Ultrasonographic and Radiographic Assessment of Prostate Gland in Perineal Hernia Dogs

Perineal hernia is a protrusion of abdominal organs into the perineal area through the weak pelvic diaphragm. Many factors were reported to be involved in the aetiology of perineal hernia, including breed predisposition, hormonal imbalance, prostatic disease, chronic constipation and weakness of the pelvic diaphragm due to chronic straining (Merck, 2019). The higher incidence among sexually intact males was the evidence, that, hormonal influences probably play a primary role (Bellenger et al., 2003; Hedlund, 2007; Merck, 2019). A study on mice has correlated that exercise can help reduce obesity and the Prostate index significantly compared to control group (Liu et al., 2019).
        
Prostate is a soft tissue structure located at the base of the urinary bladder, just below the rectum. Normally, prostate is not distinctly differentiable on radiography, but if enlarged can lead to alteration in the anatomical position of rectum and urinary bladder and thus can be distinguished. The size shape and location of prostate can be identified on radiography in normal adult dogs (Stone et al., 1978). However, the soft tissue lesions leading to its hyperplasia like cysts and abscesses are better visualized on ultrasonography. According to most classifications, seven prostatic disorders might be considered: benign prostatic hyperplasia, acute and/or chronic prostatitis, prostatic cysts, prostatic abscesses, squamous metaplasia of prostate and prostate neoplasia (Smith, 2008). Earlier reports suggests that prostate gland is enlarged if its dimensions exceed 70% of the pubic brim-sacral promontory dimension on lateral plain radiography, 90% in case of neoplasia, abscessation or cysts and 50% of the width of the pelvic inlet on ventro- dorsal radiograph (Lattimer, 1986; Feeney et al., 1987). Comparative studies on the measurements of diseased prostate using radiography and ultrasonography are reported in dogs (Atalan et al., 1999).
        
The present study was devised with the objective to assess the involvement of prostate gland in dogs suffering from perineal hernia using radiography and ultrasonography.

The study was duly approved by the Institutional Animal Ethical Committee and was carried out for a period of one year (January to December 2018) at the referral hospital of Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana, Punjab, India.
        
A total of 38 intact male dogs suffering from perineal hernia were investigated using radiography and ultrasonography for the involvement of prostate gland. Radiography and ultrasonography were the 2 modalities used to assess the size and texture of prostate respectively. Ultrasonographic assessment was preferred prior to contrast radiography studies as otherwise the air of pneumo-cystography lead to difficulty in scanning of the prostate and bladder on ultrasound.
 
Anaesthesia
 
The sedation for diagnostics included an intramuscular combination of inj. Butorphenol @ 0.2 mg/kg, inj. Acepromazine @ 0.05 mg/kg and inj. Atropine Sulphate @ 0.04 mg/kg. Dogs with chronic dehydration and debilitating condition were not administered inj. Acepromazine. Few furious dogs were sedated with a combination of inj. Xylazine (@1mg/kg), inj. Ketamine (@5mg/kg) and inj. Atropine (@0.04mg/kg), intramuscularly.
 
Ultrasonographic examination
 
The prostate was imaged through the caudo-ventral abdominal skin, with the dog in dorsal recumbency. An area of hair was clipped just cranial to the pubic brim upto mid-abdomen. The skin was prepared by cleaning the area and applying a liberal quantity of acoustic gel. Ultrasonographic measurements were done using Philips ultrasound machine using a 7.5 MHz or a 5 MHz linear probe (as per the size of the dog). The bladder was first identified until herniated. The transducer was then moved caudally to the neck of bladder and then to the prostate. In dogs where, prostate was herniated or was in the pelvic cavity, was digitally pushed inside through the herniation for ultrasound examination. Usually, the prostate could be pushed inside with digital pressure, if not; it was scanned in the perineal region. Prostate was measured from the ultrasound scan in longitudinal section only. However, transverse scan was done to visualize other abnormalities.
 
