Urine-Filled Large Prostatic Cystic Structure in Two Unrelated Male Miniature Dachshunds
ABSTRACT
A 1 yr old intact male miniature dachshund presented for posturing to urinate without voiding and nocturia. Physical examination revealed congenital reproductive abnormalities and a fluid-filled structure caudal to the urinary bladder. The dog was diagnosed with a prostatic cyst and underwent an exploratory laparotomy with an attempt to remove the cyst. Twelve weeks later, the dog returned with recurring clinical signs, and the cyst was found to have returned back to its original size. A second intact male miniature dachshund presented at 7 mo of age for stranguria. Physical examination revealed congenital reproductive abnormalities and a fluid-filled structure on rectal palpation, much like the first dog. The dog was diagnosed with a prostatic cyst and underwent an exploratory laparotomy. An attempt was made to close communication between the prostate and cyst. The dog re-presented 3 wk later for recurrence of clinical signs, and the prostatic cyst was found to have increased in size. Both dogs were euthanized because of recurrence of clinical signs. This report describes the presence of prostatic cysts in two young dogs with congenital abnormalities of the genital and reproductive tracts and the similarities seen in human boys diagnosed with prostatic utricles.
Introduction
Congenital cystic lesions associated with the prostate have been infrequently reported in dogs and are poorly defined in this species. In humans, these lesions are usually embryological remants of the Müllerian duct system.1 As traditionally described, a Müllerian duct cyst does not connect with the urethra or seminal tract, and its fluid contents are isolated from adjacent tissues. However, recent reports have described human males with large cystic structures near or within the prostate, with connections to adjacent tissues, and containing urine or spermatozoa.2 These are termed “mega-utricles,” or enlarged prostatic utricles, and are associated with hypospadias, disorder in sexual development, and cryptorchidism. Affected individuals present with lower urinary tract infections, pain, dysuria, or incontinence.1–4 This report describes two male miniature dachshunds, each with a large cystic structure associated with the prostate, with strong similarities to the enlarged prostatic utricle or “mega-utricle,” as currently described in humans.2,3
Case Reports
Case 1
A 1 yr old 4.7 kg intact male miniature dachshund was referred to the Texas A&M Small Animal Veterinary Medical Teaching Hospital (SA-VMTH) for urinary incontinence. The dog had a 3 mo history of persistent dribbling of urine and a narrowed stream during micturition. Posturing without voiding and intermittent nocturia were also observed over the previous 2 wk. No overt stranguria was reported.
The physical examination revealed microorchidism, penile hypoplasia, and galactorrhea with minimal gynaecomastia; a fluid-filled structure was digitally palpated per rectum caudal to the urinary bladder.
A routine transabdominal ultrasonographic examination was performed by a board-certified radiologist. The urinary bladder was in an appropriate position and midsized. A fluid-filled structure was present, caudodorsal to the urinary bladder, apparently communicating with the urethra, and extending toward the pelvic canal. The wall of the cystic structure (ranging from 3 mm to 1.1 cm) was thicker than the wall of the urinary bladder (1 mm thick). Two tubular structures were seen coursing from the cystic structure in a craniodorsal direction then caudally through the inguinal rings, and connecting to the testicles. The testes were smaller than normal and lacked the expected architecture. The testes were round as opposed to a normal testicular ovoid shape. The calculated testicular volume based on ultrasound measurements was 2.3 cm; however, the reported normal average volume for a young (3 yr old) dog is 8.5 cm.3,5,6 The reported normal ratio in g/kg of testicular weight to body weight is 0.89 g/kg.6 Estimating that ∼1 g testicular tissue is equal to 1 cm, this dog’s testicular weight to body ratio is below average at 0.47 g/kg.3,6
Urine collected by cystocentesis had a specific gravity of 1.035 g/mL. Microscopic sediment examination revealed pyuria (3–4/high power field) and bacteriuria; quantitative culture revealed mixed bacterial growth (>100,000 colony-forming units/mL) with Enterobacter species, Streptococcus alpha hemolytic, and Streptococcus canis. Fluid from the cystic structure was aspirated under ultrasonographic guidance; it was yellow in color and was grossly similar to the urine. Microscopic examination revealed a mixed intra- and extracellular bacterial population (rods and cocci), numerous squamous cells, and markedly degenerate neutrophils.
