Ch 93 colon Flashcards
Where is the caecocolic orifice located in dogs and in cats?
Dogs - Approximately 1cm distal to ileocolic orifice
Cats - Adjacent to ileocolic orifice
anatomy
- Grossly, there are three distinct parts to the colon: ascending, transverse, and descending
- transverse colon lies cranial to the cranial mesenteric artery and root of the mesentery
- right anf left colic flextures
- the ureter traverses obliquely and dorsally over the descending colon
- duodenocolic ligament, which is very short, joins the descending colon to the ascending duodenum
- colonic maneuver allows the intestines to be retracted to the right to expose the left sublumbar fossa.
- arteries connect to the colon via the vasa recta (penetrate the muscular layer in the antimesenteric portion)
- colon contains two arterial networks: subserous and mural.
- caudal mesenteric vein
- Serous membranes have a very rich network of lymphatic capillaries (lacteals) that play an important role in reabsorption
From which artery does the majority of the colon recieve its blood supply?
Cranial mesenteric artery
The distal half of the descending colon is supplied by the caudal mesenteric artery and the cranial rectal artery
How does colonic mucosa differ from small intestinal mucosa?
There are no villi or aggregated lymph nodules. Instead there are relatively large, elevated lymphoglandular complexes through which the colonic glands discharge. In cats, these are only found within the caecum
Colonic mucosa: columnar and cuboidal epithelial cells, goblet cells and enterochromaffin cells
List some of the key roles of the colon
Storage of faecal material
Reservoir for the colons complex microbial ecosystem
Maintaining fluid and electrolyte balance
What are main products which are absorbed and secreted at the level of the colon?
Absorbed - water, Na, Cl, short-chain fatty acids
Secreted - K, HCO3 and mucus
Roughly how much water does the colon absorb per day?
Approx 1.5L/day
What are the two main methods of solute absorption in the colon?
Electrogenic via Na channels
Electroneutral via Na/H and Cl/HCO3 exchange
What stimulates colonocytes to switch from absorption to secretion?
Secretagogues
What transported plays an improtant role in mucus secretion? What are some important roles of colonic mucus?
Cystic fibrosis transmembranne regulator (CFTM)
Mucus creates a microclimate ensuring protection of epithelial cells from abrasion and bacterial invasion
What are some important roles of short chain fatty acids in the colon?
Important in regulation of colonic pH (Stimulates increased Na absorption, increased HCO3 production and secretion and hence increased Cl absorption)
Prevents colonic irritation by reducing ionisation of bile acids and long chain FAs
What is unique about the peristalsis of the proximal colon in cats?
It exhibits retrograde peristalsis for further mixing of faecal material
How does the immune system develop to not cause colitis from commensal bacteria?
Tolerogenic Foxp3 regulatory T (Treg) cells are generated as specific populations to an individuals microbiome allowing tolerance to commensal flora within the colon
How does the colonic epithelium contribute to the innate immune system?
The epithelium provides impermeability;
It rapidly renews
Is constantly moving
Is protected by mucus and other antimicrobial molecules (cryptdins, alpha-defesins, lysozyme, phospholipase and chemokines
What cell types are important for the adaptive immune system in the colon?
M cells, D cells, dendritic cells, and intraepithelial lymphocytes
What is the reported leak rate and mortality rate in human colonic surgery?
Leak rate - 7-20%
Mortality rate - 4.1%
List the three phases of wound healing and the time frame that each occurs in the colon
Concerns over experimental data available on colonic healing
Lag Phase - from 0 - 4 days
- Fibrin clot formation (inflammation)
- has minimal strength in holding the wound edges together
- initially predominated by neutrophils but by day 2-3 these become outnumbered by monocytes and macrophages
Proliferative Phase - Day 3 - 14
- Fibroblast proliferate to transform fibrin clot with immature collagen.
- Type 3 collagen accounts for 30 - 40% (usually 20%).
- process drven by PDGF, TGF-B, FGF.
- Angiogenesis occurs in this stage and there is a rapid increased in wound strength, becoming normal within 10-17 days
Maturation Phase - Day 17+
- Reorganisation and remodelling of collagen. - Amount of type 3 collagen decreased and thin collagen fibers become thick bundles
importance of lag phase?
