Prostatic Abscess

Etiology

A prostatic abscess often develops as a complication of acute prostatitis, primarily from reflux of infected urine into the prostatic ducts during voiding. Generally, they occur in patients with poorly controlled diabetes or a compromised immune system. Over 50 percent of patients with prostatic abscesses are diabetics.[7] Though rare in the modern antibiotic era, patients who are not treated appropriately or adequately for acute prostatitis are at high risk of developing an abscess. Men at risk for prostate abscess include those with chronic foley or suprapubic catheters, neurogenic bladder dysfunction, poorly controlled diabetes, liver cirrhosis, ESRD, or immunosuppressed patients, including those who are HIV positive. Patients who do intermittent self-catheterization or have bladder outlet obstruction are also more prone to prostatic abscess formation. Any significant type of underlying voiding dysfunction, either from neurological diseases or due to severe benign prostatic hyperplasia and some forms of pelvic injury, also places patients at higher risk. In recent trends, prostatic abscesses occurring as complications after prostate biopsies are becoming more commonly reported in the medical literature despite the increasingly widespread use of antibiotics.[8][9][10] 

In literature from the pre-antibiotic era, sexually transmitted organisms like Neisseria gonorrhoeae and Chlamydia were commonly identified pathogens in prostatic abscesses. This was often complicated by spontaneous rupture into the urethra, perineum, or rectum and was associated with a 50% mortality rate.[11] More recent data indicate that the most common causative agent in the modern era is gram-negative bacteria. In a meta-analysis study, Escherichia coli has been attributed to more than 70 percent of all prostatic abscess cases followed by Klebsiella, Pseudomonas, Proteus, Enterobacter, Serratia, and Enterococcus species.[3] Staphylococcus aureus causing prostatic abscesses is also well documented, possibly through hematogenous spread from osteomyelitis, chronic gingivitis, extensive boils (furunculosis), or rheumatic fever.[7] Staphylococcus aureus also appears to be an increasingly common causative organism.[12] Such patients tend to have higher temperatures, require slightly longer antibiotic treatment, and are more likely to have diabetes than other prostatic abscess patients.[13] Klebsiella pneumoniae is increasingly being found in cultures of prostatic abscesses as well as fungal organisms like Blastomyces, Cryptococcus, and Nocardia.[14] In a case series of melioidosis, Burkholderia pseudomallei was found to be a relatively common prostatic abscess pathogen.[15] Mycobacterium tuberculosis is a rare cause and is almost always associated with some degree of immunodeficiency.

While E. coli is the most common causative organism for community-acquired prostatic infections, nosocomial infections are much more likely to involve Pseudomonas aeruginosa, Enterococcus, or Staphylococcus aureus, have a more virulent and aggressive presentation, are more likely to develop sepsis, will more frequently demonstrate increased antibiotic resistance, and are more prone to progress to a prostatic abscess.

In general, older men will develop a prostatic abscess as a complication of a prostate biopsy, benign prostatic hyperplasia, or inadequately treated acute bacterial prostatitis. Often patients will have a good initial response to antibiotic treatment. Several studies have shown that about 10% of men who present with prostatic abscesses had recently undergone prostate biopsies.[16][17] It has also developed after prostatic cryotherapy, brachytherapy, intravesical BCG therapy, and other types of urological instrumentation.[7] Risk factors include poorly controlled diabetes and an immunocompromised state. Patients at risk will often present in a debilitated state or with other signs of poor general health.

A prostate abscess may be the first sign of an underlying chronic or debilitating medical condition in younger men.[7] For example, 17 to 25% of younger men presenting with a prostatic abscess were found to have previously undiagnosed diabetes.[18]

Epidemiology

The overall incidence of prostatic abscess can be as high as 0.5% of all urologic diseases; the mortality rate is between 1% and 16%, and approximately 6% of all acute bacterial prostatitis patients will develop a prostatic abscess.[19] Generally, older age group patients are affected more frequently due to a higher incidence of underlying medical risk factors and a greater likelihood of urological procedures like prostate biopsies in this age group. Prostatic abscesses due to sexually transmitted organisms will tend to occur in younger men. Also, younger men who develop prostatic abscesses are likely to have a previously undiagnosed chronic medical condition.

