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The Anterior Abdominal Wall - A Complete Reference

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1. Boundaries and Overview

• Superior: costal margins (ribs 7-10) and xiphoid process of sternum
• Inferior: inguinal ligaments, pubic crests, and pubic symphysis
• Posterior limit (functionally): anterior superior iliac spines (ASIS) laterally

• Gray's Anatomy for Students, p. 326 - Schwartz's Principles of Surgery, p. 1549

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2. Layers of the Anterior Abdominal Wall (Deep to Superficial)

• Schwartz's Principles of Surgery, p. 1549 - Greenfield's Surgery, p. 3632

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3. Superficial Fascia in Detail

Camper's Fascia

• The outer, fatty layer of the superficial fascia
• Contains copious adipose tissue (the "panniculus adiposus") - can be enormous in obese individuals
• Contains the superficial epigastric vessels and superficial circumflex iliac vessels (both branches of the femoral artery and vein)
• Contains lymphatics draining into inguinal lymph nodes
• Inferiorly continuous with the outer perineal fascia
• Contains dartos smooth muscle fibers that form the dartos muscle of the scrotum

Scarpa's Fascia

• The deep, membranous layer of the superficial fascia
• A condensation of fibrous components - not truly a distinct layer, but compressed fibrous tissue
• Forms the fundiform ligament of the penis (suspensory ligament of the clitoris in women)
• Continues onto the penis and scrotum, fusing with superficial perineal fascia
• Clinical note: Scarpa's fascia fuses with fascia lata of the thigh just below the inguinal ligament. This seals off the potential space beneath the inguinal ligament - important in urine extravasation (see clinical section)
• Greenfield's Surgery, p. 3632 - Gray's Anatomy for Students, p. 338

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4. The Five Anterolateral Muscles

A. External Oblique

• Inguinal ligament: folded-under inferior edge running from ASIS to pubic tubercle
• Lacunar ligament (Gimbernat's ligament): horizontal fibers of the inguinal ligament that fan out medially to attach to the pectineal line of the pubis; forms the medial wall of the femoral canal
• Pectineal ligament (Cooper's ligament): extension of lacunar ligament along the pectineal line
• Superficial inguinal ring: triangular aperture in the aponeurosis, just superolateral to the pubic tubercle

B. Internal Oblique

• Its inferior free border arches over the inguinal canal forming its roof
• Cremaster muscle arises from the internal oblique and cremasteric fascia that extend onto the spermatic cord

C. Transversus Abdominis

D. Rectus Abdominis

E. Pyramidalis

• Small triangular muscle anterior to the rectus abdominis, within the rectus sheath
• Origin: pubic symphysis; Insertion: linea alba
• Often absent (20% of people)
• Action: tenses the linea alba
• Innervated by subcostal nerve (T12)
• Gray's Anatomy for Students, p. 333-336 - Schwartz's Principles of Surgery, p. 1549

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5. The Rectus Sheath

Above the Arcuate Line (most of the abdomen):

• Anterior sheath: aponeurosis of external oblique + anterior lamina of internal oblique
• Posterior sheath: posterior lamina of internal oblique + aponeurosis of transversus abdominis
• Transversalis fascia and peritoneum lie deep to the posterior sheath

Below the Arcuate Line (lower 1/4 of abdomen):

• Anterior sheath: ALL three aponeuroses pass anteriorly (external oblique + both laminae of internal oblique + transversus abdominis)
• Posterior sheath: ABSENT (only transversalis fascia and peritoneum remain)
• The arcuate line is typically located about midway between the umbilicus and the pubic symphysis

Clinical Correlate - Arcuate line significance: Below the arcuate line, the posterior rectus sheath is absent - only transversalis fascia and peritoneum cover the deep surface of the rectus muscle. A rectus sheath hematoma (from inferior epigastric artery injury) below the arcuate line can spread more freely than above it. The epigastric vessels lie posterior to the rectus in this region and are at risk during laparoscopic trocar placement.

• Greenfield's Surgery, p. 3640 - Schwartz's Principles of Surgery, p. 1549

Important Aponeurotic Structures:

• Linea alba: midline fusion of all six layers of aponeuroses (from both sides). Broad superiorly (up to 1 cm between umbilicus and xiphoid), nearly absent (a mere fibrous line) below the umbilicus
• Linea semilunaris: curved lateral border of the rectus muscle / rectus sheath - visible in lean individuals
• Spigelian line: another name for the lateral edge of the rectus sheath at the point where the transversus aponeurosis begins; site of Spigelian hernias (see below)

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6. The Transversalis Fascia

• The deep fascia lining the deep surface of the transversus abdominis
• Part of the general "endoabdominal fascia" that lines the entire abdominal cavity
• Superiorly: continuous with the diaphragmatic fascia
• Inferiorly: blends with the iliac fascia
• Medially: participates in the midline structures
• Forms the internal spermatic fascia as it evaginates at the deep inguinal ring to surround the spermatic cord/round ligament
• Iliopubic tract: a thickened band of the transversalis fascia running parallel to and posterior to the inguinal ligament - important in laparoscopic hernia repair (marks the lower limit of mesh placement to avoid femoral nerve injury)

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7. Blood Supply

Deep/Main Arteries:

Superior and inferior epigastric arteries anastomose within the rectus sheath along the posterior surface of the rectus muscle - creating a continuous channel from internal thoracic to external iliac arteries. This anastomosis is clinically exploited in TRAM (transverse rectus abdominis myocutaneous) flap breast reconstruction.

