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Intertuber- cular Plane
Subcostal Plane
Left Lumbar (Lateral)
Right Lumbar (Lateral)
Right Iliac (inguinal)
Left Iliac (inguinal)
Left hypochondriac
Right hypochondriac
Umbilical Region
Epigastrium
Hypogastrium
T L L L L L
Transpyloric Plane
Anatomy of the Abdominal Wall 1
Orhan E. Arslan
Introduction
The abdominal wall encompasses an area of the body bounded superiorly by the xiphoid process and costal arch, and inferiorly by the inguinal ligament, pubic bones and the iliac crest. Visualization, palpation, percussion, and ausculta- tion of the anterolateral abdominal wall may reveal ab- normalities associated with abdominal organs, such as the liver, spleen, stomach, abdominal aorta, pancreas and appendix, as well as thoracic and pelvic organs. Visible or palpable deformities such as swelling and scars, pain and tenderness may reflect disease process- es in the abdominal cavity or elsewhere. Pleural irrita- tion as a result of pleurisy or dislocation of the ribs may result in pain that radiates to the anterior abdomen. Pain from a diseased abdominal organ may refer to the anterolateral abdomen and other parts of the body, e.g., cholecystitis produces pain in the shoulder area as well as the right hypochondriac region. The abdominal wall should be suspected as the source of the pain in indi- viduals who exhibit chronic and unremitting pain with minimal or no relationship to gastrointestinal func- tion, but which shows variation with changes of pos- ture [1]. This is also true when the anterior abdominal wall tenderness is unchanged or exacerbated upon con- traction of the abdominal muscles (positive Carnett’s sign). Abdominal wall pain can be the result of local- ized endometriosis, rectus sheath hematoma, or ab- dominal incision or hernia.
Regions of the Abdominal Wall
To accurately describe the locations of visible abnor- malities, masses, and pain in a typical clinical write-up, the anterolateral abdomen is divided into nine regions by four imaginary planes: two verticals (midclavicular/ midinguinal) and two horizontal (transpyloric/intertu- bercular) planes (Fig. 1.1). The transpyloric plane cor- responds to the midpoint between the umbilicus and xiphoid process, crossing the pylorus of the stomach at
Fig. 1.1. Various regions of the anterior abdominal wall
the lower border of the first lumbar vertebra. The sub- costal plane that passes across the costal margins and the upper border of the third lumbar vertebra may be used instead of the transpyloric plane. The lower hori- zontal plane, designated as the intertubercular line, tra- verses the anterior abdomen at the level of fifth lumbar vertebra, and connects the iliac tubercles on both sides. A second lower horizontal plane, the interspinous plane, may also be used, interconnecting the anterior superior iliac spines on both sides and running across the sacral promontory. Of the nine areas, the centrally placed zone is the umbilical region. This region sur- rounds the umbilicus and usually corresponds to the location of the jejunum, transverse part of the duode- num, terminal ileum, transverse colon, ureter and the greater curvature of the stomach. The epigastrium is the upper middle part of the ante- rior abdomen between the umbilicus below and the cos- tal arches and the xiphoid process above. It contains the stomach, left lobe of the liver, and part of the pancreatic head. The pubic region known as the hypogastrium de-
Chapter 1
fines the zone immediately distal to the umbilical region and contains the ileum and sigmoid colon. The hypo- chondriac regions flank the epigastrium and are occu- pied on the right side by the liver, gallbladder, right colic flexure, descending duodenum, right kidney and supra- renal gland. On the left side these regions contain the spleen, left kidney and suprarenal gland, tail of the pan- creas, left colic flexure, and fundus of the stomach. Most of the hypochondriac and parts of the epigastric regions are protected by the lower ribs. Areas immediately to the right and left of the umbilical region are designated as the right and left lumbar (lateral) regions, containing the ascending and descending colon, respectively. The right and left iliac regions surround the hypogastrium. The right iliac region contains the appendix and cecum, and the left iliac region corresponds to locations of the sigmoid colon and left ureter. A simplified division of the anterolateral abdomen uses two imaginary planes that run through the umbili- cus, one passing horizontally and the other vertically. The four quadrants separated by these planes divide the anterior abdomen into the right and left upper and lower quadrants. In summary, the regions described above help medi- cal practitioners to accurately describe the pathological processes associated with the anterior abdominal wall and to document the findings in the differential diag- nosis. For example, periumbilical and hypogastric pain is felt during the initial stage of appendicitis, while pain in the right iliac region occurs at a later phase in this condition. Pancreatic or esophageal disorders produce pain that projects to the epigastrium.
Layers of the Abdominal Wall
The anterolateral abdominal wall consists, from the outside in, of the skin, superficial fascia, deep fascia, external and internal abdominal oblique, transverse abdominis and associated aponeuroses, rectus abdo- minis and pyramidalis, as well as the transversalis fas- cia.
