Changes

==Treatment==

==Treatment==

Megacolon may be managed medically, or surgically if the condition is severe or recurrent. Medical therapy aims to restore the patient's hydration and then clear the faecal impaction. Under anaethesia, the colon is manulally evacuated using warm water enemas, lubrication and gentle extraction of faeces with forceps or a finger. Care must be taken not to damage the colonic mucsoa during this procedure, and prophylactic antibiotics are recommended before commencement. Once the patient's colon is clear, the focus is shifted to preventing recurrence. Dogs and cats must have adequate access to litter or the outdoors to encourage regular defaecation, and regular exercise may be beneficial. Diets containing bulk-forming fibre may contribute to the recurrence of impaction, but a high-fibre diet may occasionally be useful in prevention. Stool softeners such as lactulose, and prokinetic drugs such as cisapride can promote motility and defaecation. Medical management is usually an ongoing, life-long committment which may be frustrating for the owner, and relapse is common.

 

Megacolon may be managed medically, or surgically if the condition is severe or recurrent. Medical therapy aims to restore the patient's hydration and then clear the faecal impaction. Under anaethesia, the colon is manually evacuated using warm water enemas, lubrication and gentle extraction of faeces with forceps or a finger. Care must be taken not to damage the colonic mucsoa during this procedure, and prophylactic antibiotics are recommended before commencement. Once the patient's colon is clear, the focus is shifted to preventing recurrence. Dogs and cats must have adequate access to litter or the outdoors to encourage regular defaecation, and regular exercise may be beneficial. Diets containing bulk-forming fibre may contribute to the recurrence of impaction, but a high-fibre diet may occasionally be useful in prevention. Stool softeners such as lactulose, and prokinetic drugs such as cisapride can promote motility and defaecation. Medical management is usually an ongoing, life-long committment which may be frustrating for the owner, and relapse is common.

Sub-total colectomy can be used to correct megacolon in the cat. However, this technique is very poorly tolerated in the dog. The term refers to the removal of the majority of the colon, and the ileocaecocolic valve may be preserved or removed. The ileocaecocolic valve prevents reflux of colonic contents into the small intestine and so some surgeons believe that removing this structure can predispose to small intestinal bacterial overgrowth,steatorrhoea and deconjugation of bile salts². However, removing the ileocaecocolic valve minimises the recurrence of megacolon.  

Sub-total colectomy can be used to correct megacolon in the cat. However, this technique is very poorly tolerated in the dog. The term refers to the removal of the majority of the colon, and the ileocaecocolic valve may be preserved or removed. The ileocaecocolic valve prevents reflux of colonic contents into the small intestine and so some surgeons believe that removing this structure can predispose to small intestinal bacterial overgrowth,steatorrhoea and deconjugation of bile salts². However, removing the ileocaecocolic valve minimises the recurrence of megacolon.  

 

As yet, there is no established figure for how much colon to remove. If the ileocaecocolic valve is removed, and enterocolostomy is performed; if not, the colon is transected 3 cm from the caecum to ensure the following colocolostomy is not under tension from the short mesocolon. Any longitudinal tension on the anastomosis site is likely to lead to dehiscence postoperatively. In surgeries where the valve is resected, an oblique incision of the ileal portion and a short antimesenteric incision of the distal colon will allow for disparities in lumen diameter. The intestine is closed in a single layer using full-thickness appositional, simple interrupted suture in an absorbable material. Staples may similary be used.

The issue of exactly how much of the colon to remove will remain

outcome and function. However, the author’s preference in

the majority of cases is to resect the ileocaecocolic valve and perform

enterocolostomy. If the ileocaecocolic valve is to be preserved,

the colon is transected 3 cm from the caecum to ensure a

tension-free colocolostomy (the short mesocolon restricts mobility).

It is essential that there is no longitudinal tension on the anastomosis

site postoperatively, as this is likely to lead to dehiscence, with

potentially disastrous results.

If the valve is resected and an enterocolostomy performed, the

disparity in luminal widths can be dealt with by oblique incision of

the ileal portion combined with a short antimesenteric incision to

spatulate the intestine. A single layer of full-thickness appositional

sutures using polydioxanone in a simple interrupted pattern is the

author’s preference. An end-to-end or end-to-side anastomosis can

also be created using surgical stapling equipment.

and are not recommended.

Although sub-total colectomy is an effective way of correcting megacolon, removal of majority of the colon has the potential to cause metabolic effects in the animal. For example, the colon normally functions to absorb water. This is achieved by the creation of an osmotic gradient by active sodium absorbtion. Additionally, extracellular potassium is lost and bicarbonate ions are exchanged for chloride ions in the colon. It could therefore be implied that sub-total colectomy disrupts water and electrolyte homeostasis, but paradoxically cats undergoing sub-total colectomy have been found to show no clinical evidence of abnormal bowel function⁶. However, other, non-clinical changes were found: small intestinal enterocytes and villi were increased in height, the absorptive area of the small intestinal muscosa was increased, serum cobalamin and faecal sodium were increased and faecal potassium was low. The significance of these results is unknown.

Although sub-total colectomy is an effective way of correcting megacolon, removal of majority of the colon has the potential to cause metabolic effects in the animal. For example, the colon normally functions to absorb water. This is achieved by the creation of an osmotic gradient by active sodium absorbtion. Additionally, extracellular potassium is lost and bicarbonate ions are exchanged for chloride ions in the colon. It could therefore be implied that sub-total colectomy disrupts water and electrolyte homeostasis, but paradoxically cats undergoing sub-total colectomy have been found to show no clinical evidence of abnormal bowel function⁶. However, other, non-clinical changes were found: small intestinal enterocytes and villi were increased in height, the absorptive area of the small intestinal muscosa was increased, serum cobalamin and faecal sodium were increased and faecal potassium was low. The significance of these results is unknown.

After surgery faeces are loose and defaecation is associated with tenesemus, but faecal consistency improved over the following months. Complications associated with the surgery itself are rare and tend to related to the anastomotic procedure². For example, the abdomen may become contaminated during surgery, leading to peritonitis, or the anastomosis site may break down. Long-term complications usually involve recurrence of constipation, which may be managed medically in most cases.

After surgery faeces are loose and defaecation is associated with tenesemus, but faecal consistency improves over the following months. Complications associated with the surgery itself are rare and tend to related to the anastomotic procedure². For example, the abdomen may become contaminated during surgery, leading to peritonitis, or the anastomosis site may break down. Long-term complications usually involve recurrence of constipation, which can be managed medically in most cases.

==Prognosis==

==Prognosis==