Abdomen Anatomy😊

Peritoneum

Lesser sac

• Enclosed space behind the stomach

• Communicates with greater sac via epiploic foramen/foramen of Winslow

• Approach: incise transmesocolon towards left (not right) to spare middle colic artery

Ligaments

• Answer: The splenic artery and vein are housed in the splenorenal ligament
• (the ligament that must be cut).

Dependent Parts

• Right Subhepatic space → Hepatorenal Pouch of Morrison
• Most dependent site in supine position
• most frequently occurring location for intraperitoneal abscess

• Rectouterine Pouch (♀)
• Most dependent part in erect posture

• Rectovesicular Pouch (♂)
• Most dependent part in erect posture

Lesser Sac Relations

Anterior Relations

• Caudate lobe

• Lesser omentum

• Stomach

• Anterior layers of greater omentum

Posterior Relations

• Stomach bed structures

• Spleen is NOT in relation of lesser sac (highlighted in red)

Peritoneal Folds & Contents (Internal Aspect of Anterior Abdominal Wall)

• Median umbilical fold:
• Contains Urachus and its remnants.

• Medial umbilical fold:
• Overlies obliterated umbilical artery.

• Lateral umbilical fold:
• Overlies inferior epigastric vessels.

Rectus Abdominis

Rectus Abdominis

• Origin: Pubic tubercle & crest

• Insertion: 5th, 6th & 7th costal cartilage

• Tendinous Intersection:
• Prevents bowstringing of RA

• Action
• Flexion → Rectus abdominis > External oblique, Internal oblique.

Stomach Bed Structures

• Separates stomach from retroperitoneal structures.

• Key Structures
• Diaphragm (left dome)
• Spleen
• Left suprarenal gland
• Left kidney (upper part)
• Pancreas (body and tail)
• Transverse colon
• Transverse mesocolon
• Splenic artery
• Gastric artery (left)
• Peritoneum (posterior wall of lesser sac)

Retroperitoneal Structure

Primary Retroperitoneal Structures

• (Develop and remain retroperitoneal)
• Kidneys
• Adrenal glands
• Ureters
• Aorta and its branches
• Inferior vena cava (IVC) and its branches

Secondary Retroperitoneal Structures

• (Initially intraperitoneal, become retroperitoneal)
• Pancreas (except tail)
• Duodenum (2nd, 3rd, and 4th parts)
• Ascending colon
• Descending colon
• Rectum (upper 2/3)

Clinical Relevance

• Retroperitoneal hemorrhage:
• No abdominal distension early

• Trauma/infection
• spread without early peritoneal signs.

Retroperitoneal fibrosis (Ormond's disease)

• Can compress ureters → hydronephrosis

• "Maiden Waist" deformity, medial indrawing of ureters.

• Causes:
• Idiopathic
• post-radiotherapy
• drug-induced (Methysergide).

• Management: DJ Stenting.

• Mnemonic: Purakil ninn (retroperioneal) DJ () kalikkunna Maid () ne Ormayundo (Ormond)

Epiploic Foramen/Foramen of Winslow

Epiploic Foramen/ Foramen of Winslow Boundaries	ㅤ
Anteriorly	Lesser omentum contains • Hepatic artery • Portal vein • bile duct
Posteriorly	• IVC • Right suprarenal gland • Body of T12 vertebrae
Superiorly	Liver (Caudate lobe)
Inferiorly	1st part of duodenum

Portal Vein Formation

• Behind the neck of pancreas

• At the level of L2
• Same level of thoracic duct origin from cisterna chyli

• By union of:
• Splenic vein
• Superior mesenteric vein

Portosystemic Anastomosis Sites

ㅤ	Portal circulation	Systemic circulation
Oesophageal varices (Lower 1/3)	Oesophageal branch of Left Gastric Vein	Oesophageal branch of Accessory Hemiazygous Vein
Rectal varices	Superior Rectal Vein	Middle and Inferior Rectal Veins
Caput medusae	Paraumbilical vein	Superficial veins of anterior abdominal wall

Gallbladder Triangles and Anatomical Relations

---

ㅤ	Calot Triangle (Cystohepatic Triangle)	Hepatobiliary Triangle
Right	Cystic duct	Cystic duct
Left	Common hepatic duct	Common hepatic duct
Superiorly	Cystic artery	Inferior surface of liver
Content	Cystic node of Lund ↳ Sentinel node of gallbladder	• Cystic artery (From R Hepatic A) • Cystic nodes

Moynihan’s Hump (Caterpillar Hump)

• Tortuous right hepatic artery.

• Lies in front/within Calot’s triangle.

• mimic cystic artery

• Injury leads to torrential bleeding.

