17 Anterior Abdominal Wall

THE ABDOMEN

Anterior Abdominal Wall 

Learning Objectives

By the end of the course students will be able to:

1. Identify important bony landmarks  that are used to define regions of the anterior abdominal wall
2. Define the innervation, blood supply, and lymphatic drainage of the anterior abdominal wall.
3. Describe the formation of the rectus sheath and the layers of the anterior abdominal wall.
4. Describe the anatomy of the inguinal canal.
5. Describe the anatomy of the various kinds of abdominal wall hernias (indirect and direct inguinal, umbilical, lumbar).
6. Define the layers of the anterior abdominal wall, their contributions to the coverings of the spermatic cord and round ligament, and the origin of these coverings as related to the descent of the gonads.
7. Identify the anatomical landmarks on the deep surface of the anterior abdominal wall and their relationships to the types of inguinal hernias.
8. Describe the blood supply, venous drainage and innervation to the testis

Reference: Moore, Clinically Oriented Anatomy, chapter 2.

Particularly relevant Blue Boxes from Moore:

●Palpation of the Anterolateral Abdominal Wall, p. 197

●Injury to nerves of the Anterolateral Abdominal Wall, p. 198

●Abdominal Surgical Incisions, p. 198

●Inguinal Hernias, p. 212

●Cremasteric Reflex, p. 212

●Cancer of the Testis and Scrotum p. 215

To access the Netter Presenter Database click here

Grant’s Dissector, 15th Edition, pp 89 – 99

To access Gray’s Photographic Dissector section on the Anterior Abdominal Wall click here

To access the Primal Pictures software click here 

Check out the Primal Pictures model of the Abdominal Wall
THE ABDOMEN – INTRODUCTION

The abdomen is the largest cavity in the body. It is oval shaped, the extremities of the oval being directed upward and downward. The upper boundary is formed by the diaphragm which extends as a dome over the abdomen, so that the cavity extends high into the bony thorax, reaching on the right side, in the mammary line, to the upper border of the fifth rib; on the left side it falls below this level by about 2.5 cm. The lower boundary is formed by the structures which attach to the inner surface of the bony pelvis, principally the Levator ani and Coccygeus on either side. These muscles are sometimes termed the diaphragm of the pelvis. The cavity is wider above than below, and measures more in the vertical than in the transverse diameter. In order to facilitate description, it is artificially divided into two parts: an upper and larger part, the abdomen proper; and a lower and smaller part, the pelvis. These two cavities are not separated from each other, but the limit between them is marked by the superior aperture of the lesser pelvis.

Boundaries.—It is bounded in front and at the sides by the abdominal muscles and the Iliacus muscles; behind by the vertebral column and the psoas and quadratus lumborum muscles; above by the diaphragm; below by the plane of the superior aperture of the lesser pelvis. The muscles forming the boundaries of the cavity are lined upon their inner surfaces by a layer of fascia.

The abdomen contains the greater part of the digestive tract; some of the accessory organs to digestion, i.e., the liver and pancreas; the spleen, the kidneys, and the suprarenal glands. Most of these structures, as well as the wall of the cavity in which they are contained, are more or less covered by an extensive and complicated serous membrane, the peritoneum.

The Apertures in the Walls of the Abdomen.—The apertures in the walls of the abdomen, for the transmission of structures to or from it, are, in front, the umbilical (in the fetus), for the transmission of the umbilical vessels, the allantois, and vitelline duct; above, the vena caval opening, for the transmission of the inferior vena cava, the aortic hiatus, for the passage of the aorta, azygos vein, and thoracic duct, and the esophageal hiatus, for the esophagus and vagi. Below, there are two apertures on either side: one for the passage of the femoral vessels and femoral nerve, and the other for the transmission of the spermatic cord in the male, and the round ligament of the uterus in the female.

   Several important landmarks of the abdomen are palpable on the anterior abdominal surface. The landmarks are represented in Netter 242.

Abdominal Regions (Netter 244; Moore 183-184)

The abdomen may be divided into quadrants using a 1) vertical line through the xiphoid process, umbilicus, and pubic symphysis and 2) a horizontal line through the umbilicus. Thus, there are upper right and left quadrants and lower right and left quadrants.

Internal Structures – Organs and Structures Palpable Through the Abdominal Wall

Theh aorta, about 2.5 cm wide, can be outlined both above and below te umbilicus from its pulse. In thin individuals, the aortic pulse may be visible. An abdominal aortic aneurysm can be discerned on palpation.

