Anterior Abdominal Wall, Inguinal Canal and Peritoneum

Question 1

[5-minute video]: 3D tour of the Inguinal Canal

Answer 1

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Question 2

[8-minute video]: the Rectus Sheath with Dr. Adel Bondok

Answer 2

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Question 3

[25-minute video]: the Peritoneum - The Noted Anatomist

Answer 3

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Question 4

List the surface landmarks of the abdomen.

Answer 4

Bony landmarks:
costal margins, xiphoid process, iliac crest, pubic symphysis

Soft tissue landmarks:
groove of groin, midline furrow/groove, umbilicus, linea semilunaris, spermatic cord, McBurney’s point, Murphy’s point

[Diagram 1] [Diagram 2] [Diagram 3]

Further notes:
costal margins: the cartilages of the 7th, 8th, 9th, and 10th ribs form the costal margins. The 7th costal cartilage is the lowest cartilage to reach the sternum. The right and left costal margins run upward and medially toward the side of the xiphoid process and enclose between them an infrasternal angle. The costal margin reaches its lowest level in the midaxillary line.
xiphoid process: it lies at the level of the T9 vertebra
groove of groin: it is a curved linear horizontal groove which extends downward and medially from the ASIS to the pubic tubercle. It is convex downward and overlies the inguinal/Poupart’s ligament, hence it is also called the inguinal/Poupart’s line. It is placed at the junction of the anterior abdominal wall and the front of the thigh.
midline furrow/groove: It is a linear furrow/groove, which extends from the xiphoid process above to the pubic symphysis below. It corresponds to the linea alba — a tendinous raphe, which separates the two rectus muscles from each other. The midline linear furrow divides the anterior abdominal wall into right and left halves.
umbilicus: It is an irregular, depressed scarred area in the linear midline
furrow, a little below its midpoint.
linea semilunaris: It is a curved furrow, which extends from tip of the 9th costal cartilage to the pubic tubercle. It lies few centimeters away from the median furrow and corresponds to the lateral margin of the rectus abdominis.
spermatic cord: It is a soft rounded cord present in the males. It can be palpated through skin as it passes downward just above the medial end of inguinal ligament to enter the scrotum.
McBurney’s point: It is a point at the junction of medial 2/3rd and lateral 1/3rd of the line extending from the umbilicus to the anterior superior iliac spine (spinoumbilical line). The base of appendix lies deep to this point.
Murphy’s point: It is a point where linea semilunaris meets the right subcostal margin. It corresponds to the tip of the 9th costal cartilage. The fundus of gall bladder lies deep to this point.

Question 5

Describe the sensory innervation of the abdominal wall.

Answer 5

The skin of the anterior abdominal wall is supplied by the six lower intercostal and subcostal nerves. The most inferior part is supplied by the first lumbar nerve through the iliohypogastric and ilioinguinal nerves. [Diagram]

Question 6

State the boundaries of the abdominal wall.

Answer 6

Superiorly: xiphoid process, costal cartilages of the 7th to 10th ribs
Inferiorly: iliac crest, anterior superior iliac spine, inguinal ligament, pubic tubercle, pubic crest and pubic symphysis

Question 7

List the layers of the anterolateral abdominal wall from the most superficial.

Answer 7

✓ skin
✓ Camper’s fascia (fatty part of superficial fascia of anterior abdominal wall)
✓ Scarpa’s fascia (membranous part of superficial fascia of anterior abdominal wall)
✓ external oblique abdominis
✓ internal oblique abdominis
✓ transversus abdominis
✓ fascia transversalis
✓ parietal peritoneum

[Diagram: Layers of the anterior abdominal wall]
♌︎ The arcuate line is an area of demarcation visible from the peritoneal surface of the abdominal wall, residing one-third the distance between the umbilicus and the pubis. The arcuate line can be a sharp demarcation, or it can be a gradual transition zone where the fibers of the posterior sheath gradually disappear. In addition, the arcuate line is the location where the inferior epigastric vessels perforate the rectus sheath, to supply blood to the inferior portion of the anterior abdominal wall.

Further notes:
Extraperitoneal fat may be found between fascia transversalis and the parietal peritoneum.
[6-minute video]: applied anatomy - Appendectomy

Question 8

List the layers of the paramedian anterior abdominal wall starting with the most superficial.