- critical phase of healing > dehiscence or breakdown is most likely to occur during first 72 to 96 hours.
- A key factor in colonic healing is that collagen is produced by the submucosa and by smooth muscle cells.
- Initially strength at the wound site is weak; > Weakness results from collagen degradation by matrix metalloproteinases
- all support and strength in the surgical wound at this stage comes from the sutures
What is the collagen content of the colonic submucosa?
68% type I
20% type III
12% type V
What is colonic wound strength at 48hr and 4 months after injury?
48hr - 30%
4month - 75%
How do bacterial products effect wound healing?
Bacterial products such as endotoxin lipopolysaccharide from E. Coli influence epithelial homeostasis and wound healing by inducing collagenase synthesis in activated macrophages, enhancing collagen breakdown
List some local (5) and systemic factors (7) which negativeyl effect colonic healing
Colonic tissue perfusion must be maintained
- correct hypovolemia.
- ension across the wound stretches the local vessels, reducing blood flow
- Local perfusion of the wound edges can be difficult to quantify clinically
What is the minimun requires PaO2 for collagen synthesis?
What is the minimum PaO2 for angiogenesis and epithelial hyperplasia?
Collagen synthesis - 40mmHg
Angiogenesis and epithelial hyperplasia - 10mmHg
List some methods for improving colonic wound healing
review suggests these techniques are not convincing clinically
Omental wraps (stimulate and augment angiogensis
rectus abdominis muscle flaps (experimental)
Porcine small intestinal submucosa (no long term studies if cuases stricture, controversial)
Amniotic membrane as an incisional patch - beneficial experimentally in rats
Cytokines - VEGF to promote neovascularisation. Concern for neoplastic transformation if used in excess. Not currently used
List options for colonic wound closure
Suture
Staples (GIA, EEA, TA, Skin)
Biofragmentable anastomotic ring
Laser
Cyanoacrylates
Fibrin Glue - A topical haemostat, sealant and tissue adhesive comprised of thrombin and fibrinogen that is approved by the US FDA for colonic sealing in humans. Experimentally mixed results…
suture closure
- single-layer, simple interrupted, appositional pattern
- low complication rate > “the current standard of care in veterinary surgery.”
- appositional anastomosis produced less scar tissue and morbidity than inverting or everting
material
- monofiliament absorbable
- debate as to the efficacy of triclosan-coated suture material in reducing colonic surgical site infection rate
staplers
- Meta-analysis of the human literature suggests that stapled colonic wounds are at a reduced risk for leakage and dehiscence compared to hand-sutured wounds
- EEA device, which creates a true inverting anastomosis
- device can be placed transcecally, through an enterotomy, or transrectally
Diagnostic Techniques for Large Intestinal Disease
- thorough clinical examination, including hydration, bloodwork etc
- RADS: extraluminal masses or malunion of pelvic bone,
- retrograde contrast or air study
- colonic ultrasonography may be challenging, good for imaging mesenteric and sublumbar (medial iliac) lymph nodes
endoscopy
- advantage of providing access for direct biopsy
- patient should be fasted for 24 to 48 hours
How do you perform a barium enema?
Barium sulphate diluted 1 part barium to 4 parts warm water and 8ml/kg is allowed to flow under the influence of gravity through a balloon catheter to fill the colon and caecum
How do you prepare the colon for surgery?
No preparation needed. Do not want to make the faeces liquid.
No oral preoperative antibiosis required but perioperative IV ABx are recommended 1hr prior to surgery and repeated intra-op as needed. Combo of cefazolin and metronidazole recommended
Why is it recommended to avoid NSAIDS for colonic surgeries?
What is the benefit or contraindication for epidural, ketamine, opioids and paracetamol
Carprofen has been shown to cause sloughing of the colonic epithelium and erosion of the colonic mucosa
Epidural is controversial as it can alter the myoelectrical impulses causing uncordinated propulsion. This combined with early feeding has been shown to lead to intussusception
Ketamine - Provides no basic change in gastrointestinal motility. A good choice
Opioids - Can cause ileus
Paracetamol - a useful alternative to NSAIDS. NOT in cats
Cats are especially susceptible to acetaminophen toxicosis, because they have low glucuronyl transferase activity and therefore have limited capacity for glucuronidation. Acetaminophen is metabolized primarily via sulfation in cats, and when this pathway is saturated, toxic metabolites are produced.
