Ultrasound-Guided Percutaneous Drainage as the Primary Treatment for Prostatic Abscesses and Cysts in Dogs
Thirteen dogs with prostatic abscesses and cysts were treated using percutaneous ultrasound-guided drainage. Eight dogs were diagnosed with prostatic abscesses and five with cysts on the basis of cytopathological examination and bacterial culture of the prostatic fluid. Antibiotic therapy, based on culture and sensitivity results, was administered for a minimum of 4 weeks. Intact dogs were castrated after initial drainage. Repeat ultrasonography of the prostate was performed every 1 to 6 weeks, and any residual cavitary lesions were drained and fluid analysis repeated. The median number of drainage procedures required to completely resolve the lesions was two (range, one to four). No complications were observed after drainage, and clinical signs resolved in all dogs. None of the dogs developed clinical signs of recurrent abscesses or cysts in the follow-up period (median, 36 months; range, 10 to 50 months). Ultrasound-guided, percutaneous drainage of prostatic abscesses and cysts appears to be a useful alternative to surgical treatment in select dogs.
Introduction
Prostate disease affects approximately 80% of male dogs >10 years of age.1–6 Two common prostatic diseases are abscesses and cysts.1–6 Prostatic abscesses develop as a result of bacterial contamination spreading from another part of the urinary tract, by hematogenous route, or from cysts that become secondarily infected.24 Prostatic cysts are cavitary lesions filled with secretions from the glandular epithelium of the prostate.3 Cysts may develop as a result of obstruction of ducts, leading to accumulation of prostatic secretion within the parenchyma of the gland.5 Clinical signs of prostatic abscesses or cysts result from compression of adjacent structures due to prostatic enlargement or from complications related to local or systemic bacterial infection. Common clinical signs include dysuria, stranguria, purulent or hemorrhagic penile discharge, tenesmus, dyschezia, ribbon-like feces, pain, pyrexia, sepsis, and shock.1–6
Current treatment recommendations for prostatic abscesses and cysts in dogs include invasive surgical procedures such as debridement and omentalization, marsupialization, subtotal prostatectomy, or placement of multiple Penrose drains.1–10 Each of these procedures is effective for draining the prostate; however, they may be associated with significant postoperative complications, prolonged hospitalization, and increased expense. Postoperative complications include urinary incontinence, scrotal and pelvic limb edema, peritonitis, re-abscessation, sepsis, shock, and death.137–10 In addition, mortality rates have been reported to range from 24% to 51% for dogs treated surgically for prostatic abscesses.57
In contrast, humans with prostatic abscesses are frequently treated by percutaneous or transrectal drainage. Ultrasonography or computed tomography is used to guide a needle or catheter into the prostate so the abscess can be drained. Percutaneous (or transrectal) abscess drainage is the preferred treatment for men with prostatic abscesses.11–17 With this technique, the morbidity is relatively low (0% to 16%), and complications after drainage are uncommon.1114
To the authors’ knowledge, there are only two reports that describe the use of percutaneous drainage as a primary treatment for prostatic abscesses in dogs. In one report, three of four dogs with prostatic abscesses were successfully treated with percutaneous drainage, and one required surgical treatment.18 In another report, 41 of 45 dogs with prostatic abscesses were successfully treated with a single drainage procedure and concurrent infusion of 3% gentamycin sulfate and alcohol into the lesion.19 Four dogs required a second drainage procedure. Repeat ultrasonography 6 months later suggested that all prostatic abscesses had resolved.19 The results of these two reports are very encouraging; however, the evaluation period was limited to 6 months, prompting further evaluation of this technique. The purpose of this study was to describe the technique, complications, and long-term outcomes in a series of dogs with prostatic abscesses or cysts treated by ultrasoundguided, percutaneous drainage.
