Surgical-ANATOMY OF ANTERIOR

ABDOMINAL WALL

Prof. M.C.BansalMBBS,MS,MICOG,FICOG

Professor OBGYEx-Principal & Controller

Jhalawar Medical College & HospitalMahatma Gandhi Medical College, Jaipur.

P&C

INTRODUCTION• The anterior abdominal wall extends from the costal

margins and xiphoid process superiorly to the iliac crests, pubis and pubic symphysis inferiorly.

• It overlaps and is connected to both the posterior abdominal wall and paravertebral tissues.

• It forms a continuous but flexible sheet of tissue across the anterior and lateral aspects of the abdomen.

• The anterior abdominal wall is made up of skin, superficial fascia, deep fascia, muscles, extraperitoneal fascia, and parietal peritoneum.

SKELETAL LANDMARKS• The superior boundary:

• In the midline superiorly lies the xiphoid process. From this point, the costal margins extend to either side from the seventh costal cartilage to the tip of the twelth rib

• The lowest part of the costal margin lies in the midaxillary line and is formed by the inferior margin of the tenth costal cartilage.

• The inferior boundary :

• In order, by the iliac crest, which descends from the tubercle of the iliac crest to the anterior superior iliac spine; the inguinal ligament, which runs downwards and forwards to the pubic tubercle; and the pubic crest, which runs from the pubic tubercle laterally to the pubic symphysis in the midline.

• The postero lateral boundary is defined by the mid axillary line.

LANDMARKS

1. Xiphoid process. 2. Costal margin. 3. Tip of the ninth costal cartilage. 4. Tendinous intersections. 5. Umbilicus. 6. Iliac crest. 7. Anterior superior iliac spine. 8. Linea semilunaris. 9. Linea alba. 10. Inguinal ligament. 11. Pubic tubercule. 12. Pubic crest. 13. Pubic symphysis.

ABDOMINAL PLANES

•Vertical planes :

• The midline, which passes through the xiphisternal process and the pubic symphysis

• There are two paramedian planes which are projected from the midclavicular line (also sometimes called the lateral or the mammary line). • This line passes through the midpoint of the clavicle, just

lateral to the tip of the ninth costal cartilage, and passes through a point mid way between the anterior superior iliac spine and the symphysis pubis.

•Horizontal planes :

• The transpyloric plane lies midway between the suprasternal notch of the manubrium and the upper border of the pubic symphysis.• It usually lies at the level of the body of the first lumbar vertebra

.

• The hilum of both kidneys, the origin of the superior mesenteric artery, the termination of the spinal cord, the neck, adjacent body and head of the pancreas, and the confluence of the superior mesenteric and splenic veins as they form the hepatic portal vein may all lie in this plane.

• The transtubercular plane joins the tubercles of the iliac crests and usually lies at the level of the body of the fifth lumbar vertebra near its upper border. • It indicates, the confluence of the common iliac veins and marks

the origin of the inferior vena cava.

• The xiphisternal plane runs horizontally through the xiphoid processes at the level of the ninth thoracic vertebra. It demarcates the level of the cardiac plateau on the central part of the upper border of the liver.

• The subcostal plane is a line joining the lowest point of the costal margins, formed by the tenth costal cartilage on each side. It usually lies at the level of the body of the third lumbar vertebra, the origin of the inferior mesenteric artery from the aorta, and the third part of the duodenum, although this varies with posture.

• The supracristal plane joins the highest point of the iliac crest on each side. It usually lies at the level of the body of the fourth lumbar vertebra, and marks the level of bifurcation of the abdominal aorta. On the posterior abdominal surface, it is a common level for the identification of the fourth lumbar vertebra, and is used to perform lumbar puncture at the L4–5 or L5–S1 intervertebral level, which is safely below the termination of the spinal cord.

• The interspinous plane joins the centres of the anterior superior spines of the iliac crests.

• The plane of the pubic crest lies at the level of the inferior end of the sacrum or part of the coccyx.

