Archive for peritoneum

Anterior abdominal wall & inguinal canal & Peritoneum (Konstantin Ravvin)

Posted in February 2012, Medical Notes with tags , , , , , , , , , on February 22, 2016 by Konstantin

Gray’s Anatomy Notes Accompanied by Dissection

Superficial fascia of the abdomen

  • Layer of fatty connective tissue
  • Is a single layer that is continuous with the superficial fascia throughout the body, however below the umbilicus , it forms two layers: a superficial fatty layer and a deeper membranous layer
  • Camper’s Fascia: superficial fatty layer of superficial layer contains fat and varies in thickness
    • Continuous over inguinal ligament with the superficial fascia of the thigh and with similar layer in the perineum
  • Scarpa’s Facia: thin and membranous; contains little or no fat
    • Just below the inguinal ligmanet, it fuses with the deep fascia of the thigh
    • In the midline, it is firmly attached to the linea alba and the symphysis pubis. It continues into the anterior part of the perineum where it firmly attaches to the ischiopubic rami and to the posterior margin of the perineal membrane (referred to as Colle’s fascia)

 

Anterolateral Muscles

 

  • Three flat muscles whose fibers begin posterolaterally, pass anteriorly and are replaced by an aponeurosis as the muscle continues towards the midline
    • External oblique, internal obliqUe and transversus abdominis muscle.
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    • Two vertical muscles, near the midline, which are enclosed within a tendinous sheat formed by the aponeurosis of the flat muscles
      • Rectus abdominis and pyramidalis muscle
        • RA, PM
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        • All of these muscles form a firm and flexible wall that keeps the abdominal viscera within the abdominal cavity
        • Contraction of these muscles assists in both quiet and forced expiration ( by pushing the viscera upwards and in coughing/vomiting) in addition to childbirth, urination and defection.
        • External Oblique (innervated by anterior rami of lower six thoracic spinal nerves T7 to T12): most superficial of all flat muscles (3).
          • Immediately deep to the superficial fascia
          • Its laterally placed muscle fibers pass in an inferomedial direction, while its large aponeurotic component covers the anterior part of the abdominal wall to the midline forming the linea alba which extends from the xiphoid process to the public symphysis.
          • Lower border of the external oblique aponeurosis forms the inguinal ligament on each side, which passes between the anterior superior iliac spine laterally and the pubic tubercle medially.
            • From the inguinal ligament, we have several extensions:
              • the lacunar ligament at the medial end that passes backwards to attach to the pectin pubis on the superior ramus of the pubic bone.
              • From the lacunar ligament, along the pectin pubis, we have Cooper’s ligament
            • Internal oblique (Anterior rami of lower six thoracic spinal nerves T7 to T12 and L1): is smaller and thinner than its external counterpart and passes into the superomedial direction (up and to the middle). Its aponeurosis blends into the linea alba at the midline
            • Transversus abdominis (Anterior rami of lower six thoracic spinal nerves T7 to T12 and L1): deepest of all three flat muscles. It ends in an anterior aponeurosis, which blends with the linea alba at the midline
            • Transversalis fascia : a fascia covers all three of the flat muscles anteriorly and posteriorly. The one posterior to the transversus abdominis muscle is the transversalis fascia, which lines the abdominal cavity and continues into the pelvic cavity
            • Rectus Abdominis (Anterior rami of lower six thoracic spinal nerves T7 to T12): long flat muscle that extends the length of the anterior abdominal wall. It is separated at the midline by the linea alba, and it widens and thins as it ascends from the pubic symphysis to the costal margin. Along its course, it is intersected by three or four transvers fibrous bands or tendinous intersections.
            • Pyramidalis (Anterior ramus of T12): triangle muscle, which may be absent, is anterior to the rectus abdominis, has its base on the pubis, and its apex is attached superiorly and medially to the linea alba, and it widens and thins as it ascends from the pubic symphysis to the costal margin.   Along its course, it is intersected by three or four transverse fibrous bands or tendinous intersections. Its apex is attached superiorly and medially to the linea alba.
            • Rectus Sheath: a tendinous sheat formed by a unique layering of the aponeuroses of the external and internal oblique, and transversus abdominis muscles
              • It encloses the upper ¾ of the rectus abdominis and covers the anterior surface of the lower ¼ of the muscle. There is no sheath covering theposterior surface of the lower quarter, so the muscle connects directly with the transversalis fascia.
              • The formation of the rectus sheat surrounding the upper ¾ of the rectus abdominis muscle has the following pattern:
                • Anterior wall: aponeurosis of the external oblique and half of the aponeurosis of the internal oblique, which splits at the lateral margin of the rectus abdominus
                • Posterior wall: consists of the other half of the internal oblique aponeurosis and the aponeurosis of the transversus abdominis
                • At a point between the umbilicus and pubic symphysis, all aponeuroses move anterior to the rectus muscle – from this point, the rectus abdominis muscle is in direct contact with the transversalis fascia marking the arcuate line.
                  • Arcuate line: where rectus sheath ends all that covers the rectus abdominis muscle is the transversalis fascia