Superficial Arteries:

• Superficial epigastric artery: branch of femoral artery; runs superiorly in Camper's fascia toward the umbilicus
• Superficial circumflex iliac artery: branch of femoral artery; runs laterally toward the ASIS
• Superficial external pudendal arteries: supply the scrotum/labia

Venous Drainage:

• Follows the arteries
• Thoracoepigastric vein: superficial longitudinal vein connecting femoral vein below to axillary vein above; becomes visible and enlarged in portal hypertension or SVC/IVC obstruction ("caput medusae")

Clinical Correlate - Caput Medusae: In portal hypertension, blood is diverted through portal-systemic anastomoses. The paraumbilical veins (running in the falciform ligament) dilate and connect with the epigastric veins of the anterior abdominal wall, creating visible dilated veins radiating from the umbilicus - "caput medusae."

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8. Nerve Supply

Anterior Rami of Intercostal Nerves (T7-T11):

• Enter the anterior abdominal wall laterally, pass between the internal oblique and transversus abdominis, and enter the posterior rectus sheath
• Pierce the anterior rectus sheath to become anterior cutaneous nerves
• Also give lateral cutaneous branches

Subcostal Nerve (T12):

• Anterior ramus of T12
• Runs in same plane as intercostal nerves, entering lateral abdominal wall

Iliohypogastric Nerve (L1):

• Branch of lumbar plexus (L1)
• Runs between internal oblique and transversus, pierces internal oblique above ASIS
• Lateral cutaneous branch: supplies skin of the gluteal and hip region
• Anterior (medial) cutaneous branch: supplies skin above the pubis

Ilioinguinal Nerve (L1):

• Closely related to iliohypogastric; passes through the inguinal canal
• Exits through the superficial inguinal ring
• Supplies skin of upper medial thigh, root of penis/clitoris, superior scrotum/labia majora

Genitofemoral Nerve (L1-L2):

• Femoral branch: passes under inguinal ligament to supply skin of femoral triangle
• Genital branch: passes through deep inguinal ring and inguinal canal; supplies cremaster muscle and skin of scrotum/labia majora

Dermatome Map:

Clinical Correlate - Referred Pain: Appendicitis classically begins as central/periumbilical pain (T10 - the level of the appendix's visceral innervation) before localizing to the right iliac fossa (via somatic innervation of the parietal peritoneum at McBurney's point). Ureteric colic from a stone at the ureterovesical junction refers to the groin/scrotum/labia (L1).

• Gray's Anatomy for Students, p. 326

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9. The Inguinal Canal

Direction: superolateral to inferomedial (from deep to superficial ring)

Walls:

Rings:

• Located midway between ASIS and pubic symphysis (approximately 1.5 cm above the midpoint of the inguinal ligament)
• Immediately lateral to the inferior epigastric vessels
• Not a true hole - is the beginning of the tubular evagination of transversalis fascia
• Forms the internal spermatic fascia

• Triangular opening in the aponeurosis of external oblique
• Located just superolateral to the pubic tubercle
• Apex points superolaterally; base = pubic crest
• Medial crus attaches to pubic symphysis; lateral crus to pubic tubercle
• Intercrural fibers (from inguinal ligament) prevent the ring from widening
• Forms the external spermatic fascia

Contents:

The Spermatic Cord contains (3+3+3):

• Arteries (3): testicular artery, artery of vas deferens, cremasteric artery
• Veins (3): pampiniform plexus (becomes testicular vein), lymphatics
• Other (3): ductus (vas) deferens, genital branch of genitofemoral nerve, sympathetic nerves

Coverings of the Spermatic Cord (from inner to outer):

1. Internal spermatic fascia - from transversalis fascia at the deep ring
2. Cremasteric muscle and fascia - from internal oblique
3. External spermatic fascia - from external oblique aponeurosis at the superficial ring

• Gray's Anatomy for Students, p. 351-353

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10. Hesselbach's Triangle (Inguinal Triangle)

The floor of Hesselbach's triangle is formed by the conjoint tendon medially and transversalis fascia laterally. Direct hernias pass through the medial aspect (posterior) and emerge directly through the superficial ring without traversing the full inguinal canal.

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11. The Umbilicus and Peritoneal Folds

Umbilicus:

• Scar of the former umbilical cord attachment
• Located at the level of the fibrocartilaginous disc between L3 and L4 vertebrae
• Weakest point of the linea alba - common site for umbilical hernias

Peritoneal Folds (visible on the inner surface of the anterior abdominal wall):

Clinical Correlate: The median umbilical fold (urachus) can persist as a patent urachus connecting the bladder to the umbilicus, causing urinary drainage at the umbilicus.

