Visceral pain referral by embryological origin of the gut
Pain from an internal organ is typically felt higher or lower on the abdomen, depending on which part of the embryonic gut tube the organ developed from.
Remember
Visceral pain follows embryological origin, rather than where the organ lies: foregut organs such as the stomach refer pain to the epigastric region (the upper central abdomen), midgut organs to the periumbilical region (around the umbilicus) and hindgut organs to the suprapubic region (low in the midline, above the pubic bone).
Pain from an internal organ is called visceral pain. It is often caused by stretch, ischaemia (poor blood supply) or inflammation. It is vague and poorly localised, because the brain cannot pinpoint the organ, and it is generally felt in the dermatome, the area of skin supplied by the spinal nerve that also supplies the organ.
Each part of the gut has its own pattern of nerve supply, so the site of the pain follows where the organ came from rather than where it lies. The embryonic gut tube is divided into the foregut (the upper part), the midgut (the middle part) and the hindgut (the last part). Foregut organs such as the stomach and pancreas typically give epigastric pain, in the upper central abdomen. Midgut organs such as the jejunum give periumbilical pain, around the umbilicus. Hindgut organs give suprapubic pain, low in the midline above the pubic bone.
The duodenum and the transverse colon are each split between two parts of the gut. The duodenum is foregut before the bile duct opening and midgut beyond it. The transverse colon (it lies in the mid-abdomen) has a proximal two-thirds that is midgut and gives periumbilical pain, and a distal one-third that is hindgut and gives suprapubic pain.
Early appendicitis pain is typically felt around the umbilicus, because the appendix develops from the midgut. If inflammation irritates the parietal peritoneum (the layer lining the inner abdominal wall), the pain turns sharp and is felt right over the organ, because this layer has a somatic nerve supply (the same type of nerves that serve skin and muscle). That is why appendicitis pain classically moves later to the right iliac fossa (the right lower quadrant).
Key facts
- Foregut pain
- organs such as the stomach and pancreas refer visceral pain to the epigastric region (T5 to T9)
- Midgut pain
- organs such as the jejunum and ileum refer visceral pain to the periumbilical region (T10 to T11)
- Hindgut pain
- organs from the distal third of the transverse colon to the rectum refer visceral pain to the suprapubic region (L1 to L2)
- Transverse colon
- the proximal two-thirds is midgut, whereas the distal one-third is hindgut
- Duodenum
- the part before the bile duct opening is foregut, and the part beyond it is midgut
- Lower anal canal
- at the end of the gut, below the pectinate line (the line of small folds that divides the canal into upper and lower parts), it develops from ectoderm (the outer embryonic layer that forms skin) and has somatic nerve supply, so its pain is sharp and well localised
Exam traps
- The distal third of the transverse colon does not typically refer visceral pain to the epigastric region, because it develops from the hindgut, and hindgut pain is felt low in the midline in the suprapubic region even though the transverse colon lies in the mid-abdomen.
- The part of the duodenum beyond the bile duct opening does not typically give epigastric pain, because that part is midgut and its pain is periumbilical; the part before the opening is foregut.
- Pain in the right iliac fossa is not the referred visceral pain of a foregut organ such as the pancreas, because the right iliac fossa is where appendicitis pain settles, as localised pain over the inflamed organ, once the parietal peritoneum is irritated.
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