Chapter 93 Colon Flashcards
Where is the caecocolic orifice in relation to the iliocolic orifice in dogs?
And in cats?
Dogs: Caecocolic orifice 1cm distal to iliocolic orifice
Cats: Caecocolic and iliocolic orifices adjacent to each other
What structures does the duodenocolic join (be specific)
Ascending duodenum - descending colon
What arteries supply the colon and what artery do they originate from?
Cranial mesenteric artery:
- Iliocolic a
- Right colic
- Middle colic
Caudal mesenteric
- Left colic
- (Caudal rectal)
Label the diagram
What is the name of the small individual arteries branching off colic arteries?
Vasa recta
The colon contains two arterial netweors - what are they
Sub-serous
Mural (predominantly within submucosa)
What LNs drain the colon?
Left, middle and right colic LNs
Label the diagram
What are the three cell types of the colonic mucosa
- Epithelial
- Goblet
- Enterocromafffin (5% of cells)
How does colonic mucosa differ from Si mucosa?
- No villi
- No aggregated lymph nodules (instead have large solitary lymphoglandular complexes (3mm. In cats the lymphoglandular complexs ate only present in the caecum)
List 3 functions of the colon
- Faecal storage
- Resevoir for microbial ecosystem
- Maintaining fluid and electrolyte balance
List 4 things that are absorbed in colon and 3 things that are excreted
Absorbed:
- Water
- Na+
- Cl-
- Short chain fatty acids
Excreted:
- K+
- HCO3-
- Mucous
What is the main driving force nehind salt and solute transport mechanism in colon?
Electrical gradients
What volume of fluid does the colon absorb (a total figure)
Up to 1.5 L/day
What is the net direction of eectrolytes in colon, under normal conditions
Absorbtion of electrolytes
What drives water movement across colon
Osmosis and active absorbtion
What cells produce mucous in coloon?
Goblet cells and columnar epithelial cells
(i.e. 2/3 cell types present in mucosa. Other type is enterochromaffin cell, making up 5% of cells)
What are the three short chain fatty acids?
Butyrate, acetate, propionate
List two mechanisms leading to mixing of faeceal contents in the dog.
And an additional mechanism in cats
- Segmentation
- Propulsion
- (Retrograde peristalsis in cats)
What is major control of colonic wall dependent on?
Intrinsic nerve plexuses (myenteric and sub-mucous)
List 3 factors that make the barrier created by colonocytes a major contributor to immunity (ie how does epithelium confer immunity)
- Rapidly renews
- Is constantly moving
- Protected by mucous and antimicrobial molecules
Whatare the three stages of wound/colonic healing?
- Lag phase (/Inflammation phase)
- Proliferative phase
- Maturation phase
What material prevents anastomotic leakage during lag phase of healing?
Fibrin
What cell type predominates in early lag phase of healing?
How does this change after 2-3 days?
Neutrophils initially –> macrophages/monocytes after 2-3 d
What cell type predominates during proliferative phase?
Fibroblasts
What is normal collagen content (i.e what proportions of each type) in colonic submucosa?
How does this differ in heling colonic tissue?
Normal colonic submucosa:
- 68% Type 1 collagen
- 20% Type 3 collagen
- 12% Type 5 collagen
Greater proportion type 3 collagen when healing (proliferative phase) (type 3 collagen smakes up 30-40%)
What are the two key amino acids for collagen synthesis?
Lysine and Proline
After what period of time following colonic wound is near normal bursting strength reached?
How long until return to full strength?
‘Near normal’ strength after 2 weeks
75% strength after 4 months
What happens during maturation phase?
- Numbers of macrophages and fibroblasts decrease.
- Collagen 3 content reduces.
By what mechanism does colonic mucosa heal?
How long does it take?
Colonic mucosa heals by cellular epithelial hyperplasia.
Complete within 3 days.
How does intestinal collagen sythesis differ from elsewhere?
Produced by fibroblasts and smooth muscle cells
How does endotoxin lipopolysaccharide affect healing?
LPS induces collagenase production in macrophages –> increased collagen breakdown
List 5 local factors and 8 systemic factors that influence colonic wound healing
At what arterial PaO2 level is collagen synthesis inhibited?
At what arterial PaO2 level do angiognesis and epithelial hyperplasia (remember - this is how colonic mucosa heals) fail?
No collagen at < 40 mmHg
No angiogenesis or epithelial hyperplasia at <10 mmHg
Down to what PCV level is healing unaffected?
15%!
List broad methods to improve colonic wound healing
-
Vascularised tissue flap
- Omentum
- Rectus abdominis (only reported experimentally)
-
Colonic reinforcement
- Porcine SIS
- Amniotic membrane
- Cytokines (VEGF). Not used cliniclly - concern re –> neoplasia
List 4 broad techniques for colonic wound closure.