The liver usually is palpable in the right upper quadrant or right hypochondriac region, depending on a person’s build. A palpable liver may or may not indicate the presence of a pathologic condition. In persons with hepatomegaly, this organ may extend to the iliac crest.

The gallbladder is palpable if it is enlarged or contains gallstones. It may be palpated in the right hypochondriac region at the junction of the linea semilunaris andn the costal margin.

The stomach is palpable only if engorged.

The spleen normally is not palpable. When it is enlarged, however, it may be felt in the left hypochondriac region and sometimes in the lower quadrants.

The lower poles of the kidneys usually can be palpated in the lateral regions.

The ascending colon usually is palpable onlyy if it is distended by gas or chyme. The descending colon and sigmoid colon, containing solidifying feces, usually are palpable in the lower left quadrant.

The urinary bladder, when distended, is palpable in the pubic (hypogastric) region. The uterus can be palpated bimanually in the pubic region with the cervix being supported by the fingers of one hand. The ovaries, if enlarged, may be palpated bimanually in the inguinal regions.

Fascias of the Anterior Abdominal Wall (Netter 245; Moore 186-187)

Two fascial layers are encountered beneath the skin of the anterior abdominal wall. The outer fatty layer, CAMPER’S FASCIA, may be several centimeters thick, whereas the inner membranous layer, SCARPA’S FASCIA, does not vary in thickness since it contains little or no fat.

Deep to Scarpa’s fascia, there are three flat muscles, external oblique, internal oblique and transverses abdominus, which form the bulk of the anterior abdominal wall.   Deep to the muscles is TRANSVERSALIS FASCIA,   which lines the abdominal cavity and the inner-  most lining of the abdominal cavity is the PERITONEUM (not shown on the diagram.) Between peritoneum and transversalis fascia is a small layer of extra- peritoneal connective tissue (fascia). Camper’s fascia continues from the abdomen onto the fatty layer of the thigh; Scarpa’s fascia is attached to the iliac crest and the fascia lata approximately 2-3 cm. inferior to the inguinal ligament. Consequently, there is free passage into the uppermost thigh deep to Scarpa’s fascia). In the area of the pubis, Scarpa’s fascia passes into the scrotum to become Colle’s Fascia.

As Camper’s fascia passes into the scrotum, it loses its fat and gains smooth muscle fibers. In the scrotum, this layer is called the TUNICA DARTOS (or Dartos fascia). The tunica dartos is responsible for the wrinkled appearance of the skin of the scrotum when the testes are drawn up toward the abdominal wall (response to cold, sexual excitation).

Over the pubis, Scarpa’s fascia contributes fibers to the suspensory ligament of the penis, the fundiform ligament. The fundiform ligament lies posterior to Scarpa’s fascia and anterior to the aponeurosis of the external oblique muscle.

MUSCLES OF THE ANTERIOR ABDOMINAL WALL (Netter 245, 246, 247; Moore 187-193)

Linea Alba

   The linea alba is a midline tendinous band which runs from the xyphoid process to the pubis. The aponeuroses of the three flat abdominal muscles contribute to its formation. In the adult, the umbilicus is a fibrous scar in the linea alba. The umbilicus represents the point of fetal attachment to the placenta via the umbilical cord.

The External Abdominal Oblique Muscle (Netter 245, 253)

The SPERMATIC CORD (Netter 245) passes to the scrotum through the superficial inguinal ring. As it passes under the external oblique and through the ring, the spermatic cord carries with it some of the fibers of the external oblique muscle. These fibers become the EXTERNAL SPERMATIC FASCIA of the spermatic cord.

The INGUINAL LIGAMENT passes from the anterior superior iliac spine to the pubic tubercle. It is formed by the aponeurotic fibers of the external oblique rolling under the lower border of the aponeurosis. Medially the inguinal ligament forms the floor for inguinal canal.

The Internal Abdominal Oblique Muscle (Netter 246)

 At the pubis, the medial fibers of the internal oblique aponeurosis join the underlying fibers of the transversus abdominis aponeurosis. Together, these fibers form the CONJOINT TENDON or FALX INGUINALIS.

The lower border of the internal oblique gives origin to the CREMASTER MUSCLE. The cremaster muscle arises from the internal oblique at approximately the center of the inguinal canal; it inserts into the pubis after forming a series of loops along the spermatic cord. This layer forms the middle fascial layer of the spermatic cord, the CREMASTER FASCIA. Contraction of the cremaster muscle raises the testis superiorly toward the superficial inguinal ring. A reflex action, the cremaster reflex, occurs when the superior, medial side of the thigh is stroked. Sensory afferent is ilioinguinal nerve and motor efferent is genitofemoral nerve to cremaster.

