34th Annual Scientific Meeting proceedings

The technique of equine large colon resection and anastomosis has been described since the early 1970s, and the consequences of removing the majority of the equine large colon have been investigated in experimental studies.  There are two main techniques for large colon resection with modifications within each broad type: the side-to-side anastomosis and the end-to-end anastomosis.  The side-to-side anastomosis can be handsewn or performed with staples, whereas the end-to-end anastomosis is hand-sewn.  Large colon resections can be segmental, partial, or near-complete (>80%).  Indications for large colon resection are large colon volvulus, focal or localized large colon disease (neoplasia, infarcts, intussusception, iatrogenic injury or contamination), or prevention of recurrent displacement or volvulus.  Evidence-based questions surrounding large colon resection include:

1. Does large colon resection improve prognosis for large colon volvulus?

2. Which technique (side-to-side vs end-to-end) is better?

3. How much colon should be resected?

4. Does large colon resection prevent recurrent colic?

Does large colon resection improve prognosis for large colon volvulus?
A long-term survival analysis following horses that had colic surgery for large intestinal disease found that large colon resection was independently associated with postoperative death in a multivariate model.¹  This remained significant despite controlling for heart rate and hematocrit, which would reflect severity of illness.¹  Older studies found 47-57% survival following large colon resection for large colon volvulus, which is not significantly different compared to contemporaneous survival rates following manual correction of large colon volvulus.^1-4  Furthermore, most large colon volvulus occur at locations proximal to the cecocolic ligament or at the base of the cecum and colon, which means that large colon resections are typically occurring in compromised tissue.⁵

More recent investigations comparing management of large colon volvulus by resection and anastomosis to manual correction in a contemporaneous population of horses have found survival rates of 70-80% for resection compared to 76-86% for manual correction and were not significantly different.^6-9  While initial interpretation could conclude that large colon resection does not provide a survival advantage in large colon volvulus, it is worth noting that there is evidence in these recent studies (beside clinical judgement) that the large colon was more compromised and likely needed resection to allow the horse a chance to survive.^6,7  Therefore, although a randomized clinical trial has not been performed for large colon resection as a treatment for large colon volvulus (and would be unethical), there is clinical evidence that large colon resection for compromised colons may improve survival closer to that of horses with less compromised colons corrected by manual correction.  Long-term survival analysis of horses undergoing resection for large colon volvulus indicates that the majority of post-operative deaths occurred during hospitalization, and 91% of horses surviving to discharge were alive after 1 year of follow-up.¹⁰

Separately, it is worth noting that the prognosis for survival after large colon resection for reasons other than large colon volvulus tend to be very good.^3,4 The surgery is challenging and prone to technical errors, but if the surgical technique is meticulous and accurate, recovery can be uncomplicated.

Which technique is better?
The side-to-side anastomosis and the end-to-end anastomosis for large colon resections have not been compared experimentally.  A stapled side-to-side anastomosis was compared to a hand-sewn side-to-side anastomosis, and both were found to be comparable, although some reduction of stoma size was documented in two-thirds of those horses.¹¹  A retrospective clinical study compared end-to-end anastomosis to a variation of a side-to-side anastomosis (functional end-to-end), and the techniques were found to be equivalent.¹²  Clinically, there are anecdotal reports that the side-to-side anastomosis are more prone to impaction than the end-to-end anastomosis.⁵

How much colon should be resected?
Partial and near total (95%) large colon resections have been performed successfully, including long-term follow-up.^11,13,14  Segmental large colon resections have been performed clinically.²  Anecdotally, it has been reported that partial large colon resections have been susceptible to displacement due to the mobility of the partially resected colon.⁵  Therefore, it seems prudent to remove as much colon as possible when doing a large colon resection, especially if the resection is for a large colon volvulus or recurrent displacement.  If the colon resection is for focal disease, a segmental resection could be considered.²

Does large colon resection prevent recurrent colic?
Recurrent colic, particularly if due to recurrent displacement, may be treated by colopexy or large colon resection.  The benefit of colopexy in reducing recurrent colic has been shown in a large population of Thoroughbred broodmares.¹⁵  A clinical study in a population of horses with elongation of the dorsal mesenteric attachments found that colon resection in these horses significantly reduced colic episodes compared to those not undergoing colon resection.¹⁶  The decision between colopexy or colon resection for prevention of recurrent colic is influenced by owner financial considerations, aspirations for future athletic performance, and surgeon preference.

