Title: Surgical Management of a Perineal Hernia in a 24-year-old Mare
Authors: Alessandro Spadari 1, Federica Meistro1, Giuditta Saragoni1,*, Riccardo
Rinnovati1 and Maria Virginia
Ralletti1
Author’s institutional affiliations :1Department of Veterinary Medical Sciences, University
of Bologna, Via Tolara di Sopra 50, 40064 Ozzano dell’Emilia, Italy
* Correspondence: giuditta.saragoni2@unibo.it
Summary : A rare case of bilateral perineal hernia was reported
in a 24-year-old Italian Trotter mare. This condition is described as a
protrusion of retroperitoneal fat, and/or the abdominal or pelvic
viscera through the pelvic diaphragm which supports the rectal wall. It
is commonly observed in olduncastrated old male dogs, but occurs very
rarely in large ruminants; to the Authors’ knowledge, it has never been
described in horses. Chronic weight loss is the main clinical sign, even
if the main concern regards the entrapment and the strangulation of the
bowel content.
Reaching a diagnosis involves clinical signs, palpation, ultrasound
evaluation and rectal examination. The approach chosen in all the cases
of perineal hernia described in large ruminants is appositional
herniorrhaphy; for this reason, it was utilised as the first surgical
choice in the present case. Due to its failure, a new surgical approach
was used The second procedure involved the transposition of the
semimembranosus muscle. The short-term outcome after the second surgery
presented no recurrence or complications. It is therefore necessary to
consider perineal hernia among the various differential diagnosis of
perineal swellings in horses. Additional cases are required to determine
its benefits.
Keywords : perineal hernia; horse; surgery; herniorrhaphy;
equine.
Introduction: Perineal hernia is a protrusion of
retroperitoneal fat, and/or abdominal or pelvic viscera through the
pelvic diaphragm which supports the rectal wall . For the most part, it
occurs consequent to weakened perineal muscles which cause an abnormal
displacement of the pelvic and caudal abdominal organs into a paranal
position . This condition is common in old uncastrated male dogs, but
occurs very rarely in large ruminants ; to the Authors’ knowledge, it
has never been described in horses. In this species, the most frequently
reported hernias are umbilical, scrotal and inguinal . To this day,
there has only been one reported case of perineal hernia in equids which
involved a seven-year-old female donkey .
In dogs, factors which lead to its development are not fully understood;
however, it is likely that they are multifactorial, including tenesmus,
associated with chronic prostatic disease or constipation, myopathy,
rectal abnormalities, and gonadal hormonal imbalances . In large
animals, there are fewer predisposing conditions, namely perineal
trauma, chronic diarrhoea, constipation and tenesmus . The presentation
of a perineal hernia in both dogs and large animals can be either
unilateral or bilateral, and also reducible or non-reducible . Animals
presenting this condition can manifest severe abdominal straining during
defecation and urination . Reaching a diagnosis involves clinical signs,
palpation, ultrasound evaluation and rectal examination .
Medical management of a perineal hernia in dogs may be achieved
conservatively by using stool softeners, periodic enemas and digital
faecal removal. However, the majority of cases require surgical
herniorrhaphy to prevent the life-threatening complications caused by
the incarceration of herniated organs . In the literature regarding
small animals, several surgical techniques have been reported. Internal
obturator muscle transposition is the most successful and commonly used
method. However, a supplementary approach may be adopted which includes
gluteal muscle transposition, semitendinosus muscle transposition,
synthetic implants and biomaterials .
Appositional herniorrhaphy was the first technique to be used on dogs;
it consists of using the external anal sphincter and any remnants of the
levator ani or coccygeus muscles for primary repair. The sacrotuberous
ligament can be utilised as a lateral component of the repair if the
levator ani muscle is significantly atrophied . This was the approach
chosen in all the cases of perineal hernia described in large ruminants
for this reason, it was the first repair technique used in the present
case. Due to the failure of the first surgery, an original surgical
procedure was carried out. Another surgical approach for a canine
perineal hernia is superficial gluteal muscle transposition .
Nevertheless, owing to the horse’s anatomy, this muscle is particularly
developed in size and quite distant from the perineal area; therefore,
it cannot be used. The last surgical choice in dogs is semitendinosus
muscle transposition which is considered to be a salvage technique . In
this particular case, none of the procedures reported were carried out,
while an innovative surgical method which involved the transposition of
the semimembranosus muscle was performed. The decision to use this
muscle was dictated by its proximity to the surgical defect, by its
superficiality and by its width which could easily fill the hernial
defect.
Anatomy
of the pelvic diaphragm: The pelvic diaphragm is the muscular basis of
the perineum. It is formed by the levator ani and the coccygeus muscles.
The levator ani arises from the ischial spine and is adjacent to the
medial surface of the sacroischiatic ligament. The majority of its
fibres end at the anus where they mingle with those of the external anal
sphincter. The coccygeus has a similar origin but passes more dorsally
to insert on the transverse process of three to five tail vertebrae and
also on the tail fascia. It has three different parts; starting from the
dorsal aspect, there is the coccygeal part, the anal part and the
perineal part .
The innervation of the levator ani and the coccygeus muscles is
controlled by the caudal rectal nerve. The space between two parts of
the coccygeus muscle dorsal to the anus is closed by the external anal
sphincter, the smooth internal anal sphincter and the rectococcygeus
muscles. The coccygeal part is composed of muscle fibres related to the
tail vertebrae surrounding the anus, the anal part is characterised by a
thickened circular muscle layer of rectum surrounding the anus, and the
perineal part is a caudal continuation of the longitudinal smooth muscle
layer of the rectum dorsal to the anus which inserts onto the fourth or
fifth coccygeal vertebra. Two parts of the coccygeus muscle are supplied
by the caudal rectal and perineal nerves, while the rectococcygeus is
innervated only by the caudal rectal nerve.The opening between the
pelvic diaphragm and the caudal margin of the pelvic floor is closed by
the urogenital diaphragm, penetrated by the urogenital canal, which
changes anatomy according to sex. In males, it is accompanied by the
bulbospongiosus muscle which is the continuation of the urethralis
muscle and extends to the glans with individual fibres which deepen
between the corpus cavernosum and median raphe.
Innervation is provided by the deep perineal nerve. Instead, in mares,
it is provided by the corresponding constrictor vestibuli (the origins
of which form the ventral border of the levator ani and end in the
muscle fibres from the other side ventral to the vestibule) together
with the constrictor vulvae muscles (which are made up of striated fibre
bundles under the skin of the vulva which fuse dorsally with the
external anal sphincter). The first one is innervated solely by the deep
perineal nerve, while the second one is also innervated by the caudal
rectal nerve. Another muscle present in the area is the paired retractor
penis/clitoridis which arises from the second caudal vertebra and
descends deep to the levator ani on each side of the rectum. It
decussates ventral to the rectum and, from here, it descends to the
ventral surface of the penis; however, it does not reach the clitoris in
the mare. It is also supplied by the deep perineal nerve. The perineal
body is a musculo-fibrous node of tissue between the anus and the
vestibule, and consequently is a median structure. It comprises the
muscular connection between the external anal sphincter and the
constrictor vestibuli, the internal anal sphincter, the subanal
decussation of the retractor clitoridis, and a fibrous plate (perineal
septum) which passes craniodorsally from the vestibule to the rectum
(Figure 1).