Rectum & Small Colon

Question 1

Grades of rectal tear

Answer 1

1. Mucosa/submucose only
2. Muscular layers only - mucosa can protrude through forming diverticulum (rare)
3. a) All layers except serosa
4. b) All 4 layers, but mesorectum and retroperitoneal tissues intact - can experience retro-peritoneal faecal packing - source of peritoneal contamination
5. Full thickness with direct comtamination of the peritoneal cavity

Question 2

Types of rectal prolapse

Answer 2

Type 1: mucosa and submucosa only

Type 2: complete prolapse full thickness of all or part of rectal ampulla. Type 1and 2 are the most common

Type 3: type 2 plus variable amount of small colon intussusepted into the rectum

Type 4: peritoneal rectum and variable length of small colon form an intussusception through the anus. Seen with dystocia in mares.

Types 1-3 present with mucosal masses protruding through ext anal sphincter, type 4 with tubular protrusion

Question 3

Indications and site for colotomy/enterotomy of the small colon

How should the enterotomy be closed?

Answer 3

Indications = simple intraluminal obstructions incl. fibrous foreign bodies, enteroliths, phytobezoars, trichobezoars, and phytoconglobates as well as meconium

Site for colotomy longitudinal incision in the anti-mesenteric taenia. Quicker, easier, more accurate apposition & less haemorrhage & inflammation than those performed adjacent to the band

Closure of the mucosa as a separate layer facilitates seromuscular closure but does not affect the postoperative healing response or lumen diameter in normal horse

Closure: 2 layer; full thickness (or mucosal only) simple continuous USP 2/0 polyglactin 910 with minimal inversion, then Lembert (or Cushing for less inversion) ovewsew - excellent holding strength although inversion can incr risk of PO stenosis

Closure of a longitudinal incision transversely may decrease the risk of PO stenosis

Question 4

Describe the blood supply to the small colon (vessel names and pattern)

Answer 4

From caudal mesenteric aa → left colic aa supplies the oral 75% of SC. Aboral 25% of SC supplied by cranial rectal aa (also from caudal mesenteric)

Transverse colon is from cranial mesenteric aa → via middle colic aa; this anastomoses with the left colic aa

Arcuate arteries in the mesentery branch into cranial and caudal marginal arteries (running parallel with the small colon) which anastomose with adjacent arcuate aas. Beyond the marginal aa’s, secondary arcades penetrate the mesenteric aspect of the serosa

Question 5

Methods of alleviating small colon impactions with foreign material

Answer 5

1. Maniupulate the obstruction (usually orally) so that it is exteriorisable and can be removed via SC enterotomy
2. Perform an alternative approach to access it eg paramedian
3. High enema and external massage of the intestine to break up and remove via the rectum, similarly can instill fluids via 14g needle and giving set from orally
4. R&A of the small colon may be indicated in severe cases where the obstruction has resulted in intestinal necrosis, provided the segment of intestine can be exteriorised