Postcastration Evisceration in a 2-year-old Standardbred
Farrell Campbell
Clinical advisor: Dr. Hayley Lang, DVM
Basic science advisors: Dr. Richard Hackett, DVM, MS
& Dr. Linda Mizer, DVM, MSc, PhD
Senior Seminar Paper
Cornell University College of Veterinary Medicine
February 12, 2014
Key words: Standardbred, castration, eventration, evisceration
Abstract
Castration has been reported as one of the most common routine surgical procedures
performed in the horse.12-14 Although the procedure is considered routine, complications
associated with castration occur commonly and, although the majority are mild and
resolve easily, potentially life-threatening complications can occur. Post-castration
evisceration, or eventration, is a rare complication of castration that occurs when a
portion of intestine prolapses through the inguinal canal and out of the scrotal incision.
This case study details an example of post-castration evisceration in a two-year-old
Standardbred gelding, and will also outline presurgical considerations, surgical
techniques, and emergency management of this surgical complication.
Signalment, history, chief complaint
A two-year-old Standardbred gelding was referred to Cornell’s Equine Hospital
following a post-castration evisceration. Earlier in the day the referring veterinarian
performed an open castration with ligation on the colt under short acting general
anesthesia. When the horse was placed on a trailer for transport, he started to kick
violently. The horse was taken off the trailer and placed in a stall which he attempted to
jump out of, subsequently becoming cast. At this time, approximately three inches of
bowel could be seen exiting the left scrotal incision which prompted immediate referral
to Cornell.
Clinical findings and treatment
After three hours of travel, the colt presented standing backwards in the trailer. He was
shocky, sweaty, and had an abrasion above his right eye. There was approximately 10
feet of small intestine exiting his left scrotal incision. The eviscerated bowel appeared
nonvital and the mesentery was ripped away. There was a large amount of blood on the
floor of the trailer and he had stepped on the bowel. A physical exam was not performed
due to the severity of the horse’s condition. The horse was sedated with detomidine and
butorphanol upon arrival. After discussing our findings with the owner and trainer
euthanasia was elected.
Discussion
Pathogenesis
Post-castration evisceration (PCE), or eventration, is a rare complication of castration that
occurs when a portion of abdominal contents prolapses through the inguinal canal and out
of the scrotal incision. Most often evisceration is seen within 4 hours of castration but has
occurred several days later. 5,7,13,17 The majority of eventrations are of the small intestine,
however omental evisceration also occur. 2,6,14 Eventration is uncommon, with a reported
incidence from 0.2 % to 4.8% .4,10,14
The exact pathogenesis of eventration is not completely understood, however, there are
multiple risk factors believed to contribute including: breed of horse; pre-existing or
history of inguinal hernia; large vaginal rings; leg position during recovery; increased
intra-abdominal pressure; reduction in the size of the pampiniform plexus and excessive
exercise. Standardbreds and draft horses have been reported to have a higher incidence of
eventration following castration.2-7, 11, 13-14 The higher incidence of postoperative
evisceration may be because of the higher incidence of congenital inguinal herniation in
these breeds.14 These breeds are also believed by practitioners to have relatively larger
vaginal rings than others. Comparative vaginal ring size amongst breeds has not been
documented however pre-surgical palpation per rectum of vaginal rings greater than two
fingers in width has been associated with greater surgical complications including
eventration.13 Others have postulated that flexing the hind legs of a horse in dorsal
recumbency, as in field castration, can enlarge the vaginal rings and allow the passage of
viscera into the inguinal canal.18
A recognized contributor of eventration are the pressure changes that occur following
castration. Open castration results in an immediate communication between the
peritoneal cavity and the exterior. Furthermore, disruption of the vaginal tunic as a result
of castration leads to a pressure gradient favoring movement of viscera from the abdomen
through the vaginal ring.2,14 Finally, castration alters the hemodynamics of the
pampiniform plexus which in mature stallions is a large structure that occludes abdominal
contents from entering the inguinal canal. This alteration in the venous drainage of the
testis could make the vaginal ring more accessible to abdominal contents.
It therefore seems plausible that the combination of altered venous distension of the
spermatic cord, vaginal ring size, presence of a patent lumen to the exterior of the
abdomen and pressure changes within the peritoneal cavity are all factors in evisceration
in the horse.