References

1. Proudman CJ, Edwards GB, Barnes J, French NP.  Modelling long-term survival of horses following surgery for large intestinal disease.  Equine Vet J. 2005;37:366-370.
2. Bertone AL, Stashak TS, Sullins KE.  Large colon resection and anastomosis in horses.  J Am Vet Med Assoc. 1986;188:612-617.
3. Driscoll N, Baia P, Fischer AT, Klohnen A.  Large colon resection and anastomosis in horses (1996-2006).  Equine Vet J. 2008;40:342-347.
4. Hughes FE, Slone DE.  A modified technique for extensive large colon resection and anastomosis in horses. Vet Surg. 1998;27:127-131.
5. Hughes FE, Slone DE.  Large colon resection. Vet Clin North Am Equine. 1997;13:341-350.
6. Mathis SC, Slone DE, Lynch TM, Hughes FE, Clark CK.  Use of colonic luminal pressure to predict outcome after surgical treatment of strangulating large colon volvulus in horses.  Vet Surg. 2006;35:356-360.
7. Kelleher ME, Brosnan RJ, Kass PH, le Jeune SS.  Use of physiologic and arterial blood gas variables to predict short-term survival in horses with large colon volvulus. Vet Surg. 2013;42:107-113.
8. Gonzalez LM, Fogle CA, Hughes FE, Law JM, Motsinger-Reif AA, Blikslager AT. Operative factors associated with short-term outcome in horses with large colon volvulus: 47 cases from 2006 to 2013.  Equine Vet J. 2015;47:279-284.
9. Orr KE, Baker WT, Lynch TM, Hughes FE, Clark CK, Slone DE, Fogle CA, Gonzalez LM.  Prognostic value of colonic and peripheral venous lactate measurements in horses with large colon volvulus.  Vet Surg. 2020;49:472-479.
10. Ellis CM, Lynch TM, Slone DE, Hughes FE, Clark CK.  Survival and complications after large colon resection and end-to-end anastomosis for strangulating large colon volvulus in seventy-three horses.  Vet Surg. 2008;37:786-790.
11. Sullins KE, Stashak TS.  Evaluation of two techniques for large intestinal resection and anastomosis in the horse.  J Invest Surg. 1989;2:115-124.
12. Pezzanite LM, Hackett ES.  Technique-associated outcomes in horses following large colon resection.  Vet Surg. 2017;46:1061-1067.
13. Bertone AL, Stashak TS, Sullins KE, Ralston SL.  Experimental large colon resection at the cecocolic ligament in the horse.  Vet Surg. 1987;16:5-12.
14. Ducharme NG, Horney FD, Baird JD, Arighi M, Burton JH.  Extensive large colon resection in the pony: I. surgical procedures and clinical results.  Can J Vet Res. 1987;51:66-75.
15. Warren AS, Werner LA, Thombs LA, Rodgerson DH, Spirito MA, Sandow CB, McCracken MJ.  Effect of a ventral midline colopexy on large colon volvulus recurrence and days to next live foal in Thoroughbred broodmares.  Vet Surg. 2025;in press (DOI: 10.1111/vsu.14269).
16. Hassel DM, Wist S, Hoblick S.  Outcomes of horses undergoing ventral midline celiotomy for colic with dorsal mesenteric attachment abnormalities of the colon and cecum.  Equine Vet Educ. 2024;36(s13):81-82.