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Abdomen 5 OVERVIEW: WALLS, CAVITIES, REGIONS, AND PLANES / 406 TABLE 5.1. Abdominal Regions, Reerence Planes, and Quadrants / 407...
Abdomen 5 OVERVIEW: WALLS, CAVITIES, REGIONS, AND PLANES / 406 TABLE 5.1. Abdominal Regions, Reerence Planes, and Quadrants / 407 Surace Anatomy o Anterolateral Abdominal Wall / 432 CLINICAL BOX: Internal Surace o Anterolateral Abdominal Wall and Inguinal Region. Spermatic Cord, Scrotum, and Testes / 433 ANTEROLATERAL ABDOMINAL WALL / 408 PERITONEUM AND PERITONEAL CAVITY / 439 Fascia o Anterolateral Abdominal Wall / 408 Embryology o Peritoneal Cavity / 440 Muscles o Anterolateral Abdominal Wall / 409 Peritoneal Formations / 441 TABLE 5.2. Muscles o Anterolateral Abdominal Subdivisions o Peritoneal Cavity / 443 Wall / 410 CLINICAL BOX: Peritoneum and Peritoneal Neurovasculature o Anterolateral Abdominal Wall / 415 Cavity / 445 TABLE 5.3. Nerves o Anterolateral Abdominal ABDOMINAL VISCERA / 448 Wall / 416 Overview o Abdominal Viscera and Digestive Tract / 448 TABLE 5.4. Arteries o Anterolateral Abdominal Esophagus / 451 Wall / 418 Stomach / 452 CLINICAL BOX: Fascia and Muscles o Anterolateral TABLE 5.7. Arterial Supply to Abdominal Foregut Abdominal Wall. Neurovasculature o Anterolateral Derivatives: Esophagus, Stomach, Liver, Gallbladder, Abdominal Wall / 419 Pancreas, and Spleen / 458 Internal Surace o Anterolateral Abdominal Wall / 423 Small Intestine / 461 Inguinal Region / 424 TABLE 5.8. Distinguishing Characteristics o Jejunum TABLE 5.5. Boundaries o Inguinal Canal / 426 and Ileum in Living Body / 466 Spermatic Cord, Scrotum, and Testes / 428 Large Intestine / 468 TABLE 5.6. Corresponding Layers o the TABLE 5.9. Arterial Supply to Intestines / 474 Anterior Abdominal Wall, Scrotum, and Spermatic CLINICAL BOX: Esophagus and Stomach. Small and Cord / 430 Large Intestine / 476 CLINICAL BOX KEY Anatomical Diagnostic Lie Cycle Surgical Trauma Pathology 404 Variations Procedures Procedures Abdomen 405 Spleen / 487 Diaphragmatic Apertures / 535 Pancreas / 488 TABLE 5.12. Neurovascular Structures o Liver / 491 Diaphragm / 535 TABLE 5.10. Terminology or Subdivisions o Liver / 497 Actions o Diaphragm / 536 Biliary Ducts and Gallbladder / 501 POSTERIOR ABDOMINAL WALL / 537 CLINICAL BOX: Spleen and Pancreas. Liver, Biliary Fascia o Posterior Abdominal Wall / 537 Ducts, and Gallbladder / 505 Muscles o Posterior Abdominal Wall / 539 Kidneys, Ureters, and Suprarenal Glands / 515 TABLE 5.13. Muscles o Posterior Abdominal CLINICAL BOX: Kidneys, Ureters, and Suprarenal Wall / 539 Glands / 523 Nerves o Posterior Abdominal Wall / 540 Summary o Innervation o Abdominal Viscera / 527 Vessels o Posterior Abdominal Wall / 541 TABLE 5.11. Autonomic Innervation o Abdominal TABLE 5.14. Branches o Abdominal Aorta / 542 Viscera (Splanchnic Nerves) / 529 CLINICAL BOX: Diaphragm. Posterior Abdominal DIAPHRAGM / 533 Wall / 544 Vessels and Nerves o Diaphragm / 534 SECTIONAL MEDICAL IMAGING OF ABDOMEN / 549 The abdomen is the part o the trunk between the thorax and and their contents is provided by musculo-aponeurotic walls the pelvis (Fig. 5.1). It is a fexible, dynamic container, hous- anterolaterally, the diaphragm superiorly, and the muscles o ing most o the organs o the alimentary system and part o the pelvis ineriorly. The anterolateral musculo-aponeurotic the urogenital system. Containment o the abdominal organs walls are suspended between and supported by two bony rings 5 Clavicle Apex of right lung Outline of parietal pleura Thorax Horizontal fissure Left lung of right lung Right dome of Cardiac notch of left lung diaphragm and 4th intercostal space 1 Apex of heart Xiphoid process of sternum Thoracic cage protecting upper Spleen abdominal viscera Liver Transpyloric plane Gallbladder Outline of pancreas Stomach Abdomen Pylorus of stomach Outline of duodenum Transverse colon Ascending colon Small intestine Descending colon Cecum Greater pelvis supporting and Interspinous plane protecting lower Anterior abdominal viscera superior Sigmoid colon iliac spine (ASIS) Urinary bladder 2 Pelvis Anterior view 1. Demarcated by diaphragm 2. Demarcated by plane of pelvic inlet FIGURE 5.1. Overview o viscera o the thorax and abdomen in situ. 406 Chapter 5 Abdomen (the inerior margin o the thoracic skeleton superiorly and the pelvic girdle ineriorly) linked by a semirigid lumbar vertebral column in the posterior abdominal wall. Interposed between Body cavities the more rigid thorax and pelvis, this arrangement enables the Thoracic cavity abdomen to enclose and protect its contents while providing Abdominal cavity Plane of superior the fexibility required by respiration, posture, and locomotion. Pelvic cavity thoracic aperture Through voluntary or refexive contraction, its muscular (thoracic inlet) roo, anterolateral walls, and foor can raise internal (intra- Thoracic cage abdominal) pressure to aid expulsion o air rom the thoracic cavity (lungs and bronchi) or o fuid (e.g., urine or vomitus), fatus (gas), eces, or etuses rom the abdominopelvic cavity. Thoracic diaphragm OVERVIEW: WALLS, CAVITIES, REGIONS, AND PLANES Abdomino- The dynamic, multilayered, musculo-aponeurotic abdomi- pelvic cavity nal walls not only contract to increase intra-abdominal pressure but also distend considerably, accommodating Plane of superior expansions caused by ingestion, pregnancy, at deposition, pelvic aperture or pathology. (pelvic inlet) Pubic symphysis The anterolateral abdominal wall and several organs lying against the posterior wall are covered on their internal Pelvic aspects with a serous membrane or peritoneum (serosa) that Medial view diaphragm refects (turns sharply and continues) onto the abdominal FIGURE 5.2. Abdominopelvic cavity. The body has been sectioned in the viscera (L., sot parts, internal organs), such as the stomach, median plane to show the abdominal and pelvic cavities as subdivisions o intestine, liver, and spleen. Thus, a bursal sac or lined poten- the continuous abdominopelvic cavity. tial space (peritoneal cavity) is ormed between the walls and the viscera that normally contains only enough extracellular is the location o most digestive organs, parts o the uro- (parietal) fuid to lubricate the membrane covering most