Methemoglobinemia and hepatotoxicosis characterize acetaminophen toxicosis in cats;
What diet is recommended after colonic surgery?
High-residue, low-fat diet to promote normal motility suggested. The ideal diet has not been determined
List some of the indications for typhlectomy.
What is the recommended suture pattern for closure following typhlectomy?
Inversion,
impaction,
perforation,
severe inflammation
neoplasia
- Continuous Parker-Kerr suture pattern (over haemostat) recommended (to invert edges), can be reinforced with a continuous inverting Lembert
- Alternatively, a TA or GIA stapling device may be used across the base of the cecum. Stapling creates everted wound edges
ileocecal fold and the small accessory ileocecal fold that attaches the ileum to the proximal colon are transected, taking care not to damage the antimesenteric ileal vessels
after closing cecocolic wound, always change gloves and instruments
Colectomy
megacolon,
neoplasia,
perforation,
trauma
chronic intussusception
- Ligation of individual vasa recta rather than occlusion of main blood vessels
- subtotal or total colectomy, distal transection approximately 2 cm cranial to the pelvic brim and 1 cm caudal to the site where the caudal mesenteric artery penetrates the serosa
- ileocolic valve is to be preserved, as in subtotal colectomy
- Luminal disparity can be addressed by spatulating the small lumen
- hadn sewn: appositional, 4-0 or 3-0 polydioxanone or polyglyconate
- omentum should be tacked along the anastomosis site.
- staplers EEA
- Biofragmentable Anastomosis Ring
What is recommended approach for used a EEA stapler in a cat?
What is the assocaited purse-string instrument called?
What size EEA stapler cartridge do most cats require?
EEA stapling deviced are recommended to be used transcaecally in cats as apposed to transrectally. 2/10 cats which underwent a transrectal approach developed a stricture at the anastomosis site
Furniss Purse-string instrument
Most cats require a 25 or 21mm cartridge
Ovoid sizers are essential to allow measurement of bowel diameter
What is the following instrument?
Furniss pursestring instrument
(To be used as part of EEA stapler)
List the two options for colostomy?
End-on colostomy
Flank loop colostomy
Colostomy
end-on colostomy
- entire end of the proximal segment of the colon is brought full thickness through the body wall at a perpendicular angle.
- Interrupted sutures between the serosa and abdominal wall musculature
- end of the colon (mucosa and submucosa) is anastomosed to the skin.
- If the distal colon is retained, the procedure is potentially reversible
flank loop
- colon is left intact, and a small segment is prolapsed through a lateral abdominal wall incision.
- a plastic subcutaneous rod entraps the colon segment superficially.
- A 4-cm-diameter circle of skin is removed, and the colonic mucosa is sutured to the skin
- Flank loop colostomy can be reversed by resecting the mucocutaneous junction and closing the stoma
- render the patient fecally incontinent
Combined Abdominal Transanal Pull-Through Colorectal Amputation
- located in the descending colon that extend into the cranial to middle third of the rectum
- midline caudal celiotomy is performed
- to make the procedure feasible, the proximal retained portion of the colon must be able to reach the distal rectum, and the anastomosis must not be under tension
- colon is divided 5 cm or more from the cranial aspect of the tumor
- Colonic ends are oversewn with a continuous Parker-Kerr
- two colonic ends are then tied together + laparotomy is closed.
- rectal wall is everted through the anus, and the rectum is incised full thickness at least 1.0 to 1.5 cm from the anus to preserve the distal rectum
- sutured colonic stumps are pulled through the anus
- the colonic end is anastomosed to the distal rectum
What are the reported post-operative complications of a combined abdominal transanal pull-through colorectal amputation?