The dog underwent an exploratory laparotomy 2 days after initial presentation to the hospital. Preoperative labwork was unremarkable.The cystic structure was located on midline, dorsal to the urinary bladder, extended caudally and joined the urethra at the prostate. Tubular structures, diagnosed as the vas deferens, extended from its cranial margin. Each of the vas deferens was ∼7 mm in diameter proximally and was traced back to its respective inguinal ring and testicle. As the vas deferens coursed toward the inguinal ring, they narrowed to a more normal diameter of ∼3 mm. Normal ureters were found entering the trigone of the bladder. A cystotomy was performed. A 2.7 mm rigid cystoscopea was introduced into the bladder and advanced antegrade into the intrapelvic urethra. Multiple punctate openings (<1 mm in diameter) were observed within the urethra at the level of the fluid-filled cyst. The cyst was isolated at its attachment at the dorsal aspect of the prostate. A transfixing suture with a 2-0 polydioxanone suture was placed at the midpoint of the cyst, which was then excised and submitted for culture and histopathology. The urinary bladder was returned to its normal anatomical position, and the cystotomy incision was extended into the proximal urethra on the ventral surface. The punctate openings leading from the dorsal aspect of the urethra to the cyst were sutured closed using 5-0 polydioxanone sutures in a simple interrupted pattern from the urethral lumen. The testes were pushed forward into the caudal aspect of the abdominal incision, and the dog was neutered using an open castration technique. Both were submitted for histopathology.
Patency of the proximal urethra was confirmed endoscopically. The cystotomy incision was closed routinely, abdominal lavage was performed, and the laparotomy incision was closed in a routine fashion.
The dog recovered from anesthesia without complications and was managed with appropriate supportive care postoperatively. The dog was administered amoxicillin trihydrate with clavulanate potassiumb (20.4 mg/kg per os [PO] q 12 hr) pending results of bacterial culture of the previously collected samples.
Histopathology of the tissues submitted concluded that the structures removed were dysplastic testicles, spermatic cord, vas deferens, and a small segment of urethra. Culture of the cyst grew small numbers of S canis and Enterobacter cloacae; both were susceptible to amoxicillin trihydrate with clavulanate potassium.
Eleven weeks after discharge, the dog returned for a follow-up visit. The owners reported decreased dribbling of urine and reduced nocturia. Abdominal ultrasonography revealed a reduction in the size of the cyst but a persistent, direct communication between it and the urethra.
Six days later, the dog presented with a 24 hr history of stranguria and vomiting. Physical examination revealed a full, firm urinary bladder. Abdominal radiographs showed a markedly distended urinary bladder and a fluid-filled structure caudal to the urinary bladder. A retrograde contrast cystourethrogram showed severe narrowing of the penile urethra. A cause for obstruction was not identified. The dog was hospitalized and intermittent urinary catheterization was performed to empty the bladder. Enrofloxacin (14.1 mg/kg PO q 24 hr), prazosin (0.2 mg/kg PO q 8 hr), buprenorphine (0.01 mg/kg IV q 8 hr), and meloxicam (0.1 mg/kg PO q 24 hr) were administered. On the third day, a small stone (2 mm in diameter) was removed from the patient’s urethra after catheterization. The following day, the dog reobstructed and the owners opted for euthanasia.
The cystolith was composed of equal amounts of struvite (magnesium ammonium phosphate) and ammonium uratec. Genetic marker testingd, specifically polymerase chain reaction testing for the AMEL gene and the SRY or ZF/CREBZF genes, was performed on a stored ethylenediaminetetraacetate blood sample. Results indicated the presence of a normal male genotype.
Case 2
A 7 mo old 4.64 kg intact male miniature dachshund was referred to the Texas A&M SA-VMTH with a 4 wk history of stranguria. The dog had initially presented to the referring veterinarian for lethargy, hyporexia, and dysuria. Urine collected via cystocentesis showed a mixed bacterial population on sediment examination, and the dog was diagnosed with a urinary tract infection. A 3 day course of marbofloxacin (5 mg/kg PO q 24 hr) and a 3 day course of carprofen (5 mg/kg PO q 24 hr) was prescribed. On examination at the SA-VMTH, penile hypoplasia and microorchidism were noted, and a fluid-filled, cyst-like structure was palpated on digital rectal examination. A urine sample was collected via cystocentesis. Urine specific gravity was 1.044, dipstick analysis and microscopic sediment examination were unremarkable, and a quantified urine culture was negative.
