Parts
- Caecum: short, comma-shaped diverticulum next to the ileocolic orifice on the right side of the abdomen.
- Ascending colon: very short, on the right.
- Transverse colon: crosses from right to left caudal to the stomach.
- Descending colon: the longest segment; it runs along the left dorsal abdomen to the pelvic inlet.
- Rectum and anal canal: in the pelvic canal, ventral to the sacrum and the first caudal vertebrae. The anal sacs open on either side of the anus.
Clinical relevance
- Megacolon: chronic dilation of the colon with severe constipation (obstipation). The most common form is idiopathic; other causes are a narrowed pelvic canal after malunited pelvic fractures and sacrocaudal injuries. On the lateral radiograph, a ratio of colon diameter to the length of the L5 vertebral body above about 1.5 suggests megacolon.
- Colitis: large-bowel diarrhoea (tenesmus, mucus, fresh blood). In young cattery cats, Tritrichomonas blagburni (formerly T. foetus) should be considered.
- Constipation: common in older cats dehydrated by chronic kidney disease.
- Neoplasia: adenocarcinoma and lymphoma; the ileocolic region is a common site.
3D model
The colon comes from the CT of a cat (pixelbeaker model), simplified and registered to the atlas skeleton; the rectum, outside the CT, is modelled through the pelvic canal to the anus (modelled fidelity).