Abdominal regions• The abdomen can be divided into nine arbitrary regions by

the subcostal and transtubercular planes and the two midclavicular planes projected onto the surface of the body

• The nine regions thus formed are:

• epigastrium;

• right and left hypochondrium;

• central or umbilical;

• right and left lumbar;

• hypogastrium or suprapubic;

• right and left iliac fossa.

SKIN OF ANTERIOR ABDOMINAL WALL

• Loosely attached to the underlying structures except at the umbilicus, where it is tethered to the scar tissue.

• The natural lines of cleavage in the skin are constant and run downward and forward almost horizontally around the trunk.

• The umbilicus is a scar representing the site of attachment of the umbilical cord in the fetus; it is situated in the linea alba and is a common site of infections.

• If possible, all surgical incisions should be made in the lines of cleavage where the bundles of collagen fibers in the dermis run in parallel rows. An incision along a cleavage line will heal as a narrow scar, whereas one that crosses the lines will heal as wide or heaped-up scars

Variations of abdominal skin

LINEA NIGRA STRIA GRAVIDARUM

INCISIONS OF ABDOMINAL SKIN IN GYNAECOLOGY

VERTICALINCISION

PFANNENSTIELINCISION

LOWER MIDLINE VERTICAL INCISIONSUBUMBILICAL INCISION

FOR LAPAROSCOPY

Superficial Fascia• The superficial fascia is divided into

a superficial fatty layer (fascia of Camper) and a deep membranous layer (Scarpa's fascia) .

• The fatty layer is continuous with the superficial fat over the rest of the body and may be extremely thick (3 in. [8 cm] or more in obese patients).

• The membranous layer is thin and fades out laterally and above where it becomes continuous with the superficial fascia of the back and the thorax, respectively.

SUPERFICIAL

FASCIA

FATTY LAYER

MEMBRANOUS LAYER

• Inferiorly, the membranous layer passes onto the front of the thigh, where it fuses with the deep fascia one fingerbreadth below the inguinal ligament.

• In the midline inferiorly, the membranous layer of fascia is not attached to the pubis but forms a tubular sheath for the penis (or clitoris).

• Below in the perineum, it enters the wall of the scrotum (or labia majora). From there it passes to be attached on each side to the margins of the pubic arch; it is here referred to as Colles' fascia.

• Posteriorly, it fuses with the perineal body and the posterior margin of the perineal membrane

Muscles of the Anterior Abdominal Wall

• The muscles of the anterior abdominal wall consist of three broad thin sheets that are aponeurotic in front; from exterior to interior they are :• The external oblique• The internal oblique• The transversus abdominis

• On either side of the midline anteriorly is, in addition, a wide vertical muscle, the rectus abdominis .

• As the aponeuroses of the three sheets pass forward, they enclose the rectus abdominis to form the rectus sheath.

• The lower part of the rectus sheath contains a small muscle called the pyramidalis.

External oblique • External oblique is the largest and the most superficial of the three

lateral abdominal muscles .• Origin : the external surfaces and inferior borders of the lower eight

ribs.• Insertion : Xiphoid process, linea alba, pubic crest, pubic tubercle,

iliac crest.• Vascular supply : Branches from the lower posterior intercostal and

subcostal arteries, the superior and inferior epigastric arteries, the superficial and deep circumflex arteries and the posterior lumbar arteries.

• Innervation : The terminal branches of the lower five intercostal nerves and the subcostal nerve from the ventral rami of the lower six thoracic spinal nerves.

• Actions : External oblique contributes to the maintenance of abdominal tone, increasing intra-abdominal pressure and lateral flexion of the trunk against resistance.

Inguinal canal

• A triangular-shaped defect in the external oblique aponeurosis lies immediately above and medial to the pubic tubercle. This is known as the superficial inguinal ring.

• Between the anterior superior iliac spine and the pubic tubercle, the lower border of the aponeurosis is folded backward on itself, forming the inguinal ligament .