Skin
The skin is of average thickness, and loosely attaches to the underlying tissue. It exhibits certain surface mark- ings such as the umbilicus, linea alba, linea semiluna- ris, epigastric fossa, and McBurney’s point. The umbilicus, a midline fibrous cicatrix covered by a folded area of skin, is an important anatomical land- mark in the anterior abdomen that marks the original attachment of the fetal umbilical cord. In young adults, it is usually located at the level of the intervertebral disc
between the third and fourth vertebrae. However, lower levels are observed in obese individuals and in condi- tions that reduce abdominal tone. In the fetus, the um- bilicus transmits the vitelline and umbilical vessels and yolk stalk. The umbilicus can be the site of an acquired umbili- cal hernia or omphalocele [2, 3]. It is surrounded by the paraumbilical veins that establish connections with both the portal vein and the inferior vena cava (porta- caval anastomosis) through a series of venous chan- nels. It is also the site of attachment of the umbilical lig- aments that consist of the median umbilical (remnant of the urachus), medial umbilical (obliterated umbilical arteries) and lateral umbilical (inferior epigastric ves- sels) ligaments/folds. A patent urachus may discharge urine because of its connection to the urinary bladder, and it can be associated with outflow obstruction or pus from an infected urachal cyst or with fecal matter if it is connected to part of the large intestine. The umbilicus may also receive the embryological remnant of the vitelline duct known as Meckel’s diver- ticulum. This diverticulum occasionally protrudes through the anterolateral abdomen and produces Lit- tre’s hernia. The umbilicus also receives the round liga- ment of the liver, a remnant of the umbilical vein. The umbilical vein remains patent for some time during early infancy and allows blood transfusion through catheterization in individuals with hemolytic diseases such as erythroblastosis fetalis [4]. The superficial abdominal reflex refers to deviation of the umbilicus toward the stimulated side when the skin of the anterolateral abdomen is stimulated by a blunt object applied to the flank at the midaxillary line inward toward the umbilicus. This reflex, which in- volves contraction of the abdominal muscles and sub- sequent deviation of the umbilicus, reveals the condi- tion of the ninth through the eleventh spinal cord seg- ments. Disappearance of this reflex is associated with postoperative pain following thoracotomy [5]. Absence of this reflex can be an early sign of syringomyelia in in- dividuals with scoliosis [6, 7]. The linea alba (white line) is formed by the midline fusion of the aponeuroses of flat abdominal muscles and may be visible through the skin of muscular indi- viduals. The linea semilunaris (Spigelian line) marks the lateral border of the rectus abdominis, extending from the costal arch near the ninth costal cartilage to the pubic tubercle. This line marks the sites of entry of motor nerves to the rectus abdominis, rendering it a surgically undesirable site for incisions. Spigelian her- nia, which consists of extraperitoneal fat covered by the skin, superficial fascia and the aponeurosis of the exter- nal oblique, may be hidden at the junction of the linea semilunaris and arcuate line of Douglas. The small de- pression below the infrasternal angle is termed the epi- gastric fossa. McBurney’s point marks the junction of
2 1 Anatomy of the Abdominal Wall
Subclavian Artery
Anterior Intercostal Arteries
Subcostal Artery
Ascending Branch of Deep Circumflex Artery
Deep Circumflex Iliac Artery Inferior Epigastric Artery
Superficial Circumflex Iliac Artery
Superficial Epigastric Artery
Rectus Abdominus (cut)
Superior Epigastric Artery
Internal Thoracic Artery
just below and parallel to the inguinal ligament. Since the superficial perineal pouch contains the urethra, rupture of the urethra may result in extravasation of blood and urine into the superficial perineal pouch. Accumulated blood and urine in this pouch may extend into the anterior abdominal wall between Scarpa’s fas- cia and the deep fascia covering the external oblique. Because of the firm attachment of Scarpa’s fascia to the fascia lata, inferior spread of fluid is not possible. The space between the two layers of the superficial fascia al- lows passage of the cutaneous vessels, nerves and lym- phatics of the superficial inguinal nodes.
Blood Supply of the Abdominal Wall
The abdominal wall receives blood supply through branches of the femoral, external iliac, subclavian and in- tercostal arteries as well as the abdominal aorta (Fig. 1.3). These branches include the superficial epigastric, su- perficial circumflex iliac, superficial external puden- dal, deep circumflex iliac, superior and inferior epigas- tric, posterior intercostal, subcostal, musculophrenic, and lumbar arteries [10].
Fig. 1.3. The diverse origin of the arterial supply to the abdomen
Superficial Epigastric Artery
The superficial epigastric artery is a branch of the fem- oral artery distal to the inguinal ligament that ascends in the superficial fascia of the abdomen toward the um- bilicus. This vessel provides the blood supply to the su- perficial fascia and skin of the abdomen, anastomosing with the inferior epigastric artery [10].
Superficial Circumflex Iliac Artery
The superficial circumflex iliac artery arises from the femoral artery near the origin of the superficial epigas- tric artery. It pierces the deep fascia of the thigh lateral to the saphenous opening and courses laterally toward the anterior superior iliac spine to supply the superficial fascia and skin. It is considered the smallest branch of the femoral artery that anastomoses with the deep cir- cumflex iliac, lateral femoral circumflex iliac and supe- rior gluteal arteries. The course of this vessel, an impor- tant structure in a groin flap, can best be localized by palpation of the anterior superior iliac spine and the pu- bic tubercle through the skin of the inguinal region [11].
4 1 Anatomy of the Abdominal Wall
Superficial External Pudendal Artery
The superficial external pudendal artery branches off the femoral artery and runs medially deep to the great saphenous vein. It travels across the spermatic cord (round ligament) to supply the lower anterior wall of the abdomen.
