Gray's Anatomy Chapter 60 - Anterior Abdominal Wall

Anterior Abdominal Wall Boundaries and Functions

• Superior boundary is the costal arches (margins) and xiphisternal junction.
• Lateral boundary is the mid-axillary line.
• Inferior boundary is the imaginary line along the iliac crests, inguinal ligament, and pubic symphysis.
• The anterior abdominal wall is continuous with the posterior abdominal wall, forming a flexible sheet of skin, muscle and connective tissue.
• The anterior abdominal wall is Contiguous with the respiratory diaphragm, the bony and myofascial structures of the thorax.
• Tissues form the myopectineal orifice and the inguinal canal.
• Maintains abdominal shape and aids physiological functions.
• Hernia repair is a common surgical operation related to abdominal wall dysfunction.

Skin and Soft Tissue Layers

• Includes skin, soft tissues, lymphatic/vascular structures, and segmental nerves.
• The skin is non-specialized and may be hirsute depending on sex and ancestry.
• All postpubertal individuals have some extension of the pubic hair on the abdominal wall, especially in males, where the hair can extend to the umbilicus in a triangular pattern.
• Subcutaneous fat varies in thickness based on sex and caloric intake.

Superficial Fascia Layers

• Consists of three layers: superficial fatty (Camper's), membranous (Scarpa's), and deep fatty layer.
• Layers are well-defined in children; the membranous layer remains distinct in adults.
• Contains adipose tissue, blood vessels, lymphatics, and nerves, especially in the inguinal region, superficial inguinal nodes.

Superficial Fatty Layer

• Contains a variable amount of fat partitioned by fibrous septa connecting the dermis with the deeper membranous layer.
• Inferiorly it is continuous with the superficial fascia of the thigh.
• Medially, it is continuous with the linea alba.
• Extends over external genitalia in males, becomes thin and contains dartos muscle in the scrotum
• Extends into the labia majora and perineum in females.

Membranous Layer

• Made of connective tissue and elastic fibers
• Thickness varies, becoming thinner proximally on the abdomen (Lancerotto et al 2011)
• Thickness histologically is between 0.5-1mm but it appears thicker on computed tomography (Chopra et al 2011, Lancerotto et al 2011)
• Loosely connected to external abdominal oblique aponeurosis and rectus sheath by oblique fibrous septa
• Continuous with superficial fascia of the trunk
• Adherent to linea alba and pubic symphysis
• Fuses with iliac crest, extends superficial to the inguinal ligament, and fuses with the fascia lata at the inguinal crease
• In males it extends onto the dorsum of the penis, forming the fundiform ligament, and onto the scrotum where it becomes continuous with the membranous layer of the superficial fascia of the perineum (Colles’ fascia)
• In females it continues into the labia majora and is continuous with the superficial fascia of the perineum
• In males, the testis can frequently be retracted out of the scrotum into the loose areolar tissue between the membranous layer of superficial fascia over the inguinal canal and the aponeurosis of external abdominal oblique

Deep Fatty Layer

• Thickness more variable than the superficial layer, thin/absent at bony prominences and linea alba.
• Adipocytes show different metabolic activities vs superficial layer (Chopra et al 2011)
• Liposuction preferentially removes this layer to avoid skin irregularities (Markman and Barton 1987)

Transversalis Fascia

• Thin connective tissue between transversus abdominis and extraperitoneal fat.
• Part of the general fascial layer between peritoneum and abdominal wall.
• Fuses posteriorly with the anterior layer of the thoracolumbar fascia; forms a continuous sheet anteriorly.
• Superiorly blends with the fascia covering the inferior surface of the respiratory diaphragm
• Inferiorly is continuous with the iliac and pelvic parietal fasciae.
• Attached to the iliac crest between the origins of transversus abdominis and iliacus and to the posterior margin of the inguinal ligament (iliopubic tract).
• The iliopubic tract consists of transverse fibers that fan out laterally towards the anterior superior iliac spine to blend with the iliopsoas fascia and run medially to the pubic bone
• The iliopubic tract is a landmark during laparoscopic inguinal hernia repair, though often incorrectly described as the inguinal ligament (Teoh et al 1999)
• Medial to the femoral sheath the transversalis fascia is fused to the pubis behind the conjoint aponeurosis (conjoint ‘tendon’)
• An inferior extension of the fascia forms the anterior part of the femoral sheath
• A further thickening of the transversalis fascia, the interfoveolar ligament, runs inferior to the inguinal ligament at the medial margin of the deep inguinal ring; it may contain muscle fibres.
• Continues as the internal spermatic fascia over structures passing through the deep inguinal ring.