Pathophysiology

Typically, the pathogenesis of a prostatic abscess is due to suboptimally treated acute or chronic bacterial prostatitis. Infection of prostatic tissue occurs as a result of the reflux of infected urine into the prostatic ducts, or there may be direct contamination through a transrectal needle during a prostate biopsy. Inadequate antibiotic prophylaxis and systemic risk factors that promote infections result in acute/chronic bacterial prostatitis and/or a prostatic abscess. Other localized infections predisposing patients to a prostatic abscess include urinary tract infections, epididymitis, gonorrhea, and pyelonephritis.[20] Hematogenous dissemination from a distant primary infected focus such as a liver abscess, abrasion, bronchitis, otitis, perirenal abscess, appendicitis, diverticulitis, boils, or other skin and subcutaneous infections causing bacteremia, primarily due to Staphylococcus aureus, could also lead to prostatic abscess formation.[3] A prostatic abscess has also been reported following the placement of hydrogel spacers prior to radiation therapy for prostate cancer.[21]

Infrequently, an emphysematous prostatic abscess can develop from a urinary tract infection with gas-forming organisms, particularly in patients with poorly controlled diabetes.[22] While rare, such cases of emphysematous prostatic abscesses demonstrate more rapid disease progression and a very high mortality rate of 25%.[22] Early diagnostic imaging in suspected cases will usually clearly demonstrate gas in the prostate or bladder wall. Typical gas-forming organisms include Escherichia coli, Klebsiella pneumonia, and Staphylococcus aureus.

History and Physical

A comprehensive history of all underlying medical illnesses and any immunocompromising risk factors should be promptly obtained in all cases of bacterial prostatitis. This helps to evaluate the potential risks of developing a prostate abscess. The persistence of symptoms in acute or chronic bacterial prostatitis, especially in patients with high-risk factors or inadequate prior treatment, should alert clinicians to the need to evaluate for an abscess. As this pathology commonly derives from an ascending urinary tract infection, patients present with a range of urinary symptoms like increased urinary frequency, urgency, dysuria, hematuria, and urethral burning. In some cases, patients can present with difficulty in urination or even acute urinary retention.[23] More specifically, perineal discomfort should point towards a prostatic etiology. Other systemic manifestations of an infectious etiology are evident by fever, chills, myalgias, and low back pain. Terminal hematuria and the expression of frank pus from the urethra are possible but uncommon presenting symptoms. Up to a third of patients may present with systemic signs of infection only.[10]

Physical examination findings that may present in the presence of a prostate abscess are a purulent urethral discharge, painful digital rectal examination, and possible fluctuant areas in the prostate. Unfortunately, the mere finding of a sore, swollen and tender prostate does not distinguish a prostatic abscess from prostatitis, and fluctuance is found in as few as 16% of prostatic abscess cases.[24] Virtually all patients will have a sore, tender prostate on a digital rectal exam, and over 90% will demonstrate both leukocytosis and pyuria.[25] Besides being quite painful for the patient, the digital rectal examination risks exacerbating the infection and possible sepsis. Therefore, clinicians should be highly suspicious of the presence of a prostatic abscess in any patient with acute prostatitis who is high risk due to presentation, comorbidities, or who fails to respond quickly (within 48 hours) to treatment.

Evaluation

The diagnosis of a prostatic abscess based solely on history and physical findings is difficult because the symptoms are non-specific and overlap with other lower urinary tract pathology. A high level of clinical suspicion, particularly in non-responding acute prostatitis patients, is necessary for early diagnosis and timely management.

Patients with acute prostatitis who do not respond to treatment after 48 hours should be evaluated for a possible prostatic abscess.[19]

Due to its rare incidence and non-specific clinical features, the diagnosis of a prostatic abscess is often delayed. Necessary investigations include a complete blood count with differential, CMP, urinalysis, and blood and urine cultures used to evaluate underlying infectious diseases and chronic medical conditions and identify the source of infection. If there is any suspicion of a prostate abscess based on history and physical findings or basic laboratory results, imaging studies should be obtained. Imaging studies confirm the diagnosis and guide treatment by assisting in drainage procedures.[23][26] Prostatic imaging can be obtained by a transrectal prostate ultrasound, CT scan, or prostatic MRI. 