Deep Circumflex Iliac Artery
The deep circumflex iliac artery originates from the ex- ternal iliac artery lateral to the point of origin of the in- ferior epigastric artery and advances laterally posterior to the inguinal ligament in a sheath formed by the transversalis and iliac fascia. After it pierces the trans- verse abdominis and enters the area between this mus- cle and the internal oblique muscle, it anastomoses with the iliolumbar, superior gluteal, lumbar, and infe- rior epigastric arteries.
Superior Epigastric Artery
The superior epigastric artery (Fig. 1.3), one of the ter- minal branches of the internal thoracic artery, arises at the level of the sixth costal cartilage, descends anterior to the transversus thoracis, and continues into the ster- nocostal triangle of Morgagni. The latter is a gap be- tween the costal and sternal attachments of the dia- phragm. It then enters the posterior layer of the rectus sheath at the middle of the xiphoid process and the an- terior sheath at the middle of the upper third of the up- per abdomen and supplies the rectus abdominis, dia- phragm and the skin of the abdomen [12]. This vessel establishes linkage with the inferior epigastric artery and with the hepatic arteries through the falciform lig- ament. The arterial anastomosis between the superior and inferior epigastric arteries provides important col- lateral circulation to the lower part of the body in indi- viduals with postductal coarctation.
Inferior Epigastric Artery
The inferior epigastric artery (Fig. 1.3) is a branch of the external iliac artery that ascends obliquely along the medial margin of the deep inguinal ring, posterior to the spermatic or round ligament. It may arise from the femoral artery, or, very rarely from the obturator artery. It pierces the transversalis fascia to enter into the poste- rior wall of the rectus abdominis at the level of the arcu- ate line. This vessel penetrates the posterior sheath near the middle of the lower abdomen and the anterior sheath in an area ranging from the upper third of the
lower abdomen to the umbilicus. The arterial anasto- mosis between the inferior and superior epigastric ar- teries and the posterior intercostal arteries at the lower third of the upper abdomen allows collateral circulation to develop with the internal thoracic artery upon ob- struction or ligation of the common or external iliac ar- tery. This arterial anastomosis is also significant in the planning and implementation of vertical fasciocutaneo- us flaps of the abdominal wall [12]. After giving rise to the pubic, cremasteric and cutaneous branches, the in- ferior epigastric artery ascends under the parietal peri- toneum as the lateral (epigastric) umbilical fold. The cremasteric branch of the inferior epigastric ar- tery supplies the cremasteric muscle and other cover- ings of the spermatic cord as well as the testis through its anastomosis with the testicular artery. In the female, it provides blood supply to the round ligament. The pubic branch descends posterior to the pubis, supplies the parietal peritoneum and anterior abdominal mus- cles, forming an anastomosis with branches of the lum- bar, circumflex iliac, and the obturator arteries. In one- third of individuals, the pubic branch may be replaced by the obturator artery. The pubic branch forms an anastomosis with and supplies the parietal peritoneum and anterior abdominal muscles. The cutaneous branches establish anastomoses with the superficial epigastric artery and supply the skin of the lower abdo- men and the adjacent part of the aponeurosis of the ex- ternal abdominal oblique.
Posterior Intercostal Arteries
The lower two or three posterior intercostal arteries cross the corresponding intercostal space into the cos- tal groove proximal to the costal angle. At this location they lie between the intercostal vein (above) and inter- costal nerve (below), continuing into the anterior ab- domen with the subcostal, superior epigastric and lum- bar arteries. The posterior intercostal arteries enter the rectus sheath from its lateral border, anastomosing with the superior and inferior epigastric arteries.
Subcostal Artery
The subcostal artery courses inferior to the last rib and anterior to the 12th thoracic vertebra. It lies posterior to the sympathetic trunk, thoracic duct, pleura and dia- phragm. Then, it descends into the posterior abdomi- nal wall posterior to the lateral arcuate ligament ac- companied by the corresponding vein and nerve. As it continues anterior to the quadratus lumborum and posterior to the kidney, the right subcostal artery courses behind the ascending colon, whereas the left subcostal artery travels behind the descending colon.
1.4 Blood Supply of the Abdominal Wall 5
T 10 intercostal nerve T 11 intercostal nerve T 12 intercostal nerve
Anterior superior iliac spine Midpoint of inguinal sulcus
Pubic tubercle
Umbilicus
Rectus Abdominis
Iliac Crest
tal vein may activate this collateral venous circulation, producing distension of the paraumbilical veins.
Thoracoepigastric Vein
The thoracoepigastric vein drains the middle portion of the anterolateral abdomen and connects the superfi- cial epigastric and superficial circumflex iliac veins to the lateral thoracic vein. The lateral thoracic vein joins the axillary, which continues with the subclavian and brachiocephalic veins and eventually drains with the great saphenous vein; this, in turn, joins the femoral vein, which continues with the external iliac and com- mon veins and later with the inferior vena cava. Through these elaborate venous connections, the later- al thoracic vein forms a venous link for cava-caval anastomosis. Occlusion of the inferior vena cava is most likely to activate this collateral venous circulation, producing dilation of the thoracoepigastric, the lateral thoracic, and the tributaries of the superficial circum- flex iliac and the superficial epigastric veins.
Paraumbilical Veins
The paraumbilical veins are relatively small veins that drain the periumbilical region and into the portal vein.
Fig. 1.5. Course of the thoracoabdominal nerves
They are involved in formation of the porta-caval anas- tomosis via their connections to the superficial epigas- tric vein. Dilation of these veins produces caput medu- sa, after a Greek mythological character whose head was covered with a multitude of snakes, referring to the radial pattern of varicosed paraumbilical veins around the umbilicus.