Specify techniques/specifics for each
-
Suture
- Monofilament, absorbable, swaged on, round bodied taper cut needle +- antibitic coating (
-
Staplers
- GIA
- TA
- EEA
-
Biofragmentable anastomosis ring
- Serosal tearing common becuase of large size
-
Sutureless closure
- Lasers
- Nd:YAG
- Gallium arsenide
- Cyanoacrylates - not recommended
- Fibrin glue - mixed result, no clinical uses reported
- Lasers
How does doxycycline coated suture –> improved anastomotic site strenght?
Doxycycline hibits MMPs
What did DeHoff study find re colonic wound closure with inverting vs appositional vs everting patterns?
Appositional –> less scar tissue and morbidity
What did Weisman JAVMA 1999 find when comparing enteric closure with simple interrupted vs simple continuous suture?
Simple continuous –>
- better histologic alignment of layers
- decreased surgical time
- decreased tissue trauma
(Clinically all cases did fine though - conclude that simple cont is an acceptable alternative)
What kind of anastomisis is created by an EEA stapler?
End to end, inverting, with 2 staggered staple rows
What is fibrin glue composed of?
Thrombin and fibrinogen
What volume/dilution of barium is used for barium enema?
Barium 20:80 warm water
8 ml/kg
(for double contrast instill barium, drain, then instill air)
What technique migth improve CT assessment of colon?
CT pneumocolonography
List 4 pre-procedure strategies to improve quality of colonoscopy/proctoscopy
- 24-48 hr fast
- Oral cleansing solution (often laxative (polyethylene glycol) + electrolytes)
- Warm water enema
- L lateral recumbency (allows fluid to drain from transverse colon)
Comment of pre-surgical mechanical prep of colon
No benefit
Name an appropriate peri-op iv abx protocol for colonic surgery
Cefuroxime + metronidazole.
Opioids acting at which receptors can prolong intestinal transit time and cause ileus?
mu and delta receptors
Comment on effect of carprofen on colonic mucosa
Shown to cause skoughing and erosion of colonic mucosa.
i.e. avoid nsaids after colonic surgery
What type of diet speeds transit time (i.e stimulates colonic motility)
High fibre/high residue, bulky diets
What is the primry enegry source of the colinic epithelial lining
Luminal nutrients inc short chain FAs
What sort of diet shoudl be fed after colonic surgery
High residue, low-fat
How long does it take for the post-anastomotic segment to regain normal motility following colonic surgery?
8 weeks
How should a typhlectomy be closed?
Draw the suture patterns.
Parker Kerr followed by Lembert
How is caecal investion managed if it cant be everted?
Antimesenteric colotomy incorporating base of caecum
What structure(s) can be dissected to aid typhlectomy?
Iliocaecal fold and accessory iliocaecal fold
What is a sub-total vs total colectomy?
Subtotal preserves iliocolic junction
Name three techniques to address luminal disparity
- Spatulation of smaler lumen along anti-mesenteric border.
- Partial closure of larger lumen
- Slanted cut along endge of smaller lumen
Name 3 approached for EEA
What is recommendation in cats and why?
- Transcaecal
- Transrectal
- Enterotomy
Use trancaecal in cats as doesnt result in strictures
What instrument is used for pursestring suture when using EEA?
Furniss purse-string instrument
(pursestring has to be v accurate to ensure proper inclusion of tissue in EEA stapler)
What are the two techniques for colostomy
End-on or side-on (= flank loop)
If rectal excision is necessary, what step is taken (if possible) to increase chace of retaining continence.
How long can it take to re-gain continence?
Preserve most distal 1.5cm of rectum
May take up to 5 months
What step should be ensured when performing colopexy fpr management of prolapse or sacculation?
Ensure abdo wall inscision is cranial enough to resolve prolapse/sacculation
What is usual age of caecal inversion cases?
<4 years
List 3 techniques to diagnose caecal inversion
- US
- Colonoscopy
- Positive contrast radiography
- (CT…)
What radiological change is seen with caecal impaction?
- Loss of gas filled caecal silhouette
- Presence of radiodense material in caecum
How is caecal impaction managed?
Typhlectomy AND multiple GI biopsies (cause for altered motility?)
What is most common canine caecal tumour?
GIST
(more likely to –> perforation that leiomyosarcoma!)
What is IHC marker for GIST?
And leiomyosarcoma?
GIST: CD117 (=c kit)
Leiomyosarcoma: Desmin and SMA (smooth muscle actin)
What is most common presentation of dogs with caecal tumour?