Transpyloric Plane (Addison's Plane)

Transpyloric Plane (Addison's Plane)

ㅤ	ㅤ
Celiac Trunk	Lower border of T12
Superior Mesenteric Artery	Lower border of L1
Inferior Mesenteric Artery	Body of L3

Mnemonic: Common (CIA) Inferior People (Inf phre) are Ready (rena) to Go (gona) Middle (middle supra) east

Definition

• Horizontal plane

• Midway between the suprasternal notch and the pubic symphysis.

• Lies at the level of lower border of L1 vertebra.

Important Anatomical Structures at Transpyloric Plane (L1)

• Tip of 9th costal cartilage
• NOT 9th costal cartilage

• Pylorus of the stomach

• Fundus of gall bladder
• Midclavicular line, not in the midline

• Hilum of kidneys

• Origin of Superior Mesenteric Artery (SMA)

• Celiac trunk (T12 - L1)

• Lower end of adult spinal cord

Spleen

Relations

• Convex surface: Diaphragm

• Visceral surface:
• Stomach
• Left kidney
• Left colic flexure
• Tail of pancreas

Important Information

Phrenicocolic ligament/Sustentaculum lienis

• ⛔downward displacement of spleen

• Enlargement of the spleen → directed downward and medially
• due to the phrenicocolic ligament.

Applied Aspects

Horseshoe Kidney

 

 

 

Nutcracker Syndrome

• Compression of left renal vein between aorta and SMA.

• Present with hematuria

• Leads to:
• Dilatation of left testicular vein.
• Dilatation of left pampiniform plexus.
• Varicocele (bag of worms appearance).

Superior Mesenteric Artery Syndrome (SMAS)

• Also known as Wilkie's Syndrome

• Normal angle b/w aorta & SMA: 
• 25-45°

• Angle <22° compresses D3
• 3rd part of duodenum

• Causes:
• Rapid weight loss
• spinal cast.

• C/F:
• Bilious vomiting after meals.

• IOC:
• CT Angiography.

• Rx:
• Encourage weight gain.
• Strong's procedure.
• Duodenal derotation (Cut ligament of Trietz).
• Duodeno-jejunostomy.

• Wilkie (Wilkie) tried to reduce weight in 3 days (D3) → to get strong (strong procedure) → got duodenal obstruction

Pancreas

• Horizontally placed retroperitoneal organ (except tail)

• Extent : Concavity of duodenum → hilum of spleen.

Tail of Pancreas

• Present in lienorenal ligament.

• Contains maximum islets of Langerhans

• Preserved in Spleen Surgery

Sphincters of the Oddi Complex

• Total 4 sphincters

• Arrangement: 4 > 3

Pancreatic Ducts and Applied Aspect

• Main Pancreatic Duct + Common bile duct (CBD)
• Opens into ampulla of Vater
• Opens into major duodenal papilla.
• Located in posteromedial part of 2nd part of duodenum.
• 8-10 cm distal to pylorus.

• Accessory Pancreatic Duct
• Opens into minor duodenal papilla.
• Located 2 cm above major duodenal papilla.

Applied Aspect:

• MRCP: Double duct sign

• First image
• Dilated CBD + Pancreatic duct
• Open at ampulla of Vater
• Seen in Periampullary carcinoma / Pancreatic head carcinoma

• Second image
• Pancreatic head mass
• pulls duodenal wall
• loss of C curve
• C loop widening
• reverse 3 sign

Important

• Stone in Retropancreatic CBD
• Irritates head of pancreas →
• Leads to acute pancreatitis

• SMA is in close proximity to Uncinate process
• Easily affected by tumor in uncinate process

• Left renal vein
• crosses aorta anteriorly below superior mesenteric artery.

• R Suprarenal vein
• drains directly to IVC.

Surgical Anatomy of Liver

Condition	Segments Seen	Image Reference
Kidney seen	3, 4b, 5, 6	Image 1
Kidney not seen	2, 4a, 8, 7	Image 2

 

• Three hepatic veins present
• Drain into IVC

• Portal vein division
• Upper half: Segments 2, 4a, 8, 7
• Lower half: Segments 3, 4b, 5, 6

 

Fissures:

• Major (3):
• LHV, MHV, RHV

• Minor (3):
• LPV, RPV, Fissure of Ganz.

• 4 Sectors: (Sections)
• 6 and 7
• 5 and 8
• 4a and 4b
• 2 and 3

• Recent Update:
• Division based on:
• Portal vein > Hepatic vein > Bile duct > Hepatic artery

Cantlie's Line:

• middle line by Middle hepatic vein

• Joins IVC to Gallbladder (MHV location).

• Divides the liver into R and L functional lobes.