Superficial Circumflex Iliac Vein
The superficial circumflex iliac vein drains the superfi- cial structures in the lower anterior abdominal wall and the proximal region of the superficial thigh. It is con- nected to the lateral thoracic vein that drains into the superior vena cava via the thoracoepigastric vein. This venous connection may also show dilation in caval ob- struction.
Innervation of the Abdominal Wall
The skin of the anterior abdominal wall is innervated by the ventral rami of the lower five or six thoracic (tho- racoabdominal) spinal nerves that continue from the intercostal spaces into the abdominal wall (Fig. 1.5). The anterolateral abdomen also receives nerve fibers from the subcostal, iliohypogastric, and ilioinguinal nerves. A typical intercostal nerve runs across the deep sur- face of the internal intercostal muscle and membrane between the internal and innermost intercostal mus- cles. It then continues in the costal groove below the in-
1.6 Innervation of the Abdominal Wall 7
tercostal artery. Each intercostal nerve is connected to an adjacent sympathetic ganglion by a white communi- cating ramus conveying presynaptic sympathetic fi- bers, and by a gray communicating ramus that trans- mits postsynaptic sympathetic fibers.
Thoracoabdominal Nerves
The seventh and eight intercostal nerves, as is the case with the rest of the intercostal nerves, divide into lateral and anterior cutaneous branches. The lateral branch further divides into anterior and posterior branches, piercing the flat abdominal muscles in the midaxillary line to reach the skin. The anterior cutaneous branches, which represent the terminal branches of the ventral rami of the intercostal nerves, pierce the rectus sheath laterally and emerge anteriorly to reach the skin. They pursue a curved course toward the lateral border of the rectus abdominis, and perforate the transverse abdo- minis to reach the internal abdominal oblique aponeu- rosis. After piercing the internal abdominal oblique, they run parallel to the costal margin, enter the posteri- or surface of the rectus abdominis to continue in its sheath to reach and supply the skin. The ninth to eleventh intercostal nerves pierce the diaphragm and transverse the abdominis and enter the gap between the transverse and internal oblique, where they pierce the posterior layer of the internal abdomi- nal oblique aponeurosis near its lateral border. Beyond this point, they travel in a similar manner to the sev- enth and eight intercostal nerves. The ninth intercostal nerve is much larger and should be preserved in a sub- costal (Kocher’s) incision, which is usually done one inch below the costal arch in individuals with a wider infrasternal angle. The downward and forward direc- tion of the anterior branches of the intercostal nerves brings the tenth intercostal nerve to the umbilicus. The lower intercostal nerves may be entrapped as they pierce the rectus sheath and cause rectus abdominis syndrome, which is characterized by numbness and paresthesia in the median and paramedian areas of the abdomen. The subcostal nerve, the ventral ramus of the 12th thoracic spinal nerve, is much larger than the intercos- tal nerves and runs inferior to the corresponding rib with corresponding vessels. It passes posterior to the lateral arcuate ligament and kidney, and anterior to the quadratus lumborum. It pierces the aponeurosis of the transverse abdominis and internal abdominal oblique and then assumes a course similar to that of the lower intercostal nerves. After crossing the iliac crest imme- diately posterior to the anterior superior iliac spine, the subcostal nerve supplies the pyramidalis via the medial branch and the anterior gluteal skin via its lateral branch.
Since thoracoabdominal nerves also convey sensa- tion from the costal and peripheral diaphragmatic pleura, pleural inflammation can produce pain felt in the abdominal wall. Appendicitis induced pain and ri- gidity in the abdominal are due to the fact that the sym- pathetic innervation of the abdominal viscera is de- rived from the same segments that supply the derma- tomes of the anterolateral abdomen. Tuberculosis af- fecting the lower five thoracic vertebrae can also pro- duce pain that projects to the anterior abdominal wall. Similarly, shingles of the lower ganglia of the thoracic spinal nerves produce diffuse pain and vesicular erup- tions in the anterolateral abdominal wall. Referred ab- dominal pain may also occur as a result of subluxation of the interchondral joints that entraps the intercostal nerves. Constrictive pain, felt as a tight cord around the abdomen, is usually a manifestation of a lesion that has affected a single pair of intercostal nerves. Clicking rib syndrome, which results from subluxation of the inter- chondral joints of the lower ribs, may cause compres- sion of the lower intercostal nerves and produce pain in the anterior abdomen. Thoracoabdominal nerves that supply the abdomi- nal muscles form an extensive communicating network that allows considerable overlap. This type of overlap is responsible for the limited or complete lack of percepti- ble clinical deficits upon damage to one or two nerves. In contrast, the segmental innervation of the rectus ab- dominis has no or very little cross-linkage. Conse- quently, individual nerve damage associated with the rectus abdominis is likely to produce deficits in the af- fected area. Tapping the anterior abdominal wall produces con- traction of the abdominal muscles and thereby reveals the conditions of certain spinal segments. A quick tap at the midclavicular line below the costal arch assesses the integrity of the seventh through the ninth spinal segments. Tapping the area immediately lateral to the umbilicus appraises the condition of the ninth to the eleventh spinal segments. Imparting a quick tap imme- diately above the inguinal ligament at the midclavicular line discloses information about the eleventh through the first lumbar spinal cord segments [13].