Signs secondary to perforation
NAme a paraneoplastic syndrome of caecal leiomyosarcoma
erythrocytosis secondary to extopic erythropoetin production
What feature is predictive f metastatic potential of caecal GISTs?
US appearance
What was MST of dogs with caecal tumours?
680d
Define constipation and obstipation.
- Constipation:* Abnormally delayed or infrequent passage of usually dry, hardened feces.
- Obstipation:* When constipation becomes severe and obstinate such that the animal cannot pass dry, hard feces.
How is megacolon classified?
Aquired
- Mechanical
- Functional
Idiopathic
List 4 broad causes of aquired megacolon. List 2 examples in each category
- Extraluminal compression
- Intraluminal obstruction
- Metabolic
- Neuromuscular abnormalities
What degree of pelvic canal narrowing is though to cause megacolon?
>45%
Aquired megacolon may be reversible if cause addressed within what tie frame?
6 months
What is first line management of cats with irreversible megacolon and perineal hernia?
Sub-total colectomy (i.e. perineal hernia may be manageable with colectomy alone)
What breed of cat is at particular risk of megacolon?
Manx
What is most and second most common caused of megacolon in cats (and what % of cases does each represent)?
Idiopathic (60%)
Pelvic canal stenosis (25%)
What is a postulated cause of vomiting in megacolon?
Colonic dilation –> vagal stimulation of chemoreceptor trigger zone –> vomiting
What is normal colonic size on rads?
What is is radiology cut off for megacolon?
Normal: colon height = length of L2
Megacolon: colon height 1.5 x length L7
List 5 factors in medical management of megacolon
- Manual evacuation i.e. enema (inc abx as mucosal damage inevitable and slowed transit time thought to facilitate bacterial multiplication)
- Laxatives
- Prokonetics (cisapride)
- Dietary modification (high fibre)
- Ensure access to litter
What is lactulose and how does it work?
Disaccharide (not metabolizable in mammals)
Colonic bacteria metabolise it –> LMW organic acids –> increased intracolonic osmotic pressure –> water into colon
What is cisapride and how does it work?
Benzamine prokinetic –> release of ACh from enteric nervous system
List 3 potential adverse effects of iliocolic junction removal
- Retrograde movement of colonic bacteria –> SIBO
- Diarrhoea
- Incontinence
Why is subtotal colectomy advised initially rather than total?
Total colectomy –> more diarrhoea but nor reduced recurrence of constipation
How does remaining intestine adapt following subtotal/total colectomy?
- Increased villous height
- Increased enterocyte number and density
How long is diarrhoea likely to persisit after sub-total colectomy?
3 months
What is recurrence rate of constipation requiring repeat surgery, after total/sub-total colectomy
Variable, 0-45%
What factors have been found in colonic/caecocolic volvulus?
EPI, Intussusception, GDV + gastropexy
What procedure might lead tocolonic entrapment?
OVHE. Adhesions between uterine stump + ovariectomy site –> colonic entrapment
What is most common colonic tumour of dogs?
And cats?
Dogs: Adenocarcinoma (others = GIST, leiomyosarcoma, lymphoma, extrmedullary plasmacytoma)
Cats: Lymphoma (followed by adenocarcinoma. Others = MCT, neuroendocrine)
What are recommended margins of colonic tumour?
5-8cm!
List 3 ‘approaches’ for colonic R+A
- Ex-lap
- Pelvic osteotomy
- Combined abdominal trans-anal pull through.
Aside from resection, name another palliative option for colonic mass
Stent
(results variable)
What is MST in dogs following colorectal adenocarcinoma removal?
6 - 22 months
What was MSt following gastrointestinal GIST excision vs leiomyosarcoma?
GIST 3 years
Leiomyosarcoma 8 months
What is metastatic rate in cats with colonic neoplasia?
>75%
What factor was associated with prolonged survival in cats following colonic adenocercinoma sx?
Chemo (50d vs 250d)
Define the types of colonic duplication.
How is colonic duplication subclassified?
Type 1 = only colon/rectum affected
Type 2 = other congenital abnormalities too
Sub-classification
- spherical non-communicating
- tubular non-communicating
- tubular communicating
What are clinical signs of colonic duplication?
- asymptomatic
- tenesmus
- increased frequency of defaecation
- faceal retention
- abdominal distension
- rectal prolapse
What is recommended tx of colonic duplication
Surgery.
(even if asymptomatic as can –> neoplastic change)
What is goal of surgery for colonic duplication?
Removal of duplicated portion
Reported techniques:
- Division of common septum
- Side-to-side anastomosis
- Excision of duplicated portion
- Mucosal stripping
