Abdomen Study Guide

4.1 Topographic Anatomy

Study Aims

At the end of your study, you should be able to:

• Understand the boundaries of the abdominal cavity

• Identify surface landmarks of the abdomen

• Know the four quadrants of the abdomen and their contents

• Know the nine regions of the abdomen

• Know the lines and planes that create the four quadrants and nine regions

Guide

Right Upper Quadrant (RUQ)	Left Upper Quadrant (LUQ)
Liver (right lobe) Gallbladder Pylorus (of stomach) Duodenum (parts 1 through 3) Pancreas (head) Right kidney and suprarenal gland Colon: distal ascending colon, hepatic flexure and right half of transverse colon	Liver (left lobe) Spleen Stomach Jejunum and proximal ileum Pancreas (body and tail) Left kidney and suprarenal gland Colon: left half of transverse colon, splenic flexure and superior part of descending colon
Right Lower Quadrant (RLQ)	Left Lower Quadrant (LLQ)
Majority of ileum Cecum with vermiform appendix Proximal ascending colon Proximal right ureter	Distal descending colon Sigmoid colon Left ureter
Ovaries Uterine tubes Right and left ductus deferens Uterus (if enlarged) Urinary bladder (if full, especially in women)

Clinical Points

Mcburney’s Point and Appendicitis

• McBurney’s point is a surface landmark that roughly indicates the location of the appendix, located approximately one third of the way along a line from the anterior superior iliac spine to the umbilicus.

• Appendicitis is inflammation of the appendix. Pain first presents in the epigastric region, moves to the umbilical region, and then localizes in the right lower quadrant. Rupture of the appendix leads to peritonitis (inflammation of the peritoneum). This presents with severe pain, fever, and abdominal rigidity.

• Muscle-splitting incision (of McBurney) is used to access the appendix. Each muscle layer is split in the direction of the fiber orientation. If the incision extends too far laterally the ascending branch of the deep circumflex iliac artery may be severed.

Grey-Turner’s Sign

• Local right flank redness or bruising (ecchymosis)

• Indicates retroperitoneal hemorrhage

• Usually takes 24 to 48 hours to appear

• Can be predictive of severe hemorrhagic pancreatitis, abdominal injury, or metastatic cancer

Cullen’s Sign

• Discoloration (ecchymosis) around umbilicus

• Result of peritoneal hemorrhage

Memory Aids

Causes for abdominal expansion (protuberance)

Remember the five F’s:

4.2 Body Wall

Study Aims

At the end of your study, you should be able to:

• Know the layers of the anterior abdominal wall from superficial to deep

• Understand the orientation and functions of the muscles of the anterolateral abdominal wall

• Describe the structure of the rectus sheath and its contents

• Describe the neurovascular supply of the abdominal wall

• Understand the boundaries of the inguinal canal and layers of the spermatic cord

• Describe the boundaries of Hesselbach’s triangle

• Know the etiology and location of the umbilical peritoneal folds

• Understand the structure and organization of the posterior abdominal wall and its neurovascular relations

Guide

Anterolateral Abdominal Wall

Fascial Layers

• Superficial fascia: two layers in abdomen

• Fatty superficial layer (Camper’s fascia)

• Deeper membranous layer (Scarpa’s fascia)

• Deep fascia—very thin layer investing most superficial muscles

• Transversalis fascia (endoabdominal fascia)

• Thin membranous sheet lining most of abdominal wall

• Lies deep to transversus muscles and linea alba

• Endoabdominal fat separates the transversalis fascia from the parietal peritoneum.

Muscles

• Functions

• Protect viscera

• Help maintain posture

• Can compress abdominal contents, thus raising intra-abdominal pressure, such as in sneezing, coughing, defecating, micturating, lifting, and childbirth

• Four paired muscles make up anterolateral abdominal wall: three flat muscles and single vertical muscle.

• Three flat muscles

• External abdominal oblique

• Largest and most superficial

• Fibers run inferiorly and medially and end in aponeurosis that contributes to rectus sheath.

• Inferior border of its aponeurosis forms inguinal ligament, where it thickens and folds back on itself.

• Innervated segmentally by T6–T12 spinal nerves and subcostal nerve

• Internal abdominal oblique

• Thin muscular layer

• Fibers run inferiorly and laterally and end in an aponeurosis that contributes to rectus sheath.