genital system (kidneys and most o the ureters), and the o the suraces o the structures orming or occupying the spleen. abdominal cavity. Visceral movement associated with diges- tion occurs reely, and the double-layered refections o Nine regions o the abdominal cavity are used to describe peritoneum passing between the walls and the viscera pro- the location o abdominal organs, pains, or pathologies vide passage or the blood vessels, lymphatics, and nerves. (Table 5.1A, B). The regions are delineated by our planes: Variable amounts o at may also occur between the walls and two sagittal (vertical) and two transverse (horizontal) planes. viscera and the peritoneum lining them. The two sagittal planes are usually the midclavicular planes The abdominal cavity that pass rom the midpoint o the clavicles (approximately 9 cm rom the midline) to the midinguinal points, mid- orms the superior and major part o the abdomino- points o the lines joining the anterior superior iliac spine pelvic cavity (Fig. 5.2), the continuous cavity that (ASIS) and the pubic tubercles on each side. extends between the thoracic diaphragm and pelvic Most commonly, the transverse planes are the subcostal diaphragm. plane, passing through the inerior border o the 10th costal has no foor o its own because it is continuous with the cartilage on each side, and the transtubercular plane, pass- pelvic cavity. The plane o the pelvic inlet (superior pel- ing through the iliac tubercles (approximately 5 cm posterior vic aperture) arbitrarily, but not physically, separates the to the ASIS on each side) and the body o the L5 vertebra. abdominal and the pelvic cavities. Both o these planes have the advantage o intersecting pal- extends superiorly into the osseocartilaginous thoracic pable structures. cage to the 4th intercostal space (Fig. 5.1). Consequently, Some clinicians use the transpyloric and interspinous the more superiorly placed abdominal organs (spleen, planes to establish the nine regions. The transpyloric liver, part o the kidneys, and stomach) are protected by plane, extrapolated midway between the superior borders the thoracic cage. The greater pelvis (expanded part o o the manubrium o the sternum and the pubic symphy- the pelvis superior to the pelvic inlet) supports and partly sis (typically the L1 vertebral level), commonly transects protects the lower abdominal viscera (part o the ileum, the pylorus (the distal, more tubular part o the stomach) cecum, appendix, and sigmoid colon). when the patient is recumbent (supine or prone) (Fig. 5.1). (continued on p. 408) Overview: Walls, Cavities, Regions, and Planes 407 TABLE 5.1. ABDOMINAL REGIONS (A), REFERENCE PLANES (B), AND QUADRANTS (C) Abdominal areas Abdominal Regions: RH Right hypochondrium RL Right flank (lateral region) RI Right inguinal (groin) E Epigastric U Umbilical P Pubic LH Left hypochondriac LL Left flank (lateral region) LI Left inguinal (groin) Abdominal Quadrants: RUQ Right upper quadrant LUQ Left upper quadrant RLQ Right lower quadrant LLQ Left lower quadrant RH E LH U RUQ LUQ RL LL Median plane Transumbilical RI P LI plane RLQ LLQ Anterior 5 superior iliac spine (ASIS) Inguinal ligament (A) Abdominal regions (C) Abdominal quadrants Right upper quadrant (RUQ) Left upper quadrant (LUQ) Liver: right lobe Liver: left lobe Gallbladder Spleen Stomach: pylorus Stomach Jugular line Duodenum: parts 1–3 Jejunum and proximal ileum Pancreas: head Pancreas: body and tail Midclavicular Right suprarenal gland Left kidney line (MCL) Right kidney Left suprarenal gland Right colic (hepatic) flexure Left colic (splenic) flexure Transpyloric Ascending colon: Transverse colon: left half plane superior part Descending colon: Transverse colon: right half superior part Subcostal plane Right lower quadrant (RLQ) Left lower quadrant (LLQ) Semilunar Transtubercular lines Cecum Sigmoid colon plane Appendix Descending colon: inferior part Most of ileum Left ovary L4 Iliac Ascending colon: inferior part Left uterine tube L5 tubercle Right ovary Left ureter: abdominal part Interspinous Right uterine tube Left spermatic cord: plane Right ureter: abdominal part abdominal part Right spermatic cord: Uterus (if enlarged) abdominal part Urinary bladder (if very full) Uterus (if enlarged) Urinary bladder (if very full) Pubic symphysis (B) Abdominal reference planes 408 Chapter 5 Abdomen Because the viscera sag with the pull o gravity, the pylorus is musculo-aponeurotic, except or the posterior wall, which usually lies at a lower level when the individual is standing includes the lumbar region o the vertebral column. The erect. The transpyloric plane is a useul landmark because it boundary between the anterior and lateral walls is indenite; also transects many other important structures: the undus thereore, the term anterolateral abdominal wall is oten o the gallbladder, neck o the pancreas, origins o the supe- used. Some structures, such as muscles and cutaneous nerves, rior mesenteric artery (SMA) and hepatic portal vein, root o are in both the anterior and lateral walls. The anterolateral the transverse mesocolon, duodenojejunal junction, and hila abdominal wall extends rom the thoracic cage to the pelvis. o the kidneys. The interspinous plane passes through the The anterolateral abdominal wall is bounded superiorly easily palpated ASIS on each side (Table 5.1B). by the cartilages o the 7th–10th ribs and the xiphoid pro- For more general clinical descriptions, our quadrants o cess o the sternum and ineriorly by the inguinal ligament the abdominal cavity (right and let upper and lower quad- and the superior margins o the anterolateral aspects o the rants) are dened by two readily dened planes: (1) the trans- pelvic girdle (iliac crests, pubic crests, and pubic symphysis) verse transumbilical plane, passing through the umbilicus or (Fig. 5.4A). navel (and typically the intervertebral [IV] disc between the L3 The anterolateral abdominal wall consists o skin and and L4 vertebrae), dividing it into upper and lower halves, and subcutaneous tissue (supercial ascia) composed mainly (2) the vertical median plane, passing longitudinally through o at, muscles and their aponeuroses and deep ascia, the body, dividing it into right and let halves (Table 5.1C). extraperitoneal