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Anatomy - Laparoscopic spigelian herniorraphy
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Surgical anatomy of the anterior abdominal wall
1. Layer by layer anatomy
The large region comprising the anterior abdominal wall from the xiphoid process and costal margins to the pelvis is characterized by its layered structure: The skin and subcutaneous fatty tissue are followed by superficial fascias, muscles and their investing fascias, then the extraperitoneal fascia and finally the parietal peritoneum.
Particularly in the infra-umbilical anterior abdominal wall the otherwise characteristic superficial single fascia layer becomes a double-layered structure comprising a superficial fatty layer (panniculus adiposus telae subcutaneae abdominis or Camper fascia) and a deeper membranous layer (stratum membranosum telae subcutaneae abdominis or Scarpa fascia). The 5 abdominal muscles comprise:
3 oblique muscles (1. external oblique, 2. internal oblique and 3. transversus abdominis) and
2 strap muscles (4. rectus abdominis and the inconsistent 5. pyramidalis)
a) Anterior muscle
Immediately posterior to the superficial fascia it courses mediocaudad to the great aponeurosis, with both sides fusing in the midline to the white line (linea alba). Its inferior margin comprises the inguinal ligament traversing from the anterior superior iliac spine to the pubic tubercle, with the medial aspect of the inguinal ligament giving rise to the lacunar and pectineal ligaments (Gimbernat and Cooper respectively).
b) Middle muscle
Its fibers course cephalomedially and fuse with fibers from 1. to form the linea alba.
c) Most posterior muscle
Its transverse coursing fibers also conjoin with the linea alba.
Each of the three oblique abdominal muscles has its own thin anterior and posterior fascia, while the posterior aspect of the transverse abdominal muscle is covered by the firm transversalis fascia. The latter lines the abdominal cavity; cephalad it fuses with the diaphragmatic fascia and posteriorly with the thoracolumbar fascia. Caudad it inserts in the iliac crest and fuses with the endopelvic fascia.
The bilateral rectus abdominis muscle is a long straight muscle crossed by 3 – 4 tendinous intersections (“six-pack”).
The pyramidalis muscle is an inconsistent triangular muscle originating at the superior pubic ramus and inserting in the linea alba. It rests anterior to the rectus abdominis and is invested by its own sheath in the anterior lamina of the rectus sheath.
2. Fascias and peritoneum
The rectus abdominis and pyramidalis muscles are invested by the rectus sheath formed by the 3 oblique abdominal muscles. While the rectus sheath completely invests the upper 3/4 of the rectus abdominis, below the arcuate line it covers the inferior 1/4 only anteriorly; here, the posterior aspect of the rectus abdominis is covered solely by the transversalis fascia and the peritoneum. Above the midpoint between the umbilicus and the symphysis pubis, the rectus muscle has a well-defined investment, formed in front by the aponeurosis of the external oblique and the anterior lamina of the aponeurosis of the internal oblique, and behind by the aponeurosis of the transversus abdominis and the posterior lamina of the aponeurosis of the internal oblique.
Depending on its location, the extraperitoneal space between the transversalis fascia and the peritoneum may be well or ill defined. The retroperitoneal abdominal organs are located in the retroperitoneum. At the anterior abdominal wall, this narrow space (e.g., at the deep inguinal ring) often is termed spatium praeperitoneale (preperitoneal space).
The peritoneum (parietal serosa) forms the completely closed (except for the fallopian tubes in women) peritoneal cavity, with the visceral peritoneum covering the intraperitoneal organs. Inferior to the umbilicus it retains three folds:
Single median umbilical fold (obliterated urachus/embryological urinary tract),
Left and right medial umbilical fold (former umbilical artery),
Left and right lateral umbilical fold (inferior epigastric vessels).
3. Innervation and blood supply
The anterior abdominal wall is innervated by the anterior branches of spinal nerves Th7 to Th11, Th12 (subcostal nerve) and L1 (iliohypogastric and ilioinguinal nerves).
The internal thoracic artery supplies the superior region of the superficial blood supply (→ musculophrenic artery), while the inferior region is supplied by the superficial epigastric and superficial circumflex iliac arteries (both being branches of the femoral artery). The superior epigastric artery supplies the superior region of the deep blood supply (← internal thoracic artery), while the lateral region is supplied by the intercostal arteries and the inferior region by the inferior epigastric and deep circumflex iliac arteries (both being branches of the external iliac artery). Venous drainage is via the corresponding veins.
Anatomy of spigelian hernia
Spigelian hernias are hernias of the linea semilunaris and mostly located where the latter crosses the semicircular line of Douglas (also known as the arcuate line) (point of least resistance).
The arcuate line is the lateral commissure of the rectus sheath and extends from the costal cartilage of the 9th rib down to the symphysis pubis. Where it fuses mediad with the tails of the aponeurosis of the external oblique to form the anterior rectus sheath, it is termed spigelian fascia. Usually, these hernias are located at the level of the inferior margin of the posterior rectus sheath.
Clinically, spigelian hernias present as a protrusion in the lateral lower quadrant, at about the projection of McBurney’s point. The hernia sac may include intestine, omentum, ovary etc.
Spigelian hernias are always acquired and become manifest between the fourth and seventh decade, with no gender predominance. Incarceration is rare.