Anterior Abdominal Wall Anatomy

• The lecture is about Anterior Addominal Wall and Surface Anatomy
• Class: Year 2, Semester 1
• Lecturer: DR. VIJAYALAKSHMI S B, Department of Anatomy, Email id: [email protected]
• Date: 8th Sept' 2024

Learning Outcomes

• Describe the anterior abdominal wall
• Describe the anatomy of the inguinal canal
• Demonstrate an understanding of how inguinal hernias develop & explain the anatomy and clinical findings
• Describe the layers and contents of the scrotum
• Explain the embryology of testicular descent, and why this is clinically relevant

The Abdomen – General Structure and Function

• The abdomen as roughly a cylindrical chamber
• The inferior thoracic aperture forms the superior opening, which is closed by the diaphragm
• The abdomen is inferiorly continuous with the pelvic wall at the pelvic inlet
• The abdomen's function includes housing and protecting major viscera, assisting in breathing, and managing changes in intraabdominal pressure

The Abdomen Wall

• Skeletal elements: Includes 5 lumbar vertebrae, intervening IV discs, pelvic bones, costal margin (ribs 11 & 12), and the xiphoid process
• Muscles:
• Lateral to vertebral column: Quadratus lumborum, psoas major, and iliacus
• Lateral of the abdominal wall: transverse abdominis, internal oblique, and external oblique
• Anterior: Rectus abdominis

Review – Important Bony Landmarks

• Important landmarks include the iliac crest, anterior superior iliac spine, sacrum (L1-L5), pubic tubercle, pubic symphysis, xiphoid process, ribs 11 and 12, and iliac tuberosity

Important Surface Anatomy

• Topographic divisions are used to describe the location of abdominal organs and pain
• Two main patterns used: Four-quadrant pattern and Nine-region pattern

Lumbar Vertebrae

• Transpyloric Plane is at L1
• The umbilicus is located at the L3/4 intervertebral disc
• The transtubercular plane is at L4-5

Transpyloric Plane – L1

• Midway between jugular notch and pubic symphysis (or xiphoid and umbilicus) at the 9th costal cartilage
• Pylorus of stomach, body of pancreas, and hila of kidneys are located here

Layers of the Abdominal Wall

• Skin
• Superficial fascia (or subcutaneous tissue)
• Muscles and associated fascia
• Parietal peritoneum

Superficial Fascia

• Consists of fatty connective tissue, and its composition depends on location
• Has two layers: a fatty superficial layer (Camper's fascia) and a membranous deep layer (Scarpa's fascia)
• Superficial vessels and nerves run between these two layers

Muscles of the Abdominal Wall

• There are 5 muscles on each side of the abdominal wall, divided into two groups
• 3 Flat muscles (situated laterally): External oblique, internal oblique, transverse abdominis
• 2 Vertical muscles (situated near the midline): Rectus abdominis, pyramidalis

Muscles of the Abdomen: The Flat Muscles

• There are 3 flat muscles: external oblique, internal oblique, and transversus abdominis
• These muscles are located laterally in the abdominal wall and stacked upon one another
• Muscle fibers run in differing directions and cross each other
• This strengthens the abdominal wall and decreases the risk of herniation

External Oblique

• It is the most superficial muscle
• Origin: Ribs 5-12
• Insertion: Iliac crest and linea alba, with fibers in the inferomedial direction
• Innervation: Thoracoabdominal T7-11 and subcostal nerve T12
• Action: Compresses abdomen contents, both muscles flex trunk, and each muscle bends trunk to the same side, turning anterior part of the abdomen to the opposite side
• The lower border folds on itself to form the inguinal ligament

Associated Ligaments

• Inguinal ligament: A rolled-in free lower border of the external oblique aponeurosis on each side, passing between the anterior superior iliac spine (ASIS) and pubic tubercle, playing an important role in the formation of the inguinal canal
• Lacunar ligament: A crescent-shaped extension of fibers at the medial end of the inguinal ligament that attaches to the pecten pubis
• Pectineal (Cooper's) Ligament: Extended fibers along the pecten pubis of the pelvic brim

Inguinal Ligament

• The midpoint of the inguinal ligament is halfway along the ligament, marking the surface of the deep inguinal ring and femoral nerve
• The mid-inguinal point is halfway between the ASIS and the superior border of the pubic symphysis: It is a surface marking for the femoral artery

Internal Oblique

• It is deep to the external oblique
• Origin: Lateral 2/3 inguinal ligament, iliac crest, and thoracolumbar fascia
• Insertion: Linea alba, pectineal line, pubic crest, inferior border of ribs 9-12, fibers passing in a superomedial direction
• Innervation: Thoracoabdominal T7-11 and subcostal nerve T12, iliohypogastric (L1), and ilioinguinal (L1)
• Action: Compresses abdomen contents, both muscles flex the trunk, and each muscle bends the trunk and turns the anterior part to the same side

Transversus Abdominis

• It is deep to the internal oblique
• Origin: Iliac crest, lateral 1/3 inguinal ligament, thoracolumbar fascia, and ribs 7-12
• Insertion: Linea alba, pubic crest, and pectineal line, with fibers passing transversely
• Innervation: Thoracoabdominal T7-11 and subcostal nerve T12, iliohypogastric (L1), and ilioinguinal (L1)
• Action: Compresses abdomen contents