Iliohypogastric Nerve
The iliohypogastric nerve courses posterior to the psoas major and exits through its lateral border posterior to the kidney and anterior to the quadratus lumborum and the iliacus muscles. Near the iliac crest, it pierces and provides innervation to the transverse abdominis and internal abdominal oblique muscles, and splits into lat- eral and anterior branches. The lateral branch distrib- utes cutaneous branches to the gluteal region, while the anterior branch pierces the internal and external oblique
8 1 Anatomy of the Abdominal Wall
Pectoralis Minor
External Abdominal Oblique Muscle
Anterior Layer of Rectus Sheath Linea Semilunaris
Linea Alba
Inlingual Ligament
Pubic Crest Pubic Tubercle
External Abdominal Oblique Aponeurosis
Tendinous Intersection
nal muscles, usually indicates that the cause of the pain is in the anterolateral abdominal wall and not due to in- testinal dysfunction. The muscles of the anterolateral abdomen maintain intra-abdominal pressure and the position of the vis- cera, by exerting compressive and twisting force. They facilitate certain physiologic functions such as parturi- tion, vomiting, defecation, urination and coughing. Contraction of these muscles also promotes expiration by depressing and compressing the lower thorax.
External Abdominal Oblique
The external abdominal oblique muscle (Figs. 1.6, 1.7) is the most superficial abdominal muscle that originates from the external surfaces of the lower seven or eight ribs and interdigitates with the serratus anterior and la- tissimus dorsi muscles. Most of the muscle fibers run downward and medially, forming an aponeurosis near the lateral border of the rectus abdominis. The muscle fibers from the lower two ribs descend vertically down- ward to attach to the iliac crest. Muscle fibers are rarely found inferior to the line that connects the umbilicus to the anterior superior iliac spine. The vessels and nerves that supply the abdominal wall are contained in the
Fig. 1.6. External abdominal oblique muscle and apo- neurosis, and inguinal ligament
double fascial layer that covers the internal surface of the external abdominal oblique and the external sur- face of the internal abdominal oblique muscle. The portion of the muscle that inserts into the outer margin of the iliac crest has a free posterior border, which forms the anterior wall of the inferior lumbar tri- gone of Petit. This trigone is bounded anteriorly by the external abdominal oblique muscle, posteriorly by the latissimus dorsi, and inferiorly by the iliac crest. It is a weak zone in the abdominal wall can that tends to her- niate (Petit’s hernia), and the hernial sac is usually broad and less likely to incarcerate. Three different groups of arteries were identified in a study conducted by Schlenz et al. [18] as the sources of blood supply to the external abdominal oblique. The cranial part of this muscle is supplied by the intercostal arteries. In 94.7 % the deep circumflex iliac artery and in 5.3 % the iliolumbar artery is responsible for the blood supply to the caudal of the muscle. The lateral branches of these arteries run on the outer surface of the muscle, while the anterior branches enter the mus- cle from its inner surface. Arterial injection studies conducted by Kuzbari et al. [19] have also confirmed the significant contribution of the deep circumflex iliac artery to the blood supply of the external abdominal oblique muscle.
10 1 Anatomy of the Abdominal Wall
DeborahRubenst
ein
Lacunar Ligament
Inguinal Ligament
Transverse Intercrural Fibers
External Oblique Abdominis Muscle and Aponeurosis
Acetabulum
Spermatic Cord
Fundiform Ligament
Lateral Crus
Medial Crus
Anterior Superior Iliac Spine
Linea Alba
Obturator Foramen
Interfoveolar Ligament Epigastric Artery and Vein
Testicular Vessels
Iliopubic Tract
External Iliac Artery
External Iliac Vein Ductus (Vas) Deferens
Obturator Artery
Admiculum Linea Alba Obturator Foramen
Interfoveolar Ligament
Feromal Canal
Iliacus Muscle
Femoral Nerve
Deep Inguinal Ring
Rectus Abdominis Muscle
Arcurate (Semicircular) Line of Douglas
Fig. 1.7. Aponeurosis of the external oblique, superficial inguinal ring, and the inguinal ligament
Fig. 1.8. Deep inguinal ring, epigastric vessels, and the structures that pass posterior to the inguinal ligament
The aponeurosis of the external abdominal oblique (Fig. 1.7) runs anterior to the rectus abdominis and joins the aponeurosis of the internal and transverse ab- dominis at the linea alba. The linea alba is a tendinous midline raphe that extends between from the xiphoid process to the symphysis pubis and pubic crest. It is wider above the umbilicus, separating the recti completely. However, this demarcation may not be eas- ily felt inferior to the umbilicus. As a fibrous structure, it is virtually a bloodless line along which a surgical in- cision can be made. The triangular part of the linea al- ba that attaches to the pubic crest is known as the admi- niculum linea alba (Fig. 1.8).