Extraperitoneal Connective Tissue

• Lies between the peritoneum and the fasciae lining the abdominal/pelvic cavities.
• Contains a variable amount of fat, often found in congenital hernias
• Adipose tissue is most common content of small congenital umbilical and epigastric hernias
• Abundant on the posterior abdominal wall around the kidneys.
• The inferior epigastric vessels contained within the fat pad as they travel from the external iliac vessels to rectus abdominis
• Fat pad serves as an anatomical landmark during various types of abdominal hernia repairs.
• Fat abundance allows for peritoneal flap creation during hernia surgery.
• Minimal fat makes separation of peritoneum and transversalis fascia difficult.

Vascular Supply: Superior Epigastric Artery/Veins

• The superior epigastric artery is a terminal branch of the internal thoracic artery.
• Arises level with the sixth costal cartilage, descends between the costal and sternal parts of diaphragm.
• They pass anterior to distal transversus thoracis and proximal transversus abdominis.
• Anastomoses with inferior epigastric arteries in the rectus abdominis (Rozen et al 2008).
• Vascular branches supply rectus abdominis and perforate the anterior rectus sheath
• Vessels penetrate rectus abdominis near the umbilicus, referred to as periumbilical perforator vessels.
• Proximal branch passes anterior to the xiphoid process, anastomosing with the contralateral branch.
• Gives small branches to the anterior diaphragm and falciform ligament (on the right).

Vascular Supply: Inferior Epigastric Artery/Veins

• Inferior epigastric artery originates from the external iliac artery proximal to the inguinal ligament.
• Vessels curve forwards in extraperitoneal tissue; ascends obliquely near the junction.
• Lies posterior to the spermatic cord, separated by the transversalis fascia.
• It pierces transversalis fascia and enters posterior layer of the rectus sheath anterior to the arcuate line.
• Its accompanying veins, usually two, unite to form a single vein that drains into the external iliac vein (Rozen et al 2009).

Blood Supply: Surgical Zones

• Surgical zones have been defined to better understand this vascular distribution.
• Zone 1 (central proximal abdomen) gets blood from the superior epigastric artery (superiorly) and inferior epigastric artery (inferiorly).
• Periumbilical perforator vessels arise from both epigastric arteries to supply overlying tissues.
• Zone 2 (hypogastric region) receives blood supply from superficial/deep branches of inferior epigastric artery (medially).
• Superficial circumflex iliac artery (from femoral artery) provides lateral blood supply.
• Zone 3 (proximal to arcuate line, lateral to semilunar line) gets blood from deep circumflex iliac artery (inferiorly).
• Musculophrenic artery (branch of internal thoracic artery) supplies zone 3 superiorly.

Inferior Epigastric Artery Branches

• Branches anastomose with the superior epigastric artery within rectus abdominis (Rozen et al 2008).
• Inferolaterally, it anastomoses with the deep circumflex iliac artery.
• Gives off the cremasteric artery, a pubic branch, and muscular/cutaneous branches.
• In the male, cremasteric artery supplies cremaster, other cord coverings, and anastomoses with the testicular artery.
• Is small in females
• A pubic branch anastomoses with a pubic branch of the obturator artery.
• Sometimes, the obturator artery is replaced with the larger inferior epigastric artery, and lies close to the femoral ring (Pai et al 2009).
• The muscular branches supply abdominal muscles and peritoneum, and Anastomose with the circumflex iliac and lumbar arteries.
• This Contributes to periumbilical perforator vessels.

Blood Supply: Additional Info

• Mapped for large lipocutaneous flaps
• Ligation of these can lead to flap necrosis (Rozen et al 2008)
• May arise from femoral artery and ascend anterior to femoral vein
• Superior and inferior epigastric arteries provide collateral blood flow between the internal thoracic artery.
• The small tributaries of the inferior epigastric vein anastomose with branches of the umbilical vein in the falciform ligament.
• In portal hypertension, leads to caput medusae and Back pressure to the skin and pattern of dilated, serpiginous superficial veins radiating out from the umbilicus

Intercostal/Subcostal/Lumbar Arteries

• Pierce transversus abdominis to enter neurovascular plane between transversus abdominis and internal abdominal oblique.
• Give muscular branches to obliques
• Before anastomosing with lateral branches of superior and inferior epigastric arteries at rectus sheath.

Anterior Abdominal Muscles

• Rectus abdominis, external/internal obliques, transversus abdominis, and pyramidalis contribute to functions involving pressure.
• Muscle tone provides support for abdominal viscera and retains normal contour.
• Contraction increases intra-abdominal pressure, mainly using respiratory diaphragm muscles.