at, and parietal peritoneum (Fig. 5.4B). The It is important to know what organs are located in each skin attaches loosely to the subcutaneous tissue, except at abdominal region or quadrant so that one knows where the umbilicus, where it adheres rmly. Most o the antero- to auscultate, percuss, and palpate them (Table 5.1) lateral wall includes three musculotendinous layers; the ber and to record the locations o ndings during a physical bundles o each layer run in dierent directions. This three- examination. ply structure is similar to that o the intercostal spaces in the thorax. ANTEROLATERAL ABDOMINAL WALL Fascia o Anterolateral Although the abdominal wall is continuous, it is subdivided Abdominal Wall into the anterior wall, right and let lateral walls, and posterior The subcutaneous tissue over most o the wall includes a wall or descriptive purposes (Fig. 5.3). The abdominal wall variable amount o at. It is a major site o at storage. Males are especially susceptible to subcutaneous accumulation o at in the lower anterior abdominal wall. In morbid obesity, Vertical anterior Linea abdominal muscles alba the at is many inches thick, oten orming one or more sag- ging olds (L. panniculi; singular = panniculus, apron). Flat Superior to the umbilicus, the subcutaneous tissue is anterolateral consistent with that ound in most regions. Inerior to the abdominal muscles umbilicus, the deepest part o the subcutaneous tissue is A reinorced by many elastic and collagen bers, so it has two nt Anterior er ol a layers: the superfcial atty layer (Camper ascia) and the te ra deep membranous layer (Scarpa ascia) o subcutaneous l tissue. The membranous layer continues ineriorly into the perineal region as the membranous layer o subcutaneous tissue o the perineum (supercial perineal or Colles ascia), Left but not into the thighs (see Fig. 5.9B). lateral (flank) Supercial, intermediate, and deep layers o investing ascia cover the external aspects o the three muscle layers o the anterolateral abdominal wall and their aponeuroses of abdomen of back (fat expanded tendons) and cannot be easily separated rom Axio-appendicular Vertical muscles* them. The investing ascias here are extremely thin, being posterior Posterior represented mostly by the epimysium (outer brous con- muscles Lumbar vertebra nective tissue layer surrounding all muscles—see Chapter Inferior view * Boundary indefinite and overlapping 1, Overview and Basic Concepts) supercial to or between muscles. The internal aspect o the abdominal wall is lined FIGURE 5.3. Subdivisions o the abdominal wall. A transverse section with membranous and areolar sheets o varying thickness o the abdomen demonstrates various aspects o the wall and its components. (*The relatively superfcial latissimus dorsi and deeper psoas constituting endoabdominal ascia. Although continu- major muscles are axio-appendicular muscles that attach distally in the ous, dierent parts o this ascia are named according to the upper and lower limbs, respectively.) muscle or aponeurosis it is lining. The portion lining the deep Anterolateral Abdominal Wall 409 Azygos vein Muscles o Anterolateral Thoracic aorta Abdominal Wall Esophagus Inferior vena cava There are ve (bilaterally paired) muscles in the anterolateral Pericardial sac abdominal wall (Fig. 5.3): three fat muscles and two vertical Thoracic cage muscles. Their attachments are demonstrated in Figure 5.5 and listed, along with their nerve supply and main actions, Xiphoid process of sternum in Table 5.2. Costodiaphragmatic The three fat muscles are the external oblique, internal recess oblique, and transversus abdominis. The muscle bers o these three concentric muscle layers have varying orientations, with the bers o the outer two layers running diagonally and per- pendicular to each other or the main part, and the bers o Gallbladder the deep layer running transversely. All three fat muscles are Greater omentum continued anteriorly and medially as strong, sheet-like apo- neuroses (Fig. 5.6A). Between the midclavicular line (MCL) Abdominal wall and the midline, the aponeuroses orm the tough, aponeu- External oblique rotic, tendinous rectus sheath enclosing the rectus abdominis Internal oblique muscle (Fig. 5.6B). The aponeuroses then interweave with their ellows o the opposite side, orming a midline raphe (G. Transversus abdominis rhaphe, suture, seam), the linea alba (L. white line), which extends rom the xiphoid process to the pubic symphysis. The decussation and interweaving o the aponeurotic bers here is Rectus abdominis not only between right and let sides but also between super- cial and intermediate and intermediate and deep layers. The two vertical muscles o the anterolateral abdominal 5 Inguinal ligament wall, contained within the rectus sheath, are the large rectus Pubic crest and symphysis abdominis and the small pyramidalis. (A) Anterior view Superficial Deep EXTERNAL OBLIQUE MUSCLE The external oblique muscle is the largest and most Skin (cut edge) External oblique supercial o the three fat anterolateral abdominal mus- Superficial fatty layer Internal oblique cles (Fig. 5.7). The attachments o the external oblique of subcutaneous Transversus are demonstrated in Figure 5.5A and listed, along with the tissue (Camper fascia) abdominis nerve supply and main actions, in Table 5.2. In contrast to Deep membranous Extraperitoneal fat the two deeper layers, the external oblique does not origi- layer of subcutaneous Endoabdominal tissue (Scarpa fascia) nate posteriorly rom the thoracolumbar ascia; its posteri- (transversalis) fascia ormost bers (the thickest part o the muscle) have a ree Investing (deep) fascia—superficial, Parietal edge where they span between its costal origin and the iliac intermediate, & deep peritoneum crest (Fig. 5.5D, E). The feshy part o the muscle contrib- utes primarily to the lateral part o the abdominal wall. Its (B) Longitudinal section aponeurosis contributes to the anterior part o the wall. FIGURE 5.4. Abdominal contents, undisturbed, and layers o the Although the posteriormost bers rom rib 12 are nearly anterolateral abdominal wall. A. The anterior abdominal wall and sot vertical as they run to the iliac crest, more anterior bers tissues o the anterior thoracic wall have been