• Inferior aponeurotic fibers join with those of rectus abdominis to form conjoint tendon, inserting onto pubic crest.

• Innervated segmentally by ventral rami of T6–T12 spinal nerves

• Transversus abdominis

• Innermost of three flat muscles

• Fibers run transversely and medially and end in an aponeurosis that contributes to rectus sheath.

• Innervated segmentally by ventral rami of T6–T12 spinal nerves

• Linea alba

• Tendinous raphe running vertically in midline

• Formed by union of aponeuroses of flat muscles on either side

• Largely avascular

• Umbilicus found in midline

• Vertical muscle = rectus abdominis

• Paired

• Separated by linea alba in midline

• Wider superiorly than inferiorly

• Typically composed of four segments connected by tendinous intersections that attach anteriorly to sheath of this muscle

• Innervated segmentally by ventral rami of T6–T12 spinal nerves

• Have the superior epigastric and inferior epigastric arteries running inferiorly and superiorly, respectively, on their deep surfaces.

• Pyramidalis muscle

• Small, insignificant, triangular muscles arising from body of pubis inferiorly

• Inserts into linea alba medially

• Absent in 20% of people

Rectus Sheath

• Tough, fibrous sheath composed of aponeuroses of three flat muscles

• Extends from xiphoid process and 5th through 7th costal cartilages to pubic symphysis and crests

• Contains superior and inferior epigastric vessels, lymphatics, and branches of ventral primary rami of T7–T12

• Encloses rectus abdominis and pyramidalis muscles

• Semilunar line marks lateral border.

• Has crescent-shaped line—the arcuate line—on its posterior wall approximately three fourths of way down wall.

• Above arcuate line

• Anterior wall composed of aponeurosis of external abdominal oblique and anterior layer of aponeurosis of internal abdominal oblique.

• Posterior wall composed of posterior layer of aponeurosis of internal abdominal oblique, aponeurosis of transversus abdominis, transversalis fascia of abdomen, and parietal peritoneum.

• Below arcuate line

• Aponeuroses of all three flat muscles pass anterior to rectus muscle, reinforcing anterior wall.

• Posterior wall composed of just transversalis fascia and parietal peritoneum.

• Vessels and nerves enter sheath at its lateral edge—the semilunar line—to supply rectus muscle.

Muscle	Proximal Attachment (Origin)	Distal Attachment (Insertion)	Innervation	Main Actions	Blood Supply
External oblique	External surfaces of ribs 5–12	Linea alba, pubic tubercle, and anterior half of iliac crest	Ventral rami of six inferior thoracic nerves	Compresses and supports abdominal viscera; flexes and rotates trunk	Superior and inferior epigastric arteries
Internal oblique	Thoracolumbar fascia, anterior 2/3 of iliac crest, lateral half of inguinal ligament	Inferior borders of ribs 10–12, linea alba, pubis via conjoint tendon	Ventral rami of inferior six thoracic and 1st lumbar nerves	Compresses and supports abdominal viscera; flexes and rotates trunk	Superior and inferior epigastric and deep circumflex iliac arteries
Transversus abdominis	Internal surfaces of costal cartilages 7–12, thoracolumbar fascia, iliac crest, and lateral third of inguinal ligament	Linea alba with aponeurosis of internal oblique, pubic crest, and pecten pubis via conjoint tendon	Ventral rami of inferior six thoracic and first lumbar nerves	Compresses and supports abdominal viscera	Deep circumflex iliac and inferior epigastric arteries
Rectus abdominis	Pubic symphysis and pubic crest	Xiphoid process and costal cartilages 5–7	Ventral rami of inferior six thoracic nerves	Flexes trunk and compresses abdominal viscera	Superior and interior epigastric arteries
Pyramidalis	Body of pubis, anterior to rectus abdominis	Linea alba	Iliohypogastric nerve	Tenses linea alba	Inferior epigastric artery

Innervation

• Neurovascular plane

• Found between internal abdominal oblique and transversus abdominis

• Contains vessels and nerves supplying skin and muscles of anterior and lateral abdominal wall.

