Anterior Abdominal Wall and Inguinal Canal



1. Define the boundaries of the abdominal cavity and the skeletal components related to the abdominal wall.

The abdomen is bordered superiorly by the thoracic diaphragm and is continuous inferiorly with the pelvic cavity. Anteriolaterally, it is bound by the abdominal wall which is a muscular sheath anchored to the ribs, costal cartilages, and the pelvis. Posteriorly, it is bound by part of the diaphragm and the lumbar vertebrae.

2. Describe the major surface landmarks of the anterior abdominal wall.

Prominent surface landmarks of the anterior abdomen include the umbilicus, the former attachment point of the umbilical cord and the anterior superior iliac spine (ASIS) on either side of the anterior-inferior abdomen where the skin attaches tightly. Running down the median through the umbilicus is the linea alba, either side of which are the linea semilunaris, which define the lateral borders of the rectus sheath (the external and internal oblique, and transversalis aponeuroses) around the rectus abdominis muscle.

3. Describe the lines and planes that are used to divide the abdomen into quadrants and regions.

4 Quadrants
Abdomen is divided up by the transumbilical plane into upper and lower halves, and by the median plane into left and right halves, forming 4 quadrants.

Right Upper
Left Upper
Right Lower
Left Lower

9 Regions
The abdomen is divided by two horizontal planes: the subcostal plane at the bottom of the ribcage, around L2, and the transtubercular planes through the iliac tubercles and the L5 vertebrae. The abdomen is then divided by two vertical planes down the midclavicular line, just medial to the nipples on both right and left sides. This produces the 9 regions:

Right Hypochondriac
Epigastric
Left Hypochondriac
Right Lumbar
Umbilical
Left Lumbar
Right Inguinal
Hypogastric
Left Inguinal

4. Define the blood supply, nerve supply, fascial layers, muscle layers, extraperitoneal fat and parietal peritoneum of the anterior abdominal wall.

The anterior abdominal wall is made up of:

(1) Skin - duh...

(2) Superficial fasia - composed of a fatty camper's fascia and membranous scarpa's fascia. Camper's fascia can vary markly in thickness, depending on the obesity of the individual. The scarpa's fascia has no fat cells with in it and is continuous with the scrotum/labia majora but not with the thigh.

(3) Muscles and deep fascia - a deep layer of fascia is intimately invested with the external oblique muscle and is extremely thin. The muscle layers are composed of the external oblique, the internal oblique, and the transverse abdominal muscle. These three muscles also contribute aponeurosis to the rectus sheath.

The external oblique muscle fibers run "fingers in pockets" direction while the internal oblique runs at right angles to it; the transversus abdominal muscle fibers run transversely.

These muscles are innervated by the thoracoabdominal nerves that are the anterior rami of the T7-T12 spinal nerves. The cremaster muscle at the inferior portion of the internal oblique muscle which extends to the testes in males is innervated by the genital branch of the genitofermoral nerve (L1).

Cutaneous innervation of T7-T11 is by the thoracoabdominal nerves, T12 by the subcostal nerve, and L1 by the iliohypogastric and ilioinguinal nerves.

Blood is supplied by in part by the internal thoracic artery superiorly which splits into the musculophrenic artery that follows the costal margin, and the superior epigastric artery which goes inferiorly. The major blood supply comes inferiorly from the external iliac artery and femoral artery. Before it crosses the inguinal ligament, the external iliac artery gives off the inferior epigastric artery and the deep circumflex iliac artery. After the external iliac passes under the inguinal ligament, its name changes to the femoral artery, where it quickly gives off the superficial epigastric artery and superficial cirumflex iliac artery, both of which supply tissues superficial to the rectus sheath.

(4) Transversalis fascia - The transversalis fascia covers the deep surface of the transverse abdominal muscle and its aponeurosis with the left and right sides of the fascia continuous deep with the linea alba.

(5) Extraperitoneal fat - separates the transversalis fascia from the parietal peritoneum.

(6) Parietal peritoneum - external to the transversalis fascia, separated by extraperitoneal fat.

5. Describe the configuration of the anterior and posterior walls of the rectus sheath superior and inferior to the arcuate line.

The anterior and posterior walls of the rectus sheath are different superior and inferior to the arcuate line, a crescent shaped area that is located approximately 1/3 the distance from the umbilicus to the pubic crest.

Superior to the arcuate line, the anterior border is made up of the aponeurosis of the external oblique. The internal oblique actually splits its aponeurosis such that is provides contributions to both anterior and posterior sides of the rectus sheath. The transverse abdominal muscle supples only the posterior side along with the transveralis fascia, extraperitoneal fat, and parietal peroitoneum.