Inguinal ligament

Internal Oblique• Broad, thin, muscular sheet that lies deep to the external

oblique.

• Most of its fibers run at right angles to those of the external oblique.

• Origin : It arises from the lumbar fascia, the anterior two thirds of the iliac crest, and the lateral two thirds of the inguinal ligament.

• The muscle fibers radiate as they pass upward and forward.

• Insertion : The muscle is inserted into the lower borders of the lower three ribs and their costal cartilages, the xiphoid process, the linea alba, and the symphysis pubis.

• Vascular supply : Branches from the lower posterior intercostal and subcostal arteries, the superior and inferior epigastric arteries, the superficial and deep circumflex arteries and the posterior lumbar arteries.

• Innervation : The terminal branches of the lower five intercostal nerves and the subcostal nerve from the ventral rami of the lower six thoracic spinal nerves, in addition to a small contribution from the iliohypogastric and ilioinguinal nerves from the ventral ramus of the first lumbar spinal nerve.

• Actions : Internal oblique contributes to the maintenance of abdominal tone, increasing intra-abdominal pressure, and enables lateral flexion of the trunk against resistance.

Lower fibres of internal oblique are joined by similar fibers

from the transversus abdominis to form the conjoint tendon .

• As the spermatic cord (or round ligament of the uterus) passes under the lower border of the internal oblique, it carries with it some of the muscle fibers that are called the cremaster muscle .

Transversus • The deepest of the lateral abdominal muscles• Its fibers run horizontally forward .• Origin : It arises from the deep surface of the lower six costal

cartilages (interdigitating with the diaphragm), the lumbar fascia, the anterior two thirds of inner lip of the iliac crest, and the lateral third of the inguinal ligament. • Insertion : It is inserted into the xiphoid process, the linea alba,

and the symphysis pubis.

• Note : the posterior border of the external oblique muscle is free, whereas the posterior borders of the internal oblique and transversus muscles are attached to the lumbar vertebrae by the lumbar fascia.

• Vascular supply : Branches from the lower posterior intercostal and subcostal arteries, the superior and inferior epigastric arteries, the superficial and deep circumflex arteries and the posterior lumbar arteries.

• Innervation : The terminal branches of the lower five intercostal nerves, the subcostal nerve and the iliohypogastric and ilioinguinal nerves.

• Actions : Transversus abdominis contributes mainly to the maintenance of abdominal tone and increasing intra-abdominal pressure.

Conjoint tendon • The conjoint tendon is formed from the lower fibres of internal

oblique and the lower part of the aponeurosis of transversus abdominis.

• It is attached to the pubic crest and pectineal line.

• It descends behind the superficial inguinal ring and acts to strengthen the medial portion of the posterior wall of the inguinal canal.

• The attachment to the pectineal line is frequently absent.

• Medially, the upper fibres of the tendon fuse with the anterior wall of the rectus sheath, and laterally some fibres may blend with the interfoveolar ligament.

Fascia Transversalis

• The fascia transversalis is a thin layer of fascia that lines the transversus abdominis muscle and is continuous with a similar layer lining the diaphragm and the iliacus muscle .

• The femoral sheath for the femoral vessels in the lower limbs is formed from the fascia transversalis and the fascia iliaca that covers the iliacus muscle .

RECTUS ABDOMINIS• 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.

• Origin : The rectus abdominis muscle arises by two heads, from the front of the symphysis pubis and from the pubic crest.

• Insertion : It is inserted into the fifth, sixth, and seventh costal cartilages and the xiphoid process .

• 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: one at the level of the xiphoid process, one at the level of the umbilicus, and one halfway between these two. These intersections are strongly attached to the anterior wall of the rectus sheath.

• The rectus abdominis is enclosed between the aponeuroses of the external oblique, internal oblique, and transversus, which form the rectus sheath.