Longitudinal section
 
The transducer was moved to obtain the maximum image size of the gland in longitudinal section. The image was then frozen and the following dimensions were measured:
1) Maximal length from the cranial to the caudal pole of the prostate.
2) Maximal depth from the dorsal to the ventral part of the prostate.
All measurements were made using electronic callipers in cms upto two decimal place.
 
Transverse section
 
Once the maximal longitudinal section of prostate was identified, the transducer was rotated through 90° to obtain a transverse section, by slightly deviating the penis sideways. Adjustment was made to obtain as symmetrical a section as possible, with the prostatic urethra visible in the centre.
        
The prostate was also examined for any abnormal ecotexture, anechoic lesions such as cysts or abscesses if any. All the findings of the ultrasound examination were recorded for analysis.
 
Radiographic examination
 
All the dogs were subjected to plain and contrast radiography of the caudal abdomen in lateral and ventro-dorsal projections.
a) The plain radiography of caudal abdomen was done in lateral projection with the catheter (baby feeding tube of suitable size) in the urinary bladder (Fig 1).
 

 
b) The contrast radiography technique was done in both the lateral and ventro-dorsal projections (Fig 2 and 3). The technique included; double contrast radiography of caudal abdomen with negative contrast of the urinary bladder and positive contrast of the rectum and partial descending colon. Negative contrast of urinary bladder was done using atmospheric air (pneumo-cystography) injected in the urinary bladder through the baby feeding tube placed in the urethra. The air was used @5ml/kg of the dog. During injecting the air the baby feeding tube and the penis tip were tightly closed with a gauze piece and fingers to avoid leakage of air.





c) The positive contrast of rectum was done using barium enema. The commercially available barium powder (Microbar HD) was dissolved in maximum 50ml water (depending on the size of the dog) for 20% concentration (w/v). The volume injected in rectum was @2ml/kg of the dog. The double contrast radiography was done to better visualize the prostate.
d) The size of prostate (objective parameters) was measured on plain radiograph in lateral projection (Fig 4) using inbuilt calipers in the computerized radiography system. The depth (ventro-dorsal) and the length (cranio-caudal) of the prostate were recorded in all the cases. If the prostate was not visible on radiograph, it was recorded accordingly. In addition, the pubic brim to sacral promontory distance (PS distance) was also measured in all the dogs in lateral projection to compare the size of prostate (Fig 4) (as described by Atalan et al., 1999).
 

 
e) The length and the depth of the prostate were compared to the 70% and 90% of the PS distance on lateral radiograph. And the findings were recorded.
f) The subjective parameters recorded included: the dorsal lifting of descending colon/rectum due to increased depth of the prostate and the cranial displacement or abnormal placement of bladder in the abdominal cavity due to increased length of prostate.
 
Statistical analysis
 
The data was analyzed using Microsoft Excel 2010. Objective parameters were processed for mean and standard deviation. The subjective data was compared using percentage, absolute and relative. Comparative data was tested for significance by using student‘t’`-test at SPSS 16.0. Correlations were examined using Pearson’s correlation two tailed.

There were 9 breeds of dogs seen affected with the condition with the maximum number of mix breed dogs followed by German shepherd (GSD) and Pomeranian. The dogs had an average age of 7.78±2.69 years (2.5 to 15 years) and an average body weight of 22.86±9.01kgs (6.8 to 46 kgs).
 
Radiographic assessment of prostatic dimensions (Table 1)
 

 
Subjective assessment
 
Out of 38 dogs, the rectum was seen deviated from normal position in 24 dogs (24/38=63.16%). In 22 dogs, the rectum was lifted dorsally (22/24=91.67%) and in 2 dogs pushed ventrally. Out of these 24 dogs, in 17 dogs (17/24=70.83%) the rectum was seen lifted dorsally (Fig 5) due to increase in the depth of prostate. While in 5 dogs (5/24=20.83%) it was due to enlarged urinary bladder pushing the rectum dorsally. In 2 dogs, where the rectum was pushed ventrally was due to herniated urinary bladder.
 

        
The urinary bladder was seen pushed cranially (elongated neck) (Fig 6) in 12 dogs (12/38=31.58%). The urinary bladder was seen herniated caudally (catheter passed prior to radiography) in 10 dogs (10/38=26.32%).
 