Transrectal ultrasound (TRUS) is usually the initial diagnostic test for a prostate abscess. It can accurately identify a prostatic abscess in at least 80% of affected patients.[27] Findings of hypoechoic areas with well-defined walls and septations suggest an abscess.[23] They are typically found in the transitional and central zones. Ultrasound also has the advantage of allowing immediate treatment through transrectal needle aspiration of the abscess for therapeutic drainage as well as culture. (Aspiration requires a large-bore needle of at least 18 gauge). Transrectal ultrasound is inexpensive, avoids radiation exposure, is familiar to most urologists, and is readily available. However, transrectal ultrasound can be uncomfortable for the patient, is very operator dependent, does not indicate spread outside the prostate, and may involve significant manipulation of an infected organ.

Computed tomography (CT) scan of the abdomen and pelvis (with and without IV contrast) can better delineate the spread of any prostatic infection to adjacent organs and is especially useful in more severe cases or sicker patients.[28][29] The imaging modality of choice is for emphysematous prostatic abscesses, as the gas/fluid mixture is clearly visualized.[22] CT scans can also identify enlarged lymph nodes, but this is often a non-specific finding. It can also be difficult to differentiate small abscesses from benign cystic prostatic nodules using CT scanning alone. Confirmation can be obtained from a transrectal ultrasound if necessary.

Magnetic resonance imaging (MRI) can also be used for prostatic imaging, even in very sick patients. The MRI demonstrates an abscess as a hypointense area on the T1 weighted image and hyperintense on the T2 weighted image.[30] The abscess will typically appear as a cystic lesion with thick walls. The interior may be septated or heterogeneous. A prostatic abscess will generally appear as an area of restricted diffusion, which correlates with the T2 weighted lesion. Contrast-enhanced MRI will easily show thick-walled fluid collections and is very useful in detecting local extraprostatic extensions.[31] In general, an MRI has better soft-tissue resolution and diagnostic accuracy than CT scan images and is more sensitive than transrectal ultrasound in the very early stages of abscess formation, where ultrasound is often inconclusive.[30] The use of MRI image targeting together with transrectal ultrasound fusion guidance can greatly assist transrectal aspiration by making the target abscess more visible than with ultrasound guidance alone. While magnetic resonance imaging is generally improved with the help of endorectal coils, such implements are often too large and painful for use in patients with prostatic abscesses and acute prostatitis. However, an external phased-array pelvic/prostatic MRI antenna is commercially available and greatly improves image quality and resolution in both 1.5 and 3 Tesla MRI machines without the need for an endorectal coil.[32] (Such an array is most often used to enhance imaging for improved prostate cancer detection.) 

In summary, high-risk (immunocompromised) acute prostatitis patients and immunocompetent patients with acute prostatitis who fail to improve within 48 hours of initial treatment should be evaluated for a prostatic abscess. Only a targeted imaging study (transrectal ultrasound of the prostate, CT scan, or prostatic MRI) can confirm the diagnosis as the clinical signs of prostatic abscess are indistinguishable from acute bacterial prostatitis. While transrectal ultrasonography is usually the initial imaging study, consideration should also be given to a prostatic MRI as it avoids radiation exposure, easily identifies extraprostatic extensions, and provides clear, detailed images of the prostate without the need for any prostatic manipulation from a transrectal probe. MRI-transrectal ultrasound fusion guidance is available, if needed, to assist with the transrectal aspiration of the abscess.

Treatment / Management

Early diagnosis is important because prostatic abscesses require prolonged treatment protocols and sometimes surgical drainage. While surgical procedures are not necessary in all cases of prostate abscesses, drainage procedures have been shown to limit the duration of antibiotics required, shorten hospitalizations, and enhance voiding function.[3] Even though currently there are no strict guidelines or algorithms for the management of prostatic abscesses, expert consensus, as discussed below, is the guiding standard. 

