Layers of the anterior abdominal wall
- Skin and superficial fascia (fatty/Camper’s and membranous/Scarpa’s)
- External abdominal oblique, Internal abdominal oblique, Transversus abdominis.
- Transversalis (endoabdominal) fascia, extraperitoneal fat, parietal peritoneum
Innervation of muscles of the anterior abdominal wall
T6-T12, L1 ventral rami of spinal nerves.
The rectus sheath
Aponeuroses of EO, IO, TA. The rectus sheath reinforces the abdominal wall creating an incomplete compartment around the rectus abdominis (and pyramidalis). It contains the superior and inferior epigastric arteries and veins, lymph vessels and distal portions of the thoracoabdominal nerves and abdominal portions of anterior rami of spinal nerves T7-12.
Differences in the anterior rectus sheath
Note there are differences between the superior ¾ and inferior ¼ of the rectus sheath. The anterior rectus sheath superiorly consists of the external oblique aponeurosis and half of the internal oblique aponeurosis. Posteriorly it consists of the transversus abdominis aponeurosis, and half of the internal oblique aponeurosis. Just below the level of the umbilicus the external oblique, internal oblique and transversus abdominis aponeuroses all travel in front of rectus abdominis. The level at which the posterior rectus sheath stops is called the arcuate line.
Median umbilical ligament
is formed by the fibrous remnant of the urachus that joined the bladder to the umbilical cord
Medial umbilical fold
The medial umbilical ligaments (fold) are formed by the remnants of the umbilical arteries
Lateral umbilical fold
The lateral umbilical fold is formed by the inferior epigastric vessels.
Ligamentum teres hepatis
Superiorly is the ligamentum teres hepatis (round ligament of the liver) a remnant of umbilical vein and a fold of peritoneum the Falciform ligament.
Nerves to the anterior abdominal wall
Supplies all layers – skin to parietal perioneum. The neurovascular plane is located between internal oblique and transversus abdominis or posterior to rectus abdominis.
The thoracoabdoinal nerves are the distal parts of T7-11 intercostal nerve. T7-9 supply skin above the umbilicus, T10 supplies skin around the umbilicus. Below the umbilicus is supplied by the subcostal nerve (T12) and the iliohypogastric and ilionguinal nerve (L1).
Arteries of the anterolateral abdominal wall
Main arteries are the superior gastric (from internal thoracic a), the inferior epigastric artery (from external iliac a), these arteries run just behind the rectus abdominis.
Also – musculophrenic branches, deep circumflex iliac (from ext iliac), lumbar/post intercostal, superficial circumflex iliac and superficial epigastric (from femoral) Provide indirect anastomoses between arch of aorta and abdominal aorta.
Veins of the anterolateral abdominal wall
Deep veins – as for arteries. Superficial veins subcutaneous venous plexus can drain to internal thoracic vein superomedially, the lateral thoracic v superlaterally and the superficial and inferior epigastric vv inferiorly. Anastamoses also occur with the paraumbilical vv.
Provide collateral pathways if SVC or IVC blocked e.g. portal hypertension.
Lymphatic drainage of the anterior abdominal wall
Superficial – above the umbilicus: to anterior axillary nodes or parasternal nodes, below umbilicus: to superficial inguinal nodes.
Deep – to external iliac, parasternal, lumbar nodes.
The inguinal canal
This is a passage through the anterior abdominal wall from deep inguinal ring to superficial inguinal ring connecting the extraperitoneal space of the asbdomen with the scrotum or labia majora.
It allows the testis which develops in the extraperitoneal connective tissue of the posterior abdominal cavity to move to the scrotum where the temperature is slightly lower. In about 3% of males (30% of premature births) the testis (usually unilaterally) is undescended. Undescended testes have a high risk of malignancy.
Muscles that make up the inguinal canal
- Anterior wall – external oblique aponeurosis and internal oblique laterally.
- Posterior wall – transversalis fascia, parietal peritoneum and conjoint tendon medially.
- Floor – inguinal ligament and lacunar ligament medially
- Roof – internal oblique and transversus abdominis.
Spermatic cord contents
The spermatic cord contains the ductus (vas) deferens, testicular artery and pampiniform plexus of vv (testicular vv), genital branch of genitofemoral nerve, lymphatics, autonomic nerves, other vessels. Fascia layers: external spermatic, cremasteric, internal spermatic and the Inguinal branch of ilioinguinal nerve.
Inguinal canal contents in females
In females the inguinal canal contains the round ligament of uterus, genital branch of the genitofemoral nerve, vessels and fascia layers and inguinal branch of ilioinguinal nerve.
The boundaries are the rectus abdominis, inferior epigastric, inguinal ligament. Note also the location of the femoral ring just below the inguinal ligament and the location of the deep inguinal ring lateral to the inferior epigastrics.
Inguinal hernias are classified as direct and indirect. An indirect hernia originates lateral to the inferior epigasteric vessels and passes through the deep inguinal ring into inguinal canal (thus indirectly through the abdominal wall) and exits via the superficial ring. Predisposing factor: congenitally patient processus vaginalis.
A direct hernia stars medial to inferior epigastric vessels and passes directly through the anterior abdominal wall (inguinal triangle region).