Session 2 ILOs - Abdominal hernia and development of the gut 1

Question 1

Describe the anatomy of the inguinal canal in the male

Answer 1

Walls:
Floor - Inguinal ligament (rolled up portion of the external oblique aponeurosis) and thickened medially by the lacunar ligament
Roof - Arching fibres on internal oblique and transversus abdominus
Anterior wall - Internal oblique (lateral side) and aponeurosis of external oblique
Posterior wall - Transversalis fascia and conjoint tendon

Opening and closing:

• Deep (internal) ring is found above the midpoint of the inguinal ligament, lateral to the epigastric vessels
• Superficial (external) ring lies just superior to the pubic tubercle

Contents of the inguinal canal:
1. Spermatic cord (males only) / round ligament (females only)
2. Ilioinguinal nerve – contributes towards sensory innervation of the genitalia (only travels through part of the inguinal canal, exiting via the superficial inguinal ring
Nerve most at risk of damage during an inguinal hernia repair
3. Genital branch of the genitofemoral nerve (supplies the cremaster muscle and anterior scrotal skin in males, and the skin of the mons pubis and labia majora in female)

Question 2

Explain how inguinal hernias develop (embryologically) and relate this to the descent of the testis in the male

Answer 2

Development:

• Tissue that will become gonads (testes or ovaries) establish in the posterior abdominal wall, and descend through the abdominal cavity
• The gubernaculum (fibrous cord of tissue) attaches the gonad guides their descent. Once descended, the gubernaculum becomes the scrotal ligament
• The inguinal canal is the pathway by which the testes leave the abdominal cavity and enter the scrotum
• The canal is flanked by the processus vaginalis (out-pocketing of the peritoneum)
• The processus vaginalis normally degenerates, but a failure to do so can cause an indirect inguinal hernia, a hydrocele, or interfere with the descent of the testes

Question 3

Describe the anatomy and clinical presentation of inguinal hernias

Answer 3

The inguinal canal is a potential weakness in the abdominal wall, and thus a common site of herniation

Indirect (more common):

• Caused by the failure of the processus vaginalis to regress (severity depends on the extent of degeneration)
• Peritoneal sac enters the inguinal canal through the deep inguinal ring
• Lateral to the inferior epigastric vessels

Direct

• Direct inguinal hernias are acquired (usually in adulthood), due to weakening in the abdominal musculature
• Peritoneal sac enters the inguinal canal though the posterior wall of the inguinal canal (bulges through Hesselbach’s triangle) and exits through the superficial inguinal ring - note it does NOT enter the canal as the only true way it can enter the canal is via the deep ring
• Medial to the inferior epigastric vessels

Question 4

Describe the relationship between the femoral canal and the inguinal ligament. Explain how femoral hernias develop including the anatomy and clinical presentation of such hernias

Answer 4

Femoral hernias occur lower in the body than inguinal hernias
- Develop in the upper part of the thigh near the groin just below the inguinal ligament, where abdominal contents pass through the femoral canal (naturally occurring weakness)

Clinical presentation:

• Lump in the groin or inner thigh and groin discomfort, may cause stomach pain and vomiting in severe cases
• More common in females
• Less common due to smaller opening of femoral ring however there is a greater risk of strangulation (cut off blood supply and ischaemia)

Question 5

Describe the anatomy and location of umbilical hernias

Answer 5

Umbilical hernias are a common condition (equal in males and females)

Pathology:

• Hernia goes through the umbilical ring (which umbilical cord passes through) due to a defect in the linea alba, as it is a point of natural weakness
• The

Clinical presentation:

• Increased incidence in premature, low weight or African descent babies
• Most usually resolve by the age of 3-4 yrs
• Unusual to have complications (if so, surgery is effective)

Question 6

Describe the common incisional sites used for abdominal surgery (relating to incisional hernias)

Answer 6

Incisional hernias - generally as a result of incisions made (during surgery)

5 common sites for incision:

1. Midline incision
   - Through linea alba
   - Extendable
   - Avoids many important vessels as aponeurosis is avascular
   - Lots of post-operative pain
2. Paramedian
   - Looks bad
   - Can damage vessels and nerves
3. Gridiron
   - Appendicectomy
4. Pfannenstiel
   - Obstetrics and urology
5. Kocher
   - Cholecystectomy (gall bladder removal)

Question 7

Explain how the process of folding in the embryo during the 4th and 5th week creates the primitive gut, the abdominal wall and the coelomic cavity

Answer 7

2 types of folding: craniocaudal and transverse

• Craniocaudal folding creates the sections of the gut (foregut, midgut and hind gut)
• A connection exists between the midgut and the yolk sac via the Vitelline duct
• Layers exist of the endoderm, mesoderm and the ectoderm

Transverse folding creates separate areas made up from the different layers
- The ectoderm layer forms the neural tube
- The endoderm layer forms the gut tube
- Splanchno-pleuric layer of the lateral plate mesoderm forms the viscera (visercal peritoneum)
- Somato-pleuric layer of the lateral plate mesoderm forms the body wall and dermis (parietal peritoneum)
= between these two layers is the coelomic cavity, which eventually gives rise to thoracic and abdominal cavities

Question 8

Describe the fate of the embryonic dorsal and ventral mesenteries

Answer 8

The foregut has both a dorsal and ventral mesentery (with the gut tube in the centre)
- The mid and hind guts both only have a dorsal mesentery

• The liver develops within the ventral mesentery
• The spleen develops within the dorsal mesentery

Rotation of the dorsal and ventral mesenteries occur at the level of the foregut leading to formation of the lesser and greater sacs (connected slightly by the foramen of Winslow)

Question 9

Explain how the greater and lesser omenta and the mesentery of the small intestine develop and relate this to their arrangements in the neonate and the adult

Answer 9

Greater omentum:

• Formed as the dorsal mesogastrium rotates anteriorly/ventrally, grows down to become the greater omentum
• Attached to the greater curvature of the stomach and the transverse colon
• Policeman of the abdomen - protects other organs from inflamed or diseased organs

Lesser omentum:

• Formed as the ventral mesogastrium rotates posteriorly and the liver grows! (space between the stomach and the liver)
• Attached to the lesser curvature of the stomach and the liver

Question 10

Describe the basic development of the foregut structures (stomach, liver, pancreas, and duodenum)

Answer 10

Stomach:

• Occurs as a dilation in the foregut (more on the dorsal side)
• Stomach rotates 90 degrees to form the lesser and greater curves

Pancreas:

• Develops in 2 buds within the dorsal and ventral mesentry
• The smaller bud (in ventral mesentry) is forced behind the larger bud (in dorsal mesentry) to form the pancreas
• The 2 buds eventually fuse

Duodenum:

• The midgut loop protrudes out into the umbilicas
• The developing duodenum forms a C-shaped loop that initially projects ventrally
• However, once the stomach rotates, the duodenum rotates to the right and becomes pressed against the posterior abdominal wall, thus becoming retroperitoneal