• Vascular supply : Rectus abdominis is supplied principally by the superior and inferior epigastric arteries

• Small terminal branches from the lower three posterior intercostal arteries, the subcostal artery, the posterior lumbar arteries and the deep circumflex artery may provide some contribution, particularly to the lateral edges and the lower attachments, and they form small anastomoses with the lateral branches of the epigastric arteries.

• Innervation : Rectus abdominis is innervated by the terminal branches of the ventral rami of the lower six or seven thoracic spinal nerves via the lower intercostal and subcostal nerves.

• Actions : The recti contribute to the flexion of the trunk. They also contribute to the maintenance of abdominal wall tone required during straining.

• Rectus abdominis provides an excellent myocutaneous flap, either pedicled or free, because of the excellent vascularity provided by the epigastric vessels and because the muscle belly is separated from surrounding tissue within the rectus sheath.

Rectus sheath• The rectus sheath is a long fibrous sheath that encloses the

rectus abdominis muscle and pyramidalis muscle (if present) .

• The rectus sheath is formed from decussating fibres from all three lateral abdominal muscles. External oblique, internal oblique and transversus abdominis .

• Description the rectus sheath is considered at three levels :

• Above the costal margin, the anterior wall is formed by the aponeurosis of the external oblique. The posterior wall is formed by the thoracic wall—that is, the fifth, sixth, and seventh costal cartilages and the intercostal spaces.

• Between the costal margin and the level of the anterior superior iliac spine, the aponeurosis of the internal oblique splits to enclose the rectus muscle; the external oblique aponeurosis is directed in front of the muscle, and the transversus aponeurosis is directed behind the muscle.

• Between the level of the anterosuperior iliac spine and the pubis, the aponeuroses of all three muscles form the anterior wall. The posterior wall is absent, and the rectus muscle lies in contact with the fascia transversalis.

Transverse sections of the rectus sheath seen at three levels. A. Above the costal margin.B. Between the costal margin and the level of the anterior superior iliac spine.C. Below the level of the anterior superior iliac spine and above the pubis

Rectus sheath in anterior view and in sagittal section

• Where the aponeuroses forming the posterior wall pass in front of the rectus at the level of the anterior superior iliac spine, the posterior wall has a free, curved lower border called the arcuate line . At this site, the inferior epigastric vessels enter the rectus sheath and pass upward to anastomose with the superior epigastric vessels.

• The rectus sheath is separated from its fellow on the opposite side by a fibrous band called the linea alba.

• Hematoma of the rectus sheath is uncommon but important. It occurs most often on the right side below the level of the umbilicus.

• The source of the bleeding is the inferior epigastric vein or, more rarely, the inferior epigastric artery. These vessels may be stretched during a severe bout of coughing or in the later months of pregnancy, which may predispose to the condition.

• The cause is usually blunt trauma to the abdominal wall, such as a fall or a kick.

• The symptoms that follow the trauma include midline abdominal pain. An acutely tender mass confined to one rectus sheath is diagnostic.

DIVARICATION OF THE RECTI • Thinning and widening of the upper linea alba may occur,

most commonly as a result of obesity or chronic straining. This process disrupts the arrangement of the fibres of the bilaminar aponeurosis.

• Contraction of the anterolateral abdominal muscles fails to be transmitted across the midline through the linea alba and increased intra-abdominal pressure causes the abdominal viscera to protrude beneath the thinned tissue as a broad midline bulge.

• The recti become widely separated or divaricated. There is not a true herniation.

PYRAMIDALIS MUSCLE

Pyramidalis • Pyramidalis is a triangular muscle that lies in front of the

lower part of rectus abdominis within the rectus sheath.

• Origin : It is attached by tendinous fibres to the front of the pubis and to the ligamentous fibres in front of the symphysis.

• Insertion : The muscle attached medially to the linea alba. This attachment usually lies midway between the umbilicus and pubis, but may occur higher.

• The muscle varies considerably in size. It may be larger on one side than on the other, absent on one or both sides, or even doubled.