Materials and Methods
Case Population
The dogs in this study were referred to the Queen Mother Hospital for Animals at the Royal Veterinary College between May 1995 and July 2000 for investigation and treatment of prostatic conditions. Dogs with prostatic cysts that were considered to be incidental findings, because they were not associated with clinical signs, were excluded. A complete history including breed, age, gender, weight, clinical signs, and prior medical or surgical treatment was obtained.
Diagnostic Evaluation
Diagnostic evaluation included physical examination, rectal palpation, complete blood count (CBC), serum biochemical profile, urinalysis obtained by cystocentesis (including aerobic bacterial culture and sensitivity), abdominal radiography, prostatic ultrasonography, and prostatic fluid analysis (including cytopathological examination and aerobic bacterial culture and sensitivity).
Sedation and Anesthetic Protocol
Eleven animals were anesthetized, and two were sedated for the ultrasound-guided, percutaneous drainage procedure. The anesthetic protocol included premedication with acepromazine (0.02 mg/kg body weight, intravenously [IV]) and pethidine (2 mg/kg body weight, intramuscularly [IM]), followed by propofol induction (4 mg/kg body weight, IV) and isoflurane in oxygen via endotracheal intubation for maintenance. The sedation protocol included acepromazine (0.01 mg/kg body weight, IM) and morphine (0.2 mg/kg body weight, IM) or acepromazine (0.04 mg/kg body weight, IM) and butorphanol (0.2 mg/kg body weight, IM).
Ultrasound-Guided, Percutaneous Drainage Technique
Dogs were placed in dorsal or lateral recumbency, and the abdomen was clipped and aseptically prepared. The prostate was examined ultrasonographically using a 7.5- or 8.5-MHz transducer.a The prostate was examined in both sagittal and transverse planes using a prepubic approach. The size and appearance of the prostate and any cavitary lesions were measured and recorded. Percutaneous drainage was performed using a 22-gauge spinal needle attached to an extension set and 20 mL syringe. The needle was directed by hand into the prostate using ultrasound guidance. The cavitary lesions were drained completely to reduce the chance of any fluid leaking from the needle tract, and suction was maintained as the needle was withdrawn to reduce the chance of fluid leaking from the needle [Figures 1, 2]. If the prostate was located caudally within the pelvic canal or if cavitary lesions were located on the caudal aspect of the prostate, an assistant displaced the prostate cranially using a gloved finger in the rectum. This improved the visibility of the lesion and reduced the potential for error in needle placement.
Prostatic Fluid Analysis
The volume and characteristics of the fluid were recorded, and samples were submitted for cytopathological examination and aerobic, bacterial culture and sensitivity. Lesions were diagnosed as either abscesses or cysts on the basis of cytopathology and bacterial culture results. Lesions were classified as abscesses if the fluid was a modified transudate or exudate with >25 g/L protein and a nucleated cell count of >3.0 to 5.5 × 106/μL, if bacteria were visible on cytopathological examination, or if the bacterial culture was positive.
Treatment Following Drainage
All dogs were monitored closely after drainage for signs of hemorrhage, peritonitis, septicemia, or shock. Additional supportive care included IV crystalloid fluid therapy and broad-spectrum antibiotics.b Antibiotic therapy was changed, if necessary, based on culture and sensitivity results and was continued for a minimum of 4 weeks in dogs with positive cultures. Intact dogs were castrated at the time of initial drainage or 2 to 3 weeks later.
Follow-Up Examination
Dogs were reexamined at 1- to 6-week intervals until the lesions were considered resolved based on clinical signs and ultrasonography of the prostate. Repeat examination included, at minimum, a physical examination, rectal palpation, and ultrasonography of the prostate. A CBC, serum biochemical profile, and urinalysis (including aerobic bacterial culture and sensitivity) were also obtained in some dogs. Any residual cavitary lesions were measured, drained, and the fluid was analyzed as previously described. Long-term follow-up information was obtained by telephone conversation with the referring veterinarian and the owner. For case nos. 1 and 6, repeat ultrasonography of the prostate was performed 24 and 34 months after resolution of clinical signs, respectively.
