ABDOMINAL WALL Anatomy Lecture 1 Dr Abeera SarfrazDr

ABDOMINAL WALL Anatomy Lecture # 1 Dr. Abeera Sarfraz/Dr. Mohammad Zubair

ANTERIOR ABDOMINAL WALL: ■ The anterior abdominal wall forms the anterior limit of the abdominal viscera. It runs, superiorly from the xiphoid process and costal cartilages of the 7 th, 8 th, 9 th and 10 th ribs to the iliac crest, inguinal ligament, anterior superior iliac spine, pubic tubercle, pubic crest and pubic symphysis inferiorly. ■ Generally, from superficial to deep, it is comprised of the skin, superficial fascia (adipose and membranous tissues), deep fascia, layers of muscles, extraperitoneal tissue and the peritoneum. Most of these structures, especially the muscles, span the anterolateral abdominal wall and there is no definite boundary between the anterior and lateral abdominal walls, thus the anterior abdominal wall is sometimes referred to as the anterolateral abdominal wall.

Regions and Quadrants: ■ The abdominal wall is divisible into four quadrants by two imaginary lines; a midline (vertical) and a horizontal line which passes through the umbilicus. The quadrants are named as follows; the right upper quadrant, left upper quadrant, right lower quadrant and left lower quadrant. This form of dividing the abdomen into four quadrants is known as the four region scheme

. Similarly, the anterior abdominal wall can also be divided into nine regions by two imaginary vertical lines called mid-clavicular lines (two vertical lines passing through the midpoint of the clavicle on the left and right side), and two imaginary horizontal lines. The mid-clavicular lines extend downwards to reach the mid inguinal point. The superior horizontal line is known as a transpyloric line (or transpyloric plane). This line is so named because of its relation to the pylorus of the stomach. It runs horizontally at the halfway point between the jugular notch and top of the pubic symphysis, passing through the pylorus of the stomach. The lower horizontal line can be drawn to join the tubercles of the right and left iliac crests of the hip bones. It is called the trans tubercular plane or intertubercular line (intertubercular plane). Therefore, these four lines divide the anterior abdominal wall and the abdominopelvic cavity into a middle epigastric, umbilical, suprapubic or hypogastric, right hypochondrium, left hypochondrium, right flank (right lumbar), left flank (left lumbar), right groin (right iliac, inguinal) and left groin (left iliac, inguinal) regions. This division of the abdomen into nine regions is aptly known as the nine region scheme.

3. The structures of the abdominal wall from out side to inside are; 1. Skin. 2. Superficial fascia. 3. Deep fascia 4. Muscles. 5. Extraperitoneal fascia 6. Parietal peritoneum.

Layers of Abdominal Wall: Skin: ■ The skin is of average thickness, and loosely attaches to the underlying tissue. It exhibits certain surface markings such as the umbilicus, linea alba, linea semilunaris, epigastric fossa, and Mc. Burney’s point. ■ It shows creases which represent the lines of orientation of collagen fibers in the dermis of the skin. These lines are referred to as Langer's lines. The Langer’s lines are of clinical relevance and incisions along them heal faster and better leaving little or no scaring; while those across them leave large and more pronounced scars. In pregnant women, obese people and those with abdominal distention, there are dark elongate lines called stretch marks or striae distansae usually on the umbilical and hypogastric regions. Stretch marks during pregnancy is specifically known as striae gravidarum.

Superficial Fascia: ■ Lying just below the skin are two layers of superficial fascia called superficial fatty layer called Camper’s fascia and deep membranous layer, Scarpa’s fascia. ■ The Camper’s fascia is a subcutaneous tissue containing variable amounts of fatty tissue. This fatty tissue is generally more in females and also in the right and left lower quadrants. ■ The Scarpa’s fascia is a membranous fatty layer containing fibrous tissue and very little fat. It runs inferiorly into the lower limbs where it changes its name to the fascia lata of the thigh. It is also continuous with the superficial perineal fascia called Colles’ fascia and also with the fascia which invests the scrotum and penis in males.

