Most prostatic diseases concern intact male dogs, but also castrated dogs can be affected [20, 21]. However, the evaluation of the prostate of castrated dogs is not easy due to the small prostatic size and the intrapelvic prostatic position of the gland. This may restrict a radiographic examination. The three-dimensional view of the CT [1] helps evaluating the prostate of castrated dogs. To the best of our knowledge, no further studies have evaluated the prostate of castrated dogs in CT, yet. By classifying the patients into three age-groups, the present CT-study showed age-related changes in the prostate structure of neutered and intact dogs. The prostates of young neutered dogs (under 4 years of age) showed a homogenous tissue pattern. Cowan et al. have shown that the prevalence of chronic prostatitis and the presence of bacterial content are reduced in castrated dogs [22]. Thus, the low prevalence of tissue alterations in young neutered dogs could therefore also explain the predominance of a homogeneous prostate tissue pattern in CT imaging in this group of dogs. Another hypothesis for the homogenous pattern of prostate tissue in neutered dogs of under 4 years of age might be that the long-term influence of sex hormones on prostate tissue is low due to castration. In this context, it should be noted that dogs of the young age group underwent castration at different time points. Some dogs were castrated early, others late in the 4 years period. Thus, it’s highly likely that there were different effects on prostatic tissue due to the shorter or longer duration of sex hormones exposal. For non-castrated dogs over 6 years O’Shea showed an increased risk of cysts and BPH [23], which can be visualized by CT as inhomogeneities [7]. In the present study only 33% of the neutered dogs between 4 and 8 years of age showed a prostate with structural changes. Also, in this group the withdrawal of androgens [23] due to castration might explain the predominant homogenous pattern of the prostatic tissue. Unfortunately, the hypothesis about the influence of sex hormone withdrawal on the prostatic tissue appearance in CT could not be proven in the present study because information about the timepoint and reason for castration as well as histopathological analyses were missing.
According to O’Shea et al. intact dogs reach the hyperplastic phase with an age between 6 to 10 years [23]. In this phase the cells can be hypertrophic and electron microscopic evaluation shows an increased glandular volume and decreased prostatic stroma [24]. Furthermore, the hyperplastic phase can result in several cysts or an irregular prostatic pattern [23]. In the study of Kuhnt et al. [7], these changes were displayed in CT examination of intact male dogs in the age group B (4–8 years), where 2/3 of the dogs had an altered prostate pattern in CT-examination. In the oldest age group C (over 8 years), 64% of the castrated dogs had a homogenous prostate. In contrast to this, 84% of the intact male dogs had altered prostates [7]. Thus, intact dogs with an age of 6 years and older have an increased evidence of BPH [25]. A BPH is characterized by an inhomogeneous tissue pattern and cystic alterations [26]. Most of the intact dogs in the oldest age group of the study by Kuhnt et al. [7] had cysts. Accordingly, it can be assumed that the presence of androgens leads to more alterations in the prostate of intact dogs compared to neutered dogs.
It is a limitation of the present study that most of the examined dogs were older than 8 years. Thus, the group size differed across age groups. The high mean age could be explained by the fact that dogs were examined in the CT for age related diseases, such as orthopedic diseases or neoplasia.
Dimitrov et al. [27] described the canine prostatic appearance in CT images as a homogenous, oval, hypodense organ compared to the hyperdense rectal wall. So far, the appearance of the prostate of castrated dogs in the CT was not described in further studies. Therefore, no comparative values are available.
While attenuation values in the two morphological groups did not differ in pre-contrast scans, attenuation values significantly differed in the post contrast CT images. Similar results were found for intact dogs in the study of Pasikowska et al. [6] and in the study of Kuhnt et al. [7]. While both studies found no statistically significant differences between the morphological groups in the pre-contrast attenuation values, both reported significant differences in the post-contrast attenuation values.
Using contrast agent, prostates of neutered dogs which formerly appeared homogenous in pre-contrast scans showed inhomogeneous tissue patterns. This underlines the need of contrast-agent application in imaging the canine prostate gland in CT.
Previous studies concluded that ultrasound is a beneficial tool for evaluating the prostatic size and tissue of intact dogs [8, 28,29,30,31]. However, it is mentioned that the beginning of a BPH could sometimes not be diagnosed in the ultrasound examination [32]. The present study indicated that structural changes in the prostate gland of neutered dogs can be seen in contrast CT while in sonographic examination no alterations were detected. It is likely that in castrated dogs pathological changes are easier to be detected in the post contrast CT than in ultrasound inter alia due to the little prostatic size of castrated dogs. Although this finding emphasizes the usefulness of CT as imaging tool, further CT investigations including histopathological analyses are needed to prove the results. Additionally, it has to be mentioned that maybe contrast enhanced ultrasound could also show early alterations in prostatic tissue. In order to find this out, a study has to be conducted with CT examination compared to contrast enhanced ultrasound of the dog’s prostate.
