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• The abdomen sits between the diaphragm and pelvis.

Abdomen Boundaries

• Roof: diaphragm
• Posterior: 5 lumbar vertebrae with their associated muscles
• Inferior: continuous with the pelvic cavity, with no defined boundary, but including the Superior Pelvic Aperture
• Anterior and Lateral: The abdominal wall muscles

Topography of Abdomen

• Imaginary lines divide the abdomen into 9 regions for descriptive purposes.
• Transverse and vertical planes pass through specific anatomical structures
• Transpyloric Plane: at the tip of the 9th costal cartilage, which correlates to the pylorus of the stomach, and the L1 vertebral level
• Subcostal Plane: at the tip of the 10th costal cartilages at the L3 vertebra
• Transtubercular Plane: passes through the tubercles of the iliac crests and the L5 vertebra level
• Interspinous Plane: passes through the anterior superior iliac spines; and promontory of the sacrum
• Mid-clavicular Plane: represents the midpoint of the clavicle to the midpoint of the inguinal ligament
• Semilunar Line: represents the lateral border of the rectus abdominis muscle

Nine Abdominal Regions

• Umbilical (around the umbilicus)
• Epigastric
• Hypogastric
• Left hypochondriac
• Right hypochondriac
• Left Inguinal
• Right Inguinal
• Left Lumbar
• Right Lumbar

Cutaneous Innervation

• Lower 5 intercostal nerves plus the subcostal nerve
• L1 spinal nerve (ilioinguinal and iliohypogastric nerves)
• All these nerves constitute anterior rami of spinal nerves
• Umbilical region innervation: T10 dermatome

Layers of the Anterior Abdominal Wall

• Skin
• Superficial fascia (2 layers):
  • Superficial fatty layer (Camper's fascia)
  • Deep membranous layer (Scarpa's fascia)
• No deep fascia
• External oblique muscle
• Internal oblique muscle
• Transversus abdominis muscle (lateral to the rectus abdominis muscle on midline)
• Transversalis fascia
• Extraperitoneal tissue layer (extraperitoneal fascia)
• Peritoneum

Superficial Fascia

• Contains two layers
• First layer is the superficial fatty layer, or Camper's fascia
• Second layer is the deep membranous layer known as Scarpa's fascia

External Abdominal Oblique

• Most superficially located muscle of the abdominal wall
• Origin: ribs 5-12
• Insertion: linea alba and inguinal ligament
• The Inguinal ligament has a reflected part, the lacunar ligament, and the pectineal ligament
• Innervation: lower 5 intercostal nerves, plus the subcostal nerve, and L1
• External Oblique Muscle has an opening in its aponeurosis: Superficial Inguinal Ring Lateral Crus-Medial Crus-intercrural fibers

Inguinal Ligament

• Extends from the anterior superior iliac spine (ASIS) to the pubic symphysis
• Extends medially as the lacunar ligament
• Pectineal ligament extends towards pectineal line

Internal Abdominal Oblique

• Located in the middle layer of the abdominal muscles
• Fibers are oriented at a 90-degree angle relative to the external oblique fibers
• Origin: thoracolumbar fascia, iliac crest, and inguinal ligament.
• Insertion: linea alba, conjoint tendon, pubic crest, and pecten pubis

Transversus Abdominis

• Innermost muscle of the abdominal wall
• Origin: inferior 6 costal cartilages, thoracolumbar fascia, and inguinal ligament
• Insertion: conjoint tendon and linea alba
• Lower 5 intercostal nerves, along with subcostal nerve and L1

Conjoint Tendon

• (Falx Inguinalis): A common tendon formed from the fusion of internal oblique and transversus abdominis muscles

Transversalis Fascia

• Located posterior (deep) to the transversus abdominis muscle
• Has the deep inguinal ring

Functions of Anterior Abdominal Muscles

• Support and protection of abdominal viscera, trunk movements
• External oblique facilitates trunk turning to the opposite side
• The internal oblique facilitates trunk turning to the same side
• Coughing, sneezing, vomiting, and parturition (childbirth): contract to raise intra-abdominal pressure

Rectus Abdominis Muscle

• Located on both sides of the midline (linea alba)
• Origin: xiphoid process (sternum)
• Insertion: symphysis pubis
• Innervation: Lower 5 intercostal nerves plus the subcostal nerve (different innervation pattern compared to the previous 3 muscles)
• Function: flexion of the trunk
• Features tendinous intersections of 3-4 in number and is enveloped by the rectus sheath

Rectus Sheath

• 4-5cm below the umbilicus forms the arcuate line, and thus the semicircular line Above the arcuate line:
  • The anterior layer contains the external oblique aponeurosis plus the anterior lamina of the internal oblique aponeurosis
  • The posterior layer contains the posterior lamina of the internal oblique aponeurosis plus the transversus abdominis aponeurosis Below this line:
  • The anterior layer consists of the aponeuroses of external oblique, internal oblique, and transversus abdominis
  • The posterior layer of contains only the transversalis fascia
• Rectus sheath contains the rectus abdominis muscle, superior and inferior epigastric arteries, and lower 5 intercostal and subcostal nerves.

Arteries of Abdominal Wall

• Musculophrenic artery
• Superior epigastric artery
• Inferior epigastric artery
• Deep circumflex iliac artery
• Superficial circumflex iliac artery

Veins of Abdominal Wall

• Same names as corresponding arteries
• The superficial epigastric vein and lateral thoracic vein form an important anastomosis; uniting the veins draining the superior and inferior body halves
• Lymphatic vessels, above the umbilical region, drain into axillary nodes, while those below the umbilical region, drain into inguinal nodes.

Inguinal Canal

• Surgically significant area due to its association with inguinal hernias
• Obliquely placed between internal abdominal ring and external abdominal ring averaging 3-4 cm in length.
• Superficial inguinal ring (external oblique aponeurosis). Located medially.
• Deep inguinal ring (transversalis fascia). Located laterally.

Walls of Inguinal Canal

• Anterior wall comprises skin, superficial fascia, and the external oblique aponeurosis (medially), as well as the internal oblique muscle (laterally)
• Posterior wall is formed by reflected inguinal ligament, conjoint tendon and transversalis fascia
• Inferior wall is formed by the inguinal ligament and lacunar ligament
• Superior wall is formed by internal oblique and transversus abdominis muscles
• Structures passing through the inguinal canal:
• Spermatic cord in males
• Round ligament of the uterus in females
• Ilioinguinal nerve
• Genital branch of the genitofemoral nerve

Inguinal Hernias

• Indirect: a piece of organ leaves the abdominal cavity through the deep inguinal ring, travels through the inguinal canal, and exits through the superficial inguinal ring, protruding outward.
• Direct: A piece of abdominal organ pushes directly forward through the abdominal wall, exiting via the superficial inguinal ring - protruding outward
• Epigastric artery is the reference for differentiating direct and indirect inguinal hernia
• • If it is lateral to this artery: indirect inguinal hernia.
• • If it is medial to this artery: direct inguinal hernia

Folds of the Ant. Abd. Wall- peritoneum

• When viewed from the inside, folds of parietal peritoneum manifest on the anterior abdominal wall
• Median umbilical fold contains the urachus.
• Medial umbilical fold contains the umbilical artery
• Lateral umbilical fold contains the vessels of the inferior epigastric