Anatomy of the Anterior Abdominal Wall

Question 1

List the layers of the anterior abdominal wall from external to internal

Answer 1

• Skin
• Subcutaneous tissue
• Muscle and fascia
• Parietal peritoneum

Question 2

What is the lateral border of rectus abdominus muscle called?

Answer 2

Linea semilunaris

Question 3

What is “divarication of recti”?

Answer 3

Laxity/weakness of the linea alba after pregnancy. Clinically presents like a hernia, but isn’t

Question 4

What separates the two vertical strips of rectus abdominis muscle?

Answer 4

Linea alba

Question 5

What is it that gives the impression of a six pack?

Answer 5

The linea alba and the tendinous intersections of rectus abdominis

Question 6

In which direction do the fibres of the external oblique muscle run?

Answer 6

Inferomedially - from the armpit down to rectus abdominis

Question 7

In which direction do the fibres of the internal oblique muscle run?

Answer 7

Superomedially - up from the lateral pelvis towards to the central ribs

Question 8

In which direction do the fibres of transversus abdominus muscle run?

Answer 8

Horizontally

Question 9

List the 3 “flat” muscles superficial to deep

Answer 9

External oblique
Internal oblique
Transversus abdominus

Question 10

What is the rectus sheath formed by?

Answer 10

Formed by the aponeuroses of the 3 flat muscles, which combine at the midline

Question 11

Explain how the role of the rectus sheath varies above and below the arcuate line

Answer 11

Above the arcuate line, the rectus sheath covers the anterior and posterior surfaces of rectus abdominus.
Below the arcuate line, the rectus sheath covers only the anterior surface of rectus abdominus, meaning the posterior surface of the muscle directly touches the transversalis fascia.

Question 12

Where is the arcuate line found?

Answer 12

1/3rd of the way between the umbilicus and the pubic symphysis

Question 13

Using what planes is the abdomen divided into 9 regions?

Answer 13

Vertically - mid-clavicular lines
Horizontally - trans-pyloric plane halfway between xiphoid process of sternum and umbilicus, inter-tubercular plane joins iliac crests

Question 14

List the 9 regions of the abdomen

Answer 14

Left and right hypochondrium
Left and right flank
Left and right groin
Epigastric, umbilical and pubic

Question 15

Where would you find the loin region?

Answer 15

On the back, where the ribs end and the lumbar vertebrae begin

Question 16

What are the 2 types of referred pain?

Answer 16

Visceral and somatic

Question 17

State the original site of somatic referred pain and the eventual site it is perceived at

Answer 17

Original site = proximal part of somatic nerve

Perceived site = distal part of same dermatome

Question 18

Give an example of somatic referred pain which may lead to confusion over the diagnosis

Answer 18

Right lower lobar pneumonia may irritate the somatic nerve supplying the right pleura –> pain felt in RIF

Question 19

Briefly explain the concept of visceral referred pain

Answer 19

Visceral afferent fibres run in the same nerves as somatic afferent fibres, back to a single spinal cord segment. The CNS then perceives the pain as coming from the somatic area supplied by this segment, rather than from the viscera.

Question 20

Why is early appendicitis felt as central periumbilical pain?

Answer 20

The visceral afferent fibres from the appendix join with the somatic afferent fibres at T10. Hence the pain is felt in the T10 dermatome, around the umbilicus.

Question 21

Why does the pain in late appendicitis then localise to the RIF?

Answer 21

Once the inflammation involves the parietal peritoneum, somatic neurones supplying this relay the pain in a localised manner

Question 22

What can cause visceral pain?

Answer 22

Stretch, inflammation and ischaemia only

Question 23

What does the anterior abdominal wall run between?

Answer 23

Anterior parts of the ribcage and pelvic girdle