Congenital perianal fistula in a thoroughbred colt.

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The Veterinary Record, September 9, 2006
FIG 1: Perianal fistula,
on the left side of the
anus, in a 14-day-old
foal
Veterinary Record (2006)
159, 362-364
C. M. Kearney, MVB,
P. J. Pollock, BVMS,
CertES(Soft tissue),
DipECVS, MRCVS,
Department of Veterinary
Surgery, Faculty of
Veterinary Medicine,
University College
Dublin, Belfield,
Dublin 4, Ireland
Correspondence to
Mr Pollock
Congenital
perianal fistula in a
thoroughbred colt
C. M. Kearney, P. J. Pollock
CONGENITAL defects are frequently reported in neonatal
equids. These abnormalities include commonly encountered
and treated developmental aberrations, such as umbilical
hernias and cryptorchidism, and more rare and potentially
fatal anomalies such as atresia coli (Huston and others 1970,
Crowe and Swerczek 1985, Young and others 1992).
Various congenital defects involving the gastrointestinal
tract have been described. Atresia ani is the most commonly
reported malformation of the perianal region in equids and
in the majority of the domestic species (Van der Gaag and
Tibboel 1980, Crowe and Swerczek 1985). Perianal fistu-
las are uncommon in the domestic species, apart from in
dogs (Amand 1974). A congenital form of perianal fistula
has been reported in human beings (Fitzgerald and others
1985, Al-Salem and others 1994), as have duplications of
the colon and rectum (Iyer and Mahour 1995, Choi and
Park 2003).
This short communication describes the clinical presenta-
tion and surgical treatment of a congenital perianal fistula in
a foal. To the best of the authors’ knowledge, this congenital
defect has not previously been reported in horses.
A 14-day-old thoroughbred colt was presented to the
university veterinary hospital in Dublin for the investigation
and treatment of a perianal fistula, which had been noted by
the referring veterinary surgeon during routine examination
shortly after birth.
During clinical examination, the foal was noted to have
a 3 cm long, mucosa-lined tract, which opened 1 cm lateral
to the anus, on the left side (Fig 1). The tract communicated
with the rectum, approximately 3 cm within the anal sphinc-
ter. The foal was bright and alert, and no other abnormalities
were detected during clinical examination. The foal was pass-
ing faeces, of normal colour and consistency, through both
its anus and the small perianal opening. The foal showed no
signs of pain or discomfort associated with its gastrointesti-
nal system or perianal region.
The foal was premedicated with 0·1 mg/kg midazolam
(Hypnovel; Roche) intravenously, and anaesthesia was
induced with 2·2 mg/kg ketamine hydrochloride (Narketan
10; Vétoquinol) intravenously. Anaesthesia was maintained
with halothane (Halothane-vet; Merial) in oxygen delivered
in a circle system. Intermittent positive pressure ventila-
tion was used throughout the duration of anaesthesia. The
foal was positioned in sternal recumbency, with its hindlegs
flexed on either side of its body and its perianal region at
the edge of the surgery table (Fig 2). A total of 3 ml of 2 per
cent mepivicaine hydrochloride solution (Intracepicaine;
Arnolds) (0·5 mg/kg) was administered into the epidural
space at the start of the period of anaesthesia, and 0·1 mg/
kg morphine sulphate (Antigen Pharmaceuticals) and 2 mg/
kg ketoprofen (Ketofen: Merial) were administered intrave-
nously for analgesia. The tail was bandaged and secured
over the foal’s back, and the perianal region was clipped and
scrubbed for aseptic surgery. The rectum and fistulous tract
were flushed with dilute chlorhexidine solution (Hibiscrub;
AstraZeneca).
The mucosal lining of the tract was isolated and resected,
using a mixture of blunt and sharp dissection, to the level of
its junction with the rectal mucosa. The rectal mucosa was
inverted into the rectal lumen and apposed with 3 metric
polydioxanone (PDS II; Johnson & Johnson) in a continuous
horizontal mattress suture pattern. The rectal submucosa was
closed in a simple continuous pattern and the subcutane-
ous tissues and perianal musculature were closed in a similar
manner. An intradermal pattern was placed in the skin. A
stent bandage was placed over the incision and the foal was
allowed to recover.
The foal received 22,000 iu/kg procaine benzylpenicil-
lin (Depocillin; Intervet) intramuscularly, 1500 iu tetanus
antitoxin (Intervet) subcutaneously, and 4 mg/kg omepra-
zole (Gastroguard; Merial) orally, preoperatively and for the
duration of hospitalisation.
Five days after surgery, the foal was observed to be strain-
ing to defecate, and on digital rectal examination some fae-
cal impaction was noted. However, the rectal mucosal repair
was still intact. Slight dehiscence of the skin would was also
observed at this time. Magnesium sulphate (Epsom Salts;
Turfmasters Ireland) was administered to the foal orally to
soften the faeces. The impaction resolved but the skin wound
