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Anterior Body Wall
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FALL 1999 Moore, pp80-93, 178-209 Lecture 10 Dr. C. Dlugos
ANTERIOR BODY WALL AND INGUINAL REGION Overview: The anterior and lateral abdominal wall is composed mainly of musculotendinous elements with the exception of the sternum, ribs, and costal cartilages. A major function of the wall is protection of the vital organs within. The inguinal area is the region where the trunk meets the thigh and is part of the abdominal wall. It is strengthened by the inguinal ligament, formed completely by the external oblique muscle. The inguinal region is important clinically in males because it is the site of inguinal hernias or "ruptures".
Objectives: To develop an understanding of: 1. the anterior body wall
wall
4. the coverings and contents of the spermatic cord 5. the types of hernias
Surface landmarks in the thorax: 1. Suprasternal or jugular notch; easily palpated concave center of the medial border of the manubrium 2. Sternal angle of Louis: between manubrium and body of sternum , landmark for second rib 3. Xiphisternal junction: xiphoid process meets the body of the sternum Surface landmarks in the abdomen: 1. Linea seminlunaris: lateral border of rectus abdominis muscle 2. Linea alba: the aponeurotic line connecting the two sheets enclosing the rectus abdominis muscles. 3. Umbilicus: where umbilical cord attached, supplied by T10 spinal nerve
Layers of anterior and lateral body wall: (M2.4., p179).
6. Serous membranes:
Muscle layers of the anterior and lateral body wall:
Embryology: The muscles of the anterior and lateral body wall consist of three flat muscles and a pair of vertical muscles in the abdomen. In the thorax, all muscles are flat. All muscles are derived from the hypomere (Sadler, p166-168, Fig. 10.1.-10.2.) and include flat and vertical muscles. Flat Muscles of Thorax : External intercostals: ( 11 pairs) run inferior and anterior from the rib above to the rib below, become continuous with the external intercostal membrane anteriorly at the costochondral junction (Moore Fig.1.16, p81)
Internal intercostals: (11 pairs) run inferior and posterior deep to and at right angles with the external intercostals. These muscles are continuous posteriorly with the internal intercostal membrane at approximately the angle of the ribs (Moore Fig. 1.17, p82). Innermost intercostals: incomplete layer occupying the middle portion of the intercostal space, lie directly beneath the internal intercostals and run in the same direction. Subcostals: incomplete layer beneath innermost intercostals and near the angle of the ribs, run internal to the innermost, can span several intercostal spaces (Moore Fig.1,18 B, p83)
Transversus Thoracis: run from sternum to costal cartilages, usually 4-5 pairs (Moore, Fig.1.17, p82)
Vertical Muscle of Thorax: Absent and replaced by bone except for a remnant, the sternalis muscle, which is sometimes present on the undersurface of the sternum.
Innervation of all these muscles is by corresponding intercostal nerves The thoracic muscles aid in inspiration with the exception of the transversus thoracis which has a weak expiratory function. Blood supply; intercostal arteries. The arteries and nerves of the thorax are segmental. Each intercostal space contains an intercostal artery which is formed posteriorly bythe posterior intercostal arteries ( Origin: the supreme intercostal artery (T1 and 2) and the thoracic aorta (T3-11) and anteriorly by anterior intercostal arteries (T1-6) arising from the internal thoracic artery and the musculophrenic artery (T7-11). The lower segmented pair associated with vertebral level T12 are termed the subcostal arteries.
Corresponding Muscles of Abdomen: (Moore, Fig.2.5, p181 and Fig 2.7, p183).
Flat Muscles:
External oblique : most superficial muscle, fibers run anterior and inferior ( your hands in outside pockets). The external oblique muscle attaches to the outer surface of the ribs well above costal arch Internal oblique: middle layer of muscle, fibers run at right angles to the external oblique (hands in inside pockets), attaches to the costal arch. Transversus abdominis: most internal muscle, fibers run transversely, attaches inside rib cage above costal arch Other attachments of these muscles:
3. External abdominal oblique muscle attaches to the pubic tubercle and the anterior supeior iliac spine as the inguinal ligament Vertical muscles:
Rectus abdominis: midline muscles connected by tendinous intersections which represent embryologic segmentation. The rectus abdominis is covered by a sheath. The arcuate line (linea semicircularis) divides the sheath into two regions. (Moore, Fig.2.8., p85) Above the arcuate line the rectus sheath has two layers; 1) an anterior layer derived from the aponeuroses of the external oblique and the anterior layer of the aponeurosis of the internal oblique muscles and 2) a posterior layer formed from the aponeuroses of the internal oblique and transversus abdominis muscles. The internal oblique aponeurosis splits to accommodate the rectus sheath. Below the arcuate line, all three flat muscles contribute to the anterior portion of the rectus sheath and there is no posterior component. At and below the arcuate line, the rectus abdominis muscle lies entirely on the transversalis fascia. It attaches proximally on the xiphoid process and lower costal cartilages and on the pubic symphysis and crest.