Answer 8

✓ skin
✓ Camper’s fascia
✓ Scarpa’s fascia
✓ anterior layer of the rectus sheath (formed by aponeurosis of external abdominal oblique muscle and anterior lamina of internal abdominal oblique muscle)
✓ rectus abdominis muscle
✓ posterior layer of the rectus sheath (formed by posterior lamina of internal abdominal oblique muscle and aponeurosis of transversus abdominis muscle)
✓ fascia transversalis
✓ parietal peritoneum

[Diagram: Layers of the anterior abdominal wall]
♌︎ The arcuate line is an area of demarcation visible from the peritoneal surface of the abdominal wall, residing one-third the distance between the umbilicus and the pubis. The arcuate line can be a sharp demarcation, or it can be a gradual transition zone where the fibers of the posterior sheath gradually disappear. In addition, the arcuate line is the location where the inferior epigastric vessels perforate the rectus sheath, to supply blood to the inferior portion of the anterior abdominal wall.

Question 9

List the structures that a needle piercing the midline of the anterior abdominal wall would pass through.

Answer 9

✓ skin
✓ Camper’s fascia
✓ Scarpa’s fascia
✓ linea alba (formed by crisscrossing fibers of rectus sheath)
✓ fascia transversalis
✓ parietal peritoneum

[Diagram: Layers of the anterior abdominal wall]
♌︎ The arcuate line is an area of demarcation visible from the peritoneal surface of the abdominal wall, residing one-third the distance between the umbilicus and the pubis. The arcuate line can be a sharp demarcation, or it can be a gradual transition zone where the fibers of the posterior sheath gradually disappear. In addition, the arcuate line is the location where the inferior epigastric vessels perforate the rectus sheath, to supply blood to the inferior portion of the anterior abdominal wall.

Question 10

List the extensions/expansions of the inguinal ligament.

Answer 10

(a) Lacunar ligament aka. Gimbernat’s ligament
(b) Pectineal ligament (ligament of Cooper)
(c) Reflected part [The superficial fibres from the medial end of the inguinal ligament expand upward and medially to form this ligament. It lies behind the superficial inguinal ring and in front of the conjoint tendon. Its fibres interlace with those of its counterpart of the opposite side at the linea alba.]

Question 11

State the contents of the rectus sheath.

Answer 11

Muscles: rectus abdominis, pyramidalis
Vessels: superior epigastric and inferior epigastric vessels
Nerves: lower 6 thoracic nerves

Question 12

Briefly discuss the cutaneous lymphatic drainage of the abdominal wall.

Answer 12

(a) Above the umbilicus, the lymph vessels run upward to drain into the axillary lymph nodes (anterior/pectoral group).
(b) Below the umbilicus, the lymph vessels run downward and laterally to drain into the superficial inguinal lymph nodes.

Question 13

State the following regarding the external oblique:
Origin, Insertion, Actions, Vascular supply, Innervation

Answer 13

Origin: external surface of the 5-12th ribs.
Insertion: linea alba, pubic tubercle and anterior half of iliac crest.
Actions: The external oblique muscle causes ipsilateral lateral flexion of the trunk and contralateral rotation of the trunk when it contracts unilaterally. Bilateral contraction flexes the trunk anteriorly, increasing intra-abdominal pressure, which is useful in processes such as breathing, singing and defecation.
Vascular supply: intercostal, subcostal and deep circumflex iliac arteries.
Innervation: intercostal nerves (T7-T11), subcostal nerve (T12) [or simply: anterior primary rami of lower six thoracic spinal nerves], and sensory innervation is provided by the iliohypogastric nerve (L1)

Further notes:
The fibres of the external oblique muscle run diagonally downward from the middle of the rib cage.

Question 14

State the following regarding the internal oblique:
Origin, Insertion, Actions, Vascular supply, Innervation

Answer 14

Origin: thoracolumbar fascia, iliac crest, iliopectineal arch.

Insertion: 9-12th ribs (aponeurosis as high as 7th costal cartilage), linea alba, pubic crest.

Actions: Upon bilateral contraction, the internal abdominal oblique flexes the trunk and causes compression of the intra-abdominal viscera thereby increasing the intra-abdominal pressure. When it contracts unilaterally, it causes ipsilateral lateral flexion and ipsilateral rotation of the torso.

Vascular supply: intercostal, subcostal, inferior epigastric and deep circumflex iliac artery.

Innervation: by the anterior primary rami of lower six thoracic nerves (T7-T12) and first lumbar nerve (L1) via iliohypogastric and ilioinguinal nerves.

Further notes:
The fibres of the internal oblique muscle are obliquely oriented, running diagonally upward from the pelvis. This orientation is perpendicular to that of the external oblique. [Diagram]

Question 15

State the following regarding the transversus abdominis muscle.
Origin, Insertion, Actions, Vascular supply, Innervation

Answer 15

Origin: 7-12th ribs, thoracolumbar fascia, iliac crest, inguinal ligament.

Insertion: linea alba, pubic crest, pectineal line.

Actions: when it contracts bilaterally, it compresses the abdominal contents, which is useful in processes such as breathing, singing, and defecation. This action also aids in expiration. When it contracts unilaterally, it causes ipsilateral trunk rotation.