• Vascular supply : Pyramidalis is supplied by branches of the inferior epigastric artery, with some contribution from the deep circumflex iliac artery. A small artery frequently crosses the midline posterior to the belly of the muscle to anastomose with the contralateral vessel. This may cause troublesome bleeding during surgical incisions that run down as far as the lower rectus sheath above the symphysis pubis.

• Innervation: the terminal branches of the subcostal nerve, which is the ventral ramus of the 12th thoracic spinal nerve.

• Actions : Pyramidalis contributes to tensing the lower linea alba, but is of doubtful physiological significance.

Linea alba • The linea alba is a tendinous raphe extending from the xiphoid

process to the symphysis pubis and pubic crest.

• It lies between the two recti and is formed by the interlacing and decussating aponeurotic fibres of external oblique, internal oblique and transversus abdominis.

• Below the umbilicus, the linea alba narrows progressively as the rectus muscles lie closer together.

• Above the umbilicus, the linea alba is correspondingly broader.

• The linea alba has two attachments at its lower end: its superficial fibres are attached to the symphysis pubis, and its deeper fibres form a triangular lamella that is attached behind rectus abdominis to the posterior surface of the pubic crest on each side. This posterior attachment of linea alba is named the ‘adminiculum lineae albae'.

• The linea alba is crossed from side to side by a few minute vessels.

• It is visible only in the lean and muscular, as a slight groove in the anterior abdominal wall.

Umbiicus

• A fibrous cicatrix, the umbilicus, lies a little below the midpoint of the linea alba, and is covered by an adherent area of skin. • In the fetus, the umbilicus transmits the umbilical vessels,

urachus and, up to the third month, the vitelline or yolk stalk. • It closes a few days after birth, but the vestiges of the vessels

and urachus remain attached to its deep surface. • The remnant of the fetal left umbilical vein forms the round

ligamentum of the liver.• The obliterated umbilical arteries form the medial umbilical

ligaments, enclosed in peritoneal folds of the same name. • The partially obliterated remains of the urachus persist as the

median umbilical ligament.

Umbilical hernia • There are three varieties of umbilical hernia:

• In true congenital herniation, a defect is present from birth. This is usually simply the result of failure of closure of the umbilicus after retraction of the umbilical gut loop. Less commonly, the gut loop does not retract and remains, in part, outside the abdominal cavity.

• An infantile umbilical hernia is caused by stretching of the

umbilical scar tissue, associated with increased intra-abdominal pressure.

• An acquired umbilical or paraumbilical hernia actually occurs through small areas of weakness in the linea alba, above or below the umbilical scar.

Deep Fascia (FASCIA OF SCARPA)

• The deep fascia in the anterior abdominal wall is merely a thin layer of connective tissue covering the muscles; it lies immediately deep to the membranous layer of superficial fascia.

• In the female, it is continued into the labia majora and from there to the fascia of Colles.

Extraperitoneal Fat

• 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.

SKIN

EXTRA PERITONEAL FAT

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 .

Action of the muscles of the anterior and lateral abdominal walls. Arrows indicate line of pull of different

muscles

NERVE SUPPLY• The nerves of the anterior abdominal wall are:

• The anterior rami of the lower six thoracic nerves – include the lower five intercostal nerves and the subcostal nerves • The first lumbar nerve - represented by the

iliohypogastric and ilioinguinal nerves, branches of the lumbar plexus.

• They pass forward in the interval between the internal oblique and the transversus muscles.

• They supply the skin of the anterior abdominal wall, the muscles, and the parietal peritoneum.

SUB COSTAL NERVE

ILIOHYPOGASTRIC N.

ILIOINGUINAL N.

ANTERIOR SUPERIOR ILIAC SPINE

DERMATOMES

The dermatome of

• T7 : in the epigastrium over the xiphoid process, • T10 : umbilicus• L1 : just above the

inguinal ligament and the symphysis pubis.