• Nerves and vessels are transversely oriented and segmental

• Nerves

• Thoracoabdominal nerves

• Anterior cutaneous branches of ventral primary rami of T7–T11

• T7–T9 supply skin above umbilicus

• T10 supplies skin around umbilicus

• T11 (plus subcostal and ilio-inguinal and iliohypogastric nerves) supplies skin below umbilicus

• Subcostal nerves (T12) supply skin below umbilicus

• Iliohypogastric and ilio-inguinal nerves (terminal branches of L1) supplies skin below umbilicus

Vascular Supply

• Arteries

• Anterior and collateral branches of posterior intercostal arteries

• Branches of internal thoracic arteries

• Superior epigastric

• Musculophrenic

• Inferior epigastric (from external iliac)

• Branches of femoral artery

• Superficial epigastric

• Superficial circumflex iliac

• Veins

• Venous drainage is via venae comitantes (veins corresponding to the arteries listed).

• Blood drains away from umbilicus

• Venous drainage to caval system

• Lymphatics

• Superficial lymphatics above umbilicus lymph drain to axillary nodes.

• Superficial lymphatics below umbilicus drain to superficial inguinal nodes.

• Deep lymphatics

• Accompany deep veins

• Drain to external iliac, common iliac, and lumbar nodes

Posterior Abdominal Wall

Fascial Layers

• Superficial fascia: single layer

• Deep fascia— very thin layer investing the most superficial muscles

• Transversalis fascia (endoabdominal fascia)

• Endoabdominal fat separates transversalis fascia from parietal peritoneum

• Psoas sheath

• Fascia covering psoas muscle

• Attaches to lumbar vertebrae and pelvic brim

• Thickened superiorly to form medial arcuate ligament— site of origin of muscle of diaphragm

• Fascia of quadratus lumborum

• Fuses medially with psoas fascia

• Thickened superiorly to form lateral arcuate ligament—site of origin of muscle of diaphragm

• Thoracolumbar fascia (see Section 2, Back and Spinal Cord)

• Composed of anterior and posterior layers

• Encloses deep muscles of the back

• Thick and strong in lumbar region

• Extends from 12th rib to iliac crest and continuous laterally with deep fascia of internal oblique and transversus abdominis muscles

Muscles

• Psoas major

• Long and thick

• Lies lateral and is attached to lumbar vertebrae

• Tendon passes deep to inguinal ligament to lesser trochanter of femur

• Together with iliacus forms iliopsoas muscle, which flexes the hip, helps maintain erect posture

• Lumbar plexus of nerves embedded within it

• Iliacus

• Attaches to superior two thirds of iliac fossa

• Joins psoas to form iliopsoas

• Quadratus lumborum

• Thick quadrangular muscle of posterior wall

• Extends from 12th rib and tips of lumbar transverse processes to iliac crest

• Flexes and laterally extends vertebral column

Muscle	Proximal Attachment (Origin)	Distal Attachment (Insertion)	Innervation	Main Actions	Blood Supply
Psoas major	Transverse processes of lumbar vertebrae, sides of bodies of T12–L5 vertebrae, intervening intervertebral discs	Lesser trochanter of femur	Ventral rami of first four lumbar nerves	Acting superiorly with iliacus, flexes hip; acting inferiorly, flexes vertebral column laterally; used to balance trunk in sitting position; acting inferiorly with iliacus, flexes trunk	Lumbar branch of iliolumbar artery
Iliacus	Superior 2/3 iliac fossa, ala of sacrum, and anterior sacro-iliac ligaments	Lesser trochanter of femur and shaft inferior to it, to psoas major tendon	Femoral nerve (L2–L4)	lexes thigh at hips and stabilizes hip joint, acts with psoas major	Iliac branches of iliolumbar artery
Quadratus lumborum	Medial half of inferior border of 12th rib, tips of lumbar transverse processes	Iliolumbar ligament, internal lip of iliac crest	Ventral rami of T12 and first four lumbar nerves	Extends and laterally flexes vertebral column, fixes 12th rib during inspiration	Iliolumbar artery
Diaphragm	Xiphoid process, lower six costal cartilages, L1–L3 vertebrae	Converge into central tendon	Phrenic nerve (C3–C5)	Draws central tendon down and forward during inspiration	Pericardiacophrenic musculophrenic, superior and inferior phrenic arteries