However, after the arcuate line, all three aponeurosis of the external and internal oblique and transverse abdominal muscle only supply the anterior side of the rectus sheath. The posterior side is supplied only by the transveralis fascia, extraperitoneal fat, and parietal peritoneum. This is so that the blood supply can get through without crossing so many aponeurosis layers.

6. Define the inguinal canal, including the location of the deep and superficial inguinal rings.

The inguinal canal is the oblique intermuscular passage through the inferior portion of the anterior abdominal wall. It extends from the deep inguinal ring laterally to the superficial inguinal ring medially.

Know the structures forming the walls of the inguinal canal.
The anterior wall is formed by the aponeurosis of the external abdominal oblique muscles and reinforced on the lateral part by fibers from the internal oblique.

The posterior wall is formed by the transversalis fascia, except medially where it is reinforced by the conjoined tendon from the internal oblique and transverse abdominal aponeurosis.

The floor is formed by the inguinal ligament and lacunar ligament, which attaches the inguinal ligament to the pectineus muscle.

The roof is made of arching fibers from the internal oblique and transverse abdominal muscles.

One way to remember these structures is with the mnemonic "MALT", starting at the top and going counterclockwise
  • M - muscles
  • A - aponeuroses
  • L - ligaments
  • T - transversalis/tendon


Define the function and mechanics of the inguinal canal.
It is the passage for the testes from the posterior abdominal wall to descend into the scrotum during males development

Describe the contents of the inguinal canal. How do these differ between sexes?
In males, it contains the spermatic cord; in females, it contains the round ligament that is equivalent to the gubernaculum in males.

Describe the borders of the inguinal triangle.
The inguinal triangle is bordered medially by the lateral border of the rectus abdominis muscle, laterally by the inferior epigastric vessesl that supply the rectus abdominis muscle, and inferiorly by the inguinal ligament which follows the iliopubic tract.

7. Define the processus vaginalis, spermatic cord, epididymus, cremaster muscle, testes, and scrotum.

Process Vaginalis
The parietal peritoneum that is pulled into the scrotum during development, providing communication between the peritoneum and the testes that usually closes off in adults.

Spermatic Cord
Suspends the testes in the scrotum and contains structures running to and from the testes such as the ductus deferens, testicular artery, pampiniform plexus of veins, lymph vessels, and nerves.

Epididymis
Contains a head, body and tail portion and stores sperm.

Cremaster Muscle
Continuation of the internal oblique muscle that descends into the scrotum.

Testes
Male reproductive organs located in the scrotum where sperm develop.

Scrotum
Cutaneous sac containing the testes.

8. Describe the coverings of the spermatic cord and their relation to the development of the inguinal canal. How do these layers relate to the coverings of the scrotum?

The coverings of the spermatic cord superficial to deep include the extenral spermatic fascia derived from the external oblique aponeurosis, the cremasteric muscle and fascia derived from the fascia of both the deep and superficial surfaces of the internal oblique muscle and its muscle fibers, and the internal spermatic fascia derived from the transversalis fascia. The transverse abdominal muscle does not provide a aponeurosis covering for the spermatic cord because the muscle insertion is on the lateral 1/3 of the ASIS, too lateral to reach the spermatic cord.

The external and internal oblique, and transversalis fascia, which make up the coverings of the spermatic cord, lie within the scrotum. The layers of the scrotum from superficial to deep include skin and superficial (dartos) fascia containing smooth muscle responsible for contraction of the skin, and continuous with the scrotal septum.

9. Chart the blood supply and lymphatic drainage of the testis. How do they differ from the scrotum.


Blood Supply
Lymph Drainage
Scrotum
Posterior scrotal branchs of perineal a. Anterior scrotal branches of the deep pudendal a. Cremaster a.
drain into suprificial inguinal lymph nodes
Testis
testicular a. arising from abdominal aorta just inferior to renal a. pampiniform venous plexus forming R&L testicular veins
drain into R&L lumbar (caval/aortic) and preaortic lymphnodes (delayed detection of cancer)

10. What is an inguinal hernia? What features distinguish a direct from an indirect inguinal hernia?

Inguinal hernia is an abdominal hernia through anterior abdominal wall in the inguinal region.

Direct: leaves the abdominal cavity medial to the inferior epigastric artery within the inguinal triangle, travels anteriorly through the posterior wall of the inguinal canal that is formed by the transversalis fascia and exits via the superficial inguinal ring, hence only the medial portion of the inguinal canal is traveled. Covered by one or two layers of the spermatic cord. Less common than indirect hernia, usually occurs in men older than 40.

Indirect: leaves the abdominal cavity lateral to the inferior epigastric artery and travels through the deep inguinal ring, the entire inguinal canal, and the superficial inguinal ring. Is covered by all 3 layers of the spermatic cord with remains of the process vaginalis forms the hernial sac. 20 times more common in males than females.