Transabdominal ultrasonography revealed an enlarged prostate gland (25.6 mm wide) with a cystic structure located on its dorsal aspect, a bihorned structure located between the urinary bladder and descending colon, hypoplastic testes, and enlarged medial iliac lymph nodes. The calculated testicular volume was 2.4 cm; however, the reported normal average volume for a young (3 yr old) dog is 8.5 cm.3,5,6 Using the same estimations as in the previous dog, this dog’s testicular weight to body ratio is below average at 0.54 g/kg, with average being 0.86 g/kg.6 The bihorned structure could be traced heading cranially before extending caudally toward the inguinal rings. The dog was discharged at this time and scheduled to return for an exploratory laparotomy, neuter, and cyst drainage.
Five weeks after the initial visit, the dog presented for an exploratory laparotomy. Presurgical laboratory work was unremarkable. A repeat abdominal ultrasound was performed, and the findings were unchanged. An ultrasound guided cystocentesis was performed, and the fluid-filled structure was aspirated. Urinalysis was unremarkable, although a quantified urine culture grew a Mycoplasma species (>100,000 colony-forming units/mL). Biochemical analysis of the fluid in the cystic structure was consistent with urine (serum creatinine 0.56 mg/dL, serum potassium 4.0 mg/dL, fluid creatinine 89.4 mg/dL, and fluid potassium 21.9 mg/dL).
The following day, the dog was placed under general anesthesia. A fluid-filled structure was present dorsal to the urinary bladder (Figure 1). The structure joined the urethra caudal to the trigone in the area of the prostate gland. Bilateral tubular structures were present on the ventral surface of this structure and coursed to the inguinal rings and out of the body wall to the testes. The tubular structures were larger than expected for vas deferens. Normal ureters were found entering the trigone of the urinary bladder. Urine was collected from the urinary bladder via intraoperative cystocentesis and submitted for culture. A cystotomy was performed in a routine fashion, and an 8-French flexible videoscopee was passed through the bladder to visualize the connection between the urethra and cystic structure. Numerous tiny punctate openings were noted in the urethra. Methylene blue was injected into the cystic structure, and the urethral lumen was observed with the flexible scope. Blue-colored fluid was seen coming from multiple small communications between the cystic structure and urethra. The cystotomy incision was closed routinely, and a routine closed castration was performed; both testes were submitted for histopathology. An abdominal lavage was performed, and the laparotomy incision was closed routinely. The testes were small and spherical as opposed to the normal ovoid testicular profile, but the epididymis was relatively large and firm (Figure 2). Histopathology of testes showed evidence of testicular hypoplasia and epididymal fibrosis without spermatogenesis. The intraoperative urine culture grew a Mycoplasma species. The dog recovered from anesthesia without complications, was given supportive care and pain relief, and was discharged from the hospital 2 days later on tramadol (5.4 mg/kg PO q 8 hr) and carprofen (2.7 mg/kg PO q 12 hr).
Citation: Journal of the American Animal Hospital Association 54, 6; 10.5326/JAAHA-MS-6743
Citation: Journal of the American Animal Hospital Association 54, 6; 10.5326/JAAHA-MS-6743
The dog returned 20 days later with a history of acute dysuria. A complete blood count, chemistry panel, and urinalysis were performed 1 day after presentation; all results were essentially unremarkable. The urine specific gravity was 1.025 with no evidence of protein, glucose, ketones, bilirubin, or blood. A urine culture submitted at this time was negative. Abdominal ultrasonography showed echogenic material within the urinary bladder and the cystic structure. The dog was intermittently catheterized until he was able to void on his own and was instructed to follow up with the referring veterinarian. The dog was discharged with bethanechol (1.25 mg/kg PO q 8 hr), doxycycline (12.5 mg/kg PO q 12 hr), and prazosin (0.06 mg/kg PO q 12 hr).
Four days later, the dog re-presented for dysuria and lack of clinical improvement. A brief ultrasonographic examination revealed a large urinary bladder; the cystic structure had greatly increased in size since the previous scan. Patient-side laboratory work showed normal electrolytes, blood urea nitrogen, and creatinine. The following day, the dog was anesthetized for an abdominal computed tomography scan and urinary catheterization. Computed tomography examination revealed the previously identified midline cyst on the dorsal aspect of the prostate with numerous openings from the urethra to the cystic structure (Figure 3). A urinary catheter was placed and attached to a closed collection system. The dog recovered from anesthesia without complications.
Citation: Journal of the American Animal Hospital Association 54, 6; 10.5326/JAAHA-MS-6743
The owner declined further surgical interventions and requested humane euthanasia for the dog the following day.