Presurgical Exam
To prevent postsurgical complications such as eventration a presurgical physical exam
should be performed in every patient. The horse’s inguinal region should be palpated for
the presence of both testicles in the scrotum and structures in the inguinal region as
evidence of herniation.5 Some authors recommend performing an examination per rectum
on at-risk horses prior to castration to determine the size of vaginal rings; however, this
isn’t always practical or safe.4 Owners should be queried about the presence of congenital
inguinal hernia the horse may have endured as a foal. This is especially important in
Standardbred and Draft breeds that have a relatively high incidence of congenital inguinal
herniation. Older horses have previously been reported to be at higher risk for the
development of complications postoperatively speculating larger scrotal size and
testicular vessel size; however another study did not reveal any significant association
between age of horse and development of complication.7,10 A thorough physical exam
prior to surgery allows the practitioner to identify potential complications that may arise
and therefore make appropriate recommendations for surgery. Ideally, for horses that
have a higher than normal risk for evisceration, castration should be performed at a
surgery clinic with the horse under general anesthesia.
Anatomical Considerations
To understand the causation of postcastration evisceration a knowledge of male equine
reproductive anatomy and the surgical techniques of castration are required.
In a mature horse the two testicles are suspended within the left and right sides of the
scrotum, a prepubic pouch of thin skin. Deep to the scrotal skin lies the tunica dartos
which consists of loose connective tissue and involuntary muscle which vary the size of
the scrotum in response to temperature.4 Further inwards, the testicles and accompanying
structures, epididymis and spermatic cord, lie invested by an outpocketing of abdominal
peritoneal lining known as the tunica vaginalis, or vaginal tunic. The vaginal tunic
consists of visceral and parietal layers. The visceral layer is tightly adhered to the testicle,
ducts and vessels, and the parietal layer is continuous with the parietal peritoneum.12
The cremaster muscle, which retracts the testicle, is an extension of the internal
abdominal oblique muscle and is continuous with the parietal layer of the vaginal tunic
attaching at the caudal pole of the testicle.
The spermatic cord courses from the abdomen to the scrotum through the inguinal canal.
The inguinal canal is a flat potential space between the external and internal abdominal
oblique muscles that connects the abdominal cavity with the subcutaneous structures in
the groin. The inguinal canal contains the spermatic cord, external pudendal artery, vein
and the genitofemoral nerve.1 The inguinal canal is bounded by deep and superficial
inguinal rings. The deep inguinal ring is a dilatable opening between the free edge of the
internal abdominal oblique muscle and the free aponeurosis of the external abdominal
oblique muscle. The superficial inguinal ring is formed by a small opening in the
aponeurosis of the external abdominal oblique muscle.
Importantly the vaginal ring is the opening formed by the peritoneum as it leaves the
abdomen and enters the inguinal canal to form the vaginal tunic. This out pouching or
ring-like structure is the anatomical landmark practitioners palpate per rectum to
determine vaginal ring size.
Castration
Castration is the surgical removal of male gonads, specifically the testicles and the
epididymis and a portion of the ductus deferens and accompanying blood vessels. The
castration techniques utilized by equine practitioners can be categorized into three forms:
open, closed, and semi-closed. These techniques refer to whether the vaginal tunic
surrounding the testes is incised during castration. There are several modifications of
each technique but, regardless of whether the horse is sedated and standing or recumbent
and anaesthetized, the surgical principles for castration remain the same.
For the open technique, the parietal layer of the vaginal tunic is incised. The ligament of
the tail of the epididymis, which attaches the parietal layer to the epididymis, is cut or
bluntly transected. The testis, epididymis and distal portion of the spermatic cord are
completely freed from the parietal tunic and removed using an emasculator.6
For the closed technique, the parietal layer of the testis remains intact. The testis, still
encapsulated by the parietal layer is grasped, and the scrotal fascia is stripped from the
parietal layer until the cremaster muscle and tunic are fully exposed. The emasculators
are then applied to the entire spermatic cord.13 In some horses that have a large spermatic
cord the cremaster muscle can be bluntly dissected from the spermatic cord and the
emasculators applied separately prior to crushing and severing the entire spermatic cord
with emasculators.6
The semi-closed technique is similar to the closed method however after the parietal layer
and cremaster muscle are exposed, a small incision is made in the tunic just proximal to
the testis. The contents within the parietal tunic can then be inspected to ensure the
presence of a testicle rather than simply epididymis which can occur in cryptorchid
animals and also to ensure that there is no evidence of herniated tissue.6 Following
inspection, emasculators are then applied to the entire spermatic cord, including the
parietal tunic, proximal to the testis. Alternatively, for some horses in which a large
spermatic cord is encountered, the spermatic vasculature can be exteriorized from the
tunic and the emasculators applied to these separately before crushing and severing the
entire spermatic cord within the parietal tunic.12,13 The semi-closed technique should be
considered a closed technique as the parietal tunic is removed along with the testis and
distal portion of the spermatic cord.