 
Objective assessment
 
The prostate was visualized and investigated for objective parameters in 29 dogs (29/38=76.31%) as in other 9 dogs (23.68%), the prostate was not fully visualized on radiography. The reasons for non-visualization included: herniation of urinary bladder and /or prostate in the perineal region (n=6), large para-prostatic cyst (n=1) (Fig 7), in the pelvic cavity (n=2).
 

        
The mean prostate length was 5.49±3.67cm (ranging from 1.35 to 18.28 cm), with minimum in a Pomeranian and maximum in a GSD. The mean prostate depth was 4.54±2.14 cm (ranging from 1.79 to 13.1cm) with minimum in a Daschund and maximum in a GSD.
        
While comparing the length and depth of prostate with the 70% of PS distance of the respective dog in lateral radiograph, the following findings were recorded:
• In 1+10=11 dogs (in one only depth and in 10 both length and depth), the depth was found to be more than 70% of PS distance (11/29=37.93%).
• In 4+10=14 dogs (4 only length and 10 both length and depth), the length was found to be more than 70% of the PS distance (14/29=48.28%).
i.e. in 15 dogs (54.72%=15/29) the prostate length and /or depth was more than 70% of PS distance.
        
While comparing the length and depth of prostate with the 90% of PS distance of the respective dog in lateral radiograph, the following findings were recorded:
• In 1+2=3 dogs (1 only depth and 2 both length and depth), the depth was found to be more than 90% of PS distance (3/29=10.34%). Out of these 2 dogs (with both length and depth more than 90%); one had a cyst and one had prostatic carcinoma on cytology.
• In 7+2=9 dogs (7 only length and 2 both length and depth), the length was found to be more than 90% of the PS distance (9/29=31.03%). Out of these 9 dogs, 2 dogs had large para-prostatic cysts and one had prostatic carcinoma, while the other 6 had benign prostatic hyperplasia on cytology. i.e. in 34.48% (10/29) dogs, the prostate length and/or depth was more than 90% of PS distance.
 
Correlations and student t test for radiographic observations (Table 3)
 
• There was a significant positive correlation between the PS distance and prostate length (r=0.375; p<0.045) and prostate depth (r=0.491, p=0.007).
•There was a significant positive correlation between the body weight and the PS distance (r=0.668, p=0.000). However, the age and PS distance were not significantly correlated.
• The body weight and the length or depths were also not found significantly correlated.
• The prostate length was significantly higher than the prostate depth (paired t test, p=0.023).
 
Comparison of subjective and objective results of radiographic measurements
 
On subjective analysis, the rectum was seen deviated from its normal position (dorsally lifted or ventrally pushed) in 24 out of 38 dogs (63.16%). Out of these, in 17 dogs (44.74%) it was due to the increase in the depth of the prostate. While, on objective analysis 11 out of 29 (37.93%) dogs had prostate depth more than 70% of the PS distance. Thus, suggesting that subjective assessment may overemphasize the prostate depth compared to objective measurements.

For prostate length, the subjective analysis showed the bladder neck to be pushed cranially in 12 out of 38 dogs (31.58%). While on objective analysis, 14 out of 29 dogs (48.28%) dogs had prostate length more than 70% of the PS distance. Thus, the subjective assessment under estimated the prostate length compared to objective measurements.
        
The subjective parameters of rectal lifting on radiography may sometimes be biased in perineal hernia dogs as the caudal displacement of rectum or urinary bladder into the hernia sac may also lead to lifting of rectum. However, the cranial displacement of urinary bladder used to assess the increase in length of prostate was found more reliable as the pnuemo-cystography and barium enema clearly marked the prostate and the neck of bladder.
        
The mean length and depth of prostate on radiography were similar to that reported by Atalan et al., (1999), who also studied them in diseased prostate. Sjollema and Sluijs (1989) reported the prostatic enlargement in 54% dogs with perineal hernia, although the criteria used to define enlargement were rectal and abdominal examination and positive contrast radiography of the urinary bladder and urethra. The length of the prostate had been reported to be significantly higher than the depth of the prostate and prostate length rather than depth had been recommended when evaluating prostate size from lateral abdominal radiograph (Atalan et al., 1999).
 