Deep Fascia: ■ Deep fascia Is a thin layer of connective tissue covering the muscles. It lies immediately deep to the membranous layer of superficial fascia

Muscles: ■ There are five (bilaterally paired) muscles in the anterior abdominal wall. These muscles are arranged into three muscular layers by the deep fascia. Of these five muscles, three are flat. ■ The external oblique ■ The internal oblique ■ The transversus abdominus ■ On either side of the midline anteriorly is a wide vertical muscle, the rectus abdominis and a small pyramidalis muscle. As the aponeuroses of the three sheets pass forward, they enclose the rectus abdominis to form the rectus sheath

External Oblique Muscle: The external oblique muscles are a pair of broad, thin, superficial muscles that lie on the lateral sides of the anterior abdominal wall Origins: 5 th to 12 th ribs Insertions: Linea alba, pubic tubercle, and anterior half of iliac crest Innervation: Intercostal nerves (T 7 - T 11), subcostal nerve (T 12), iliohypogastric nerve (L 1) Function: Flexion and rotation of the trunk, support and compression of the abdominal viscera. Also assists in forced expiration, micturition, defecation, parturition, and vomiting

■ Above and medial to the pubic tubercle , a small triangular defect in its aponeurosis is termed as superficial inguinal ring. The spermatic cord (or round ligament of the uterus) passes through this opening and carries the external spermatic fascia (or the external covering of the round ligament of the uterus) from the margins of the ring ■ The inferior border of the aponeurosis between the anterior superior iliac spine and pubic tubercle, folds backward and forms the inguinal ligament. ■ The lacunar ligament extends backward and upwards towards pectineal line from the medial end of the inguinal ligament. Muscle fibers in the external obliques run medially and inferiorly from the origins to the insertions across the lateral sides of the abdomen and end just lateral to the rectus abdominis muscles.

Internal Oblique Muscle ■ Origins: Anterior two-thirds of iliac crest, Iliopectineal arch, thoracolumbar fascia ■ Insertions: Inferior borders of ribs 1012, linea alba, junction with cremaster muscle, pectinal line of pubis (via conjoint tendon) ■ Innervation: Intercostal nerves (T 7 - T 11), subcostal nerve (T 12), iliohypogastric nerve (L 1), ilioinguinal nerve (L 1) ■ Function: Flexion and rotation of the trunk, support and compression of the abdominal viscera. Also assists in forced expiration, micturition, defecation, parturition, and vomiting

Transverse Abdominal Muscle: ■ Origins: 7 th to 12 th costal cartilages, thoracolumbar fascia, iliac crest, connective tissue deep to lateral third of inguinal ligament ■ Insertions: Linea alba, pubic crest, pectineal line of the pubis via the cojoint tendon ■ Innervation: Anterior rami of T 7 to T 12 spinal nerves (a. k. a 7 th- 11 th intercostal nerves and subcostal nerve), Iliohypogastric nerve (L 1), Ilioinguinal nerve (L 1) ■ Function: Support and compression of the abdominal viscera ■ A conjoint tendon is formed by the joining of the lowest tendinous fibres of the internal oblique and transverse abdominal muscle.

Rectus Abdominis Muscle: ■ The rectus abdominis is a long strap muscle that extends along the whole length of the anterior abdominal wall. It is broader above and lies close to the midline, being separated from its fellow by the linea alba. ■ Origins: Pubic crest and symphysis ■ Insertions: Xiphoid process and 5 th to 7 th costal cartilages ■ Innervation: Intercostal nerves (T 6 - T 11), Subcostal nerve (T 12) ■ Function: Trunk flexion, compression of abdominal viscera, stability of the pelvis

■ When it contracts, its lateral margin forms a curved ridge that can be palpated and often seen and is termed the linea semilunaris. This extends from the tip of the ninth costal cartilage to the pubic tubercle. The rectus abdominis muscle is divided into distinct segments by three transverse tendinous intersections at the level of: ■ xiphoid process. ■ umbilicus. ■ halfway between these two