 

Extraperitoneal Fascia

 

  • Deep to the fascia transversalis – essentially separates it from the peritoneum and lines the abdominal cavity
  • Continues over organs covered by peritoneal reflections — and extends into mesenteries with the blood vessels
  • Clinical note: in description of specific surgical procedures, the terminology used to describe the extraperitoneal fascia is further modified: the fascia towards the anterior side of the body is preperitoneal and towards the posterior side is

 

Peritoneum

 

  • Deep to the extraperitoneal fascia is the peritoneum. The peritoneum lining the body wall is parietal and the peritoneum covering the viscera is the visceral peritoneum.
  • The sac formed in the peritoneum (peritoneal sac) is closed in men but has two openings in women where the uterine tubes provide a passage to the outside.
  • Innervation:
    • parietal peritoneum of the anterolateral abdominal wall (T7 to T12 and L1) — these nerves pass from the posterior to anterior, in an inferomedial direction (down and to the middle) then give off the lateral cutaneous branch and end as an anterior cutaneous branch.
    • Intercostal nerves (T7 to T11) pass deep to the costal cartilages and continue onto the anterolateral abdominal wall between the internal oblique and trasnversus abdominis muscles. They enter the rectus sheath and pass to the posterior aspect of the rectus abdominis muscle – approaching the midline, an anterior cutaneous branch passes through the rectus abdominis muscle and the anterior wall of the rectus sheath to supply the skin. Spinal nerve T12 (subcostal nerve) follows similar course.
    • Branches of L1 (iliohypogastric and ilio-inguinal nerve) originate from the lumbar plexus follow a similar course but deviate from this patern near their final destination.
    • All nerves terminate by supplying the skin
    • Nerves T7-79: skin from the xiphoid process to just above the umbilicus
    • T10: skin around the umbilicus
    • T11,T12,L1: below umbilicus to the pubic region (inclusive)
    • Ilioinguinal nerve: supplies the anterior surface of the scrotum or labia majora, and sends a small cutaneous branch to the thigh

 

Arterial Supply and Venous Drainage

 

  • Musculophrenic artery (terminal branch of internal thoracic artery): superior part of the abdominal wall
  • Superficial epigastric artery supplies the medial side (branch of femoral artery)
  • Superficial circumflex iliac artery supplies the lateral side (branch of femoral artery)
  • At a deeper level:
  • Superior epigastric artery supplies the superior part (branch of internal thoracic artery)
  • 10th and 11th intercostal + subcostal artery supplies the lateral side
  • Inferior epigastric artery and deep circumflex iliac artery (branches of external iliac artery) supply the inferior.
  • Superior and inferior epigastric arteries both enter the rectus posterior to the rectus abdominis muscle throughout their course, and anastomose with each other.

 

Lymphatic drainage

 

 

Groin

 

  • The junction between the abdominal wall and the thigh quite susceptible to inguinal hernia
  • Peritoneal outpunching in abdominal wall eventually forms testes/ovaries, protruding through the various layers of the anterior abdominal wall and acquiring coverings from each
    • The transversalis fascia forms its deepes covering, followed by musculature of internal oblique and the most external covering is the aponeurosis of the external oblique
    • This structure forms into a tubular structure knows as the inguinal canal.
  • Processus vaginalis
  • In men, the accompanying vessels, ducts, and nerves pass through the inguinal canal and are therefore surrounded by the same fascial layers of the abdominal wall, forming the spermatic cord
  • In women, the overaies descend into the pelvic caity and become associated with the developing uterus – therefore the only relevant structure passing through the inguinal canal is the round ligament of uterus.

Inguinal Canal

 

  • Begins at the deep inguinal ring and continues for approximately 4 cm, ending at the superficial inguinal ring.
    • Contents: genital branch of the genitofemoral nerve, the spermatic cord in men and the round ligament of the uterus in women. Additionally the ilio-inguinal nerve passes through part of the canal

 

Deep Inguinal Ring

 

  • Beginning of the inguinal canal and is midway point between the anterior superior iliac spine and the pubic symphysis
  • Just above the inguinal ligament and is the beginning of the tubular evagination of transversalis fascia that forms one of the coverings of the spermatic cord in men and round ligament in women.

