Multiple Gas-Containing Renal Stones: A Case Report

Introduction

Gas formation within the renal system can occur secondary to several causes, including recent instrumentation or infection. When caused by infection, this is a serious condition that is often associated with renal calculi. However, the radiographic finding of gas within the renal calculus itself is a much rarer phenomenon, with only about 12 cases being described [1]. The presence of a gas-containing stone can occur alongside a gas-forming infection, which can be life threatening [2].

The most common predisposing factors associated with the formation of gas-containing renal stones in the setting of infection have been reported to be female sex and comorbid medical conditions such as diabetes mellitus, gout, hyperparathyroidism, and sarcoidosis [3,4]. In addition, most patients have experienced prior stone events [3]. The presentation of patients with this finding varies from signs of sepsis to isolated flank pain [1–5]. While the finding of a single gas-containing renal calculus is rare, we present a case of a 63-year-old woman who was found to have multiple gas-containing calculi and developed subsequent sepsis following antibiotic treatment and lithotripsy.

Case Report

A 63-year-old White woman presented to the urology clinic for cystoscopy. Her medical history was significant for diabetes mellitus with a glycated hemoglobin (HbA1C) of 8.0%, hypertension, obesity, and Grave’s disease (status-post radioactive iodine therapy). Her home medications included Bactrim (sulfamethoxazole and trimethoprim) for a urinary tract infection (UTI), fexofenadine, glimepiride, Canagliflozin, losartan, and levothyroxine. Her family history was significant for a brother with nephrolithiasis.

She had been following with the urology service for a history of right-sided partial ureteral obstruction at the ureteropelvic junction and prior episodes of obstructive nephrolithiasis and urolithiasis. Since her last visit, she had a new episode of hematuria and underwent computed tomography (CT) prior to her appointment, which revealed multiple stones in the right renal pelvis with fully encapsulated central air. The largest was 2.5×0.9×2.6 cm. The ureteropelvic junction was also noted to be strictured with a tortuous proximal ureter, which was likely congenital, but worsened due to recurrent nephrolithiasis, causing obstruction and urinary stasis (Figure 1). Her most recent prior CT scan was performed 2 years prior and revealed persistent right-sided hydronephrosis, renal parenchymal scarring, and a small right renal calculus. However, no gas was present in this prior scan. Given this new finding of gas within renal stones, she was advised to continue her antibiotic treatment and undergo surgical intervention. A urine culture and antibiogram were not obtained prior to intervention.

She subsequently underwent laser lithotripsy with ureteral stent placement 1 week later. Intraoperatively, the stones were noted to be calcified externally with a mucoid consistency internally. Cultures of the calculi were sent following the procedure and showed heavy growth of Proteus mirabilis. Two days following lithotripsy, she presented to the Emergency Department with sepsis secondary to a urinary tract infection. At the time of presentation, she stated that she “just did not feel well.” She was afebrile at presentation, with a temperature of 36.8°C. Her white blood cell count in the Emergency Department was 13.4 cells/µL. Other infectious diseases lab tests (C-reactive protein, erythrocyte sedimentation rate, interlukein-6) were not performed. A postoperative CT scan was performed and the gas-containing renal stones were no longer visualized (Figure 2). Cefepime was begun for empiric coverage. She remained afebrile during her admission and was discharged on ciprofloxacin 2 days later. Cefepime was initiated prior to blood and urine cultures being drawn, which subsequently did not reveal any growth. However, it is suspected the sepsis was endotoxin-mediated from Proteus mirabilis given her recent lithotripsy of P. mirabilis-laden renal stones 2 days prior.

Discussion

The literature focuses on the radiographic findings of air within the renal collecting system (emphysematous pyelitis) or parenchyma (emphysematous pyelonephritis), but few reports exist regarding the radiographic findings of gas within a renal calculus. Emphysematous pyelitis will be limited to air within the pelvicalyceal system, while emphysematous pyelonephritis, a much more serious condition, will demonstrate gas within the renal parenchyma, collecting system, and perinephric tissues [6]. In this case, we demonstrate intra-calculus gas, which appeared as central air encapsulated by the stone and its potential complications.

The pathophysiology underlying gas-containing renal stones is multifactorial but is often related to a combination of infectious and metabolic etiologies. In general, females are more likely to experience a urinary tract infection than males due to their shorter urethra. In the United States, over 60% of women will have a UTI at least once in their lifetime [7]. Our patient was female and also had ureteropelvic junction stenosis on her CT scan, likely causing urinary stasis, a predisposing cause of urinary tract infections. Her ureteropelvic junction stenosis developed over years of recurrent stone disease.

Our patient was diabetic with a HbA1C of 8.0%. Diabetes mellitus with poor glycemic control has been found to be a host factor strongly associated with emphysematous pyelonephritis [8]. Multiple pathways for this association have been proposed, such as higher glucose concentrations within the urine or renal parenchyma, immune system impairment, or dysfunctional voiding and urinary retention [9], all of which would create a favorable environment for bacteria to form.

Gas-producing bacteria form carbon dioxide, nitrogen, and hydrogen by metabolism of glucose [10]. In most cases, Escherichia coli or Klebsiella pneumoniae are the most common gas-producing microbes identified in urinary tract infections. Other causative agents include Proteus mirabilis, Streptococcus, and Staphylococcus [3]. In our case, Proteus mirabilis was isolated from intraoperative cultures taken during lithotripsy. Proteus mirabilis produces renal stones through its ability to catalyze urea, which results in the alkalinization of urine [11].

Another factor is the role of pharmacologic agents in the development of urinary tract infections and renal stones. Our patient was taking Canagliflozin for her diabetes, which inhibits renal glucose reabsorption, thus increasing glucosuria and predisposing to urinary tract infections [12]. Other medications, such as loop diuretics, carbonic anhydrase inhibitors, or certain antibiotics such as ciprofloxacin, can also predispose to renal stones [13].

Given the severity of emphysematous renal infections, management includes broad-spectrum antibiotics followed by drainage if an obstruction is present and then definitive stone removal at a later time [3]. Antibiotics include a carbapenem or cephalosporin plus vancomycin, and then narrower coverage once culture results are obtained. Proceeding directly to stone removal is an option if the patient does not exhibit signs of sepsis [3]. At the time of presentation, our patient appeared clinically stable and we proceeded directly to lithotripsy and stent placement. Unfortunately, she re-presented with sepsis 2 days following the procedure.

While lithotripsy has proven to be an effective method of treating urinary stones, urosepsis is a potential complication [14]. When bacteria are inactivated during lithotripsy, they release many lipopolysaccharides and endotoxins, which can cause an inflammatory response and septicemia [15,16]. Although antibiotics are unable to penetrate infected renal stones [17], they are recommended prophylactically along with percutaneous drainage first to avoid this complication [16]. In our patient, it is likely Proteus mirabilis persisting within the stone was released into the bloodstream during lithotripsy, resulting in endotoxin-mediated sepsis. While our patient was already on Bactrim, this complication may have been avoided if her coverage had been broadened prior to lithotripsy or if she underwent percutaneous drainage and avoided lithotripsy.

Conclusions

Emphysematous renal infections are multifactorial conditions requiring urgent attention and are often associated with renal stones. They rarely present with the radiologic finding of gas-containing renal stones. These stones are differentiated from typical nephrolithiasis by an area of encapsulated air within the calculus. Proper management includes broad-spectrum antibiotics (carbapenem plus vancomycin if obstruction is present) and drainage. Lithotripsy should be avoided in the setting of gas-containing renal or ureteral stones to avoid endotoxin-mediated sepsis.