Results
Case Population
Thirteen dogs were included in this study [Table 1]. Eight dogs were diagnosed with prostatic abscess, and five had cysts. Dogs were of various medium to large breeds, with a median weight of 32 kg (range, 20 to 41 kg) and median age of 9 years (range, 6 to 13 years). Ten dogs were intact, and three had been castrated. Five dogs received antibiotic therapy prior to referral. The most frequently reported history was dysuria and stranguria for several weeks to months. Case nos. 3, 7, 8, and 11 had concurrent perineal hernias. Case nos. 1 and 12 had urinary incontinence. Case no. 12 had a mass of unknown type, surgically removed from the neck of the bladder 2 years before developing signs of prostatic disease, and case no. 1 had reflex dysnergia of unknown cause. Case no. 13 had recurrent urolithiasis treated by scrotal urethrostomy 1 year before developing signs of prostatic disease.
Diagnostic Evaluation
Clinical signs included mild to moderate systemic illness, inappetence, abdominal pain, pyrexia, dysuria, stranguria, penile discharge, tenesmus, and ribbon-like feces. Rectal examination revealed prostatic enlargement in 12 dogs. In six dogs with abscesses, the prostate was asymmetrical or the dogs appeared to experience pain on palpation. In dogs with prostatic cysts, only one dog appeared to be in pain on palpation. Hematology and serum biochemical results from the eight dogs with prostatic abscesses were variable. The most common abnormalities included mild to moderate leukocytosis, lymphopenia, or both. Alkaline phosphatase was elevated in three dogs with prostatic abscesses. No hematological or biochemical abnormalities were noted in the five dogs with prostatic cysts. Urinalysis was performed in seven dogs diagnosed with abscesses and in three dogs with cysts. Urinalysis was normal, and cultures were negative in three of the dogs with abscesses and in the three dogs with cysts [Table 2]. In the other four dogs with abscesses, bacteria were present in the urine in three dogs, and cultures yielded a pure growth of Escherichia coli (E. coli) in three dogs and Staphylococcus intermedius at the time of second drainage in one dog. Lateral radiographs of the abdomen revealed prostatomegaly or dorsal displacement of the colon in six dogs [Table 1].
Prostatic Ultrasonography
Ultrasonography revealed signs of prostatic enlargement and cavitary lesions in all dogs. Cavitary lesions ranged from 0.5 to 6.5 cm in diameter [Table 2]. Abscesses typically contained hypoechoic or anechoic fluid in the central areas, with the internal margin of the cavity typically being irregular. Cystic lesions were typically, but not always, more regular or distinct with anechoic fluid in the central areas.
Prostatic Fluid Analysis
Fluid aspirated from abscesses was either purulent or serosanguineous. Cytopathological examination revealed predominantly degenerate neutrophils. Bacteria were identified in five of the abscesses. Fluid aspirated from cysts was clear or straw colored. Cytopathological examination revealed predominately a modified transudate of low or moderate cellularity, containing a mixed population of macrophages, degenerate neutrophils, and lymphocytes. No bacteria were identified in any of the cysts. Aerobic bacterial culture of the prostatic fluid was positive in five dogs with abscesses and negative in all five dogs with cysts [Table 2].
Treatment Following Drainage
None of the dogs required additional supportive care besides IV fluids and antibiotics. The mean number of days the dogs were hospitalized was 3 (range, 2 to 5 days). No complications associated with drainage of the cavitary lesions were observed in any of the dogs.
Follow-Up Examination
Eleven dogs were reexamined after initial drainage. The mean time until reexamination was 4 weeks (range, 1 to 6 weeks). Seven dogs required more than one drainage procedure. Six of these dogs were diagnosed with abscesses, and one was diagnosed with a cyst. The mean number of drainage procedures was two (range, two to four). The mean interval between drainages was 6 weeks (range, 1 to 64 weeks).