 

Superficial Inguinal Ring

 

  • End of the inguinal canal
  • The triangular opening of the aponeurosis of the external oblique
  • Ends of the triangle are the medial and lateral crus and are attached to the pubic symphysis and the pubic tubercle, respectively; prevent widening of the superficial ring.

 

Anterior Wall of Inguinal Canal

 

  • Formed along its entire length by the aponeurosis of the external oblique muscle.
  • Reinfroced laterally by the lower fibers of the internal oblique, which contributes a layer to to the deep inguinal ring (cremasteric muscle/fascia)

 

Posterior Wall of Inguinal Canal

 

  • Formed by the transversalis fascia
  • Reinforced along medial one-third by the conjoint tendon ( a combined tendon of the transversus abdominis and internal oblique)

 

Roof of Inguinal Canal

 

  • Formed by arching fibers of the transversus abdominis and internal oblique muscles

 

Floor of the Inguinal Canal

 

  • Medial ½ of the inguinal ligament
  • Lowest part of the aponeurosis of the external oblique. Forms the trough on which the contents of the inguinal canal are position.
  • The lacunar ligament reinforces most of the medial part of the trough.

 

Contents of Inguinal Canal

 

  • The spermatic cord in men
  • The round ligament of the uterus and genital branch of the genitofemral nerve in women
  • Ilio-inguinal nerve enters the theinguinal canal and continues down the canal to exit through the superficial inguinal ring.
  • All structures enter through the deep inguinal ring and exit through the superficial inguinal ring.

 

Spermatic Cord

 

  • Begins proximally at the deep inguinal ring and consists of structures passing between the abdominopelvic cavities and the testis, and the three fascial coverings that enclose these structures. Structures of spermatic cord:
    • Ductus deferers (+ artery), testicular artery, pampiniform plexus of veins, cremasteric artery and vein, genital branch of genitofemoral nerve, sympathetic and visceral afferent nerve fibers.
  • Structures acquire the three fascial coverings during their journey:
    • Internal spermatic fascia (deepest) arises from transversalis fascia
    • Cremaster fascia associated with cremasteric muscle
    • External spermatic fascia (superficial covering of the spermatic cord); arises from the aponeurosis of external oblique

 

Round Ligament of Uterus

 

  • Passes from the uterus to the deep inguinal ring where it enteres the iguinal canal
  • Exists through the superficial inguinal ring
  • As it traversus through the inguinal canal, it acquires the same coverings as the spermatic cord in men.
  • Continues to the ovary as the ligament of the overy.
  • Clinical Note: cremaster muscle and fascia form the middle covering of the spermatic cord (supplied by genitofermoral nerve)
    • Cremaster reflex: gentle touch at and around the skin of the medial aspect of the superior part of the thigh stimulates the sensory fibers of the ilio-inguinal nerve à sensory fibers to L1 à response from motor fibers of genital branch of the genitofemoral nerve
  • Clinical note:
    • Indirect Inguinal Hernia: peritoneal sac enters the inguinal canal by passing through the deep inguinal ring just lateral to the inferior epigastric vessels
      • Congenital in origin
    • Indirect Inguinal Hernia: peritoneal sac enters the medial end of the inguinal canal directly through a weakened posterior wall
      • Does not traverse the entire length of the inguinal canal
      • Is acquired and develops when abdominal musculature has weakened
      • Bulging occurs medial to the inferior epigastric vessels in the inguinal (Hasselbach’s) triangle bounded laterally by the inferior epigastric artery, medially by the rectus abdominis muscle and inferiorly by the inguinal ligament.
    • Clinical Note: Determining Masses Around Groin
      • The key to groin examination is determining the location of the inguinal ligament
        • Passes between the anterior superior iliac spine laterally and the pubic tubercle medially.
        • Inguinal hernias are above the inguinal ligament and are usually apparent upon standing
        • Scrotal masses in men, in tandem with the inability to feel its upper edge suggests that it may originate from the inguinal canal and might be a hernia. Upon coughing, the lump bulges outwardly
        • Inguinal hernia location: through superficial inguinal ring above the pubic tubercle
        • Femoral hernia location: through the femoral canal below and lateral to the pubic tubercle. Usually acquired.
        • Umbilical hernia: result from the failure of the small bowel to return to the abdominal cavity from the umbilical cord during development
        • Incisional hernias: occur from a defect in a scar of a previous abdominal operation
        • Spigelian hernia: passes upward from the arcuate line into the lateral border at the lower part of the posterior rectus sheath.

