Written by: Nathaniel Greenwood, DO, FACEP
Medical Director Cedar Park Emergency Center
Chief Medical Officer of Family Emergency Rooms
It’s a Saturday morning in your local FSED. The volume is starting to pick up when a 27 year old female presents with two weeks of nausea. She also complains of malaise, subjective fever, mild cough, and difficulty getting a full breath, some left flank pain and cold intolerance. She denies abdominal pain, diarrhea, vomiting, headache or rash.
Two weeks prior she had a left ureteral stent placed due to a renal stone that was thought to be causing the patient to have frequent UTIs. She otherwise does not have any other medical/ surgical history.
She followed up with her urologist 1 week after the procedure and had the stent removed. She relayed her symptoms to her urologist and was told that it was likely due to residual UTI. She was given one dose of an unknown antibiotic in the office. Today the patient is quite tearful thinking that something is really wrong and no one is listening to her.
She is noted to have a T of 38.0 C° (took Advil one hour ago) and a HR of 103. The rest of her vitals are normal. On exam she is noted to have mild left CVA tenderness to percussion as well as tachycardia. The rest of her exam is normal. At this point there is not an obvious source for her low-grade fever and overall feeling of being sick.
An IV is placed and a work-up is begun. You decide to get a CBC, CMP, Blood Culture, UA, Urine Pregnancy, Influenza A and B swab as well as a CXR to look for occult pneumonia. The patient is given ondansetron for her nausea, acetaminophen for her low-grade fever and one liter of NS secondary to her poor PO intake recently.
As the labs quickly come back she is noted to have an elevated WBC count of 11.8 with a left shift and small leukocyte esterase in her urine. Other than that, the rest of her labs are unremarkable (Blood Cx is pending). The CXR showed normal, aerated lungs without any infiltrate.
At this point the patient is told that the source of her infection has not been found. You recommend to her that a 64-slice helical CT would need to be done of her abdomen and pelvis to evaluate for the possibility of a complication related to her recent urologic procedure. The patient is agreeable to this plan. When you see the CT, you’re a little bit surprised, but you were thinking this might be the issue all along.
CT of a large 8.5 x 6.5 cm subscapular left renal abscess with flattening of the left kidney.
There is also extensive left perinephric fat stranding suggestive of inflammatory or infectious process.
Typically is the result of a urologic infection (usually due to gram-negative enteric bacilli or a polymicrobial infection) or occur secondary to hematogenous seeding (mostly due to Staphylococcus aureus).
Risk factors include diabetes mellitus, pregnancy, and urinary tract abnormalities. Anatomical abnormalities that can be complicated by infection include a renal stone (especially large staghorn calculi), vesicoureteral reflux, neurogenic bladder, obstructive tumor, papillary necrosis, benign cyst, and polycystic kidney disease.
Renal abscesses are characterized by the insidious onset of fever, vague lumbo-abdominal pain, pallor, fatigue, sweats, and general signs and symptoms of deep-seated suppuration such as weight loss. Symptoms that are typical of a UTI, such as dysuria and/or urinary frequency, are not usually reported by patients with a renal abscess.
A Korean study1 of 56 hospitalized patients with renal abscess showed that the most common symptoms were fever and chills (noted in 75% and 63% patients respectively). Other symptoms were abdominal pain, anorexia and dysuria (46%, 38% and 9%).
In the same study, it was determined that CVA tenderness is the most common physical exam finding (75%).
Laboratory findings typically show a leukocytosis, as well as elevated inflammatory markers, such as ESR and CRP. Urine abnormalities depend upon whether or not the abscess communicates with the collecting system. If it does communicate you will typically see significant pyuria, moderate proteinuria and bacteriuria. If there is not a communication the patient may have sterile urine2. Blood cultures may grow a causative organism if the abscess is the result of hematogenous seeding.
The preferred imaging modality is contrast enhanced CT, which allows for evaluation of renal vs. perinephric abscess, as well as evaluation for extension of perinephric suppuration to adjacent structures, including liver, diaphragm and mediastinum. Ultrasound can be helpful but can be limited by inability to discern pus from blood or urine, as well as echoes from renal tissue debris. On rare occasion, with plain radiography, you may see scoliosis with the concavity toward the lesion, an abdominal mass, an enlarged kidney with indistinct outlines, a loss of psoas margin, a radio-opaque calculus and/or a poorly defined renal shadow. Chest x-ray may show pleural effusion, ipsilateral pneumonia, atelectasis and/or an elevated hemidiaphragm.
Management of a renal abscess includes empiric antibiotic therapy and percutaneous drainage. Antibiotic choice is based on the likely source of the abscess (pyelonephritis vs bacteremia). For pyelonephritis the antibiotic should target Enterobacteriaceae. In the case of bacteremia, the most common pathogen is staphylococcal. In the case of a perinephric abscess, when a causative organism is not clear, empiric antibiotic therapy may be delayed if the abscess can be promptly drained and evaluated for organisms. Antibiotics are typically given for 2-3 weeks. (See Table 1 for antibiotic recommendations)
Percutaneous drainage is preferred in abscesses >5 cm and is typically done by IR. The drain is left in place until the discharge is minimal (up to 1 week). Urologic intervention may be warranted for abscesses in which there are anatomic abnormalities or are too large in size, making antibiotics and catheter drainage alone ineffective.
The patient is relieved to finally have an answer as to why she was feeling so poorly the last couple of weeks. You start the patient on empiric antibiotic therapy of piperacillin-tazobactam and vancomycin. After a little over 2 hours from the time the patient walked through the front door you are on the phone with her urologist who is more than happy to admit. Once the patient is transferred she has a percutaneous drain placed with large drainage. Her blood cultures are negative. She is discharged home four days later with oral Ciprofloxacin based on sensitivity. Three days after that her urologist removes the drain. One week after that, the patient calls you up to tell you that she is feeling much better. She tells you that she had such a great experience at your FSED that she wants you to be her primary care doctor. You tell her that unfortunately you cannot do that, but you are more than happy to take care of her, as well as her family and friends anytime they have an emergency. You hang up the phone and go back to your awesome life as a free-standing emergency physician.
1 Recent clinical overview of renal and perirenal abscesses in 56 consecutive cases. Lee BE, Seol HY, Kim TK, Seong EY, Song SH, Lee DW, Lee SB, Kwak IS. Korean J Intern Med. 2008 Sep;23(3):140-8.
2 Hill GS. Renal infection. In: Uropathology, 1st Ed, Hill GS (Ed), Churchill Livingstone, New York 1989; 33.