Fossae between the folds (laparoscopic landmarks):

• Supravesical fossa: between median and medial folds
• Medial inguinal fossa: between medial and lateral umbilical folds (the area of Hesselbach's triangle - site of direct hernia)
• Lateral inguinal fossa: lateral to the lateral umbilical fold, over the deep inguinal ring (site of indirect hernia emergence)

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12. Clinical Correlates

A. Hernias

The relationship to the inferior epigastric vessels is the definitive intraoperative distinction: indirect hernia sac is lateral, direct hernia sac is medial to the vessels.

• Passes through the femoral canal (medial compartment of the femoral sheath) below the inguinal ligament
• More common in women (wider pelvis, wider femoral canal)
• Has the highest strangulation risk of all groin hernias (narrow neck of femoral ring)
• Presents as a swelling below and lateral to the pubic tubercle (vs. inguinal hernia, which is above and medial to pubic tubercle)

• Through the umbilical ring (physiological hernia is normal in neonates - closes by 2 years)
• True umbilical hernias in children vs. paraumbilical hernias in adults (through linea alba near umbilicus)
• Associated with obesity, ascites, multiple pregnancies

• Protrusion of preperitoneal fat (and occasionally peritoneum) through defects in the linea alba between xiphoid and umbilicus
• More common in males, 20-50 years
• Usually small, can be multiple, frequently painful disproportionate to size

• Hernia through the linea semilunaris (lateral border of rectus sheath), typically at the level of the arcuate line
• Often interparietal (between layers of the abdominal wall) - can be missed clinically
• Diagnosis often requires CT or ultrasound

• Omphalocele: midgut fails to return to abdomen at ~12 weeks gestation; contents herniate through umbilical ring covered by an amniotic/peritoneal membrane
• Gastroschisis: paraumbilical defect (usually right side) without amniotic sac coverage; bowel is exposed, thickened, and matted; associated with vascular compromise rather than genetic defects

B. Rectus Sheath Hematoma

• Rupture of the superior or inferior epigastric artery (or directly from the rectus muscle)
• Causes: violent coughing, physical exertion, anticoagulant therapy, trauma
• Presents as sudden onset unilateral abdominal pain with a tender abdominal mass
• Carnett's sign: pain increases (not decreases) on tensing the abdominal muscles (distinguishes from intra-abdominal pathology)
• Below the arcuate line: hematoma can spread across the midline because of the absent posterior sheath
• Diagnosed by CT or ultrasound; usually managed conservatively

C. Surgical Incisions

Nerve injury in subcostal incisions: Cutting the subcostal and lower intercostal nerves (T7-T11) during right subcostal (Kocher) incisions can cause denervation of the ipsilateral rectus abdominis, leading to unilateral bulging of the abdomen.

D. Urine Extravasation

• Rupture of the urethra in the perineum allows urine to track in the superficial perineal pouch
• Because Scarpa's fascia fuses with fascia lata below the inguinal ligament, urine cannot track down into the thigh
• Instead, urine tracks up the penis, over the scrotum, and into the anterior abdominal wall deep to Scarpa's fascia
• Clinically: penile/scrotal bruising and swelling + suprapubic swelling tracking up the abdomen

E. Nerve Injuries in Hernia Surgery (Inguinodynia)

• Ilioinguinal nerve (most commonly injured): numbness/pain in inner thigh and scrotum/labia
• Iliohypogastric nerve: numbness of suprapubic skin
• Genitofemoral nerve (femoral branch): numbness of anterior thigh
• Nerve entrapment in mesh is a common cause of chronic groin pain (inguinodynia) after herniorrhaphy

F. Cremasteric Reflex

• Stroking the upper inner thigh (L1 afferents via ilioinguinal/genitofemoral nerve) causes contraction of the cremaster muscle (genital branch of genitofemoral, L1-2) and retraction of the ipsilateral testis
• An absent cremasteric reflex on one side raises concern for testicular torsion
• The reflex arc: L1-L2 spinal level

G. Inguinal Lymph Node Enlargement

• Superficial inguinal lymph nodes drain the lower limb, perineum, lower anterior abdominal wall (below umbilicus), scrotum/labia majora, lower anal canal, and skin of the penis/clitoris
• The testis (being an embryological retroperitoneal structure) drains to para-aortic lymph nodes, NOT inguinal nodes
• Clinical pearl: A scrotal skin melanoma drains to inguinal nodes; testicular cancer drains to para-aortic nodes at the L1-L2 level

H. McBurney's Point

• Located 1/3 of the way from the ASIS to the umbilicus on the right side
• The surface marking of the base of the appendix
• Point of maximum tenderness in acute appendicitis
• Rebound tenderness (Blumberg's sign), Rovsing's sign, psoas sign, obturator sign are elicited near this landmark

I. Surface Anatomy and Regions

• Right Upper Quadrant (RUQ): liver, gallbladder, right kidney, hepatic flexure
• Left Upper Quadrant (LUQ): stomach, spleen, left kidney, splenic flexure, tail of pancreas
• Right Lower Quadrant (RLQ): appendix, cecum, right ovary, right ureter
• Left Lower Quadrant (LLQ): sigmoid colon, left ovary, left ureter

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Key Images Available from Textbooks

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Summary Table: Muscles at a Glance

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