Inferiorly, the external oblique aponeurosis attaches to the pubic tubercle, pubic symphysis and crest. The aponeurosis infolds backward and slightly upward up- on itself between the anterior superior iliac spine and the pubic tubercle to form the inguinal (Poupart) liga- ment (Figs. 1.6, 1.7). This ligament, which measures ap- proximately 15 cm, marks the transition between the abdominal wall and thigh. Its curved surface consti- tutes the floor of the inguinal canal, and maintains an oblique angle to the horizontal. The reflected part of the inguinal ligament is repre- sented by the fibers of the external oblique aponeurosis that course superiorly and medially to join the rectus
1.9 Musculature of the Anterior Abdominal Wall 11
Cut Margin of the External Oblique Abdominis Aponeurosis
Rectus Abdominis
Deltoid Muscle
Serratus Anterior
Internal Oblique Abdominis
Symphysis Pubis
External Oblique Abdominis
Rectus Sheath
Pubic Tubercle
Pectoralis Major
Serratus Anterior Muscle
Internal intercostal Muscle
Camper's Fascia
Skin
Rectus Abdominis
Internal Abdominal Oblique
External Intercostal Muscle
Fig. 1.9. Direction of the fibers of the external and internal abdominal oblique muscle
Fig. 1.10. Fibers of the internal abdominal oblique muscle and aponeurosis in relationship to the rectus abdominis muscle
1.10 Innervation 13
DeborahR ubenst ei n
Debor ahR u benst ei n
Rectus Abdominis
Anterior Layer of the Rectus Sheath Camper's Fascia
Internal Abdominal Oblique
External Abdominal Oblique Muscle
Transversalis Fascia
Transverse Abdominis Muscle
DeborahR ubenst ei n
Camper's Fascia Rectus Abdominis
Anterior Layer of the Rectus Sheath External Abdominal Oblique Muscle Internal Abdominal Oblique Posterior Layer of Rectus Sheath (^) Transversalis Fascia Transverse Abdominis Muscle
Rectus Abdominis External Abdominal Oblique Muscle
Posterior Layer of Rectus Sheath
Transverse Abdominis Muscle & Aponeurosis External Abdominal Oblique Aponeurosis Costal cartilage
band that connects the transverse abdominis to the su- perior pubic ramus. However, variations do exist in re- gard to the extent of attachment of the conjoint tendon and its structural characteristics. The part of the tendon that inserts on the pecten pubis extends posterior to the superficial inguinal ring, forming a natural barrier that prevents the occurrence of inguinal hernia. A direct in- guinal hernial pouch may pass through this tendon, ac- quiring the coverings of this structure. The posterior fibers of the internal abdominal ob- lique muscles that gain origin from the iliac crest ex- tend upward and laterally to the inferior border of the lower three or four ribs, continuing with the internal intercostal muscles. They become aponeurotic towards the midline and contribute to the formation of the linea alba by joining the aponeurosis of the flat abdominal muscles of the same and opposite side. Superior to the midpoint between the umbilicus and the symphysis pubis (upper two-thirds), the internal oblique aponeurosis divides into two layers. The anteri- or layer covers the anterior surface of the rectus abdomi- nis and the posterior layer invests the posterior surface of the rectus abdominis. Distal to this site (lower one- third), the aponeurosis of the internal oblique remains a single layer anterior to the rectus abdominis (Fig. 1.11). The loosely arranged fasciculi of the internal ob- lique muscle and its aponeurosis, which extend around the spermatic cord and testis, constitute the cremaste- ric muscle and fascia that invariably receive fibers from
Fig. 1.11. Patterns of lamina- tion of the rectus sheath
the transverse abdominis. The cremasteric, a striated muscle with a lateral and a medial part, is an involun- tary muscle innervated by the genital branch of the ge- nitofemoral nerve (L1, L2). The lateral part is thicker, directly arises from the inguinal ligament, and extends to the anterior superior iliac spine. The medial part of the internal abdominal oblique, which is sometimes absent, arises from the pubic tubercle, conjoint tendon, and possibly the transverse abdominis. From the inferior edge of the internal abdominal oblique, the cremasteric muscle and fascia loop over the spermatic cord and testis to terminate at the pubic tubercle and merge with the anterior layer of the rectus sheath. This muscle is considered to have internal and external components separated by the internal sper- matic fascia [27]. Redman [28] concluded that expo- sure of the inguinal canal and deep inguinal ring in her- nial repair is greatly enhanced by careful dissection of the cremasteric muscle and fascia. In the female, the round ligament is invested by the sporadic fibers from the lateral part of the cremasteric muscle. Contraction of the cremasteric muscle medi- ates the cremasteric reflex, a brisk reflex, particularly in children, which involves elevation of the testicles to- wards the superficial inguinal ring upon stimulation of the inner thigh.
14 1 Anatomy of the Abdominal Wall
Sternal Angle of Louis
Xyphoid Process
Rectus Abdominis Muscle Umbilicus
Pubic Tubercle
Linea Alba
Tendinous Intersections
Pubic Symphuysis
Latissimus Dorsi
Serratus Anterior Muscle
External Intercostal Muscle
Cut Edge of the Superficial Fascia and Skin
Iliac Crest Transverse Abdominis Muscle and Aponeurosis
Rectus Abdominis Muscle
Camper's Fascia (Cut)
Skin (Cut)
Internal Intercostal Muscle
Fig. 1.14. Proximal and distal attachments of the rectus abdominis
¸ Fig. 1.15. Rectus abdominis muscle in relation to the transverse abdominis and superficial fascia of the abdomen
zontal course deep to the internal abdominal oblique muscle. It maintains a similar origin to the internal oblique, arising from the thoracolumbar fascia, iliac crest and the lateral third of the inguinal ligament. The transverse abdominis receives additional origin from the inner surface of the lower five or six ribs, partly in- terdigitating with the origin of the muscular dia- phragm. This muscle may be absent or fused with the internal abdominal oblique and may contain openings filled with fascia. It becomes aponeurotic as it ap- proaches the lateral border of the rectus abdominis, blending with the linea alba. At the level of the xiphoid process, the transverse abdominis becomes aponeurot- ic near the linea alba, allowing the muscular part to pursue a course deeper to the rectus abdominis. Superior to the midpoint between the umbilicus and symphysis pubis (upper two-thirds), the aponeurosis of the transverse abdominis joins the anterior layer of
the aponeurosis of the internal abdominal oblique and the external oblique to form the anterior layer of the rectus sheath. Inferior to the midpoint, the transverse aponeurosis runs posterior to the rectus abdominis and anterior to the muscle. The lower fibers of the apo- neurosis curve downward and medially and join the aponeurosis of the internal abdominal oblique at the pubic crest to form the conjoint tendon.