Ultrasonographic assessment of prostatic dimensions (Table 2)
 

 
In 35 dogs (35/38=92.11%) the prostate was investigated ultrasonographically (as, one was much compromised for study and in 2 dogs, the prostate was not visualized on USG being very small or indiscernible in herniated sac).    
        
The mean prostate length was 4.84±1.72 cm (ranging from 1.55 to 7.89cm), with lowest in a Pomeranian and highest in 2 Labrador dogs. The measurement of length does not include para-prostatic cysts. The mean prostate depth was 3.38±1.14 cm (ranging from 1.54 to 5.99cm) with lowest in a Pomeranian and highest in a GSD and a Labrador dogs. The mean prostate measurements were less on ultrasonography compared to radiography as full prostate may not be visualized in one view on USG and angle of transducer may vary so, ultrasonography was better in differentiating the textural abnormalities of abscesses, cysts or neoplasia and radiography for measurements. Radiography was found to be limiting in measuring prostate, if prostate was herniated/pulled in the pelvic cavity or perineal region with rectum or urinary bladder. Although, on ultrasonography, the pulled or herniated prostate can be pushed inside the abdomen with digital pressure and can be evaluated.
        
One or more cystic lesions of average diameter 1.67cm (range 0.5cm to 2.85cm) were seen in the prostatic parenchyma of 11 dogs (Fig 8). Three dogs had large abdominal prostatic cysts with diameter of 4.35, 8.3 and 11.5cm on ultrasound (Fig 9). Two other dogs had herniated prostatic cysts. Small prostatic cysts had been reported to be asymptomatic in intact adult male dogs with a prevalence of 14% (Black et al., 1998), however, Bakalov et al., (2004) reported prostatic cyst to be rare in dogs. Para prostatic cysts were recommended to be included in the list of differential diagnosis for perineal swelling (Welsh et al., 2000). Such large para prostatic cyst may also compress the descending colon and can even be a factor in developing perineal hernia (Paclikova et al., 2006).
 

 

        
In 12 out of 35 dogs (34.28%), the prostate was not visualized in the abdominal cavity on first instance and required to be pushed inside from the perineal region or was scanned in the perineal region itself.
 
Correlations and student t test for ultrasonographic observations (Table 3)
 

 
• The prostate length was significantly more than the prostate depth on ultrasound (paired ttest, p=9.95E-07).
• There was a significant positive correlation between the radiographic PS distance and the prostate length (r=0.382; p=0.022) and depth (r=0.526; p=0.001) measured, ultrasonographically.
 
Comparison of radiographic and ultrasonographic measurements
 
There was a significant correlation between prostate lengths measured on radiography and ultrasonography (r=0.512, p=0.005) and no significant difference was found between the lengths measured by 2 modalities. However, the prostate depth measured on radiography and ultrasonography were not significantly correlated (r=0.225, p=0.241) and the depth showed significant difference in 2 modalities (paired t test, p=0.010689). The average radiographic length and depth were more than that recorded on ultrasonography.

• The prostate affections may not always be the primary etiology in dogs suffering from perineal hernia, so prior investigation of prostate using radiography and ultrasonography is recommended as a deciding factor for whether castration should be done a few weeks prior to or simultaneously with the perineal herniorrhaphy.
• The increased length of the prostate is better indicator of prostatomegaly than the depth, so lateral radiograph of the caudal abdomen is recommended to determine the size of the prostate.
• Radiography fails to delineate herniated or intra-pelvic prostate, whereas, it can be visualized on ultrasonography by repositioning using digital manipulation.
• Ultrasonography facilitates identification of nature and extent of the parenchyma lesions in prostate.

Authors are thankful to Indian Council of Agricultural Research (ICAR), India for the financial support provided under the project, ‘All Indian Network Program on Diagnostic Imaging and Management of Surgical Affections in Animals. Authors also acknowledge Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana, Punjab, India for providing necessary facilities to conduct this study.