 

 

 

 

 

 

 

 

Peritoneum

 

  • A thin membrane lines the walls of the abdominal cavity and covers much of the viscera. Between the parietal and visceral layers of peritoneum is a potential space (peritoneal cavity)
    • Abdominal organs are either suspended in peritoneal cavity by folds of peritoneum (mesenteries) or are outside the peritoneal cavity.
    • Innervation:
      • Parietal peritoneum: somatic afferents carried in branches of the associated spinal nerves; sensitive to well-localized pain.
      • Visceral peritoneum: visceral afferents that accompany autonomic nerves (sympathetic and parasympathetic). Activation can lead to referred and poorly localized sensations of discomfort,and to reflex visceral motor activity

 

Peritoneal Cavity

 

  • Subdivided into greater sac and omental bursa
    • Greater sac accounts for most of the space, beginning superiorly at the diaphgragm and continuing inferiorly into the pelvic cavity (you enter it as you penetrate the parietal peritoneum).
    • Omental Bursa: smaller subdivision of the periteoneal cavity posterior to the stomach and liver and is continuous with the greater sac through an opening called the omental foramen
      • Surrounding the omental (epiploic) foramen are
        • Anteriorly: the portal vein, hepatic artery proper, and bile duct d
        • Posteriorly: vena cava
        • Superiorly: caudate liver of the lobe
        • Inferiorly: first part of the duodenum
      • Clinical Note:
        • Ventriculoperitoneal shunts: excessive CSF in the cerebral ventricular system.   Clinical drainage requires a fine-bore catheter through the skull into the cerebral ventricles and placing the extracranial part of the tube beneath the scalp and skin of the chest wall and passing it to the peritoneal cavity from where it is drained.
        • Peritoneal Dialysis: peritoneum is used as dialysis membrane — a small tube is inserted from the abdominal wall and dialysis fluid is injected into the peritoneal cavity. Electrolytes and molecules are exchanged aross the peritoneum between the fluid and blood.
        • Peritoneal spread of disease: if malignant cells enter the peritoneal cavity by direct invasion, spread may be rapid. It can also act as a barrier to contain the disease

Omenta, mesenteries and ligaments

 

  • Throughout peritoneal cavity numerous peritoneal folds connect organs to each other or to the abdominal wall. They are known as omenta, mesenteries and ligaments.
    • They develop from the original dorsal and ventral mesenteries, which suspend the developing gastrointestinal tract in the embryonic coelomic cavity
  • Omenta: consists of two layers of peritoneum, which pass from the stomach and the first part of the duodenum to other viscera.
    • Greater Omentum: derived from dorsal mesentery
      • Attaches to the greater curvature of the stomach and first part of duodenum
      • Drapes over transverse colon and the coils of the jejunum and ileum
      • It associates with the peritoneum on the superior surface of the transverse colon and the anterior layer of the transverse mesocolon before arriving at the posterior abdominal wall
      • Usually contains an accumulation of fat
      • Contains right and left gastro-omental vessels.
      • Clinical Note: when a laparotomy is performed and the peritoneal cavity is opened, the first structure usually encountered is the greater omentum.
        • An important site for metastatic tumors
      • Lesser Omentum: derived from the ventral mesentery
        • Extends from lesser curvature of the stomach and the first part of the duodenum to the inferior surface of the liver
        • Divided into:
          • Medial hepatogastric ligament
            • Passes between stomach and liver
          • Hepatoduodenal ligament
            • Passes between duodenum and liver
          • Mesenteries: attach viscera to the posterior abdominal wall.
            • The mesentery: associated with parts of the small intestine
              • Connects the jejunum and ileum to the posterior abdominal wall
              • Attaches superiorly at the duodenojejunal junction
              • Ends at the ileocecal junction
              • Incases the arteries, veins , nerves and lymphatics that supply the jejunum and ileum.
            • The transverse mesocolon: associated with the transverse colon
              • connects transverse colon to the posterior abdominal wall
              • Traverses the head and body of the pancreas and surround the transverse colon.
              • Incases the arteries, veins, nerves and lymphatics that supply the transverse mesocolon
            • The sigmoid mesocolon: associated with the sigmoid colon
              • Attaches the sigmoid colon to the abdominal wall
              • Shaped in a V whose apex is near the division of the left common iliac artery and divides it into its internal and external branches, with the left limb of the V along the medial border of the left psoas major muscle and the right limb descending into the pelvis to end at the level of vertebra S3.

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