removed. Most o the an out, taking an increasingly medial direction so that most intestine is covered by the apron-like greater omentum, a peritoneal old hanging rom the stomach. B. Layers o the anterolateral abdominal wall, o the feshy bers run ineromedially—in the same direc- including the trilaminar at muscles, are shown. tion as the ngers do when the hands are in one’s side pock- ets—with the most anterior and superior bers approaching surace o the transversus abdominis muscle and its aponeu- a horizontal course. The muscle bers become aponeu- rosis is the transversalis ascia. The glistening lining o the rotic approximately at the MCL medially and at the spino- abdominal cavity, the parietal peritoneum, is ormed by a umbilical line (line running rom the umbilicus to the ASIS) single layer o epithelial cells and supporting connective tis- ineriorly, orming a sheet o tendinous bers that decussate sue. The parietal peritoneum is internal to the transversalis at the linea alba, most becoming continuous with tendinous ascia and is separated rom it by a variable amount o extra- bers o the contralateral internal oblique (see Fig. 5.6A). peritoneal at. Thus, the contralateral external and internal oblique muscles (continued on p. 411) 410 Chapter 5 Abdomen 7 7 8 8 9 9 Cut attachments 10 External oblique 10 of internal oblique Free posterior External oblique (cut) border of external Rectus sheath Transversus oblique (anterior layer) Thoracolumbar abdominis fascia Internal 5 7 6 oblique 7 8 9 8 Costal Anterior 10 9 cartilages superior 10 11 iliac spine 12th rib Rectus (ASIS) L1 abdominis Inguinal L2 ligament L3 Tendinous intersections (C) Layer 3 (A) Layer 1 Internal oblique Quadratus Attachment of lumborum external oblique (posterior to iliac crest Inguinal abdominal ligament wall) Pubic crest (A)–(C) = Three layers of muscles of (B) Layer 2 Lateral views (D) Anterior & posterior anterolateral abdominal wall wall muscles Origin of (2) & (3) Layers of anterolateral from lateral part abdominal wall muscle: Psoas muscle of thoracolumbar (1) External oblique Quadratus lumborum fascia (2) Internal oblique (3) Transversus abdominis Thoracolumbar fascia: Anterior layer Free posterior border Middle layer of external oblique (1) Posterior layer Latissimus dorsi Deep muscles of back (E) Inferior view of transverse section of posterolateral abdominal wall FiGURe 5.5. Muscles of the anterolateral abdominal wall. taBle 5.2. mUsCles oF anteRolateRal aBdominal wall Muscle Origin Insertion Innervation Main Actiona External External surfaces of 5th–12th Linea alba, pubic tubercle, Thoraco-abdominal nerves oblique (A) ribs and anterior half of iliac crest (T7–T11 spinal nerves) and subcostal nerve Compresses and supports abdominal viscerab and flexes Internal Thoracolumbar fascia, anterior Inferior borders of 10th–12th and rotates trunk oblique (B) two thirds of iliac crest, and ribs, linea alba, and pecten connective tissue deep to lat- pubis via conjoint tendon eral third of inguinal ligament Thoraco-abdominal nerves (anterior rami of T6–T12 Transversus Internal surfaces of 7th–12th Linea alba with aponeurosis spinal nerves) and first Compresses and supports abdominis costal cartilages, thoracolum- of internal oblique, pubic lumbar nerve abdominal viscerab (C) bar fascia, iliac crest, and con- crest, and pecten pubis via nective tissue deep to lateral conjoint tendon third of inguinal ligament Rectus Pubic symphysis and pubic Xiphoid process and Thoraco-abdominal nerves Flexes trunk (lumbar vertebrae) abdominis crest 5th–7th costal cartilages (anterior rami of T6–T12 and compresses abdominal (D) spinal nerves) viscera;b stabilizes and controls tilt of pelvis (antilordosis) a Approximately 80% of people have an insignificant muscle, the pyramidalis, which is located in the rectus sheath anterior to the most inferior part of the rectus abdominis. It extends from the pubic crest of the hip bone to the linea alba. This small muscle draws down on the linea alba. b In so doing, these muscles act as antagonists of the diaphragm to produce expiration. Anterolateral Abdominal Wall 411 Fibers passing from superficial to deep (and vice versa) Fibers of left external at linea alba oblique aponeurosis, which run deep on the Right external right side and running oblique muscle superficially on the left side Fibers of left Umbilical ring Fibers of right internal oblique external oblique aponeurosis Deep fibers of right aponeurosis external oblique aponeurosis Left internal Deep fibers of left oblique muscle external oblique aponeurosis Intramuscular exchange of superficial and deep Intermuscular exchange of fibers between aponeuroses of fibers within aponeuroses of contralateral contralateral external and internal oblique muscles. external oblique muscles. (A) Anterior views Investing (deep) fascia: Transversus abdominis Parietal peritoneum Deep Internal oblique Extraperitoneal fat Intermediate External oblique Transversalis fascia Superficial Rectus abdominis Aponeurosis 5 of transversus Skin abdominis Superficial fatty layer of subcutaneous tissue Aponeurosis Deep membranous layer of internal of subcutaneous Rectus Linea alba oblique tissue sheath (note fibers passing from superficial to deep, Aponeurosis Linea of external alba and vice versa, as in right side of figure A) oblique (B) Anterior view Transverse sections FIGURE 5.6. Structure o the anterolateral abdominal wall. A. Intramuscular and intermuscular fber exchanges within the bilaminar aponeuroses o the external and internal oblique muscles are shown. B. Transverse sections o the wall superior and inerior to the umbilicus show the makeup o the rectus sheath. together orm a “digastric muscle,” a two-bellied muscle Palpate your inguinal ligament by pressing deeply into sharing a common central tendon that works as a unit (see the center o the crease between the thigh and trunk and Chapter 1, Overview and Basic Concepts). For example, the moving the ngertips up and down. Ineriorly, the inguinal right external oblique and let internal oblique work together ligament is continuous with the deep ascia o the thigh. The when fexing and rotating to bring the right shoulder toward inguinal ligament is thereore not a reestanding structure, the let hip (torsional movement o trunk). although—as a useul landmark—it is requently depicted as Ineriorly, the external oblique aponeurosis attaches to such. It serves as a retinaculum (retaining band) or the mus- the pubic crest medial to the pubic tubercle. The inerior cular and neurovascular structures passing deep to it to enter margin o the external oblique aponeurosis is thickened as the thigh. The inerior parts o the two deeper anterolateral an undercurving brous band with a ree posterior edge that abdominal muscles arise in relationship to the lateral por- spans between the ASIS and the pubic tubercle as the ingui- tion o the inguinal ligament. The complex modications and nal ligament (Poupart ligament) (Figs. 5.7B and 5.8). attachments o the inguinal ligament, and o the ineromedial (continued on p. 413) 412 Chapter 5 Abdomen Serratus anterior 5th costal cartilage Anterior layer of rectus sheath Anterior layer of rectus sheath Rectus abdominis Linea alba External oblique External oblique Lateral abdominal Tendinous intersection cutaneous branches Anterior abdominal cutaneous branches Anterior superior iliac spine External oblique aponeurosis Superficial circumflex iliac artery and vein Deep membranous layer of subcutaneous tissue Superficial epigastric artery and vein Intercrural fibers Superficial inguinal ring External pudendal artery and vein Ilio-inguinal nerve Great saphenous vein Spermatic cord (A) Anterior view Internal oblique External oblique Anterior superior iliac spine Transversus abdominis External oblique aponeurosis Musculo-aponeurotic arcade of transversus abdominis Inguinal falx Deep inguinal ring (transversalis fascia) Spermatic cord Incurved lower margin (gutter) of aponeurosis Inguinal ligament (passing forming inguinal ligament anterior to pecten pubis) (floor of inguinal canal) Nerve Pubic tubercle Femoral Artery Vein Pubic crest (B) Anterior view Testis FIGURE 5.7. Anterolateral abdominal wall. A. In this superfcial dissection, the anterior layer o the rectus sheath is reected on the let side. Observe the anterior cutaneous nerves (T7–T12) piercing the rectus abdominis and the anterior layer o the rectus sheath. B. The three at abdominal muscles and the ormation o the inguinal ligament are demonstrated. Anterolateral Abdominal Wall 413 External oblique Linea alba Internal oblique Rectus sheath (anterior wall) Iliohypogastric nerve Ilio-inguinal nerve Inferior aponeurotic fibers of internal oblique Aponeurosis of external oblique Fundiform ligament of penis Medial crus of external Inguinal ligament oblique Lateral crus aponeurosis Cremaster Superficial inguinal ring (exit Saphenous opening from inguinal canal) Inguinal lymph nodes 5 Inguinal falx (conjoint tendon) Reflected (reflex) Inguinal inguinal ligament canal FIGURE 5.8. Inerior abdominal wall and inguinal region o a male. The aponeurosis o the external oblique is partly cut away, and the spermatic cord has been cut and removed rom the inguinal canal. portions o the aponeuroses o the anterolateral abdominal muscle also end in an aponeurosis, which contributes to the wall muscles, are discussed in detail with the inguinal region ormation o the rectus sheath (Fig. 5.9). The attachments o (later in this chapter). the transversus abdominis are demonstrated in Figure 5.5C and listed, along with the nerve supply and main actions, in INTERNAL OBLIQUE MUSCLE Table 5.2. The intermediate o the three fat abdominal muscles, the Between the internal oblique and the transversus abdomi- internal oblique is a thin muscular sheet that ans out nis muscles is a neurovascular plane, which corresponds with anteromedially (Figs. 5.5B, 5.8, and 5.9A). Except or its a similar plane in the intercostal spaces. In both regions, the lowermost bers, which arise rom the lateral hal o the plane lies between the middle and deepest layers o muscle inguinal ligament, its feshy bers run perpendicular to those (Fig. 5.9A). The neurovascular plane o the anterolat- o the external oblique, running superomedially (like your eral abdominal wall contains the nerves and arteries sup- ngers when the hand is placed over your chest). Its bers plying the anterolateral abdominal wall. In the anterior part also become aponeurotic at the MCL and participate in the o the abdominal wall, the nerves and vessels leave the neu- ormation o the rectus sheath. The attachments o the inter- rovascular plane and lie mostly in the subcutaneous tissue. nal oblique are demonstrated in Figure 5.5B and listed, along with the nerve supply and main actions, in Table 5.2. RECTUS ABDOMINIS MUSCLE A long, broad, strap-like muscle, the rectus abdominis TRANSVERSUS ABDOMINIS MUSCLE (L. rectus, straight) is the principal vertical muscle o the The bers o the transversus abdominis, the innermost anterior abdominal wall (Figs. 5.5D, 5.6B, 5.7A, and 5.9B). o the three fat abdominal muscles (see Figs. 5.5C and The attachments o the rectus abdominis are demonstrated in 5.7B), run more or less transversally, except or the inerior Figure 5.5D and listed, along with the nerve supply and main ones, which run parallel to those o the internal oblique. actions, in Table 5.2. The paired rectus muscles, separated by This transverse, circumerential orientation is ideal or the linea alba, lie close together ineriorly. The rectus abdomi- compressing the abdominal contents, increasing intra- nis is three times as wide superiorly as ineriorly; it is broad abdominal pressure. The bers o the transversus abdominis and thin superiorly and narrow and thick ineriorly. Most o 414 Chapter 5 Abdomen Plane of section for (B) Pectoralis major Origin of rectus abdominis from costal cartilages (no sheath posterior Diaphragm to muscle here) Thoraco- abdominal Superior epigastric artery Termination nerves of internal Posterior wall of upper rectus thoracic sheath consisting of: artery Posterior lamina of internal oblique aponeurosis External Transversus abdominis oblique aponeurosis Peritoneum (cut edges) Anterior wall of upper rectus Internal sheath consisting of: oblique Transversalis External oblique fascia Anterior aponeurosis superior Anterior lamina of internal iliac spine oblique aponeurosis Iliohypo- gastric Level of umbilicus Deep nerve Inferior epigastric artery membranous Ilio-inguinal layer