An Atypical Presentation of a Patient with Renal Abscess

Renal and perirenal abscesses are two uncommon diagnoses that carry the potential for significant mortality, but those entities often present with vague and nonspecific symptoms as demonstrated with our patient. In earlier decades, case fatality rates for these conditions were as high as 39-50% [1]. More recent studies have shown mortality rates ranging from 0-7% [2]. Incidence is presently estimated at 1-10 per 10,000 admissions, and increases with predisposing conditions such as diabetes mellitus, obstructing stones, and other urinary tract abnormalities [3]. The most common risk factor for both conditions has consistently been shown to be diabetes mellitus [2,4].


Introduction
Renal and perirenal abscesses are two uncommon diagnoses that carry the potential for significant mortality, but those entities often present with vague and nonspecific symptoms as demonstrated with our patient. In earlier decades, case fatality rates for these conditions were as high as 39-50% [1]. More recent studies have shown mortality rates ranging from 0-7% [2].
Incidence is presently estimated at 1-10 per 10,000 admissions, and increases with predisposing conditions such as diabetes mellitus, obstructing stones, and other urinary tract abnormalities [3]. The most common risk factor for both conditions has consistently been shown to be diabetes mellitus [2,4].
The pathophysiology of renal and perirenal abscesses involves ascending infection of the urinary tract, largely by gram-negative bacilli, which is the likely cause for our patient. The alternative is hematogenous spread from distal sites of infection, the majority of which is caused by staphylococcal species. Renal abscesses are confined to the cortex or medulla of the kidneys, whereas perirenal abscesses involve infection that has spread to the space between the renal capsule and Gerota's fascia. 10% of renal cortical abscesses will lead to perinephric abscesses [4], and many patients present with mixed renal and perirenal disease. As compared to perirenal abscesses, renal abscesses were more likely to be caused by enteric gram-negative bacteria, specifically E. coli and K. pneumonia [2] as was seen with our patient.
Multiple studies have demonstrated that the most common presenting complaints include fever, chills, and flank pain or tenderness [5], but only a minority will have the typical indication of a urinary tract infection with dysuria [2]. However, given that ascending infections are the typical source, a history of symptoms may be key to diagnosis. The average duration of fever in these patients is 10-14 days [2,5] which indicates a deeper infection. Lab work commonly reveals leukocytosis with left shift [2]. Predictors of poor prognosis include increased age, lethargy as a presenting complaint and impaired kidney function, as evidenced by elevated BUN [5].
Examination revealed a comfortable appearing 86-year-old female who was fully alert and oriented and able to provide an extensive history. Vital signs showed temperature of 37.6C, heart rate of 80bpm, respiratory rate of 20rpm, blood pressure of 136/61, and oxygen saturation of 95% on room air. Patient had dry oral mucosa with poor skin turgor. Auscultation revealed an irregularly irregular heart rhythm and vesicular lung sounds bilaterally.
Abdomen was soft and nontender with normoactive bowel sounds and mild left costovertebral angle tenderness. She had no focal motor or sensory deficits.
Our initial impression of this patient was a non-toxic but

Management and Outcome
Patient was initially started on IV fluids for dehydration upon arrival in the ED. Given her vital signs, suspicion for sepsis was low so antibiotics were held until a cause of her symptoms became apparent. Once imaging was available showing the source of infection, the patient was started on piperacillin with tazobactam.
Urology was consulted and recommended that the patient be admitted for drainage of the abscess by interventional radiology with continuation of her prescribed antibiotic regimen.
Our patient was admitted to the hospital for 3 days.
Interventional radiology was able to aspirate 17mL of purulent She was discharged with a 3-week course of ceftriaxone 2g daily and plan for a repeat CT abdomen at 3 weeks. Follow-up CT showed improvement of the abscess. Radiology described the findings as "Significant interval decrease in size of a bilobed left lower pole thick-walled cystic lesion measuring up to 1.6cm transverse, previously 3 cm. Adjacent perirenal fat stranding is also significantly decreased from previous exam" (Figure 2).

Conclusion
It is important to have a high index of clinical suspicion for renal and perirenal abscesses in the emergency department, as early diagnosis and antibiotic therapy have led to significant decreases in their associated morbidity and mortality. A review of the literature indicates that aggressive early imaging with ultrasound or CT has been a major contributor for improved clinical outcomes. In this case, the patient appeared well with largely normal vital signs, though her history of diabetes mellitus and recent recurrent urinary tract infections lowered our threshold to obtain abdominal imaging. Thus, we were able to diagnosis and treat her abscess before more significant complications arose.