XIPHOID PROCESS

UMBILICUS

PUBIC SYMPHYSIS

Anterior Abdominal Nerve Block

• Area of Anesthesia : The area of anesthesia is the skin of the anterior abdominal wall.

• The nerves of the anterior and lateral abdominal walls are the anterior rami of the 7th through the 12th thoracic nerves and the first lumbar nerve (ilioinguinal and iliohypogastric nerves).

• Indications : An anterior abdominal nerve block is performed to repair lacerations of the anterior abdominal wall.

BLOOD SUPPLY• 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, the lumbar, and the deep circumflex iliac arteries • the skin in the inguinal region

is supplied by the superficial epigastric, the superficial circumflex iliac, and the superficial external pudendal arteries, branches of the femoral artery.

ARTERIES :• The superior epigastric artery, one of the terminal branches of the

internal thoracic artery, enters the upper part of the rectus sheath between the sternal and costal origins of the diaphragm.

• 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 runs upward and medially along the medial side of the deep inguinal ring . It pierces the fascia transversalis to enter the rectus sheath anterior to the arcuate line .

• It ascends behind the rectus muscle, supplying the lower central part of the anterior abdominal wall, and anastomoses with the superior epigastric artery.

• Gives rise to the cremasteric artery , which accompanies the spermatic cord.

• The deep circumflex iliac artery is a branch of the external iliac artery just above the inguinal ligament.• It runs upward and laterally toward the anterosuperior

iliac spine and then continues along the iliac crest.• 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 wall

• Superficial epigastric arteriesArise from the femoral artery and run superiorly toward the umbilicus over the inguinal ligament.• Anastomose with branches of the inferior epigastric artery.

• Superficial circumflex iliac arteryArises from the femoral artery and runs laterally upward, parallel to the inguinal ligament.• Anastomoses with the deep circumflex iliac and lateral

femoral circumflex arteries.

• Superficial (external) pudendal arteriesArise from the femoral artery, pierce the cribriform fascia, and run medially to supply the skin above

VEINS

• 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.

• A few small veins, the paraumbilical veins, connect the network through the umbilicus and along the ligamentum teres to the portal vein. This forms an important portal-systemic venous anastomosis.

• 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.

• The posterior intercostal veins drain into the azygos veins, and the lumbar veins drain into the inferior vena cava.

Portal Vein Obstruction• In cases of portal vein obstruction , the superficial veins around

the umbilicus and the paraumbilical veins become grossly distended.

• The distended subcutaneous veins radiate out from the umbilicus, producing in severe cases the clinical picture referred to as caput medusae.

Caval Obstruction• If the superior or inferior vena cava is obstructed, the venous

blood causes distention of the veins running from the anterior chest wall to the thigh.

• The lateral thoracic vein anastomoses with the superficial epigastric vein, a tributary of the great saphenous vein of the leg.

• In these circumstances, a tortuous varicose vein may extend from the axilla to the lower abdomen

Caput medusae

Lymphatic Drainage• Lymphatics in the region above the

umbilicusDrain 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 umbilicusDrain into the superficial inguinal nodes. Their efferent vessels primarily enter the external iliac nodes and, ultimately, the lumbar (aortic) nodes.

• The deep lymph vessels follow the arteries and drain into the internal thoracic, external iliac, posterior mediastinal, and para-aortic (lumbar) nodes.

Abdominothoracic Rhythm• The abdominal muscles contract and relax with respiration,

and the abdominal wall conforms to the volume of the abdominal viscera.

• There is an abdominothoracic rhythm. Normally, during inspiration, when the sternum moves forward and the chest expands, the anterior abdominal wall also moves forward.

• If, when the chest expands, the anterior abdominal wall remains stationary or contracts inward, it is highly probable that the parietal peritoneum is inflamed and has caused a reflex contraction of the abdominal muscles.

Visceroptosis• The shape of the anterior abdominal wall depends on the

tone of its muscles.