of Arcuate line subcutaneous nerve Posterior wall of lower rectus tissue (Scarpa Opened sheath; transversalis fascia only fascia) inguinal canal External Anterior wall of lower iliac artery rectus sheath consisting of all three Body of pubis Level of aponeurotic layers Skin pubic crest Membranous Dartos fascia layer of subcutaneous Scrotum tissue (Colles fascia) (A) Anterior view (B) Schematic sagittal section FIGURE 5.9. Formation o rectus sheath and neurovascular structures o the anterolateral abdominal wall. A. In this deep dissection, the eshy portion o the external oblique is excised on the right side, but its aponeurosis and the anterior wall o the rectus sheath are intact. The anterior wall o the sheath and the rectus abdominis are removed on the let side so that the posterior wall o the sheath may be seen. Lateral to the let rectus sheath, the eshy part o the internal oblique has been cut longitudinally; the edges o the cut are retracted to reveal the thoraco-abdominal nerves coursing in the neurovascular plane between the internal oblique and the transversus abdominis. B. Sagittal section through the rectus sheath o the anterior abdominal wall. the rectus abdominis is enclosed in the rectus sheath. The pyramidalis tenses the linea alba. When present, surgeons use rectus muscle is anchored transversely by attachment to the the attachment o the pyramidalis to the linea alba as a land- anterior layer o the rectus sheath at three or more tendinous mark or median abdominal incision (Skandalakis et al., 2009). intersections (transverse brous bands, see Figs. 5.5D and 5.7A). When tensed in muscular people, the areas o muscle RECTUS SHEATH, LINEA ALBA, AND UMBILICAL RING between the tendinous intersections bulge outward. The intersections, indicated by grooves in the skin between the The rectus sheath is the strong, incomplete brous com- muscular bulges, usually occur at the level o the xiphoid pro- partment o the rectus abdominis and pyramidalis muscles cess, at the umbilicus, and halway between these structures. (Figs. 5.7 to 5.9). Also ound in the rectus sheath are the supe- rior and inerior epigastric arteries and veins, lymphatic vessels, and distal portions o the thoraco-abdominal nerves (abdomi- PYRAMIDALIS nal portions o the anterior rami o spinal nerves T7–T12). The pyramidalis is a small, insignicant triangular muscle The rectus sheath is ormed by the decussation and inter- that is absent in approximately 20% o people. It lies anterior weaving o the aponeuroses o the fat abdominal muscles to the inerior part o the rectus abdominis and attaches to (Fig. 5.6B). The external oblique aponeurosis contributes the anterior surace o the pubis and the anterior pubic liga- to the anterior wall o the sheath throughout its length. ment. It ends in the linea alba, which is especially thickened The superior two thirds o the internal oblique aponeuro- or a variable distance superior to the pubic symphysis. The sis splits into two layers (laminae) at the lateral border o Anterolateral Abdominal Wall 415 the rectus abdominis; one lamina passing anterior to the abdominal viscera. The rectus abdominis participates little, muscle and the other passing posterior to it. The anterior i at all, in this action. Compressing the abdominal viscera lamina joins the aponeurosis o the external oblique to orm and increasing intra-abdominal pressure elevates the relaxed the anterior layer o the rectus sheath. The posterior lamina diaphragm to expel air during respiration and more orcibly joins the aponeurosis o the transversus abdominis to orm or coughing, sneezing, nose blowing, voluntary eructation the posterior layer o the rectus sheath. (burping), and yelling or screaming. When the diaphragm Beginning approximately one third o the distance rom contracts during inspiration, the anterolateral abdominal the umbilicus to the pubic crest, the aponeuroses o the three wall expands as its muscles relax to make room or the organs, fat muscles pass anterior to the rectus abdominis to orm such as the liver, that are pushed ineriorly. The combined the anterior layer o the rectus sheath, leaving only the rela- actions o the anterolateral muscles also produce the orce tively thin transversalis ascia to cover the rectus abdominis required or deecation (discharge o eces), micturition posteriorly. A crescentic arcuate line (Fig. 5.9) demarcates (urination), vomiting, and parturition (childbirth). Increased the transition between the aponeurotic posterior wall o intra-abdominal (and intrathoracic) pressure is also involved the sheath covering the superior three quarters o the rec- in heavy liting, the resulting orce sometimes producing a tus and the transversalis ascia covering the inerior quarter. hernia. Throughout the length o the sheath, the bers o the ante- The anterolateral abdominal muscles are also involved rior and posterior layers o the sheath interlace in the ante- in movements o the trunk at the level o the lumbar ver- rior median line to orm the complex linea alba. tebrae and in controlling the tilt o the pelvis when stand- The posterior layer o the rectus sheath is also decient ing or maintenance o posture (resisting lumbar lordosis). superior to the costal margin because the transversus abdom- Consequently, strengthening the anterolateral abdominal inis is continued superiorly as the transversus thoracis, which wall musculature improves standing and sitting posture. The lies internal to the costal cartilages (see Fig. 4.14), and the rectus abdominis is a powerul fexor o the thoracic and internal oblique attaches to the costal margin. Hence, supe- especially lumbar regions o the vertebral column, pulling rior to the costal margin, the rectus abdominis lies directly on the thoracic wall (Fig. 5.9B). The linea alba, running vertically the length o the ante- the anterior costal margin and pubic crest toward each other. The oblique abdominal muscles also assist in movements o the trunk, especially lateral fexion o the lumbar vertebrae 5 rior abdominal wall and separating the bilateral rectus sheaths and rotation o the lower thoracic vertebral column. The (Fig. 5.7A), narrows inerior to the umbilicus to the width o transversus abdominis probably has no appreciable eect on the pubic symphysis and