The Anterolateral Abdominal Wall By Prof. Dr. Muhammad Imran Qureshi

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1 1 P age The Anterolateral Abdominal Wall By Prof. Dr. Muhammad Imran Qureshi Introduction The abdomen is the region of the trunk located between the thorax and the pelvis. It includes the anterolateral walls of the trunk, the deep regions of the posterior wall of the trunk, and the abdominal cavity and viscera within the abdominal cavity. However, the abdominal and pelvic cavities are contiguous / adjoining, forming the abdominopelvic (peritoneal) cavity. Some visceral organs or systems are located partly in the abdominal cavity and partly in the pelvic cavity. Therefore, it is necessary to consider some aspects of the abdomen (especially the viscera) within the larger context of the abdominopelvic cavity. The abdominal cavity and pelvic cavity can be separated by an imaginary plane defined by the pelvic brim of the pelvic bone. Boundaries of the Abdominal Cavity The posterior longitudinal boundary of the abdominal cavity is defined by the lumbar vertebrae and their intervertebral discs. Superior Boundary: Anteriorly, the superior boundary is demarcated by the xiphoid process and infrastenal angle. It comprises of the costal cartilages of ribs 6 to 10, the tips of ribs 11and 12, and the inferior border of rib 12. Posteriorly, the superior boundary is demarcated by the intervertebral disc between vertebrae T12 and L1. The superior boundary of the abdominal cavity rises and falls with the dome of the diaphragm. Inferior Boundary: the inferior boundary of the abdominal cavity is described by the pelvic brim, which may be palpated only in the region of the pubic symphysis and pubic crest anteriorly. The outline of the Pelvic brim from midline posteriorly to midline anteriorly is as follows: Sacral promontory, ala of sacrum, then across the sacroiliac joint, the arcuate line, Pectin pubis, pubic crest and pubic symphysis. Regions of the Abdominal Wall Conventional descriptions of abdominal surface anatomy are useful in determining the location of somatic pain of the body wall and referred pain from abdominal and pelvic viscera In order to identify the location of direct somatic or referred visceral pain in the abdominal wall, clinicians divide the abdominal wall into four or nine regions by drawing imaginary lines between certain bony landmarks. Thus: The anterior abdominal wall can be divided into four regions by drawing a longitudinal line at the midline and the transumbilical line (a transverse line through the umbilicus). This divides the abdomen into upper right, upper left, lower right, and lower left quadrants

2 The anterior abdominal wall can also be divided into nine regions by drawing two longitudinal mid clavicular (mid inguinal) lines, a superior subcostal line, and an inferior intertubercular line OR a superior trans pyloric line (The lies slightly above the subcostal line and bisects the tip of the 9 th costal cartilage), and an inferior intercristal line (that joins the highest points of the two iliac crests----it also lies slightly above the intertubercular line). These lines divide the anterior abdominal wall into the left hypochondriac, epigastric, right hypochondriac, left lateral (lumbar), umbilical, right lateral (lumbar), left iliac (inguinal), hypogastric (pubic), and right iliac (inguinal) regions. Sometimes it is also useful to draw a spin umbilical line on the anterior abdominal wall to describe the relative location of the appendix. This line passes upwards and medially, from the Anterior Superior Iliac Spine (ASIS) to the Umbilicus. Typically, the appendix is located at a point between the lower one third and upper two thirds of the spin umbilical line. This is called McBurney's point. LAYERS OF THE ABDOMINAL WALL The skin on the outside of the abdomen and the mesothelium lining the abdominal cavity enclose three intermediate layers of muscle and associated fascia The layers in most regions of the abdominal wall are organized symmetrically. From superficial to deep, these layers are the integument (skin), superficial fascia (hypodermis, or subcutaneous fat), deep fascia, external oblique muscle, deep fascia, internal oblique 2 P age

3 muscle, deep fascia, transversus abdominis muscle, deep fascia, and peritoneal membrane (peritoneum), which has a layer of more superficial sub serous fascia and a deeper layer of mesothelium. In the specialized regions of the rectus sheaths and inguinal canals, the arrangement of these layers has been modified Integument of the Abdomen The Integument of the abdomen contains specialized integumentary organs It has a superficial layer of epidermis and a deep layer of dermis. The epidermis contains sensory nerve endings and end organs of the spinal nerves, which sense pain, temperature, and touch. The dermis contains blood vessels, which exchange nutrients and wastes and regulate the temperature of the body. Hair, sebaceous glands, and sweat glands are present in the epidermis and grow downward into the dermis. However, the abdominal region does not have specialized apocrine glands such as those located in the areola of the breast Superficial Fascia The Superficial fascia (hypodermis) lies just deep to the dermis. This is a layer of loose connective tissue. In the abdominal wall, it comprises of two layers that can be easily identified. A thick fatty outer layer (Camper's fascia), and a thin membranous inner layer (Scarpa's fascia). The outer layer (Camper's fascia), which is a major fat depot, is easy to appreciate as a definitive entity at dissection. This layer may become thickened with age, even if it is transplanted with its associated integument to some other region of the body (e.g., the dorsal surface of the hand, as done in reconstructive surgery). The superficial fascia is continuous into the labium majus and perineum of females and into the scrotum and perineum of males. In these regions, it is known as Colles' fascia (in both sexes). In the scrotal wall of the male, the superficial fascia also contains nonstriated muscle and is called the dartos muscle. The dartos contracts to pull the testes closer to the body wall in cold temperatures. Scarpa's fascia is difficult to appreciate at dissection because it tends to be closely adherent to the overlying layer of Camper's fascia. Because Scarpa's fascia is not firmly bound to the underlying deep fascia covering the external oblique muscle, a space may develop between these layers, resulting from seepage of blood or urine following injury to the urethra or perineal vessels. 3 P age