Bleeding and tenesmus are expected - usually self limiting and resolve within 2 weeks
Faecal incontinence - Usually resolves if 1-1.5cm of distal rectum has been left in placed. Resolution can take up to 5 months
Wound dehisence and subsequent peritonitis - Commonly reported
List the two colopexy techniques
Simple appositional
Incisional
indications: rectal prolapse, perineal hernia
Cecal disease
Inversion
- may present with acute signs of obstruction.
- Confirmation of diagnosis requires positive-contrast radiography, ultrasonography or colonoscopy.
- Management involves colotomy and typhlectomy
Impaction
Neoplasia
- GIST most common, adenocarcinomas and undifferentiated sarcomas
- The treatment of choice is mass removal. Excision may require resection of the cecum, distal ileum, and proximal colon to achieve adequate tumor-free margins.
- Prognosis good with complete excision. MST 681 days, 1yr and 2yr recurrence free in 83.3% and 61.9%
Define megacolon
End-stage obstipation characterised by colonic hypomotility and a permanent increase in the diamter of the colon as a result of severe and irreversible dilatation.
Can be mechanical, functional or commonly idiopathic
List some possible causes of megacolon
Mechanical Causes
- Hypertrophic megacolon can develop with any form of outlet obstruction and is potentially reversible if the cause of the obstruction is removed early in the disease process
- pelvic fracture malunion is the most common cause of hypertrophic or obstructive megacolon in cats
Functional Causes
Acquired megacolon secondary to neuromuscular dysfunction occurs as a consequence of spinal cord disease,
Feline Megacolon
62% idiopathic;
23% pelvic stenosis,
6% neurologic disorders,
5% Manx
cats with idiopathic megacolon present with a dilated colon and no evidence of physical or functional obstruction. There is thought to be a generalized dysfunction of longitudinal and circular smooth muscle (casue or effect of obstruction?)
feline megacolon is rarely successfully managed medically
Clinical Findings and Diagnosis
What is the normal radiographic diameter of the colon?
What radiographic measurement confirms megacolon?
Normal colon diameter is approx equal to the length ot the vertebral body of L2 on a lateral projection
Megacolon is diagnosed if the colonic diameter is 1.5x the length of the verteral body of L7 on a lateral projection
When is megacolon considered irreversible?
What does medical management consist of?
Surgical treatment?
When the colon has been dilated for 6 months or longer.
Medical management consists of stool softeners, warm-water enemas with lubricant, IV ABx during manual deobstipation, dietary fibre, lactulose, cisapride
Cisapride is no longer available on the market due to its cardiotoxicity and fatal arrhythmias seen in humans. This is exacerbated by the concurrent use of macrolide antibiotics or antifungals
Surgical treatment is a subtotal colectomy
medical mgmt
Laxatives
Addition of dietary fiber is well tolerated, effective, and more physiologic than other laxatives
- lactulose: disaccharide that is not hydrolysable by mammals; instead, it is metabolized by colonic bacteria, resulting in the formation of low-molecular-weight organic acids. These acids increase intraluminal colonic osmotic pressure
Why are phosphate enemas contraindicated in cats?
They cause rapid dehydration, hypocalcaemia, hypophosphataemia and death
subtotal colectomy
- preserve the ileocolic junction and transects the ascending colon 1 to 2 cm distal to the cecum. The descending colon is resected 2 cm cranial to the pelvic brim
- 4/0 PDS
correct pelvic fracture or perineal hernia if <6mths duration
Should you remove the ileocolic junction when performing a subtotal colectomy for the treatment of megacolon?
This is a debated topic…
Ileocolic valve helps to prevent retrograde movement of colonic material into the small intestine and subsequent bacterial overgrowth
Increased incidence of severity of diarrhoea seen with removal of ileocolic junction however there is no greater incidence of recurrence in cats which do not have the junctions removed.
Preservation of the ICJ is recommended where possible
What are the expected outcomes following subtotal colectomy?