widens superiorly to the width o the vertebral column (Standring, 2016). the xiphoid process. The linea alba transmits small vessels and nerves to the skin. In thin muscular people, a groove Neurovasculature o Anterolateral is visible in the skin overlying the linea alba. At its middle, Abdominal Wall underlying the umbilicus, the linea alba contains the umbili- cal ring, a deect in the linea alba through which the etal DERMATOMES OF ANTEROLATERAL umbilical vessels passed to and rom the umbilical cord and ABDOMINAL WALL placenta. All layers o the anterolateral abdominal wall use The map o dermatomes o the anterolateral abdominal wall at the umbilicus. As at accumulates in the subcutaneous tis- is almost identical to the map o peripheral nerve distribution sue postnatally, the skin becomes raised around the umbilical (Fig. 5.10). This is because the anterior rami o spinal nerves ring and the umbilicus becomes depressed. This occurs 7–14 T7–T12, which supply most o the abdominal wall, do not days ater birth, when the atrophic umbilical cord “alls o.” participate in plexus ormation. The exception occurs at the FUNCTIONS AND ACTIONS OF ANTEROLATERAL L1 level, where the L1 anterior ramus biurcates into two named peripheral nerves. Each dermatome begins posteri- ABDOMINAL MUSCLES orly overlying the intervertebral oramen by which the spinal The muscles o the anterolateral abdominal wall nerve exits the vertebral column and ollows the slope o the ribs around the trunk. Dermatome T10 includes the umbili- orm a strong expandable support or the anterolateral cus, whereas dermatome L1 includes the inguinal old. abdominal wall. support the abdominal viscera and protect them rom NERVES OF ANTEROLATERAL ABDOMINAL WALL most injuries. compress the abdominal contents to maintain or increase The skin and muscles o the anterolateral abdominal wall are the intra-abdominal pressure and, in so doing, oppose the supplied mainly by the ollowing nerves (Figs. 5.9A and 5.10; diaphragm (increased intra-abdominal pressure acilitates Table 5.3): expulsion). Thoraco-abdominal nerves: these are the distal, move the trunk and help to maintain posture. abdominal parts o the anterior rami o the inerior six The oblique and transverse muscles, acting together bilat- thoracic spinal nerves (T7–T11); they are the ormer ine- erally, orm a muscular girdle that exerts rm pressure on the rior intercostal nerves distal to the costal margin. 416 Chapter 5 Abdomen Lateral (thoracic) cutaneous branches o the thoracic The thoraco-abdominal nerves pass inero-anteriorly rom spinal nerves T7–T9 or T10. the intercostal spaces and run in the neurovascular plane Subcostal nerve: the large anterior ramus o spinal between the internal oblique and the transversus abdominis nerve T12. muscles to supply the abdominal skin and muscles. The Iliohypogastric and ilio-inguinal nerves: terminal lateral cutaneous branches emerge rom the musculature branches o the anterior ramus o spinal nerve L1. o the anterolateral wall to enter the subcutaneous tissue Rectus abdominis T2 ACB Xiphoid process External oblique T3 Internal oblique T4 Anterior Transversus cutaneous abdominis T5 branches TA (ACB) Thoraco-abdominal T6 nerves (T7–T11) Lateral cutaneous Anterior rami (AR)/ T7 branches continuations of SG (LCB) intercostal nerves (TA) T8 RC T9 Lateral cutaneous branch LCB of subcostal nerve (T12) AR/TA T10 Anterior cutaneous branch of subcostal nerve (T12) DR T11 Anterior superior iliac spine (ASIS) T12 Iliohypogastric nerve (L1) L1 Ilio-inguinal nerve (L1) (B) Transverse CT, L3 vertebrala level Inguinal ligament (A) Anterior view FIGURE 5.10. Innervation o the anterolateral abdominal wall. A. Dermatomes and distribution o cutaneous branches. B. Neurovascular plane (path) o lumbar spinal nerve branches. A, aorta; DR, dorsal ramus; RC, ramus communicans; SG, sympathetic ganglia o sympathetic trunk. TABLE 5.3. NERVES OF ANTEROLATERAL ABDOMINAL WALL Nerves Origin Course Distribution Thoraco- Continuation o lower Run between second and third layers o abdomi- Muscles o the anterolateral abdominal abdominal (7th–11th) intercostal nal muscles; branches enter subcutaneous tissue wall and overlying skin (T7–T11) nerves distal to the costal as lateral cutaneous branches o T10–T11 (in margin anterior axillary line) and anterior cutaneous branches o T7–T11 (parasternal line) 7th–9th lateral 7th–9th intercostal nerves Anterior divisions continue across costal margin in Skin o right and let hypochondriac cutaneous (anterior rami o spinal subcutaneous tissue regions branches nerves T7–T9) Subcostal (anterior Spinal nerve T12 Runs along the inerior border o the 12th rib; Muscles o the anterolateral abdominal ramus o T12) then passes onto the subumbilical abdominal wall wall (including most inerior slip o external between second and third layers o abdominal oblique) and overlying skin, superior to the muscles iliac crest and inerior to the umbilicus Iliohypogastric As superior terminal Pierces the transversus abdominis muscle to Skin overlying iliac crest, upper inguinal, (L1) branch o anterior ramus course between second and third layers o and hypogastric regions; internal oblique o spinal nerve L1 abdominal muscles; branches pierce external and transversus abdominis muscles oblique aponeuroses o most inerior abdomi- nal wall Ilio-inguinal (L1) As inerior terminal branch Passes between second and third layers o Skin o the lower inguinal region, mons o the anterior ramus o abdominal muscles; then traverses the inguinal pubis, anterior scrotum or labium majus, spinal nerve L1 canal and adjacent medial thigh; ineriormost internal oblique and transversus abdominis Anterolateral Abdominal Wall 417 along the anterior axillary line (as anterior and posterior divi- o altered venous ow) between the superfcial epigastric sions), whereas the anterior abdominal cutaneous branches vein (a emoral vein tributary) and the lateral thoracic vein pierce the rectus sheath to enter the subcutaneous tissue a (an axillary vein tributary). The deeper veins o the antero- short distance rom the median plane. Anterior abdominal lateral abdominal wall accompany the arteries, bearing the cutaneous branches o thoraco-abdominal nerves (Fig. 5.10; same name. A deeper, medial venous