Classic symptoms

Classic patient

Phrenic nerve injury / traumatic rupture

CXR finding in phrenic injury

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

Why left hemidiaphragm more vulnerable to rupture

⚠️ "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
Iliacus
Quadratus lumborum
Transversus abdominis

Psoas sign

Test maneuver

Positive test indicates

Classic diagnosis

Psoas abscess — classic triad

Symptom 1

Symptom 2

Symptom 3 (posture)

Lumbar plexus nerves — within/through psoas

Nerve	Roots	Main function
Iliohypogastric
Ilioinguinal
Genitofemoral
Lateral femoral cutaneous
Femoral
Obturator

Adrenal gland

Arterial supply (3 sources)

Venous drainage — right adrenal v.

Venous drainage — left adrenal v.

Zones (outer → inner) + products

Meralgia paresthetica

Nerve involved

Location of entrapment

Symptoms (area + quality)

Risk factors

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 — Active Recall