continued to break down and had completely dehisced two
days later. The wound remained clean, and at the time of
discharge, nine days after surgery, healthy granulation tissue
was evident and the wound was contracting.
One year after the surgery, the foal had grown normally,
the wound had completely resolved and there was no evi-
dence of the fistula (Fig 3).
Duplications of various parts of the alimentary tract have
been reported in human infants; duplication of the anal canal
is the rarest manifestation of this unusual developmental
abnormality (Choi and Park 2003). Mucosa-lined tracts that
open out in the perianal region have been described in some
of these patients; however, these structures most commonly
lie adjacent to the normal rectum, rather than actually com-
municating with it as in the case described here (Iyer and
Manhour 1995).
The only examples of perianal fistulation previously
described in the veterinary literature have been in dogs.
Perianal fistulas are seen in adult dogs, in which the sug-
gested aetiology is infection of, or trauma to, the anal sacs,
possibly due to poor conformation in certain breeds, such
as German shepherd dogs. Canine perianal fistulas are not
associated with congenital abnormalities (Harvey 1972).
In dogs, the surrounding tissues are diseased, and it is rela-
tively unusual for the tract to communicate with the rectum
(Amand 1974).
Fistula in ano in infant human beings is a condition
that has long been recognised, but which remains relatively
uncommon (Al-Salem and others 1994). The literature
suggests infection of the anal sacs, or anorectal abscess, as
the initiating cause of the condition (Poenaru and Yazbek
1993). However, a congenital aetiology has also been sug-
gested, as affected individuals generally present within the
first two years of life. Abnormalities of the small anal apo-
Short Communications
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Short Communications
The Veterinary Record, September 9, 2006
crine glands have been noted in these patients (Poenaru
and Yazbek 1993). In a number of cases presented in the
first months of life, epithelially lined tracts were reported,
which were destroyed by chronic irritation or infection
as the condition progressed (Al-Salem and others 1994).
In contrast to the case described here, it would seem that,
as in dogs, abnormalities of the small anal glands are an
intrinsic factor in the pathogenesis of perianal fistula in
human beings.
In the foal described here, the defect was noticed within
hours of birth, and there was no indication of infected or
inflamed tissue in the tract itself or in the surrounding struc-
tures before surgery. The clinical presentation in this case
perhaps bears greatest resemblance to those cases of fistula in
ano in human infants where epithelia-lined tracts are present
before inflammatory change. There was no evidence to
suggest any involvement of the anal sacs in the present case.
The treatment of choice for fistula in ano in human
beings appears to be surgical removal of the abnormal
tissues. The prognosis is generally good, although com-
plications have been reported in some cases due to the
presence of infection or persistence of the abnormal small
anal glands (Poenaru and Yazbek 1993). Unfortunately,
histopathology was not performed on the resected tissue
in the present case, but the foal’s prognosis was considered
to be favourable as there was no diseased tissue present.
By removing the abnormal tract in its entirety the fistula
was completely eliminated. The complication of dehis-
cence of the outermost layers of repair could perhaps have
been avoided had greater care been taken to eliminate dis-
comfort in the region after surgery. The problem of faecal
impaction in the rectum, which led to further strain on the
surgical repair, could also have been prevented by more
timely use of faecal softeners and by restricting the foal’s
access to hard feed. However, due to the multilayer closure
performed, the dehiscence did not prove catastrophic as the
rectal mucosal seal remained intact. The excellent blood
supply of the perianal region probably further contributed
to the rapid development of granulation tissue and healing
by secondary intention.
ACKNOWLEDGEMENTS
The authors thank Bridget McGing for referring the case, and
the staff and students of the University Veterinary Hospital,
Dublin, and Sandro Garavelli for assistance with the postop-
erative photograph.
References
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FIG 2: Intraoperative
image showing the foal
in sternal recumbency
FIG 3: Foal, one year after surgery. The wound has healed
completely and there is no evidence of the perianal fistula
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doi: 10.1136/vr.159.11.362
2006 159: 362-363 Veterinary Record

C. M. Kearney and P.J. Pollock
thoroughbred colt
Congenital perianal fistula in a

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