4 Scarpa's fascia and Colles' fascia, are firmly fused to the underlying deep fascia at the boundary between the abdomen and the thigh, at the boundary between the perineum and the thigh, and along a strip of deep fascia connecting the ischial tuberosities of the pelvic bone. This fusion prevents blood and urine from seeping into the thigh and anal triangle of the perineum. Abdominal Muscles The three layers of abdominal wall muscles are homologous to muscles of the thoracic wall, but there is also a fourth segment of muscle in the abdominal wall (and sometimes a fifth one) Three of these parts correspond to the precursors that give rise to the external, internal, and innermost intercostals muscles of the thoracic region. In the abdominal wall, these are the external oblique, internal oblique, and transversus abdominis muscles. The fourth segment gives rise to the rectus abdominis muscles (rectus columns), which flank the abdominal ventral midline. A fifth pair of muscles, the pyramidalis muscles, is also present sometimes. The External Oblique The external oblique muscles are the most superficial of the abdominal wall muscles The fibers of the external oblique muscles course obliquely from a lateral superior region of the abdomen to more inferior medial regions (hands in the pockets). The superolateral attachments (often referred to as origins) of these paired muscle sheets are from the outer surfaces and lower borders of the lower eight ribs. The fleshy fibers rarely descend further than the level of spinoumbilical line. At this point, muscle fibers give way to a strong tendinous aponeurosis, which is an expanded fibrous sheet of tendon. The medial and inferior terminations of this aponeurosis are the insertions of the external oblique muscle Thus, the medial insertion of the external oblique muscle is a ventral midline tendon formed by fusion of the paired external oblique, internal oblique, and transverses abdominis muscle tendons. This is called the linea alba, which is characterized as a tendinous raphe (i.e., the line of union of two contiguous bilaterally symmetric structures). The most inferior border of the external oblique muscle is a thickened tendon called the inguinal ligament. This tough band of tendon extends from the pubic tubercle to the ASIS of the iliac bone. Below, it is folded slightly inward, forming a shallow trough deep to the inferior edge of the external oblique aponeurosis. The most posterior region of the external oblique muscle, which arises from ribs 11 and 12, is inserted onto outer lip of the anterior half of the iliac crest. 4 P age

5 The Internal Oblique Internal oblique muscles lie deep to the external oblique muscles The internal oblique muscles are thinner than the external oblique muscles, and their fibers course at an angle approximately 90 degrees from the direction of the external oblique muscle fibers. The internal oblique muscles arise from the anterior edge of the thoracolumbar fascia, the anterior two thirds of the iliac crests, and the lateral two thirds of the inguinal ligament Fibers of the internal oblique muscles arising from the most medial regions of their attachments to the inguinal ligaments arch over the spermatic cord in males or round ligament of the uterus in females to blend with deeper fibers of the transversus abdominis muscles, forming the conjoined tendon (falx inguinalis). The fibers of the conjoined tendon insert upon the pubic crest and pubic symphysis Internal oblique fibers arising from the more lateral regions of the inguinal ligament and most regions of the iliac crest insert along the ventral midline within the linea alba and superiorly upon the cartilages of ribs7 to 9. The internal oblique fibers arising from the most posterior regions of the iliac crest insert onto the inferior borders of 10 th to 12 th ribs The cremaster muscle is a specialized region of the internal oblique muscle that invests the spermatic cord in males. Transversus Abdominis The deepest layer of anterolateral abdominal muscles is the transversus abdominis muscles The transversus abdominis muscles are named for the direction of their fibers, which course horizontally. The origins of these muscles include: The lateral one third of the inguinal ligament, anterior two thirds of the iliac crest, thoracolumbar fascia, ribs 11 and 12, and costal cartilages of ribs 7 to 10. The most inferomedial fibers of the transversus abdominis muscle intermingle with fibers of the internal oblique muscle to form the conjoined tendon, which inserts on the pubic crest and pubic symphysis. All of the 5 P age

6 remaining fibers of the transversus abdominis muscle insert upon the entire length of the linea alba, from the pubic symphysis to the xiphoid process. Rectus Abdominis The fourth group of muscles in the abdominal region is the paired rectus abdominis muscles The rectus abdominis muscles are attached inferiorly to the pubic crest and pubic symphysis and superiorly to the costal cartilages of ribs 5 to 7, in the vicinity of the xiphoid process. The rectus abdominis muscles are usually marked by three to five horizontal bands of connective tissue called tendinous intersections. These bands develop at the points where muscle precursors of adjacent myotomes have fused to form the rectus muscles. The bands are also fused to the inner aspect of the overlying tendon of the rectus sheath, which is a specialized tendinous structure enclosing each of the rectus columns. The sheath is formed by tendons of the external oblique, internal oblique, and transverses abdominis muscles. A fifth pair of small triangular-shaped muscles is sometimes found within the inferior region of the anterior abdominal wall The small paired pyramidalis muscles may be attached inferiorly to the pubic symphysis and pubic crest and superiorly to the linea alba at a point midway between the pubic crest and the umbilicus. The pyramidalis muscles tense the linea alba and, like the rectus abdominis muscles, are enclosed within the rectus sheath. 6 P age

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