Vascular supply: intercostal, subcostal, superior/inferior epigastric, superficial/deep circumflex iliac and posterior lumbar arteries.

Innervation: By the anterior primary rami of lower six thoracic nerves (T7–T12), and first lumbar (L1) nerve via iliohypogastric and ilioinguinal nerves.

Further notes:
The fibres of the transversus abdominis muscle run horizontally, except the lowest ones, which run obliquely downwards.

Question 16

The rectus abdominis is a paired, vertical structure running each side of the linea alba and contained within the rectus sheath. State its origin, insertion, actions, vascular supply, innervation.

Answer 16

Origin: pubic symphysis & pubic crest.
Insertion: xiphoid process & 5-7th costal cartilage.
Action: flexion of the trunk, maintain abdominal tone.
Vascular supply: superior and inferior epigastric arteries.
Innervation: T6-T11 intercostals, subcostal and ilioinguinal nerves.

Question 17

The pyramidalis is small triangular muscle that is located anterior to the inferior part of the rectus abdominis. State its origin, insertion, action, vascular supply and innervation.

Answer 17

Origin: pubic symphysis and pubic crest.
Insertion: linea alba.
Action: tenses the linea alba.
Vascular supply: inferior epigastric artery.
Innervation: subcostal nerve.

☮︎ The pyramidalis sits in the rectus sheath anterior to the lower rectus abdominis. It is thought to have little clinical significance and is absent in 20% of people.

Question 18

State the extents and direction of the inguinal canal.

Answer 18

The inguinal canal extends from deep inguinal ring (an oval opening in the fascia transversalis) to the superficial inguinal ring (a triangular gap in the external oblique aponeurosis). It is directed downward, forward, and medially. It is superior and parallel to the inguinal ligament. [Diagram]

Question 19

State where the superficial and deep inguinal rings are found.

Answer 19

superficial inguinal ring: triangular aperture in external oblique aponeurosis above and lateral to the pubic crest
deep inguinal ring: oval aperture in fascia transversalis 1.25 cm above the midinguinal point

Further notes:
The midinguinal point is the halfway point between the pubic symphysis and the anterior superior iliac spine.

Question 20

Name the structures that pass through the deep inguinal ring in males.

Answer 20

✈ Ductus deferens and its artery
✈ Testicular artery and the accompanying veins
✈ Obliterated remains of processus vaginalis
✈ Genital branch of genitofemoral nerve
✈ Autonomic nerves and lymphatics

[All these form the spermatic cord.]

Further notes:
The ductus deferens, also known as the vas deferens, is a part of the male reproductive system. It is a partially coiled tube that transports sperm from the epididymis to the ejaculatory ducts in anticipation of ejaculation.

Question 21

Name the structures that pass through the deep inguinal ring in females.

Answer 21

✈ Round ligament of uterus
✈ Obliterated remains of processus vaginalis
✈ Lymphatics from the uterus

Question 22

Name the structures that pass through the superficial inguinal ring in males.

Answer 22

✈ Spermatic cord
✈ Ilioinguinal nerve

Note:
The ilioinguinal nerve enters the inguinal canal by piercing the wall and not through the deep inguinal ring.

Question 23

Name the structures that pass through the superficial inguinal ring in females.

Answer 23

✈ Round ligament of uterus
✈ Ilioinguinal nerve

Note:
The ilioinguinal nerve enters the inguinal canal by piercing the wall and not
through the deep inguinal ring.

Question 24

structures that form the anterior wall of the inguinal canal from superficial to deep

Answer 24

✈ skin
✈ superficial fascia
✈ external oblique aponeurosis
✈ internal obliqe muscle fibres [in the lateral 1/3 only]

The first three are present in the whole extent of the inguinal canal.

Question 25

structures that form the posterior wall of the inguinal canal from deep to superficial

Answer 25

✈ fascia transversalis in the whole extent
✈ conjoint tendon in the medial two third
✈ reflected part of the inguinal ligament in the medial-most part

Further notes:
Fascia transversalis aka. transverse fascia is the fascial lining of the anterolateral abdominal wall. It is situated between the inner surface of the transverse abdominal muscle and the preperitoneal fascia. It is directly continuous with the iliac fascia, the internal spermatic fascia, and pelvic fascia.
In the inguinal region, the transversalis fascia is thick and dense; here, it is joined by fibers of the aponeurosis of the transverse abdominal muscle.

The conjoint tendon is a sheath of connective tissue formed from the lower part of the common aponeurosis of the abdominal internal oblique muscle and the transversus abdominis muscle, joining the muscle to the pelvis. It forms the medial part of the posterior wall of the inguinal canal. The conjoint tendon serves to protect what would otherwise a weak point in the abdominal wall. A weakening of the conjoint tendon can precipitate a direct inguinal hernia. A direct inguinal hernia will protured through Hesselbach’s triangle.