Once there is clinical suspicion of a prostate abscess, a diagnostic evaluation takes place with transrectal ultrasonography or alternate prostate imaging modality to determine the size, number, extent, and exact location of any abscesses. Conservative management is reasonable for abscesses up to 1 cm in diameter. Conservative treatment can be done between 1 cm and 2 cm in diameter, but surgical aspiration and drainage will generally speed recovery and reduce hospitalization time.

Conservatively treated patients should be closely monitored as they may need a surgical drainage procedure if no significant improvement occurs. Patients not responding to initial ultrasound-guided drainage should have additional imaging, such as a CT scan or MRI, to rule out extraprostatic spread of the abscess, in which case open drainage may be warranted.[6] According to the available literature, smaller abscesses (less than 2 cm in diameter) responded well to medical management, whereas larger abscesses (more than 2 cm in diameter) responded better with surgical unroofing, transurethral prostate resection, or similar drainage procedures.[33]

Smaller abscesses, typically 2 cm or less, may respond to non-operative treatment, but complete resolution is likely to take longer without a surgical drainage procedure.[3][5][6] Conservative management includes broad-spectrum intravenous antibiotics necessitating inpatient hospital admission. Empiric antibiotic therapy should initially be targeted mainly toward gram-negative organisms. The antibiotic adjustment could be through urine cultures and Gram stain results showing evidence to suspect another etiology like gram-positive bacteria or rare causes such as fungal organisms. Commonly used first-line antibiotics are levofloxacin (renal adjusted dose), broad-spectrum beta-lactam penicillin, or a cephalosporin. The addition of an aminoglycoside (tobramycin 5 mg/kg daily) in the initial treatment regimen should be considered, depending on the severity of the disease. A minimum two-week course of antibiotics is required for complete resolution, although four weeks is the traditionally recommended duration of medical therapy. Many men require a longer course of treatment, with the average patient receiving slightly over 30 days of medical therapy.[34] Serial imaging should be used to monitor and confirm the complete resolution of the abscess.[9](B3)

The emergence of more resistant organisms, such as extended-spectrum beta-lactamase-producing enterobacteria and methicillin-resistant Staphylococcus aureus, has greatly complicated treatment as up to 75% of organisms causing prostatic abscess infections are resistant to first-generation antibiotics. This requires the use of intravenous carbapenem, third-generation cephalosporins, aztreonam, amikacin, or various combinations while awaiting blood and urine culture results, especially in patients who present with febrile urinary tract infections or sepsis after prostatic biopsies.[7] Oral fluoroquinolones or trimethoprim-sulfamethoxazole can be used later and in afebrile patients, if cultures confirm bacterial sensitivity. Repeat cultures after one week of treatment are recommended. Traditional therapy has required four weeks of continuous antibiotic therapy, but some studies have shown that two weeks may be sufficient, at least in some cases.[35] (A1)

There is some controversy regarding urethral catheter drainage vs. a suprapubic tube. Urethral drainage with a Foley or intermittent catheterization can induce more prostatic manipulation, be uncomfortable or painful to the patient, and become infected. The standard recommendation for patients with poor bladder emptying is to use a suprapubic tube to avoid further irritation and manipulation of a swollen and infected prostate. 

About 80% of patients will ultimately require early surgical drainage based on their overall condition or the size of the abscess.[7] Different approaches have been described for ultrasound-guided abscess drainage, namely transrectal drainage, transurethral unroofing, resection, or aspiration, and transperineal evacuation of the abscess. Each approach has its advantages and disadvantages. After a single aspiration, the reported recurrence rate ranges from 15 to 33%.[7] About one-third of patients will eventually require transurethral prostate resection.[7]