Ultrasound examination of the prostate of case nos. 1 and 6, performed 24 and 34 months after resolution of clinical signs, respectively, revealed a very small lesion in each dog. A 0.8-cm diameter cavitary lesion was found in case no. 1 (previously diagnosed with a prostatic abscess), and a 0.3-cm diameter lesion was found in case no. 6 (previously diagnosed with a prostatic cyst).
Long-term follow-up information was obtained from detailed telephone conversations with the referring veterinarians and owners of all dogs. None of the dogs were reported to have clinical signs or required additional medical or surgical treatment for prostatic disease. At the time of writing, case nos. 3, 4, 10, and 11 had died from conditions unrelated to prostatic disease, including suspected hemangiosarcoma, severe arthritis, a growth on the hock, and unspecified cardiac disease. Of the nine dogs that were still alive, case nos. 1 and 13 were treated periodically for cystitis. Case no. 1 had persistent urinary incontinence that was diagnosed before prostatic drainage, and case no. 13 had recurrent urolithiasis. The median follow-up time was 36 months (range, 10 to 50 months). Follow-up time was determined from the first drainage to the time of owner contact or the time of the dog’s death.
Discussion
The results of this study indicate that ultrasound-guided, percutaneous drainage is an effective treatment for some dogs with prostatic abscesses and cysts. All dogs in this study experienced resolution of clinical signs, and no complications were detected after drainage. The primary advantage of this technique is that it is minimally invasive and avoids the potential postoperative morbidity, hospitalization, and expense of conventional surgical procedures.
The dogs in this study had only mild to moderate signs of systemic illness, and none had evidence of peritonitis or severe systemic signs that would have required more aggressive medical or surgical treatment. The diagnosis of prostatic abscesses and cysts was based on physical examination, prostatic ultrasonography, and cytopathological examination and bacterial culture of prostatic fluid. On palpation, prostatic abscesses are typically enlarged and painful with asymmetrical swelling that may be either soft or firm, depending upon the size of the lesion. Prostatic cysts are typically enlarged and asymmetrical, but they tend not to be painful. In this study, there was overlap of physical examination findings between the dogs with abscesses and the dogs with cysts. However, the dogs with abscesses tended to experience more pain than dogs with cysts. On ultrasound examination, prostatic abscesses typically appear as hypoechoic, cavitary lesions, with irregularly defined margins. The fluid within the lesion may have mixed echogenicity or a flocculent appearance. In contrast, prostatic cysts typically appear as anechoic cavitary lesions with more regularly defined margins. However, both abscesses and cysts may have similar ultrasound characteristics; therefore, cytopathological examination and bacterial culture of prostatic fluid are recommended to aid in differentiating the two lesions.20
Five (62.5%) of the eight dogs diagnosed with prostatic abscesses, based on cytopathological examination, had positive prostatic fluid cultures. The most common bacteria cultured was E. coli, which is similar to previous studies.56 Four (50%) of eight dogs with prostatic abscesses also had positive urine cultures. For case no. 13, culture of the prostate fluid was negative despite the presence of bacteria seen on cytopathology of the fluid. This was most likely due to previous antibiotic therapy that may have already killed the bacteria seen on cytopathology. However, technical error in the culture process cannot be completely ruled out.
All of the dogs were treated with broad-spectrum IV antibiotics after the percutaneous drainage procedure. Once the culture and sensitivity results were obtained, therapy was adjusted as necessary according to the sensitivity results. Despite the negative culture results for some of the dogs, antibiotic therapy was continued for 4 to 6 weeks to reduce the potential for infection that may have occurred during the drainage procedures.
Ten dogs were castrated as an adjunct treatment to percutaneous drainage. Castration is recommended to decrease the size and secretory function of the prostate and reduce the potential for persistent infection.2122 For dogs with moderate signs of systemic illness, castration was delayed for 2 to 3 weeks to allow improvement after initial drainage and antibiotic therapy.
