Friday, October 12, 2012

Anterior Abdominal wall

Anterior Abdominal wall

The attachments of the muscles of  interpolate abdominal wall are given in this chapter. The formation and contents of rectos sheath are mentioned. The inguinal canal has been described in detail as its relations are of importance in the reduction/repair of the inguinal hernia. The heading "anterior abdominal wall" usually includes both the front as well as the side walls of the abdomen and needs to be called interpolate abdominal wall.

Surface landmarks

Before taking up the description of the abdominal wall proper it is desirable to draw attention to some surface landmarks that can be
identified on the region. In the anterior median plane, the abdominal wall extends from the xiphoid process which lies at the level of the ninth thoracic vertebre to the pubic symphysis, which lies at the level of the coccyx. Posteriorly and laterally, the vertical extent of the abdominal wall is much less, as it is replaced by the thoracic cage, above and behind; and by the gluteal region, on the posterior aspect of the lower part.The superolateral margins of the anterior abdominal wall are formed by the right and left costal margins. Each margin is formed by the seventh, eighth, ninth, and tenth costal cartilages.The costal margin reaches its lowest level in the midaxillary line.Here the margine is formed by the tenth costal cartilage. The transverse plane passing through the lowest part of the costal margin is called the subcostal plane. It passes through the third lumber vertebra. The infasternal or subcostal angle is formed between the right and left costal margins.The xiphoid process lies in a despression at the apex of the infasternal angle at the level of the ninth thora-cic vertebra. The iliac crest forms the lower limit of the abdominal wall at the side. The highest point of the iliac crest lies at the level of the fourth lumbar vertebra slightly below the normal level of the umbilicus. The anterior superior iliac spine lies at the level of the sacral prormontory. The tubercle of the iliac crest is situated on the outer lip of iliac crest about 5 cm behind the anterior superior iliac spine.The intertubercular plane passes through the tubercles. It passes through the fifth lumbar vertebra. The inguinal ligament extends from the anterior superior iliac spine to the pubic tubercle. It is convex downwards. It is placed at the junction of the anterior abdominal wall with the front of the thigh. The spermatic cord is a soft rounded cord present in the male. It can be felt through the skin as it passes dowenwards near the medial end of the inguinal ligament to enter the scrotum. It can be picked up between the finger and the thumb.When palpated in his way a firm cord-like structure can be felt within the posterior part of the spermatic cord.This is the ductus deferens.The anterior abdominal wall is divided into right and left halves by a
vertical groove. It marks the position of the underlying Linea Alba. A little below the middle of the median furrow there is an irregular depressed or elevated area called the umbilicus. It lies at the level of the junction between third and fourth lumbar vertebrae. A few centimeters lateral to the median furrow,the abdominal wall shows a curved vertical groove. Its upper end reaches the coastal margin at the tip of the ninth coastal cartilage.Inferiority it reaches the pubic tubercle. This line is called the Linea seminarians. It corresponds to the lateral margin of a muscle called the rectos abdominal. The trans pyloric plane is an imaginary transverse plane often referred to an anatomical descriptions. Anterior, it passes through the tips of the ninth costar cartilages; and posterior, through the lower part of the body of the first lumbar vertebra. This plane lies midway between the supernatural notch and the pubic symphonists. It is roughly a hand's breadth below the paternalist joint. The angle between the last rib and outer border of erector spine is known as renal angle. It rib may only be just palpable lateral to erector spine or may extend for some distance beyond it. Posterior superior lilac spine lies about 4 cm lateral to the median plane.Three transverse furrows may be seen crossing the upper part of rectos abdominal, corresponding to the tendinous intersections  of the muscle. One usually lies opposite the umbilicus, the other opposite free end of xiphoid process, and the third midway between the two.                    
        

Cutaneous nerves

The skin of the anterior abdominal wall is supplied by the lower six thoracic nerves and by the first lumbar nerve in the following manner. The anterior cutaneous nerves (seven in number) are derived from the lower five intercostal nerves, the subcostal nerve and the iliohypogastric nerve. T7-T12 nerves enter the abdominal wall directly. They pass between internal oblique and transversus muscle, pierce the posterior lamina of internal oblique aponeurosis to enter rectus sheath. Within the sheath, they pass behind rectus abdominis, then pierce the rectus muscles and the anterior wall of the rectus sheath close to the median plane,divide into medial and lateral branches and supply the skin of the front of the abdomen. They are arranged in serial order; T7near the xiphoid process,T10 at the level of umbilicus,the iliohypogastric nerve 2.5 cm above the superficial inguinal ring,and others at proportionate distances between them subcostal nerve supplies pyramidalis, iliohypogastric and ilioinguinal do not enter rectus sheath. Iliohypogastric becomes cutaneous 2.5 cm above the superficial inguinal ring. The terminal part of the ilioinguinal nerve emerges through the superficial inguinal ring, pierces the external spermatic fascia and descends to supply the skin of the external genitalia and the upper part of the medial side of thigh. The lateral cutaneous nerves are two in number and are derived from the lower two intercostal nerves. Each nerve pierces the external intercostal muscle and divides into a large anterior branch and a smaller posterior branch,both of which emerge between the lower digitations of the external oblique muscle and supply the skin of the side of the abdomen.The larger
anterior branches also supply the external oblique muscle. The lateral cutaneous branches of the subcostal and iliohypogastric (T12-L1) nervs descend ovar iliac crest and supply the skin of the anterosuperior part of the gluteal region.            

Cutaneous veins : The veins accompany the arteries. The superficial inguinal veins drain into the great saphenous vein. When the portal vein, or the superior vena cava, or the inferior vena cava is obstructed the superficial abdominal veins are dilated and provide a
collateral circulation.The dilated veins that radiate from the umbilicus are given the name caput medusae. They are seen typically in in portal obstruction, the thoracoepigastric veins open up, connecting the thoracoepigastric veins open up, connecting the great saphenous vein with the axillary vein. In superior vena caval obstruction, the blood in the thoracoepigastric vein flows doweneards,breaking the barrier of watershed line.In inferior vena caval obstruction,the blood flows upwards,once again crossing the watershed line. Deep arteries of anterior abdominal wall The superior epigastric artery is one of the two terminal branches of the internal thoracic artery. It begins in the sixth intercostal space,and enters the abdomen by passing behind the seventh costal cartilage between the costal and xiphoid origins of the diaphragm.
It enters the rectus sheath and runs vertically downwards, supplies the rectus muscle, and ends by anastomosing with the inferior epigastric artery.In addition to muscular and cutaneous branches, it gives a hepatic branch which runs in the falciform ligament,and an anastomotic branch, at the level of the xiphoid process,which anastomoses with the artery of the oppsite side. The musculophre nic artery is the other terminal branch of the internal thoracic artery. It runs downwards and laterally behind the seventh costal cartilage, and enters the abdomen by piercing the diaphragm between the seventh and eighth cartilage. It continues downwards and laterally along the deep surface of the diaphragm as far as the tenth intercostal space.It gives branches to the diaphragm, the anterior abdominal wall and the seventh, eighth, and ninth intercostal spaces as the anterior intercostal arteries. The inferior epigastric arery arises from the external iliac artery near its lower end just above the inguinal ligament. It runs upwards and medially in the extraperitoneal connective tissue, passes just medial to the deep inguinal ring, pierces the fascia transversalis at the lateral border of the rectus abdominis and enters the rectus sheath by passing in fornt of the arcuate line. Within the sheath it supplies the rectus muscle and ends by anastomosing with the superior epigastric artery.            
                          

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