The Transversus Abdominis Muscle (Netter 247)

The transversus abdominis takes origin from the lateral one-third of the inguinal ligament, the anterior 3/4 of the iliac crest, the thoraco-lumbar fascia, and from the inner surfaces and cartilages of ribs 5-12. The muscle terminates on an aponeurosis which fuses with the aponeurosis of the internal oblique.

The aponeurosis of the transversus splits to form the ARCUATE LINE. The rostral portion joins the internal oblique in forming the posterior (dorsal) rectus sheath. The caudal portion passes anterior to the rectus sheath. (This is further explained with the “Sheath of the Rectus Abdominis”.)Innervation of the Three Flat Muscles of the Anterior Abdominal Wall (Moore 193-194)

The anterior abdominal wall muscles are innervated by intercostal nerves 7-12, (Netter 253) the ilio-hypogastric nerve, and the ilioinguinal nerve.

The ILIO-HYPOGASTRIC nerve pierces the transversus in the lumbar region, the internal oblique antero-laterally, and lies posterior to the external oblique.

The ILIO-INGUINAL nerve follows the same course as the ilio-hypogastric nerve, but it exits through the superficial inguinal ring and proceeds into the scrotum.

The GENITO-FEMORAL nerve enters onto the anterior abdominal wall through the deep inguinal ring to supply the cremaster muscle.

The actions of the three flat muscles are to assist in expiration, micturition (urination), defecation, emesis (vomiting), parturition, and support for abdominal contents. These actions occur when these muscles contract.

Contraction of the diaphragm opposes the action of these muscles, i.e., assists in inspiration.

 Rectus Abdominis (Netter 246)

The rectus abdominis takes origin from the pubic crest via two tendons. It is separated along its middle by the linea alba. The rectus abdominis inserts into the cartilages of ribs 5-7 and into the sides of the xyphoid process. Fibrous bands, the tendinous intersections traverse the rectus muscle in three or four places. One tendinous intersection lies at the umbilicus; one lies at the xiphoid process; one lies between the umbilicus and the xyphoid process; a partial or complete tendinous intersection may exist between the umbilicus and pubis. These tendinous intersections are firmly attached to the anterior rectus sheath, but the dorsal rectus sheath lies free of the attachments.

   The rectus abdominis flexes the vertebral column and tenses the abdomen. It is innervated by intercostal nerves 7-12.

 THE RECTUS SHEATH (Netter 248; Moore 192-193)

The rectus sheath is a covering for the rectus abdominis muscle. It is formed by the aponeurosis of the external oblique, the internal oblique, and the transversus abdominis muscles. The three aponeuroses form two layers, an anterior (ventral) layer and a posterior (dorsal) layer, at the lateral border of the rectus abdominis muscle, the LINEA SEMILUNARIS (semi-lunar line).

The aponeurosis of the external oblique remains anterior to the rectus abdominis muscle for its entire course.

The aponeurosis of the internal oblique ABOVE the ARCUATE LINE splits to contribute to both the anterior and posterior layers. The aponeurosis of the internal oblique BELOW the ARCUATE LINE contributes to the anterior layer only.

The aponeurosis of the transversus abdominis contributes to the posterior layer above the ARCUATE LINE, and it contributes to the anterior layer below the ARCUATE LINE.

The aponeuroses of ALL THREE muscles lie anterior to the rectus abdominis muscle inferior to the arcuate line; thus, the rectus sheath is deficient inferior to the arcuate line on its posterior aspect.

Remember that near the pubis the internal oblique and the transversus abdominis have formed the conjoint tendon.

The Transversalis Fascia (Netter 247)

The transversalis fascia lines the entire internal wall of the abdomen. It extends a covering over the diaphragm, the internal surface of the quadratus lumborum muscle, and the psoas muscles. The transversalis fascia is the only internal covering of the rectus abdominis muscle below the arcuate line. The transversalis fascia is the posterior layer of the DEEP INGUINAL RING, and at the deep ring, it becomes the INTERNAL SPERMATIC FASCIA of the spermatic cord.