Innervation
This muscle is innervated by the ventral rami of the lower five or six intercostal nerves, as well as by the sub- costal, iliohypogastric and ilioinguinal nerves.
Action
The effect of contraction of the transverse abdominis on the vertebral column is not clear, despite its role as a compressive force resisting intra-abdominal pressure.
16 1 Anatomy of the Abdominal Wall
Rectus Abdominis
Tendinous Intersection
Transverse Abdomonis Muscle
Internal Abdominal Oblique
Anterior Layer of the Rectus Sheath
Spermatic Cord Spermatic Cord
Pyramidalis Rectus Abdominis (Cut)
Transversalis Fascia
Arcurate Line of Douglas
Internal Abdominal Oblique
Posterior Layer of the Rectus Sheath
Transverse Abdominis Muscle
Fig. 1.16. Posterior layer of the rectus sheath, arcuate line of Douglas, internal abdominal oblique, and transverse abdominis
It is believed that the actions of the transverse abdomi- nis are basically common to the internal and external abdominal oblique muscles. The transverse abdominis is believed to respond more to increases in chemical or volume-related drive than the rectus abdominis and external abdominal oblique. This is supported by neu- roanatomical studies that have demonstrated many more inputs to, and outputs from, the motor neurons that innervate the transverse abdominis muscle than can be accounted for by its respiratory role [29].
Rectus Abdominis
The rectus abdominis (Figs. 1.5, 1.6, 1.8 – 1.10, 1.16), a paired longitudinal muscle on both sides of the mid- line, widens as it descends through the rectus sheath, maintaining distal and proximal attachments. Proxi- mally, it attaches to the xiphoid process and the costal cartilages of the fifth through the seventh ribs. Distally it attaches via a medial tendon to the pubic symphysis, interlacing with the opposite muscle and via a lateral tendon to the pubic crest, extending to the pecten pubis and pubic tubercle. The site of intersection of the lateral border of the right rectus and costal arch marks the to- pographic location of the fundus of the gallbladder.
The recti muscles are completely separated in the mid- line above the umbilicus by the linea alba and less so below it. Its lateral border forms the semilunar line, a curved groove that extends from the pubic tubercle to the ninth costal cartilage, which is particularly visible in muscular individuals. This muscle is usually inter- rupted by three transversely running tendinous inter- sections that assume a zigzag path and firmly adhere to the anterior layer of the rectus sheath. The upper tendi- nous intersection is usually near the xiphoid process; the lower one is at the level of the umbilicus and is seg- mentally related to the tenth rib and tenth intercostal nerve; and the middle one is found between the above intersections. In order to gain access to the rectus abdominis, the rectus sheath should carefully be dissected off the rec- tus muscle and the associated segmental artery and vein are severed at each of the intersections. A parame- dian incision that cuts through the anterior layer of the rectus sheath and rectus abdominis carries the advan- tage of protecting the sutured peritoneum when the rectus abdominis slips back into its proper anatomical position. Since this muscle receives innervation through its lateral border (Figs. 1.4, 1.5) by piercing the tendinous intersections, incisions immediately lateral to the rectus abdominis near the linea semilunaris can
1.10 Innervation 17
particularly in the supine position, overcoming gravi- tational pull.
Pyramidalis Muscle
The pyramidalis (Fig. 1.17), an inconstant small muscle which is absent in approximately 25 % of the popula- tion, originates from the symphysis pubis and pubic crest and inserts into the linea alba as far as one-third of the distance to the umbilicus. This triangular muscle lies anterior to the lower end of the rectus abdominis and becomes smaller and pointed as it ascends towards the junction of the linea alba and the arcuate line. Al- though the significance of this muscle is not clear, it is thought to tense the linea alba.
Innervation
The pyramidalis muscle is innervated by the subcostal nerve and occasionally by branches of the iliohypogas- tric and ilioinguinal nerves.