Loose stools initially due to decreased absorptive capacity and transit time. With time, the remaining intestine adapts by increasing villus heigth, enterocyte number and density (Experimentally, normal enteric motility takes 8 weeks to reestablish)
Cats in which the ICJ is removed are likely to have poorly formed faeces for up to 3 months and some may be incontinent. A small proportion will have soft faeces for years
Recurrence is uncommon (usually be managed medically unless an obstruction is present i.e stricture > consider repeat Sx)
Colonic and Cecocolic Volvulus
rare
- some involved the left colic and caudal mesenteric vessels, resulting in ischemia of the transverse and descending colon
- Cecocolic volvulus compromises the cranial mesenteric artery, similar to that seen in true mesenteric volvulus
- Cecocolic volvulus therefore results in dilatation, congestion, and ischemia of the cecum and small intestine and colonic dilatation.
- Abdominal radiographs reveal marked gaseous distention of intestine loops, particularly in the caudal abdomen.
- Treatment includes aggressive fluid resuscitation, antibiotics, analgesics, and exploratory celiotomy.
What is the prognosis for colonic or caecocolic volvulus?
Depends on the duration and degree of the volvulus.
However, 3 of 6 dogs described in the literature and the only cat, died despite intensive treatment
What are the main reported causes of colonic entrapment?
Following OVH or castration
- prognosis good after resection of the fibrous band compressing the colon
Following rupture of the duodenocolic ligament in a GSD and a St. Bernard
- colon and small intestine are located in the right side of the abdomen because of herniation through the torn duodenocolic ligament.
What are the most common forms of colonic neoplasia in dogs and cats?
What are the recommended margins for removal?
What is an option for palliative care?
majority of colonic tumors are malignant,
Dogs - Most common adenocarcinoma (MST with Sx 6-22m)
Cats - Most common lymphoma and adenocarcinoma. Highly metastatic (80% ADC, 75% lymphoma, 75% MCT). MST 49 - 138d, can be increased to 280d with chemo
Recommended margins are 5-8cm of healthy intestine on each side
Placement of a colonic stent is an option for palliative care - mixed results in the literature
neoplastic sx
- Surgical resection is advocated for nonmetastatic nonlymphomatous lesions
- enterocolic, colocolic, or colorectal anastomosis.
- Colorectal anastomosis can be either immediately cranial to the pelvic brim, within the pelvic canal via osteotomy or via a combined abdominal transanal pull-through procedure.
- preoperative metastasis is present, surgery is palliative, and adjunctive procedures, such as chemotherapy or intraoperative irradiation of metastatic lymph nodes, should be considered.
What are the 2 types of colonic duplication?
How is colonic duplication subclassified?
What is the recommended treatment?
Type 1 - The duplications is limited to the colon and rectum
Type 2 - The duplication is associated with other congenital abnormalities such as urogenital duplication and vertebral column abnormalities
Subclassified into spherical noncommunicating, tubular noncommunicationg and tubular communicating
Surgical treamtent is recommended even if asymptomatic as they have been associated with neoplastic transformation in humans.
Surgical options include division of the common septum, side-to-side anastomosis, excision of noncommunicating portion, mucosal stripping.
Complications and putative risk factors
for cecal or colonic surgery in dogs:
79 cases (2002-2015)
James 2024
multi-institutional
retrospective study
The complication and mortality rates
for full thickness and partial thickness (pexy) cecal/colonic surgeries were not statistically different. The dehiscence
rate of colonic anastomosis in this study was four of 47 (8.5%).
prolonged healing and increased collagenase activity theoretically
increasing the risk for intestinal dehiscence
A recent retrospective study evaluated dehiscence rates and
potential risk factors for death following full thickness colonic
surgeries in 90 dogs. They identified dehiscence and mortality
rates of 10% and 17%, respectively (Latimer et al., 2019). Five
out of the nine dogs diagnosed with dehiscence died or were
euthanased (Latimer et al., 2019).
Computed tomographic findings in all dogs with surgically
confirmed colonic torsion include: “whirl sign,” displacement and distension of the cecum and
colon, focal narrowing of the colon, and distension of the mesenteric vasculature in all dogs (5/5);
Ex vivo comparison of different thoracoabdominal stapler
sizes for typhlectomy in canine cadavers
Matz 2022
Study design: Randomized, experimental cadaveric study.
Animals: Twenty-four fresh canine cadavers
(TA 30 V3 2.5 mm, TA 60 3.5 mm, and TA 60 4.8 mm).