anastomosis may exist Table 5.3) are as ollows: or develop between the inerior epigastric vein (an external iliac vein tributary) and the superior epigastric/internal tho- T7–T9 supply the skin superior to the umbilicus. racic veins (subclavian vein tributaries). The superfcial and T10 supplies the skin around the umbilicus. deep anastomoses may aord collateral circulation during T11, plus the cutaneous branches o the subcostal (T12), blockage o either vena cava. iliohypogastric, and ilio-inguinal (L1), supply the skin The primary blood vessels (arteries and veins) o the inerior to the umbilicus. anterolateral abdominal wall are as ollows: During their course through the anterolateral abdominal Superior epigastric vessels and branches o the musculo- wall, the thoraco-abdominal, subcostal, and iliohypogastric phrenic vessels rom the internal thoracic vessels. nerves communicate with each other. Inerior epigastric and deep circumex iliac vessels rom the external iliac vessels. vessels oF anteRolateRal aBdominal wall Superfcial circumex iliac and superfcial epigastric ves- The skin and subcutaneous tissue o the abdominal wall are sels rom the emoral artery and greater saphenous vein, served by an intricate subcutaneous venous plexus, draining respectively. superiorly to the internal thoracic vein medially and the lat- Posterior intercostal vessels o the 10–11th intercostal eral thoracic vein laterally and ineriorly to the superfcial spaces and the anterior branches o subcostal vessels. and inerior epigastric veins, tributaries o the emoral and The arterial supply to the anterolateral abdominal wall is external iliac veins, respectively (Fig. 5.11). Cutaneous veins surrounding the umbilicus anastomose with para-umbilical veins, small tributaries o the hepatic portal vein that parallel demonstrated in Figure 5.12 and summarized in Table 5.4. The distribution o the deep abdominal blood vessels reects the arrangement o the muscles: The vessels o the anterolat- 5 the obliterated umbilical vein (round ligament o the liver). eral abdominal wall have an oblique, circumerential pattern A relatively direct lateral superfcial anastomotic channel, the (similar to the intercostal vessels; Fig. 5.11), whereas the ves- thoraco-epigastric vein, may exist or develop (as a result sels o the central anterior abdominal wall are oriented more vertically. The superior epigastric artery is the direct continu- To parasternal Axillary ation o the internal thoracic artery. It enters the rectus lymph nodes vein sheath superiorly through its posterior layer and supplies the superior part o the rectus abdominis and anastomoses with the inerior epigastric artery approximately in the umbilical region (see Fig. 5.9; Table 5.4). The inferior epigastric artery arises rom the exter- Axillary lymph nal iliac artery just superior to the inguinal ligament. It nodes runs superiorly in the transversalis ascia to enter the rec- tus sheath below the arcuate line. It enters the lower rec- tus abdominis and anastomoses with the superior epigastric Lateral To anterior thoracic artery (Fig. 5.9). diaphragmatic vein Lymphatic drainage o the anterolateral abdominal wall lymph nodes Thoraco- ollows the ollowing patterns (Fig. 5.11): epigastric Transumbilical vein Superfcial lymphatic vessels accompany the subcutane- plane Peri-umbilical ous veins; those superior to the transumbilical plane drain veins mainly to the axillary lymph nodes; however, a ew drain Superficial to the parasternal lymph nodes. Superfcial lymphatic ves- Superficial epigastric sels inerior to the transumbilical plane drain to the super- inguinal vein lymph fcial inguinal lymph nodes. nodes Femoral Deep lymphatic vessels accompany the deep veins o the vein abdominal wall and drain to the external iliac, common iliac, and right and let lumbar (caval and aortic) lymph nodes. Anterior view FiGURe 5.11. Lymphatics and superfcial veins o the anterolateral For an overview o superfcial and deep lymphatic drain- abdominal wall. age, see Chapter 1, Overview and Basic Concepts. 418 Chapter 5 Abdomen Internal thoracic a. Musculophrenic a. Superior IEA Rectus epigastric a. abdominis 10th posterior External oblique intercostal a. External oblique 11th posterior Internal oblique intercostal a. Internal oblique Subcostal a. Transversus Transversus abdominis abdominis Lumbar artery (LA) Inferior epigastric a. (IEA) Deep circumflex LA iliac a. Superficial epigastric a. Superficial circumflex iliac a. External iliac a. Femoral a. Transversalis fascia (A) Anterior view (B) Transverse CT, L3 vertebral level; A, abdominal aorta FIGURE 5.12. Arteries o the anterolateral abdominal wall. A. Distribution o arteries. B. Neurovascular plane (path) or deep arteries o abdominal wall. A, aorta; LA, lumbar artery. TABLE 5.4. ARTERIES OF THE ANTEROLATERAL ABDOMINAL WALL Artery Origin Course Distribution Musculophrenic Descends along the costal margin Superfcial and deep abdominal wall o the hypochondriac region; anterolateral diaphragm Internal thoracic artery Superior epigastric Descends in rectus sheath deep to Rectus abdominis muscle; superfcial and rectus abdominis deep abdominal wall o the epigastric and upper umbilical regions 10th and 11th posterior Arteries continue beyond ribs to Superfcial and deep abdominal wall o the intercostal arteries descend in the abdominal wall between lateral (lumbar or ank) region Aorta internal oblique and transversus Subcostal abdominis muscles Inferior epigastric Runs superiorly and enters rectus Rectus abdominis muscle; deep abdomi- sheath; runs deep to rectus abdominis nal wall o pubic and inerior umbilical regions External iliac artery Deep circumflex iliac Runs on deep aspect o the anterior Iliacus muscle and deep abdominal wall o abdominal wall, parallel to the inguinal the inguinal region; iliac ossa ligament Superficial circumflex Runs in subcutaneous tissue along the Superfcial abdominal wall o inguinal region iliac inguinal ligament and adjacent anterior thigh Femoral artery Superficial epigastric Runs in subcutaneous tissue toward Superfcial abdominal wall o the pubic and the umbilicus inerior umbilic regions Anterolateral Abdominal Wall 419 CLINICAL BOX FASCIA AND MUSCLES OF or a large mass (e.g., a tumor, a etus, or an enlarged organ