The Inguinal Region and Inguinal Canal (Netter 247, 249, 256, 257; Moore 202-206)

   The INGUINAL CANAL is a tunnel which runs deep to the arching fibers of the aponeuroses of the three flat abdominal muscles: the external oblique, the internal oblique, and the transversus abdominis. These arches are formed as the muscle fibers pass from their site of origin on the iliac crest to their insertion on the pubis. The inguinal canal runs from the region of the DEEP INGUINAL RING to the SUPERFICIAL INGUINAL RING; it is about 4 cm. long. During development, the testes pass through the inguinal canals to the scrotum.

The INGUINAL LIGAMENT (Netter ) 247)or POUPART’S LIGAMENT passes from the anterior superior iliac spine to the pubic tubercle. Just before its attachment to the pubic tubercle, the inguinal ligament gives rise to fibers that reflect laterally along the pectineal line. The curving portion of this reflected ligament is the LACUNAR LIGAMENT or GIMBERNAT’S LIGAMENT. The portion that attaches along the pectineal line is the PECTINEAL LIGAMENT. or COOPER’S LIGAMENT. All three ligaments are continuous, but they have three separate names depending on their location.

The Spermatic Cord (Netter 255, 256; Moore 206-208)

 The spermatic cord exits from the inguinal canal through the superficial inguinal ring and then passes to the scrotum. The spermatic cord may be palpated as it leaves the superficial inguinal ring and courses toward the scrotum.

The conjoint tendon supports the area of the superficial ring posteriorly, but this is a potential area of weakness as there are only two fused layers of aponeuroses to support the abdominal viscera.

The spermatic cord leaves the abdominal cavity at the deep inguinal ring. It passes inferiorly to the arching fibers of the transversus abdominis to lie deep to the internal oblique. In the deep inguinal ring, transversalis fascia lies deep to the spermatic cord. Again, there is a potential area of weakness in the abdominal wall. Abdominal viscera may gain access to the inguinal canal via the deep inguinal ring opening.

As the spermatic cord passes through the deep inguinal canal, it carries with it some transversalis fascia. This fascial layer surrounds the cord and becomes the internal spermatic fascia of the cord and testes.

When the spermatic cord passes under the arching fibers of the internal oblique, it picks up another covering. There are muscle fibers from the cremaster muscle in this middle fascial layer of the cord, the cremaster fascia. The external spermatic fascia is the contribution of the external oblique to the spermatic cord. This is the final layer received from the muscular abdominal wall.

Summary: If you examine a cross sectional area of the spermatic cord, you will see the following layers:

• external spermatic fascia
• cremasteric muscle and fascia
• genitofemoral nerve
• internal spermatic fascia
• ductus deferens
• lymph vessels
• pampiniform plexus of veins  These veins will become the testicular vein.
• testicular artery

The anterior surface of the spermatic cord is toward the top. During physical examination, the ductus deferens can be felt as a rope-like cord. Surgeons who perform vasectomies can roll the spermatic cord over the pubic bone so that they know exactly where to make their incisions

NOTE: The transversus abdominis muscle does NOT contribute to the layers of the cord and testis

TESTIS (Netter 368; Moore 209)

The testis, the organ which produces sperm and the EPIDIDYMIS, the organ which stores sperm are located in the scrotum. The VAS DEFERENS arises from the tail of the epididymis and conveys sperm from the epididymis toward the exterior of the body.

All of these structures are surrounded by the fascias of the spermatic cord. In addition, immediately surrounding the testis anteriorly and laterally, there is a sack-like structure, the TUNICA VAGINALIS, which is embryologically derived from peritoneum during descent of the testis from abdominal region to the scrotum. It is a double serous membrane, a peritoneal sac that covers the front and sides of the testis and epididymis.

The  PROCESSUS VAGINALIS is a fetal structure that evaginates into the developing scrotum and forms the visceral and parietal layers of the tunical vaginalis. Normally it closes before birth or shortly thereafter and loses its connection with the peritoneal cavity.

At times, the tunica vaginalis may become filled with a clear fluid (hydrocele) or blood (vericocele).

The blood supply to the testis is the testicular artery which arises from the ventral aorta and passes in the cord to the scrotum. This artery is diagramed with the general blood supply to the abdomen.

The GUBERNACULUM TESTIS is the fetal ligament that connects the bottom of the fetal testis to the developing scrotum. It is important in testicular descent and is homologous to the ovarian ligament and round ligament of the uterus.

Clinical Note: The Cremasteric reflex is a drawing up of the testis by contraction of the cremaster muscle when the skin of the upper medial thigh is stroked. The efferent limb of the reflex arc is the genital branch of the genitofemoral nerve; the afferent limb is the ilioinguinal nerve as well as the femoral branch of the genitofemoral nerve.