• A middle-aged woman with poor abdominal muscles who has had multiple pregnancies is often incapable of supporting her abdominal viscera.

• The lower part of the anterior abdominal wall protrudes forward, a condition known as visceroptosis.

• This should not be confused with an abdominal tumor such as an ovarian cyst or with the excessive accumulation of fat in the fatty layer of the superficial fascia.

Inguinal Canal• The inguinal canal is an oblique passage through the lower part

of the anterior abdominal wall. • In the males, it allows structures to pass to and from the testis

to the abdomen. • In females it allows the round ligament of the uterus to pass

from the uterus to the labium majus.• The canal is about 1.5 in. (4 cm) long in the adult and extends

from the deep inguinal ring , downward and medially to the superficial inguinal ring.• It lies parallel to and immediately above the inguinal ligament. • In the newborn child, the deep ring lies almost directly

posterior to the superficial ring so that the canal is considerably shorter at this age. • Later, as the result of growth, the deep ring moves laterally.

• The deep inguinal ring is an oval opening in the fascia transversalis, lies about 0.5 in. (1.3 cm) above the inguinal ligament midway between the anterior superior iliac spine and the symphysis pubis.

• Related to it medially are the inferior epigastric vessels.

• The margins of the ring give attachment to the internal spermatic fascia (or the internal covering of the round ligament of the uterus).

• The superficial inguinal ring is a triangular-shaped defect in the aponeurosis of the external oblique muscle and lies immediately above and medial to the pubic tubercle.

• The margins of the ring, sometimes called the crura, give attachment to the external spermatic fascia.

Parts of external and internal oblique muscles removed

Walls of the Inguinal Canal

• Anterior wall: Skin,Superficial fascia External oblique aponeurosis and fleshy fibre of Internal oblique laterally. This wall is therefore strongest where it lies opposite the weakest part of the posterior wall, namely, the deep inguinal ring.

• Posterior wall: Conjoint tendon medially, fascia transversalis laterally. This wall is therefore strongest where it lies opposite the weakest part of the anterior wall, namely, the superficial inguinal ring.

• Roof or superior wall: Arching lowest fibers of the internal oblique and transversus abdominis muscles.

• Floor or inferior wall: Upturned lower edge of the inguinal ligament and, at its medial end, the lacunar ligament

Inguinal canal showing the arrangement of the external oblique muscle (A), the internal oblique muscle (B), the transversus muscle (C), and the fascia transversalis (D)

Deep structures of the inguinal canal. The aponeurosis of external oblique has been

removed

Function of the Inguinal Canal• The inguinal canal allows structures of the spermatic

cord to pass to and from the testis to the abdomen in the male. (Normal spermatogenesis takes place only if the testis leaves the abdominal cavity to enter a cooler environment in the scrotum.)

• In the female, the smaller canal permits the passage of the round ligament of the uterus from the uterus to the labium majus.

Mechanics of the Inguinal Canal• The inguinal canal in the lower part of the anterior

abdominal wall is a site of potential weakness in both sexes.

• Except in the newborn infant, the canal is an oblique passage with the weakest areas, namely, the superficial and deep rings, lying some distance apart.

• The anterior wall of the canal is reinforced by the fibers of the internal oblique muscle immediately in front of the deep ring.

• The posterior wall of the canal is reinforced by the strong conjoint tendon immediately behind the superficial ring.

• On coughing and straining, as in micturition, defecation, and parturition, the arching lowest fibers of the internal oblique and transversus abdominis muscles contract, flattening out the arched roof so that it is lowered toward the floor. The roof may actually compress the contents of the canal against the floor so that the canal is virtually closed.

• When great straining efforts may be necessary, as in defecation and parturition, the person naturally tends to assume the squatting position; the hip joints are flexed, and the anterior surfaces of the thighs are brought up against the anterior abdominal wall. By this means, the lower part of the anterior abdominal wall is protected by the thighs

Action of the muscles on the inguinal canal. the canal is obliterated when the muscles contract