Pyramidalis: ■ The pyramidalis muscle is a small triangular muscle lying anterior to the rectus abdominis muscle. It is contained in the rectus sheath and originates from the bony pelvis. ■ Origins: Pubis and pubic symphysis ■ Insertions: Linea alba ■ Innervation: Subcostal nerve (T 12) ■ Function: Tenses the linea alba

■ EXTRAPERITONEAL FASCIA: ■ The extraperitoneal fat is a thin layer of connective tissue that contains a variable amount of fat and lies between the fascia transversalis and the parietal peritoneum ■ PARIETAL PERITONEUM: ■ The walls of the abdomen are lined with parietal peritoneum. This is a thin serous membrane and is continuous below with the parietal peritoneum lining the pelvis

Nerve Supply: ■ The nerves of the anterior abdominal wall are the anterior rami of the lower six thoracic and the first lumbar nerves. ■ The thoracic nerves are the lower five intercostal nerves and the subcostal nerves ■ First lumbar nerve is represented by the iliohypogastric and ilioinguinal nerves, branches of the lumbar plexus They supply the skin of the anterior abdominal wall, the muscles, and the parietal peritoneum. ■ The lower six thoracic nerves pierce the posterior wall of the rectus sheath to supply the rectus muscle and the pyramidalis (T 12 only).

■ The oblique and transversus abdominis muscles are supplied by the lower six thoracic nerves and the iliohypogastric and ilioinguinal nerves (L 1). ■ The rectus muscle is supplied by the lower six thoracic nerves. ■ The pyramidalis is supplied by the 12 th thoracic nerve. ■ Dermatomes of the abdominal wall are ■ � The xiphoid process: T 7 ■ � The umbilicus: T 10 ■ � The pubis: L 1

Blood Supply: ■ The superficial branches include: ■ Musculophrenic artery, which is a branch from the internal thoracic artery. It supplies the superior part of the superficial anterolateral abdominal wall. ■ Superficial epigastric artery and lateral to it the superficial circumflex iliac artery. They are branches of the femoral artery and supply the inferior part of the wall. ■ The skin near the midline is supplied by branches of the superior and the inferior epigastric arteries. The skin of the flanks is supplied by branches of the ■ Intercostal arteries ■ Lumbar arteries ■ Deep circumflex iliac arteries

■ The deep layers of the anterolateral abdominal wall are supplied by the following: ■ The superior epigastric artery, one of the terminal branches of the internal thoracic artery, enters the upper part of the rectus sheath It descends behind the rectus muscle, supplying the upper central part of the anterior abdominal wall, and anastomoses with the inferior epigastric artery. ■ The inferior epigastric artery is a branch of the external iliac artery just above the inguinal ligament. It enters the rectus sheath after piercing the fascia transversalis. It runs upwards, supplies the lower central part of anterior abdomen and anastomoses with superior epigastric artery. ■ The deep circumflex iliac artery is a branch of the external iliac artery just above the inguinal ligament. It supplies the lower lateral part of the abdominal wall. ■ The lower two posterior intercostal arteries, branches of the descending thoracic aorta, and the four lumbar arteries, branches of the abdominal aorta, pass forward between the muscle layers and supply the lateral part of the abdominal

Venous Drainage: ■ SUPERFICIAL VEINS: ■ The superficial veins form a network that radiates out from the umbilicus. Above, the network is drained into the axillary vein via the lateral thoracic vein. Below, into the femoral vein via the superficial epigastric and great saphenous veins. ■ DEEP VEINS: ■ The deep veins of the abdominal wall, the superior epigastric, inferior epigastric, and deep circumflex iliac veins, follow the arteries of the same name and drain into the internal thoracic and external iliac veins.

Lymphatics: ■ Superficial lymph vessels: ■ Lymphatics in the region above the umbilicus drain into the axillary lymph nodes which can be palpated just beneath the lower border of the pectoralis major muscle. ■ Lymphatics in the region below the umbilicus drain into the superficial inguinal nodes. ■ The deep lymph vessels follow the arteries and drain into the internal thoracic, external iliac, posterior mediastinal, and para-aortic (lumbar) nodes.