Discussion
The miniature dachshunds described in this report had similar abnormalities, namely a midline cystic structure associated with the prostate and communicating with the prostatic urethra. These findings are distinctly different from those previously described in dogs with a uterus masculinus/persistent Müllerian duct, as those structures did not contain urine or spermatozoa and were not connected to the urinary or seminal systems.7,8 Instead, the structures identified in these dachshunds bear a close resemblance to a disorder seen in young boys known as cystic dilation of the prostatic utricle or “mega-utricle.”
The utricle is a pouch located in the verumontanum of the prostate between the two ejaculatory ducts analogous to a uterovaginal canal in females.9 A cystic dilation of the prostatic utricle is an area of focal dilation in the prostatic utricle that communicates with the prostatic urethra.1,10 Enlarged prostatic utricle in humans has been associated with a disruption in male embryological development, and it is likely that a similar process occurred in these dogs. Normal genotypic sex is determined at fertilization, giving a diploid embryo that is either XX or XY. In the early stages of development, male and female embryos are very similar, with Wolffian and Müllerian ducts and undifferentiated gonads. The genotypic sex triggers phenotypic differentiation through the SRY gene. This gene is located in the sex determining region of the Y chromosome and initiates male embryonic gonadal development.11–14 The absence of the SRY gene results in the development of ovaries and external female genitalia.13–15 In the male, the testes produce Müllerian inhibiting substance (MIS) and testosterone, which leads to the further development of the external male genitalia.13–15 Androgens inhibit the formation of the vagina, and MIS causes regression of the Müllerian ducts.12–16 Lack of MIS may result in an enlarged prostatic utricle as well as other disorders in sexual development.3 Karyotyping was not performed in these dogs but may be informative to perform in future cases.
Cystic prostatic structures with connection to the urethra have been previously described in small numbers of dogs.17 Bokemeyer et al. recently described 16 dogs with cysts containing urine out of 87 dogs with an ultrasound-proven cavitary lesion within the prostate and associated clinical signs.17 Affected dogs were mostly large (>25 kg) and ranged in age from 5 to 13 yr. A solitary urethral defect was identified in four out of seven undergoing laparotomy. In addition to their age and breed type, the dogs described in that paper are substantially different from the dachshunds reported here, in that the two dogs reported here had multiple communications between the cystic structure and the urethra, along with overt genital abnormalities (i.e., penile hypoplasia and microorchidism). It seems probable, therefore, that the underlying etiologies for the Bokemeyer group and these two dachshunds are different.
In human patients, various symptoms associated with enlarged prostatic utricle are reported, including frequent micturition, urgency of urination, urine pain, and dysuria.1 It seems likely that the clinical signs noted in these dogs, namely urine dribbling and dysuria, were related to passive emptying of the cystic structure independent of micturition and compression on the proximal urethra during normal voiding, respectively. Dog 1 reportedly began having clinical signs at 9 mo of age. We suspect that clinical signs may have developed or were recognized at 9 mo of age because the dog was working on housebreaking prior to this time, or the clinical signs were exacerbated by the development of a urinary tract infection. Although transabdominal ultrasonography confirmed the presence of the cystic structure, it may have been useful to have performed urethroscopy ± computed tomography imaging prior to exploratory laparotomy. Unfortunately, routine retrograde urethroscopy was not possible in either dachshund because of size limitations; however, a percutaneous fluoroscopically assisted perineal approach could have been attempted.18 In humans, radiographic contrast material is injected into the lesions and permits identification of connections to adjacent tissues. More detailed imaging may have provided some useful insight into these cases and may have aided surgical planning. Although we uncommonly see incontinent male dogs, the presence of a prostatic utricle should be considered in patients with obvious congenital abnormalities of the genitalia and urinary tract.
Conclusion
The similarity of the malformations in these two young miniature dachshunds suggests that this may be a recognizable, physical clinical entity. Clinicians should be alert for miniature dachshunds with small dysplastic testes and underdeveloped external genitalia, particularly those with a history of dysuria. A coexistant prostatic lesion may need to be resolved, but also, by identifying other animals, the potential exists that by characterizing these animals better, clinicians may identify a disorder in sexual development and perhaps identify the genetics and pathogenesis of this condition.
The bladder is exteriorized and pulled caudally to expose the dorsal aspect of the bladder. The fluid-filled structure is joining the urethra caudal to the trigone. Two small tubular structures coursed to the inguinal rings.
Lateral (left) and medial (right) photograph of the gross testicles from dog 2. The testicles are considered hypoplastic. The size marker is 1 cm.
Computed tomography image with contrast cystourethrogram. The midline cyst can be seen communicating with the urethra in several locations.
Contributor Notes
