Taeniae coli, haustra and appendices epiploicae
Mnemonic
Four features distinguishing large from small bowel:
- Taeniae coli - three longitudinal muscle bands
- Haustra - sacculations between them
- Appendices epiploicae - fatty tags
- Wider calibre
“The taeniae converge on the base of the appendix”, which is the reliable way to find it at operation.
On imaging the distinction is by the folds: valvulae conniventes cross the full width of small bowel and lie centrally; haustra cross only part of the width and the colon lies peripherally.
The 3, 6, 9 rule gives the upper limits of normal calibre: 3 cm small bowel, 6 cm colon, 9 cm caecum.
The taeniae are shorter than the bowel, which is what gathers it into haustra, and they end at the rectosigmoid junction, which is why the rectum has a complete longitudinal muscle layer and no haustra.
Expansion
- Taeniae coli - three longitudinal muscle bands. The outer longitudinal layer is incomplete, gathered into these three strips
- Haustra - sacculations produced because the taeniae are shorter than the bowel
- Appendices epiploicae - small fatty peritoneal tags on the surface
All three are absent from the rectum, where the longitudinal muscle spreads out into a complete layer, and from the appendix, where the taeniae converge, which is what makes them a reliable guide to the appendix base.
On an abdominal radiograph:
| Small bowel | Large bowel | |
|---|---|---|
| Folds | Valvulae conniventes, crossing the full width | Haustra, partial |
| Position | Central | Peripheral |
| Calibre limit | 3 cm | 6 cm (9 cm at caecum) |