POSTERIOR ABDOMINAL WALL: ■ The posterior abdominal wall is formed by the lumbar vertebrae, pelvic girdle, posterior abdominal muscles and their associated fascia. Major vessels, nerves and organs are located on the inner surface of the posterior abdominal wall ■ The fascia of the posterior abdominal wall lies immediately below the skin and subcutaneous tissue. The thoracolumbar fascia is a large, roughly diamondshaped area of connective tissue formed by the thoracic and lumbar parts of the deep fascia. The thoracolumbar fascia is continuous with the transversalis fascia of the anterolateral abdominal wall and it is divided into three layers: anterior, middle and posterior. The intrinsic deep back muscles are enclosed between the posterior and middle layers, while the quadratus lumborum muscles lay between the middle and anterior layers. More profound to the anterior layer runs the psoas major muscle with its psoas fascia.

Muscles of Posterior Abdominal Wall: ■ Three or four muscles are present in the posterior abdominal wall, depending on the individual: psoas major, iliacus, quadratus lumborum and psoas minor muscles. The latter is variable, being present in about 40% of the population.

■ QUADRATUS LAMBORUM: ■ The quadratus lumborum muscle is located laterally in the posterior abdominal wall. It is a thick muscular sheet which is quadrilateral in shape. The muscle is positioned superficially to the psoas major. ■ Attachments: It originates from the iliac crest and iliolumbar ligament. The fibres travel superomedially, inserting onto the transverse processes of L 1 – L 4 and the inferior border of the 12 th rib. ■ Actions: Extension and lateral flexion of the vertebral column. It also fixes the 12 th rib during inspiration, so that the contraction of diaphragm is not wasted. ■ Innervation: Anterior rami of T 12 - L 4 nerves.

■ PSOAS MAJOR: ■ The psoas major is located near the midline of the posterior abdominal wall, immediately lateral to the lumbar vertebrae. ■ Attachments: Originates from the transverse processes and vertebral bodies of T 12 – L 5. It then moves inferiorly and laterally, running deep to the inguinal ligament, and attaching to the lesser trochanter of the femur. ■ Actions: Flexion of the thigh at the hip and lateral flexion of the vertebral column. ■ Innervation: Anterior rami of L 1 – L 3 nerves.

PSOAS MINOR: ■ The psoas minor muscle is only present in 60% of the population. It is located anterior to the psoas major. ■ Attachments: Originates from the vertebral bodies of T 12 and L 1 and attaches to a ridge on the superior ramus of the pubic bone, known as the pectineal line. ■ Actions: Flexion of the vertebral column. ■ Innervation: Anterior rami of the L 1 spinal nerve.

ILIACUS: ■ The iliacus muscle is a fan-shaped muscle that is situated inferiorly on the posterior abdominal wall. It combines with the psoas major to form the iliopsoas – the major flexor of the thigh. ■ Attachments: Originates from surface of the iliac fossa and anterior inferior iliac spine. Its fibers combine with the tendon of the psoas major, inserting into the lesser trochanter of the femur. ■ Actions: Flexion of the thigh at the hip joint. ■ Innervation: Femoral nerve (L 2 – L 4). Diaphragm ■ The posterior aspect of the diaphragm is considered to be part of the posterior abdominal wall

NEUROVASCULATURE: ■ Branches derived from the descending aorta supply the posterior abdominal wall. These include paired subcostal arteries, which run right below the 12 th ribs and four pairs of lumbar arteries arising from the back of the aorta. A variable fifth pair of lumbar arteries arising from the median sacral artery can be present. Subcostal and lumbar arteries anastomose with one another and with the superior epigastric, lower intercostal and iliolumbar arteries, supplying the posterior abdominal wall and related structures. ■ Venous drainage of the posterior abdominal wall is carried out mainly by the lumbar veins which empty into the inferior vena cava. ■ There is a plethora of nerves and vessels coursing through the abdominal cavity which are closely related to the posterior abdominal wall. These include: abdominal aorta and its major branches, inferior vena cava with its tributaries, lumbar plexus, sympathetic ganglion chain and sympathetic plexus. The lumbar plexus is formed by the divisions from L 1 – L 4 spinal nerves with contribution of T 12, which merge on the anterior surface of psoas major.