In the past, transurethral drainage (unroofing or resection) was the most commonly selected therapy due to its reduced length of hospital stay. It is also the procedure of choice for larger abscesses and in those cases where aspiration alone has been inadequate. However, some experts are concerned about possible complications such as post-operative voiding dysfunction. Transurethral resection can also overlook or miss small prostatic abscesses.[30][34] Transurethral drainage of a prostatic abscess can be accomplished using a holmium laser. This has the advantage of minimizing manipulation of the infected tissue and can safely be used in anti-coagulated patients as well as those with untreated coagulopathies.[36][37] Another approach that has been used successfully involves endoscopic transrectal ultrasound-guided drainage, which may be appropriate for selected individuals, especially when the abscess is larger and close to the rectum. For some reason, a transurethral procedure cannot be done or is otherwise inadvisable.[38](B2)

As the abscess is not always visible cystoscopically, clinicians should be prepared to perform an extensive transurethral resection.[39] Transient bacteremia is not uncommon after transurethral prostate resection, but limited unroofing rarely progresses to septicemia.[16] Massage of the prostate after transurethral unroofing to more completely clean out and drain the abscess cavity has been recommended by some, but this entails significant additional manipulation of an infected organ with the potential for disseminating the infection. Therefore, this should only be done after carefully considering the benefits and potential risks.

Currently, transrectal drainage with transrectal ultrasound guidance is the first choice approach, especially for smaller abscesses less than 2 cm in diameter, because it is done using only local anesthesia, has a low risk of complications, and is easily repeatable if necessary.[40] An 18 gauge or larger bore needle should be used as abscess contents can be particularly thick and heavy, making aspiration difficult with smaller instruments. A specimen should be sent for culture even if previous cultures were performed. Irrigation through the needle may also be needed to lower the viscosity of the purulent material and permit aspiration. Aspiration and irrigation should be repeated and continued until clear, if possible. While a single aspiration is usually sufficient for most cases, a repeat procedure should be considered if the patient fails to improve, and imaging suggests another treatment would be helpful. If there is a lack of improvement after two aspirations, consideration should be given to an alternate drainage procedure, usually a transurethral resection or unroofing.(B3)

The transcutaneous perineal route of aspiration is also an option at times, and CT guidance can be used. MRI-transrectal ultrasound fusion-guided aspiration is also possible utilizing the same technology currently used for targeted prostatic biopsies. Transurethral resection is recommended for larger abscesses and patients who have failed transrectal ultrasound-guided aspirations. Open surgical drainage may be necessary if the abscess has spread to deeper tissue, such as the levator ani muscle, but should be avoided whenever possible due to prolonged wound healing, possible fistula formation, and the potential development of superinfections.[9][41](B2)

Differential Diagnosis

The common conditions which could present with similar presentations are urethritis, urinary tract infection, and acute or chronic bacterial prostatitis. A prostate abscess should be strongly suspected if there is a palpable fluctuant mass. Other differential diagnoses are benign prostatic hyperplasia perirectal and perineal abscess, which could mimic a prostatic abscess by being painful and causing local swelling.

Prognosis

The prognosis of patients with a prostate abscess mainly depends on a timely diagnosis and proper treatment as well as their prior general health and comorbidities. Early recognition of this disorder with timely and appropriate treatment modalities dramatically improves the prognosis. Conservatively treated patients may avoid a surgical procedure but will typically need a longer duration of antibiotic therapy. Regardless of interventions, the treatment period with antibiotics is longer in prostatic abscess cases than in similar acute bacterial prostatitis patients without such abscesses.[3] The prognosis also depends on the underlying medical conditions contributing to abscess development.

Poor prognostic factors include age above 65 years, presenting temperatures higher than 100.4 F (38 C), history of urinary retention or symptomatic benign prostatic hyperplasia, chronic Foley catheterization, uncontrolled or poorly controlled diabetes, HIV/AIDS, debilitated general health status, and renal failure. It is a potentially lethal condition if not promptly diagnosed and properly treated in a timely fashion. 

Complications

Any delay in the prompt diagnosis and timely treatment of a prostatic abscess can lead to severe complications with significant morbidity and mortality. The infection can spread locally to adjacent perineal areas, which could necessitate more invasive interventions with long-term complications involving genitourinary functions. Bacteremia and sepsis subsequently causing septic shock and multi-organ failure can occur in severe cases, increasing mortality.[20] Emphysematous prostatitis, which manifests as having gas within the abscess cavity, is particularly virulent and carries a high mortality.[22]