Prostatic abscesses are difficult to treat in dogs, and it is not unexpected that multiple drainages may be required before resolution. Multiple drainage procedures were required in seven dogs (six abscesses and one cyst). Due to the small number of dogs involved in this study, it was not possible to determine if the type of lesion had a significant influence on the number of drainage procedures required to resolve the lesion. For case no. 13, it is possible that persistent urolithiasis was a source of reinfection of the prostate, necessitating a third drainage after 16 months. In humans, multiple drainage procedures may also be required to resolve prostatic abscesses; however, satisfactory outcome after a single procedure is more common. In two separate studies, repeat drainage was necessary in only two (8%) of 24 and four (33%) of 11 men with prostatic abscesses.1516
All dogs in this study experienced resolution of clinical signs, despite the need for multiple drainage procedures in seven of the dogs. In humans, clinical signs resolved in 20 (83.3%) of 2415 and in 12 (86%) of 1417 men treated with percutaneous drainage. Treatment failure occurred in four (16%) of 2415 and in two (14%) of 1417 men, and additional treatments such as drainage catheters, perineal incision and drainage, and transurethral resection were used. For the dogs in this study, if it had not been possible to completely drain any of the lesions or if the lesions had not consistently decreased in size after each drainage procedure, surgical drainage would have been pursued. How the anatomical and physiological differences between the prostates of dogs and humans influence the success of percutaneous drainage is not known; however, the differences in glandular secretion and flow through the prostate may affect the success of treatment.
The potential complications with this technique include contamination of the abdominal cavity from leakage of fluid from the prostate or accidental laceration of adjacent vascular structures. To avoid these potential complications, all dogs were anesthetized or heavily sedated for the drainage procedure. Ultrasound guidance was used to avoid accidental injury to adjacent structures, and a relatively small-gauge needle (22 gauge) was used to decrease the size of needle tract made in the prostate. The lesions were completely drained to decrease the pressure within the cavitary lesion and reduce the chance of any fluid leaking from the needle tract. All dogs were monitored closely for a minimum of 48 hours after the procedure, and no complications were observed.
Long-term outcome was based on the referring veterinarian’s and the owner’s evaluations of the dog’s clinical signs. None of the referring veterinarians or owners reported recurrence of clinical signs related to prostatic disease. For case nos. 1 and 6 that had ultrasonography of the prostate 24 and 34 months after resolution of clinical signs, it is not known whether the two small lesions were residual or new lesions. However, neither dog was experiencing clinical signs, and the lesions were not considered large enough to warrant drainage.
In the study by Bussadori et al., 45 dogs with prostatic abscesses were treated successfully with ultrasound-guided, percutaneous drainage.19 The technique involved complete drainage of the abscess followed by injection of 3% gentamycin sulfate solution and alcohol into the lesion. Only four dogs required a second drainage procedure, and ultrasonography of the prostate performed 6 months later revealed all of the lesions had resolved. Although the follow-up time was limited to 6 months, the results were likewise very encouraging, and the practice of injecting antibiotics into the lesion after drainage warrants further investigation.
Conclusion
Ultrasound-guided, percutaneous drainage of prostatic abscesses and cysts appears to be an effective and safe treatment for dogs with well-defined lesions in the prostate. The technique is not recommended for dogs with peritonitis or severe systemic signs that may require more aggressive medical and surgical treatment. Dogs should be monitored closely for 24 to 48 hours after drainage for complications related to leakage from the prostate or injury to adjacent structures. Owners should be made aware that multiple drainage procedures might be necessary to completely resolve clinical signs.
Apogee CX; ALT (U.K.) Ltd., United Kingdom (before September 1999) and Sequoia 512, Acuson Corp., United Kingdom (after September 1999)
Enrofloxacin (Baytril); Bayer plc, Eastern Way, United Kingdom
Citation: Journal of the American Animal Hospital Association 39, 2; 10.5326/0390151
Citation: Journal of the American Animal Hospital Association 39, 2; 10.5326/0390151
Ultrasonographic appearance of the prostatic abscess from case no. 13 immediately prior to percutaneous drainage. The abscess measured 2.6 cm × 1.5 cm.
Contributor Notes