Question 26

structures that form the roof and floor of the inguinal canal

Answer 26

roof: lower arched fibres of the internal oblique and transversus abdominis muscles
floor: (a) grooved upper surface of the inguinal ligament in the whole extent, (b) abdominal surface of the lacunar ligament at the medial end
[Diagram: Boundaries of inguinal canal]

Question 27

contents of the inguinal canal in males and females

Answer 27

male: spermatic cord and and ilioinguinal nerve
female: round ligament of the uterus and ilioinguinal nerve

Question 28

What is an inguinal hernia?

Answer 28

This is a protrusion of abdominal viscera (e.g. loops of intestine) into the inguinal canal.

Question 29

Distinguish between direct and indirect inguinal hernias.

Answer 29

The direct inguinal hernia occurs if the hernial sac enters the inguinal canal directly by pushing the posterior wall of the inguinal canal forward, medial to the inferior epigastric artery through the Hesselbach’s triangle. It is common in the elderly due to weak abdominal muscles.
The indirect inguinal hernia occurs if the hernial sac enters the inguinal canal through the deep inguinal ring, lateral to the inferior epigastric artery. It is common in children and young adults, due to the complete or partial competency of the processus vaginalis.

Question 30

State the coverings of an indirect inguinal hernia.

Answer 30

✈ extraperitoneal tissue and parietal peritoneum
✈ internal spermatic fascia
✈ cremasteric muscle and fascia
✈ external spermatic fascia
✈ skin

Question 31

State the coverings of a direct inguinal hernia.

Answer 31

✈ extraperitoneal tissue and parietal peritoneum
✈ fascia transversalis
✈ conjoined tendon [in medial direct hernia]
✈ cremasteric muscle and fascia [in lateral direct hernia]
✈ external spermatic fascia
✈ skin

Question 32

Which lines divide the abdomen into 4 quadrants?

Answer 32

A vertical trans-umbilical line and a horizontal trans-umbilical line.

Question 33

Which lines divide the abdomen into 9 regions?

Answer 33

♌︎ 2 mid-clavicular lines - vertical lines that pass down from the mid-point of the clavicle to the
mid-inguinal point.
♌︎ The subcostal plane - a transverse line that passes across the abdomen at the level of the inferior aspect of the 10th costal cartilage. This line bisects the 3rd lumbar vertebrae.
♌︎ The transtubercular plane - a transverse line that passes across the iliac tubercles. These are located approximately 5cm posterior to the anterior superior iliac spine (ASIS). The line bisests the 5th lumbar vertebrae.

Note:
♌︎ Another commonly discussed plane is the ‘Transpyloric plane of Addison’ or more simply the transpyloric plane. It is located halfway between the suprasternal notch and the top of the pubic symphysis. It is approximately a hands breath below the xiphoid process.

Question 34

List the key structures that lie on the transpyloric plane.

Answer 34

♌︎ L1 vertebrae
♌︎ Pancreatic neck
♌︎ Pylorus of the stomach
♌︎ First part of the duodenum
♌︎ Duodenojejunal flexure
♌︎ Fundus of the gallbladder
♌︎ Renal hila

Question 35

The inguinal triangle (Hesselbach’s triangle) is situated deep to the posterior wall of the inguinal canal; hence, it is seen on the inner aspect of the lower part of the anterior abdominal wall. State its boundaries.

Answer 35

medial: lower 5 cm of the lateral border of the rectus abdominis muscle
lateral: inferior epigastric artery
inferior: medial half of the inguinal ligament
floor: peritoneum, extraperitoneal tissue, fascia transversalis

Question 36

State the contents of the:
1. right hypochondrium
2. epigastric region
3. left hypochondrium

Answer 36

1. right hypochondrium: right lobe of liver, gall bladder, right adrenal gland, right colic flexure (hepatic flexure of colon)
2. epigastric region: left lobe of liver, body and pylorus of stomach, head and body of pancreas, duodenum, descending aorta
3. left hypochondrium: fundus of stomach, spleen, tail of pancreas, left adrenal gland, left colic flexure (splenic flexure of colon)

Question 37

List the intraperitoneal organs.

Answer 37

stomach, appendix, liver, transverse colon, duodenum (first part), small intestines (jejunum and ileum), tail of pancreas, upper third of the rectum, spleen, sigmoid colon

Question 38

List the primarily retroperitoneal organs.

Answer 38

kidneys, suprarenal glands, ureters

Question 39

List the secondarily retroperitoneal organs.

Answer 39

pancreas (except tail), duodenum (except the initial 2 cm), ascending colon, descending colon, caecum, lower 2/3 of rectum