Transversalis Fascia
The transversalis fascia [33, 34] is a segment of the en- doabdominal fascia that forms the lining of the entire abdominal cavity. It contributes to the posterior wall of the rectus sheath and contains the deep inguinal ring midway between the anterior superior iliac spine and the symphysis pubis. It lies between the transverse ab- dominis and the extraperitoneal fat and continues infe- riorly with the iliac and pelvic fascia and superiorly with the fascia on the inferior surface of the diaphragm. Although it is a very thin layer on the inferior surface of the diaphragm, it shows some thickening in the ingui- nal region. In the posterior abdominal wall it joins the anterior layer of the thoracolumbar fascia. The trans- versalis fascia attaches to the iliac crest and to the pos- terior margin of the inguinal ligament as well as to the conjoint tendon and the pecten pubis. Its prolongation around the spermatic cord, known as the internal sper- matic fascia, fuses with the parietal layer of the tunica vaginalis. It blends with the iliac fascia as it forms the anterior layer of the femoral sheath. Anterior to the femoral vessels, the transversalis fas- cia is augmented by the transverse crural arch, a hori- zontally disposed layer that descends to attach medially to the pecten pubis and laterally to the anterior superi- or iliac spine. The transverse crural arch plays an im- portant role in strengthening the medial and inferior margins of the deep inguinal ring. Menck and Lierse [35] have demonstrated that the transversalis fascia
consists of an internal and an external layer; the inter- nal layer contributes to the sphincteric mechanism that reduces the size and strengthens the deep inguinal ring. The role of the transversalis fascia in inguinal hernial repair and reinforcement of the dorsal wall of the ingui- nal canal has been suggested by Morone et al. [36] and Witte et al. [37]. The study conducted by Teoh [38] con- firmed the presence of the iliopubic tract as a thicken- ing of the transversalis fascia that runs parallel to the inguinal ligament and believed to be a significant structure in various approaches to repair of inguinal hernia. It attaches to the superomedial part of the pubic bone medially, but laterally it joins the iliac fascia with no bony attachments.
Extraperitoneal Fatty Tissue
The extraperitoneal tissue (subserous fascia) is a gener- ally thin connective tissue layer that occupies the area between the peritoneum and the transversalis fascia in the abdomen, and between the peritoneum and the en- dopelvic fascia in the pelvis. It is loose and fatty in the lowest portion, allowing for the expansion of the blad- der. The potential space represented by this loose pre- peritoneal layer, the space of Bogros, is used for the placement of prostheses in the repair of inguinal her- nia. This layer is particularly thick and fatty in the pos- terior abdomen as it surrounds the major vessels and also the kidney to form the perinephric renal capsule. The extraperitoneal tissue also shows thickening around the iliac crest and pubic bone.
Peritoneum
The peritoneum is part of the coelomic cavity that be- comes separated from the pleural cavities by the devel- opment of the diaphragm. The free surface of this ex- tensive membrane is covered by a layer of mesotheli- um, saturated by a thin film of serous fluid. The perito- neum is a serous membrane that resembles, but is much more complicated than, the pleura essentially due to the fact that in the course of fetal development rotations of the gut allow certain parts of the abdomi- nal viscera to variably invaginate into the peritoneum. However, this process does not occur in the thoracic cavity and the pleura maintains a much simpler ar- rangement. In general the peritoneum consists of pari- etal and visceral layers separated by the peritoneal cavi- ty. The parietal layer forms the lining of the abdominal walls and the diaphragm separated from the transver- salis fascia by an extraperitoneal connective tissue. Al- though loosely attached to the abdominal wall, it is
1.13 Peritoneum 19
Patent Processus vaginalis
Ductus (Vas) Deferens
Obliterated Process vaginalis
Pampiniform Plexus Within the Spermatic cord
Tunica Vaginalis
Epididymis
Ductus (Vas) Deferens
Peritoneal Sac
Epididymis
Testis
Testis
Epididymis
Peritoneum
Peritoneum
denser and firmly adherent to the linea alba and inferi- or surface of the diaphragm. It converts the umbilical ligaments into folds. The median umbilical fold covers the urachus, an embryological remnant of the allantois, which is connected to the apex of the urinary bladder. The medial umbilical fold, located lateral to the median umbilical fold, is formed by the (upper) obliterated part of the umbilical artery. The lower (non-obliterat- ed) part of the umbilical artery remains functional in the adult. The lateral umbilical (epigastric) fold is lo- cated lateral to the medial umbilical fold, covering the inferior epigastric vessels. Since the lower five intercostal nerves and branches of the first lumbar spinal segment innervate the skin, muscles and also the parietal peritoneum, peritonitis may stimulate these nerves, thereby producing pain, involuntary spasmodic contraction of all abdominal muscles, and palpable rigidity (guarding). These im- portant manifestations signify inflammation of the pa- rietal peritoneum. In contrast, the visceral peritoneum invests the ab- dominal viscera to various degrees. An organ which is completely invested by the visceral peritoneum is con- sidered an intraperitoneal organ. Intraperitoneal or-
Fig. 1.18. Formation of the process vaginalis, descent of the testis, and the spermatic cord
gans include the spleen, stomach, initial part of the du- odenum, tail of the pancreas, jejunum, ileum, trans- verse colon, and sigmoid colon. Conversely, a retroper- itoneal organ is covered by the peritoneum anteriorly and laterally or only anteriorly. Retroperitoneal organs include the kidney, ureter, suprarenal gland, inferior vena cava, abdominal aorta, ascending and descending colon, most of the duodenum, and the rectum. The visceral peritoneum is innervated by sympa- thetic and parasympathetic fibers. Since sympathetic fibers are the principal carriers of visceral pain, inflam- mation of the visceral peritoneum produces referred pain in the dermatomes that correspond to the seg- mental sympathetic innervation of the affected organs.
Inguinal Canal
The inguinal canal [39] is an oblique tunnel that bor- ders the anterior thigh and extends from the superficial to the deep inguinal ring, running parallel to and above the inguinal ligament. It develops between the 5th and the 32nd week of prenatal life, initially as the processus
20 1 Anatomy of the Abdominal Wall