Segment Significance:

ㅤ	Right Functional Lobe	Left Functional Lobe	Caudate Lobe
Blood Supply	ㅤ	ㅤ	ㅤ
ㅤ	(R) hepatic artery	(L) hepatic artery	(R) & (L) hepatic artery
ㅤ	(R) portal vein	(L) portal vein	(R) & (L) portal vein
Venous Drainage	ㅤ	ㅤ	ㅤ
ㅤ	(R) hepatic vein	(L) hepatic vein	Directly to IVC
Bile Drainage	ㅤ	ㅤ	ㅤ
ㅤ	(R) hepatic duct	(L) hepatic duct	(R) & (L) hepatic duct
Segments	ㅤ	ㅤ	ㅤ
ㅤ	5: (R) antero inferior	2: (L) lateral superior	1: (Independent lobe)
ㅤ	6: (R) postero inferior	3: (L) lateral inferior	ㅤ
ㅤ	7: (R) postero superior	4a: (L) medial superior	ㅤ
ㅤ	8: (R) antero superior	4b: (L) medial inferior	ㅤ

Space of Disse

• Space between hepatocytes & sinusoids.

• Site of amyloid deposition in liver.

• Contains Ito cells or stellate cells.

Key Points regarding Ito cells

• Ito cells = hepatic stellate cells, located in space of Disse.

• Store vitamin A in lipid droplets (80% of liver’s retinoids).

• Transform into myofibroblasts in liver injury, causing bridging fibrosis.
• Key role in liver regeneration, fibrosis, and cirrhosis.

• Produce collagen (types I, III) and other matrix proteins.

• Act as antigen-presenting cells and regulate sinusoidal blood flow.

• Identified by gold chloride, cytoglobin, or ASMA staining

Ito Cells vs. Stellate Cells

• Anatomically same, functionally different states.
• Stellate cells: "hyperactive" version
• active in collagen formation
• relevant in cirrhosis.
• Ito cells: "eat, sleep, chill" version
• primarily Vitamin A storage.

Stem Cells

• Liver stem cells for regeneration are oval cells.

• Found in canals of Hering.

Large Intestine

Note

• Taenia coli are absent in:
• Appendix
• Caecum
• Rectum

• Appendices epiploicae are absent in:
• Appendix
• Rectum

• Appendix lacks:
• Taenia coli (Sacculations)
• Appendix epiploicae

Surgical Anatomy

• Appendicular artery:
• Branch of lower division of ileocolic artery.

• Appendicular base:
• Junction of 3 taenia coli.

Positions

Blood Supply

• Appendicular artery (end artery).

Nerve Supply

• Parasympathetic fibres: Vagus nerve.

• Sympathetic fibres: T₁₀ - T₁₁ fibres.
• T₁₀ fibres also innervate umbilicus (present at L₃-L₄ level).
• Therefore in any Midgut Pathology
• Pain referred to umbilicus.

Infection in Paracolic Gutters

• Right Paracolic Gutter
• Infection reaches up to Morison’s pouch

• Left Paracolic Gutter
• Infection is limited by the Phrenicocolic ligament

Anterior Abdominal Wall

Layers

Note:

• Deep fascia is absent in the anterior abdominal wall.

Neurovascular Plane

• Lies between internal oblique and transverse abdominis muscles.

Muscles

Rectus Sheath

• Formed by aponeuroses of 6 lamellae
• External oblique (EO)
• Internal oblique (IO)
• Transversus abdominis (TA)

• Each muscle contributes 2 lamellae

Vascular Contents within Rectus Sheath

• Superior epigastric artery

• Inferior epigastric artery

• Both anastomose within the rectus sheath.

Arcuate Line

• Also called Semicircular Line of Douglas

• Not always present

• Bilateral Curved Line → Found Posterior to Rectus Abdominis

• Location may vary

Above Arcuate Line:

Below Arcuate Line:

Clinical Significance

• Site of Weakness in the Abdominal Wall
• Spigelian Hernias close to the arcuate line.
• Less likely to develop a ventral hernia without arcuate line.

• Inferior Epigastric Vessels
• Perforate the rectus sheath.
• Supply blood to the anterior abdominal wall.

Contents: Muscles

Functions of Anterior Abdominal Wall Muscles

• Maintains tone of anterior abdominal wall.

• Protects viscera.

• Increases intra-abdominal pressure.

• Action on Vertebral Column:
• Flexion: 
• By Rectus abdominis > External oblique, Internal oblique.
• Lateral Flexion: 
• Ipsilateral (I/L) External oblique & Internal oblique.
• Rotation:
• Ipsilateral (I/L) External oblique.
• Contralateral (C/L) Internal oblique.

Layers of Abdomen Pierced

Midline Approach

• Skin

• Superficial fascia
• Camper’s
• Scarpa’s

• Linea alba

• Transversalis fascia

• Extraperitoneal fat

• Parietal peritoneum

• No muscles are pierced in midline approach.

Flank Approach

• Skin

• Superficial fascia
• Camper’s
• Scarpa’s

• External oblique

• Internal oblique

• Transversus abdominis

• Transversalis fascia

• Extraperitoneal fat

• Parietal peritoneum