Muscles of the Abdomen: Vertical Muscles

• Rectus Abdominis
• Origin: Pubic crest, tubercle & symphysis
• Insertion: Costal cartilage of ribs 5-7, xiphoid process
• Innervation: Thoracoabdominal T7-11, subcostal T12
• Action: Compresses abdomen contents, flexes the vertebral column, and tenses the abdominal wall
• Pyramidalis
• Origin: Pubic symphysis and pubic bone
• Insertion: Linea alba
• Innervation: Subcostal nerve (T12)
• Action: Tenses the linea alba

Gym Anatomy

• The rectus abdominis muscles are engaged during flexion of the torso, assisted by the abdominal obliques
• Full sit-ups also engage the hip flexors (rectus femoris and iliopsoas muscles)
• Abdominal oblique muscles are more active when a rotation to one side is added to flexion

Rectus Sheath

• Formed by the aponeuroses of the 3 flat muscles
• Anterior wall=Aponeuroses of the external oblique and half of the internal oblique
• Posterior wall=Aponeuroses of half of the internal oblique and of the transversus abdominis
• Above the arcuate line in the upper abdomen: The arcuate line is midway between the umbilicus and pubic symphysis, where all the aponeuroses move to the anterior wall of the rectus sheath

Nerve Supply

• Motor and sensory nerves course between the internal oblique and transversus abdominis muscles
• They innervate the muscles and terminate by supplying the skin

Dermatomes

• Skin dermatome on the xiphoid process is T7
• Skin dermatome around the umbilicus is T10
• Skin dermatome on the inguinal ligament is L1
• Clinical application: Umbilicus T10, Referred pain from appendix and testis

Blood Supply

• Deep supply: Includes the superior epigastric vessel (from the internal thoracic artery), inferior epigastric vessels and deep circumflex (from the external iliac), and the 10th and 11th intercostal arteries and subcostal artery (from the abdominal aorta)
• Superficial supply: Includes the musculophrenic artery (from the internal thoracic artery) and the superficial epigastric and superficial circumflex (from the femoral artery)

Inguinal Canal

• About 4 cm long
• Begins: at the deep inguinal ring
• Ends: at the superficial inguinal ring

Deep inguinal ring:

• It is a defect in transversalis fascia
• Located midway between the ASIS and the pubic symphysis
• Above the inguinal ligament
• Lateral to the inferior epigastric vessels
• Superficial inguinal ring:
• It is a triangular opening in the aponeurosis of the external oblique
• Found superior to the pubic tubercle
• Contents include:
• In males: the genital branch of the genitofemoral nerve and the spermatic cord
• In females: the genital branch of the genitofemoral nerve and the round ligament of the uterus
• The ilio-inguinal nerve passes through part of the canal in both sexes

Inguinal Canal details

• Floor: Formed by the inguinal ligament and medially by the lacunar ligament
• Anterior wall: Formed by the aponeurosis of the external oblique and, laterally, by the internal oblique
• Roof: Formed by the arching fibers of the transversus abdominis and internal oblique
• Posterior wall: Formed by the transversalis fascia and, medially, by the conjoint tendon

Spermatic Cord

• Layers:
• Internal spermatic fascia (transversalis fascia)
• Cremasteric layer (internal oblique)
• External spermatic fascia (external oblique)
• Arteries:
• Testicular (from Aorta at L2)
• Cremasteric (from Inferior Epigastric)
• Artery of Vas (from Superior Vesical)
• Nerves:
• Nerve to cremaster (from Genitofemoral)
• Sympathetic (deep pain sensation)
• (Ilioinguinal – separate)
• Other things:
• Vas deferens
• Pampiniform plexus of veins (asymmetric, varicosities)
• Lymphatics to para-aortic nodes at L2

Hernia Definition

• It is an abnormal protrusion of an organ, tissue, or structure in part or in whole through a defect in the cavity that normally contains it
• Groin Hernias: 75% of hernias, with 25% of males and 2% of females having inguinal hernias in their lifetime
• Inguinal hernia: Neck is above & medial to the pubic tubercle
• Femoral hernia: Neck is below and lateral to the pubic tubercle

Inguinal Hernia - Indirect

• Congenital
• Passes Through the deep ring, along the inguinal canal, to the superficial ring and then to the scrotum
• If reduced, can be controlled from deep ring
• The abdominal content passes through the deep ring, so the bulge occurs lateral to the epigastric vessels

Inguinal Hernia - Direct

• Occurs Through a weakness in the transversalis fascia & superficial ring
• The bulge occurs medial to the epigastric vessels (in Hesselbach's triangle)
• Acquired causes: Heavy lifting, constipation and sports e.g. Rugby

Descent of Testes

• Testes descend from the abdomen to the scrotum during fetal development
• This process involves gubernaculum which helps the testes descend, and the processus vaginalis that evaginates into the scrotum
• The layers of the scrotum are derived from the abdominal wall

Scrotum Anatomy

• Processus vaginalis, is an extension/outpouching that projects into the labioscrotal swelling
• It usually disappears except the distal part
• As the testis moves into the scrotum, it acquires layers from the abdominal wall

Lymphatic Drainage

• Abdominal wall superficial lymphatics:
• Above the umbilicus: drain to the axillary nodes
• Below the umbilicus: drain to the superficial inguinal nodes
• Abdominal wall deep lymphatics follow the deep arteries:
• To parasternal nodes along the internal thoracic artery
• To lumbar nodes along the abdominal aorta
• To external iliac nodes along the external iliac artery
• Testis drain to para-aortic nodes at L1
• Skin of the Scrotum drains into inguinal nodes