A hydrocele (Netter 344) is an accululation of fluid in the cavity of the tunica vaginalis  of the testis or along the spermatic cord. It may result from an infection or injury to the testis that causes the layers of the tunica vaginalis to secrete excess serous fluid. A hematocele is an effusion of blood into the cavity of the tunica vaginalis.

A varicocele (Netter 344) occurs when varicose veins in the pampiniform plexus of the spermatic cord appear like a “bag of worms” in the scrotum. It may cause infertility in men because the pampiniform plexus of veins is unable to cool the testes, resulting in a declining sperm count or sterility. Thevaricocele is accompanied by a constant pulling and dragging and is more common on the left side, probably as a result of a malignant tumor of the left kidney which blocks the exit of the left testicular vein. It can be treated surgically by removing the varicose veins.

A vasectomy (Netter 344) is a surgical excision of a portion of the vas deferens through the scrotum. It stops the passage of sperm but neither reduces the amount of ejaculate greatly nor diminishes sexual desire.

Testicular torsion is twisting of the spermatic cord and testis within the scrotum. It results in blockage of blood supply to the testis and produces sudden urgent pain, swelling and reddening of teh scrotum. It may be caused by trauma or a spasm of the cremaster muscle and can be treated by surgery to undo the twist.

Orchitis is inflammation of the testis and is marked by pain, swelling and a feeling of heaviness in the testis. It may be caused by the mumps, gonorrhea, syphilis or tuberculosis.

Testicular cancer develops commonly from the rapidly dividing early stage spermatogenic cells. Tumor also develops from Leydig cells which produce androgen and Sertoli cells which support and nourish germ cells and produce androgen-binding protein and the hormone inhibin. SIgns and symptoms inculde a painless mass or lump, testicular swelling, hardness and a feeling of heaviness or aching in the scrotum or lower abdomen. The cause of testicular cancer is unknown but the major risk factors are cryptorchidism (condition of the undescended testis) and Klinefelter’s syndrome (47, XXY sex chromosome). Metastasis occurs via lymph and blood vessels. It can be treated by surgical removal of the affected testis and spermatic cord (orchiectomy), radiotherapy and chemotherapy.

Internal Surface of the Anterolateral Abdominal Wall (Moore 201-202)

 If one looks at the innermost aspect of the intact abdominal wall from the inside, five ridges (Netter 249) are seen on the abdominal wall within the transversalis fascia covering the rectus abdominis muscle (see next page).

Blood Supply of the Abdominal Wall (251, 252; Moore 195-196)

●The superficial vessels of the abdomen run between Camper’s fascia and Scarpa’s fascia, actually are attached to Scarpa’s fascia. The superficial vessels include the superficial inferior epigastric vessels, the circumflex iliac vessels, and the external pudendal vessels.

●The superficial arteries arise from the femoral artery in close relation to the inguinal ligament. The superficial veins empty into the femoral vein by passing through the saphenous opening.

●The deep vessels include the superior and inferior epigastric vessels, the deep iliac circumflex vessels, and the testicular vessels. The inferior epigastric artery arises from the external iliac. The inferior epigastric vein empties into the femoral vein.

●The cremasteric artery arises from the inferior epigastric artery and supplies the cremaster muscle. The inferior epigastric artery is an important landmark in the identification of types of inguinal hernias.

●The superior epigastric artery arises from the internal thoracic artery. Both the inferior and superior epigastric vessels anastomose on the posterior surface of the rectus abdominis within the rectus sheath.

●The deep circumflex artery arises from the external iliac artery and courses laterally.

The testicular artery arises from the anterior aorta. It travels in the spermatic cord to supply the testis.

 Lymphatic Drainage

Axillary nodes (Netter 181) receive the superficial drainage above the umbilicus.

Inferior to the umbilicus, drainage is to superficial inguinal lymph nodes. Recall that the buttocks, external 1/3 of the anal canal and the scrotum, penis, labia majora, clitoris all drain to superficial inguinal nodes (Netter 261).

NOTE: the lymphatic drainage for the testes is to the para-aortic nodes (remember their embryologic origin.)

The deep lymphatic drainage is to the lateral (para-aortic) lymph nodes. Lymph flows from these nodes to the CYSTERNA CHYLI, the beginning of the THORACIC DUCT.

Because the indirect inguinal hernia traverses the same route as the testes and spermatic cord, it has the same coverings when palpated through the skin.