Nerves

• Damage to nerves that innervate rectus abdominis can cause segmental denervation of portions of rectus abdominis.
• Transversus abdominis plane (TAP) blockade is a regional anesthetic technique for abdominal surgery.

Lymphatic Drainage

• Highest concentration in the dermis (Friedman et al 2015)
• Vessels from lumbar and gluteal pass with with the superficial circumflex iliac vessels
• Lymphatic vessels from the skin beyond the umbilicus is passed via the superficial epigastric vessels
• Vessels from the lumbar region drain to axillary/parasternal nodes
• The vessels can drain to the lateral aortic nodes.
• Deeper Lymphatic vessels accompany the arteries.

Segmental Nerves

• Thoracic spinal nerves innervate the abdominal wall.
• Seventh to twelfth thoracic ventral rami continue anteriorly into the abdominal wall.
• All these segmental nerves run anteriorly within a thin layer of fascia in the neurovascular plane between transversus abdominis and internal abdominal oblique.
• Supply the skin of the lateral and anterior abdominal walls
• Ninth intercostal nerve supplies the skin proximal to the umbilicus.
• Tenth intercostal nerve supplies the skin that consistently includes the umbilicus.
• Eleventh intercostal nerve supplies the skin distal to the umbilicus.

Rectus Abdominis

• Paired, long muscle extending along the anterior abdominal wall on either side of the linea alba
• Interrupted by fibrous bands (tendinous intersections) (Rai et al 2018)
• Muscle arises from the anterior border of the sixth and seventh ribs and the xiphoid process
• Supplied by superior and inferior epigastric arteries as well as the distal thee posterior Intercostal arteries
• Receives innervation from thoracic spinal nerves
• It acts in flexion of the trunk

Rectus Sheath

• Encloses the rectus abdominis
• The anterior layer extends the length of the muscle and fuses with the periosteum
• Distal to the arcuate line, the three aponeuroses from EO, IO and TA form the anterior layer with transversalis fascia on the posterior layer
• Functions as attachments for the EAO, IAO and TA muscles

External Abdominal Oblique

• Largest muscle and lies most superficially
• Curves and attaches to the ribs muscles are the serratus anterior/latissimus Dorsi and attaches to iliac crest
• Fibres diverge to attach distally
• Receives blood supply from the distal Posterior Intercostal and subcostal arteries proximally, and the deep circumflex iliac artery distally. -
• There are additional smaller contributions (Schlenz et al 1999).
• The Innervation comes form the Spinal Nerves to maintain abdominal tone, increasing intra-abdominal pressure, and lateral flexion of the trunk against resistance from the Spinal Nerves

Internal Abdominal Oblique

• Lies deeper than external abdominal oblique and thinner than EAO
• Runs from iliopectineal arch, a thickened band of the fascia (Acland 2008)
• It is attached to the last ribs and merges with internal intercostal muscles function of which is Innervation and lateral flexion of the trunk against resistance

Transversus Abdominis

• It is attached to the inner top of the anterior part of crest, the throacolumbar fascia, and the costal cartilages
• Ends that curve downwards through the fibres to have the body
• Receives blood from the superior Epigastric arteries and lumbar arteries in order to maintain the core

Conjoint Aponeurosis

• Aponeurosis in form with the muscles attached as a Conjunction
• Runs through to act

Hernias of the Anterior Abdominal Wall (Overview)

• Anterior abdominal wall hernias can occur in inguinal, femoral, umbilical, epigastric and Spigelian regions.
• These types of hernia occur where the layers of the abdominal wall are intrinsically weak
• 60% are on the right, 25% are on the left and only 15% are both

Myopectineal Orifice

• Infermedial part of anterior abdominal wall
• Encompasses the inguinal ring, and inguinal triangle, and portal that transmits femoral parts
• Is a major target, but if it is arranged poorly can result in conditions such as hernias

Indirect Inguinal

• A result of development as internal rings, direct hernias, or femoral hernias in combination with the aponeuroses
• Results in the abnormal parts

Direct Inguinal Hernias

• Arise as direct hernias within the tissue and enlarge or become larger than normal and can become a risk

Femoral Structures/Concerns of Health

• Hernias start to come from the potential of the areas of attachment causing concerns

Umbilical Abnormalities

• Occurs in the ring of the umbilical causing hernias and weaknesses
• Occurs after the return of parts of the fetus in the womb

Spigelian Hernia

• Spigelican is a hole for the fat and peritoneal sac and causes major health defects

Incisional Concerns

• Occurs with a mass that leads to failure and infection which increases major health complications

The Parastomal Area

• When there is a disruption the health leads from a hernia in the gut and can be bad for you
• Pyramidalis contributes to tensing the distal linea alba but is of doubtful physiological significance.