The choice of castration technique should be governed by the age, temperament and size
of the horse, the presence of concurrent abnormalities, the preferences of the clinician or
owner and by the facilities available.5 Some clinicians maintain that various techniques of
castration are necessary for certain individual breeds which have characteristic
complications associated with the procedure. There are many ancillary claims that one or
another castration technique has greater success and fewer PCE complications, but in
fact, no controlled study has been performed to investigate the superiority of one
technique.5,13 That being said there are surgical techniques practitioners can implement in
either field or hospital surgery that have been shown to reduce the rate of eventration.
In the field, castration with ligation is essential in at-risk-horses. It is important to note
that if the surgeon does not place a ligature around the parietal layer of the vaginal tunic
during castration, there is the same communication between the peritoneal cavity and the
exterior or the scrotum no matter which technique is employed.13,14 The application of the
emasculators provides only a tenuous seal after the crushing action of the device on the
severed end of the spermatic cord. This seal provides little or no mechanical resistance to
the passage of intestines from the inguinal canal to the exterior of the scrotal incisions
advocating vaginal tunic ligation in patients at risk of eventration. 3-4,14
In one study that looked at surgical complications with a population of 568 draft colts, a
breed considered at risk for postsurgical eventration, the rate of eventration was no
different between animals that were castrated with either the open or closed techniques.14
In this study, PCE occurred in 27 horses (4.8%). Open and closed castration techniques
resulted in 8 (29.6%) and 19 (70.4%) eviscerations respectively. The lack of statistical
significance between the open and closed techniques in this case was attributed to the
lack of ligation utilization. Another study found that common vaginal tunic ligation
significantly reduced the incidence of omental herniation and evisceration in population
of draft colts with only 1/131 (0.8%) evaluated horses developing eventration.2
Another form of castration ligation utilized in the field is colloquially referred to as “twist
and tack”. The twist and tack method utilizes ligation of the spermatic cord but goes a
step further in securing the surgical remnants. After stripping, the cord is twisted along
it’s long axis and ligated. Then a bite from the same suture used to ligate is then placed
into the superficial inguinal ring to “tack” it into place. Although performed, this
technique of ligation is challenging in the field from a scrotal approach. Some surgeons
also question the necessity of twisting and tacking having been shown in the literature
that ligation alone dramatically decreases the incidence of PCE.2 Both standard ligation
and the twist and tack method essentially seal off the lumen of the vaginal tunic to the
exterior while the later form of ligation not only seals off the lumen of the vaginal tunic it
further obliterates the space within the remaining vaginal tunic post-castration. It should
be noted that herniation into the remnant of the vaginal tunic after ligation is a theoretical
concern, but the condition has never been reported.1,2
Traditionally, castration techniques allow for second intention healing of scrotal wounds,
however some surgeons advocate primary closure castration in patients at greater risk for
postoperative complications including eventration. Castration with primary wound
closure can be carried out using a scrotal or inguinal approach with the latter being a
more recently described method that is routinely used at Cornell’s Equine Hospital. A
specific inguinal approach described by Kummer et al. 2009, that involves leaving the
vaginal tunic in situ, is believed by some surgeons to cause less soft tissue trauma than a
scrotal approach primary closure castration. In either primary closure approach, the testes
are retracted, the spermatic cord is then ligated, emasculated and excised using the same
techniques employed in the field (i.e. open, closed) however in primary closure incisions
are sutured closed in multiple layers rather than left open to heal by second intention. One
study showed the complication rate of horses castrated standing and non-sutured to be
22% vs. a 6% complication rate in those castrated using a primary closure under general
anesthesia in aseptic hospital conditions.10 Primary closure has been shown to speed
healing and recovery as well as decrease the possibility of complications including PCE
and infection. Although primary closure castration has benefits the procedure itself is
more time-consuming and requires general anesthesia and strict aseptic technique which
is not possible in field surgery. Primary closure castration can also be prohibitively
expensive as on average primary closure castration is three times more expensive than
conventional field castration.10
Prevention, diagnosis and emergency management
Even with proper surgical technique, complications can occur making prompt recognition
and initiation of appropriate therapy essential to prevent further morbidity. Once
eventration is suspected a thorough examination in a well-sedated horse should be
performed to assess the nature of the tissue protruding – occasionally subcutaneous tissue
may be found protruding through the scrotal incision.7 If herniated abdominal contents
are suspected it is important to differentiate omental tissue from intestines as the former
can usually be managed out in the field while the latter is a surgical emergency.11 After
intestinal eventration occurs, initial therapy is aimed at keeping the bowel safe from
damage, further contamination, further eventration and preparing the horse for transport
to a referral center.