Innervation of the abdominal muscles: Of the twelve thoracic nerves, the lower six supply almost all the abdominal muscles. The internal oblique and the transversus abdominis receive a minor supply from the ventral ramus of L1 via the iliohypogastric and ilioinguinal nerves. . Function of the abdominal muscles:
Blood supply: five lower intercostal and subcostal arteries supply the flat abdominal muscles.The superior epigastric artery, a branch of the internal thoracic artery, and the inferior epigastric artery, a branch of the external iliac artery, anastamose and supply the rectus abdominis and sheath.
The Inguinal Region: Hesselbach’s Triangle: surface landmark important due to the underlying inguinal region. Borders of the triangle are: 1. lateral: a line which begins at a point midway between the pubic symphysis and the anterior superior iliac spine and extends to the umbilicus (demarcates the path of the inferior epigastric artery as it branches from the external iliac artery and courses behind the rectus abdominis muscle)
2. medial: the edge of the rectus abdominis or the linea semilunaris 3. inferior: the inguinal ligament Hesselbach’s triangle is of clinical importance since it is the site of a direct hernia. In addition, the path of the inferior epigastric artery forms the lateral border of this triangle. Important clinical information concerning the type of hernia present in your patient can be ascertained by understanding the relationship between the hernia site and the inferior epigastric artery.
Inguinal Ligament: (Moore, Fig.2.12, p194 )important structure within the inguinal region. The inguinal ligament is formed from the inferior border of the aponeurosis of the external oblique muscle as it extends between anterior superior iliac spine and the pubic tubercle. The lateral third of this ligament is attached to a band of iliac fascia which is continuous with the fascia lata of the thigh. The medial portion forms the superficial inguinal arch where the femoral vessels pass through (site of femoral hernia, most common in women) The majority of the medial surface of the inguinal ligament is attached to the pubic tubercle although it also includes specific ligaments discussed below. Specific parts:
Inguinal Canal: oblique passage, 4 cm long in adults, runs inferiormedially and from deep to superficial . The inguinal canal is formed from the three flat abdominal muscles and has two openings, the superficial inguinal ring (described above) and the deep inguinal ring. The deep ring of the inguinal canal is a slit like opening within the transveralis fascia formed lateral to the inferior epigastric artery. The ductus deferens and associated structures in the male and the round ligament of the uterus in the female enter the inguinal canal through the deep inguinal ring (Moore, Fig.2.13, p195). Walls of the inguinal canal include: 1. anterior wall-aponeurosis of the external oblique
3. roof-arching fibers of internal oblique and transversus abdominis muscle 4. floor-lacunar ligament and superior surface of remaining inguinal ligament
Descent of the testes (Sadler pp305-308, Moore, Fig. 2.19, p196). The testes originate retroperitoneally in the lumbar region in association with the mesonephric kidney and is attached to the posterior body wall by the urogenital ligament. During the second month of embryonic development, a cord, the gubernaculum testes is formed which extends from the caudal pole of the testis to the future scrotum. During the third month, the rapid growth of the body and the failure of the gubernaculum to elongate, causes a downward shift in the position of the testis. At seven months, the testes reach the inguinal canal and, at birth, the scrotum. Independent and in advance of the testis, an evagination of peritoneum, the processus vaginalis travels through the body wall and into the scrotum pushing fascial and muscular portions of the anterior abdominal muscles with it to form the inguinal canal. The testis uses the inguinal canal as a path into the scrotum and the spermatic cord, consequently becomes covered with the fascial and muscle layers. Eventually, the connection between the processus vaginalis and the abdominal cavity is obliterated but a potential weakness always exists due to the continuation of the peritoneal cavity between the body wall and the scrotum during embryonic development. In the adult, the gubernaculum testis forms the scrotal ligament and the processus vaginalis becomes partially obliterated to form the tunica vaginalis a two-layered peritoneal remnant covering the anterior and lateral surfaces of the testis.
Coverings over the spermatic cord:
Spermatic cord: the vas or ductus deferens and associated structures which run to and from the testis (components listed below). The coverings of the spermatic cord are:
Constituents of the spermatic cord:(Moore, Fig.2.16., p199).
The ilioinguinal nerve passes through the inguinal canal but is not within the fascial sheath which encloses structures within the spermatic cord . The ilioinguinal nerve, therefore is not included in the constituents of the spermatic cord although it traverses the canal.
Females: (Moore, Fig. 2.15., p197, Grants 2.13, A-D)
Descent of the ovaries: The ovaries also descend from the lumbar region but stop near the uterus. In the female, the processus vaginalis is obliterated and the gubernaculum becomes subdivided by the fallopian tubes into the ovarian ligament and the round ligament of the uterus. The free end of the round ligament in the female travels through the inguinal canal, and terminates in the the female homologue to the scrotum, the labia majora. (Moore, Fig.2- 18).
Contents of the inguinal canal in females, the round ligament of the uterus, the ilioinguinal nerve, a fat pad and the artery of the round ligament. The cremaster muscle in females covers the constituents in the canal but does not travel through the superficial inguinal ring. See Grants Atlas .
Femoral Hernia (Moore, p548): more common in women than men due to the pressure on the leg created by pregnancy and helped along by the fact that females have smaller bones but wider hips.
Case studies pertinent to these topics, Case 2.22, p325, 329 Case 2.7, p302, 305
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