The results of this cadaveric study support the use of
any of the stapler sizes evaluated in similarly sized dogs. A prospective study is
needed to be able to correlate stapler size and clinical outcome
Evaluation of outcomes following subtotal colectomy
for the treatment of idiopathic megacolon in cats
Grossman 2021
166 client-owned cats.
retrospective cohort study
Major perioperative complications 10%
dehiscence rate was 2.1% (3/142)
14% (12/87) of cats died as a direct result of treatment or complications of megacolon.
revision surgery (3/24 [13%]).
The median survival time was not reached
Constipation recurrence occurred in 32%
ICJ removal was associated with long-term liquid feces and a fair or poor outcome on owner assessment
Ex vivo comparison of hand-sutured versus circular stapled anastomosis in canine large intestine
Sapora 2021
Animals: Colon from 11 canine cadavers.
hand-sewn
colonic anastomoses performed with 4-0 glycomer 631 (G) and 4-0 barbed glycomer
631 (BG), and circular stapled colonic anastomoses using 4.8 mm Endto-
End Anastomosis (EEA C4.8mm) and 3.5 mm End-to-End Anastomosis
(EEA C3.5mm),
Anastomoses leaked at lower pressures when stapled rather than hand-sewn
Use of the EEA stapler
with a staple height of 3.5 mm did not result in safe colonic anastomoses.
Clinical significance: These results provide evidence to support handsuturing
colonic anatomoses with G and BG in dogs. The 4.8 mm staples may
be considered in anatomical locations difficult to reach.
Evaluation of short-term risk factors associated
with dehiscence and death following full-thickness incisions
of the large intestine in cats: 84 cases (1993–2015)
Cassie N. Lux 2021
The overall dehiscence and survival to
hospital discharge rates were 8.3% (7/84 cats) and 94% (79/84 cats
colonic trauma or dehiscence and postoperative
intestinal dehiscence were associated with
failure to survive to hospital discharge
Factors suggestive of systemic illness were associated with colonic dehiscence or death, and focused prospective studies of risk factors are warranted
Factors associated with dehiscence only included hypoalbuminemia, renal dysfunction, administration of blood products or > 2 classes of antimicrobials, and intra-abdominal
fecal contamination.
Influence of closure technique on leakage pressures
in an ex vivo canine typhlectomy model
Duffy 2020
Experimental, ex vivo.
Sample population: Grossly normal cecal segments from 24 adult canine
cadavers.
simple continuous closure with a Parker-Kerr pattern with 4-0 polydioxanone
(group 1), closure with a 60-mm gastrointestinal stapler loaded with a 3.8-mm
staple cartridge (group 2), and placement of a Cushing suture to augment the
stapled closure (group 3).
provide evidence to support placement of
a Cushing suture pattern to augment the staple line for typhlectomies in dogs,
although in vivo studies are required to determine the clinical significance of
these findings.
The case described here represents a unique combination of anatomic
anomalies including a communicating colonic duplication and
a concomitant anogenital cleft
Evaluation of short-term outcomes and potential risk factors
for death and intestinal dehiscence following full-thickness
large intestinal incisions in dogs
Latimer 2019
retrospective 90 dogs
Overall 7-day postoperative intestinal dehiscence and mortality rates were
9 of 90 (10%) and 15 of 90 (17%).
Preexisting colon trauma or dehiscence, preexisting peritonitis, administration of blood products, administration of > 2 classes
of antimicrobials associated
with development of intestinal dehiscence.
Five of 9 dogs with intestinal
dehiscence died or were euthanized.
Factors associated with failure to survive to discharge were considered suggestive
of sepsis. Results suggested the dehiscence rate for full-thickness
large intestinal incisions may not be as high as previously reported
Full-thickness small and large intestinal incisions
in dogs have reported dehiscence rates of 28 of 225 (12%) to 42 of 295 (14%).
It has been theorized that dehiscence is
more likely to develop in small animal patients after
surgery of the large intestine than after surgery of the
small intestine because of the poor collateral blood
supply, high intraluminal pressure during passage of
fecal boluses, and high bacterial load in the large intestine.