Once eventration is identified the horse should be immediately anesthetized. Prolapsed
bowel should be grossly cleaned with copious sterile irrigation and reduced back into the
abdomen to avoid ischemic damage.4 To prevent strangulation, bowel must be placed
fully into abdomen, not just into the scrotum. If needed, one should fully open the
remnant of the vaginal tunic as necessary to allow full reduction of hernia into the
abdomen.
If a large amount of intestine is present, and reduction is not possible then a moist towel
or drape should be made into a sling and used to support the bowel during transport. A
hand towel can also be sutured to the inguinal region to keep the bowel in place.4,11
Failure to support the intestine adequately often leads to further eventration of intestine
which is then traumatized and results in catastrophic and untreatable intestinal
compromise. Affected horses should also be given broad spectrum antimicrobials and
flunixin meglumine for analgesic and anti-endotoxic therapy and sedation for
transportation if stable enough.
Conclusion
Castration is a very established and common procedure, often performed in the field. The
ubiquity of the procedure, however, should not suggest that it is without complications.
Should eventration arise in particular cases, knowledge of the basic first aid steps and
emergency care protocols should be known to field and hospital practitioners alike.
References:
1. Boussauw B, Wilderjans H. Case Report: Inguinal herniation 12 days after a unilateral
castration with primary wound closure. Equine Vet Educ 1996; 8(5): 248-250.
2. Carmalt JL, Shoemaker RW, Wilson DG. Evaluation of common vaginal tunic ligation
during field castration in draught colts. Equine Vet J 2008; 40(6): 597-598.
3. Getman LM. Review of Castration Complications: Strategies for Treatment in the
Field. 2009 Vol. 55 AAEP Proceedings.
4. Getman LM. Post castration evisceration. Equine Vet Educ 2013; 25(11): 563-564.
5. Green P. Equine Practice: Castration techniques in the horse. In Practice 2001; 23(5):
250-261.
6. Kilcoyne I. Equine castration: A review of techniques, complications and their
management. Equine Vet Educ 2013; 25(9): 476-482.
7. Kilcoyne I, Watson J, Kass PH, et al. Incidence, management, and outcome of
complications of castration in equids: 324 cases (1998-2008). J Am Vet Med Assoc 2013;
242(6):820-825.
8. Kummer M, Gygax D, Jackson M, et al. Results and complications of a novel
technique for primary castration with an inguinal approach in horses. Equine Vet J
2009;41:547–551.
9. Mason BJ, Newton JR, Payne RJ, et al: Costs and complications of equine castration: a
UK practice-based study comparing ‘standing nonsutured’ and ‘recumbent sutured’
techniques. Equine Vet J 2005;37:468–472.
10. Moll HD, Pelzer KD, Pleasant RS, et a. A survey of equine castration complications
in the horse. J Equine Vet Sci 1995;15: 522-526.
11. Pollock PJ. Complications of castration: Part 1. Companion Animal 2012; 17(5): 913.
12. Searle D, Dart AJ, Dart CM, et al. Equine castration: review of anatomy, approaches,
techniques and complications in normal, cryptorchid and monorchid horses. Aust Vet J
1999; 77(7): 428-434.
13. Schumacher J. Testis. In: Equine Surgery, 4th edn, 2012, Ed: J.A. Auer, Elsevier
Saunders, St. Louis. pp. 804-836.
14. Shoemaker R, Bailer J, Janzen E, et al. Routine castration in 568 draught colts:
incidence of evisceration and omental herniation. Equine Vet J 2004; 36(4): 336-340.
15. Steiner J, Hillman R, Orsini J, et al. Reproductive System. In: Equine Emergencies
Treatment & Procedures, 3rd edn, 2008: A. Orsini & T.J. Divers, Saunders Elsevier, St.
Louis. pp. 3rd edition, 2008 p. 411-434
16. Thomas HL, Zaruby JF, Smith CL, et al. Postcastration eventration in 18 horses: the
prognostic indicators for long-term survival (1985-1995). Can Vet J 1998; 39: 764-768.
17. Torre F, Gasparin J, Bassi Andreasi M. Herniation of the small intestine through the
femoral canal after castration in a 3-year-old Thoroughbred. Equine Vet Educ 2013;
25(11): 558-562.
18. van der Velden MA, Rutgers LJE. Visceral prolapse after castration in the horse: a
review of 18 cases. Equine Vet J 1990;22:9-12.