Due to the use of contrast-agent an altered vascularization of the prostatic tissue could be visualized. Only in two cases, an inhomogeneous cystic prostate pattern was found in pre-contrast scans, it was primarily seen in post-contrast CT images. Since alterations like cysts and abscesses are not always reduced after castration [13], inhomogeneities in castrated dogs may be residuals. Inhomogeneous prostates in castrated dogs with a higher amount of enhancement might be indicative for a recently castrated dog. Main limitations of the present study are that the date of castration and the reason for castration were not known. Therefore, it could not be evaluated if more dogs show inhomogeneities shortly after castration. Accordingly, for future studies in this field of research a larger patient collective of dogs with known castration history is indispensable.
One reason for the inhomogeneous appearance of the prostate in post- contrast images could be a prostatic carcinoma. According to Saunders et al. [26] the prostate of affected dogs shows a higher vascularization of the prostate tissue. Regarding the post-contrast prostatic density values of the castrated dogs, the present study found lower values compared to the values of intact dogs in the study of Kuhnt et al. [7]. In canine prostates with hyperplastic tissue, a higher vascularization exists [12]. This may lead to a higher contrast enhancement than in the prostatic tissue of castrated dogs. Unfortunately, the connection between an inhomogeneity or hyperplasia of the prostate due to an increased vascularization could not be proven in our study because no histopathological data were available. Accordingly, a diagnosis based on cytology or histopathology would be of interest and should be included in follow-up studies. Prostatic mineralization and mineralized prostatic cysts are findings which have been reported in dogs suffering from prostatic disease [33, 34]. Bradbury et al. reported that “neutered dogs with prostatic mineralization were very likely to have prostatic neoplasia” [33] and Feeney et al. found that 4/7 dogs with prostate neoplasia had radiographically detectable tissue mineralization [34]. Surprisingly, in the group of 36 dogs examined by us, no mineralization of the prostate was detected. It is likely that these results are due to the very small sample size and the fact that no dog with confirmed prostate neoplasia was among the patient collective. Hypothetically, CT should be well suited to detect tissue mineralization of the prostate at an early stage. Thus, future CT-studies of the canine prostate using a larger group of neutered patients should also investigate the mineralization of the prostate and prove the results by histopathological investigations. A further limitation of the study is that no information about the structure of the prostate gland before castration existed. Further studies are needed, which image the prostate gland before and after castration to describe these image patterns.
Due to the small size of the homogenous prostates in castrated dogs, HUs were measured placing elliptic ROIs over the whole prostate gland. Consequently, the urethra could not be excluded, which may have had an influence on the measured HUs and should be considered as a limitation of the study.
The prostatic size of intact male dogs was examined according to previous research [5,6,7]. In both morphological groups (homogenous prostate and prostate with alterations) the prostatic ratio parameters were correlated. Consequently, the prostate of castrated dogs seems to grow uniformly, independent of its tissue structure. In the present study the ratio of the prostate size was bigger in the altered prostate than in the homogeneous prostate. These alterations and cysts can be caused by inflammation and ageing processes. After castration the prostatic tissue undergoes atrophy [12, 13, 17, 35] and the prostatic size does not increase with age like in the intact dogs. This atrophy can be also seen in the CT images. By comparison, with higher age the prostate size of castrated dogs does not increase, whereas the prostate size of intact dogs increases.
The ratio of the prostatic height, width and length differed between the prostates of castrated and intact male dogs. In the study of Pasikowska et al. [6] only intact male dogs were included and the ratio of the prostate size in intact dogs with BPH was significantly higher than in dogs with homogenous prostate. The values for the rW, rH and rL of the homogenous prostate in the study of Pasikowska et al. [6] were on average 60% higher than in the present study. Concerning the altered prostate, the values of the intact dogs in the study of Pasikowska et al. [6] were on average 68% higher than in castrated dogs of the present study. It can therefore be said, that the prostate of castrated dogs is significantly smaller than in intact dogs of the study of Pasikowska et al. [6]. In conclusion, the atrophy of the prostate after castration is reflected in the lower post-contrast density as well as in the lesser prostatic size.