Discussion:
This case report describes a case of 2 urethral diverticula in a
26-year-old gelding. There is one other case that reports a urethral
diverticulum in a breeding stallion (Diel de Amorim et al. 2014)
and one report that describes a vesical diverticulum in a 6-year-old
gelding (Odenkirchen et al. 1994).
The origin of the diverticula in the present case could not been
determined but a congenital origin was strongly suspected. The horse was
owned since the age of 2 years by the owner and no previous
catheterization or trauma, except for the urine dribbling, were
reported. Also, the diverticula were symmetrical, which made an acquired
origin less likely.
However, in human medicine, in males, acquired diverticula are more
frequently reported than congenital (Cinman et al. 2012; Popoolaet al. 2009; El Ammari et al. 2012; Mohanty et al.2014). The case described by Diel de Amorim et al . (2014) was
suspected to have an acquired urethral diverticulum due to a breeding
injury.
Congenital anomalies of the urinary tract in horses are rare although
some are reported such as ureteral ectopia, ureteral defects, renal
dys-/hypoplasia, polycystic kidney disease and rectovaginal or
rectourethral fistula (Chaney 2007). If the lesion in this case was
congenital, the reason why the horse did not show clinical signs before
is unknown. In women however, it has also been described that a urethral
diverticulum can be asymptomatic and an incidental finding (Crescenzeet al. 2015; El-Nashar et al. 2014).
The main hypothesis in order to explain the permanent dribbling of the
urine is that, during voiding of the bladder, the diverticula fill up
with urine and that there is a slow emptying caused by gravity
afterwards. This was also a hypothesis in the case report of Henryet al . in a cat with urinary incontinence. The stagnation of the
urine in the diverticula was also thought to have caused the urinary
tract inflammation. Another hypothesis is that the urinary tract
inflammation was responsible for the permanent dribbling of the urine
but this theory seems less likely because the horse showed signs of
urinary incontinence for 6 years and the signs of urinary tract
infection were recent. Dysuria was probably caused by the urinary tract
infection, which could have also been responsible for the reported signs
of colic. Another hypothesis for the colic could have been pain, caused
by urine accumulation but other none identified causes could not be
excluded.
In human medicine, described techniques for diagnoses are
cystourethroscopy, voiding cystourethrogram, MRI, CT and transperineal
and transvaginal ultrasound.
Different reports in humans demonstrate a variable ability, 15-89%, to
visualize the ostium with cystourethroscopy (Crescenze et al.2015; Romanzi et al. 2000; Kim et al. 1993; Ljungqvistet al. 2017). Diagnosis in this case was purely based on
cystourethroscopy, as in the described case of a breeding stallion (Diel
de Amorim et al . 2014).
Another modality often used in human medicine is ultrasound. Some
studies however have shown that the sensitivity is depending on the
skills of the sonographer, some studies even report that the sensitivity
is lower than 50% when evaluating cases with confirmed urethral
diverticulum (Crescenze et al. 2015; Reeves et al. 2014).
Other studies showed a sensitivity of transvaginal and transperineal
ultrasound of 95-100% (Crescenze et al. 2015; Stav et al.2008; Gugliotta et al. 2015). In the here reported case, we were
however unable to identify the urethral diverticula with transrectal and
transabdominal ultrasound. Visualization of the urinary tract by
transperineal ultrasound in horses is not possible due to the pronounced
muscle mass in this region. In one of the previous described cases in a
kitten, transabdominal ultrasound did not reveal any abnormalities and
also in this case, no transvaginal or transperineal ultrasound were
performed (Henry et al.). In the stallion described by Diel de Amorimet al. (2014), the authors were able to identify the diverticulum
with penile ultrasound, in our case the diverticula were localized too
high for this technique
Voiding cystourethrogram is another described imaging modality with a
reported sensitivity of 67-95% (Crescenze et al. 2015; Ockrimet al. 2009). This technique and retrograde contrast
cystourethrogram were used successfully in small animals (Henry et
al. 2018; Foster et al. 1999; Atilla 2018; Watanabe et
al. 2015). In this case, the use of a contrast cystourethrogram could
have helped to determine the extent of the diverticula. However, the use
of abdominal radiographs in adult horses is limited to the ventral part
of the abdomen to identify sand impaction and enteroliths.
The “gold standard” for diagnosis of urethral diverticula in humans is
MRI (Pathi et al. 2013; Dwarkasing et al. 2011; Blanderet al. 2001). In none of the described cases in small animals,
this technique was used and neither in this case. In one case of a dog,
CT was successfully used to identify the diverticulum.
In this case, due to financial restraint and the age of the horse, a
medical treatment with large spectrum antibiotics and anti-inflammatory
drugs was attempted with resolution of the clinical signs according to
the owner.
Treatment in human medicine consists mainly of surgical excision and
reconstruction in symptomatic patients with high success rate of 84% to
98%. Re-operation rate has been reported to be 2% to 13% (Crescenzeet al. 2015; Reeves et al. 2014; Nickles et al.2014; Stav et al. 2008).
In asymptomatic patients, conservative treatment with prophylactic
antibiotics can be attempted (Greimann et al. 2019). Surgical
treatment was successfully performed in the 4 described cases in small
animals (Henry et al. 2018; Foster et al. 1999; Atilla
2018; Watanabe et al. 2015Diverticulectomy has also been
described to be successful in goats and calves (Temi̇zsoylu
2005; Bokhari 2013; Sylla et al. 2019; Abd-El-Hady 2014;
Maiti et al. 2018). Surgical treatment by perineal urethrostomy
and distal urethrostomy over the diverticulum was performed in the
stallion described by Diel de Amorim et al. (2014).
To conclude, urethral diverticula are a rare condition in equids and
should be considered in cases of colic with urinary incontinence and
urinary tract infection. We were unable to identify the origin in this
case but a congenital defect was strongly suspected.