Gas in the pelvicalyceal system (pyelitis) and/or gas in the renal parenchyma (emphysematous pyelonephritis-EPN) is a relatively common finding. However, gas trapped inside a stone (we propose a new term pneumourolithiasis to describe this condition) is exceedingly rare and was reported for the first time in 1998 [1]. Renal or ureteric stones containing gas are rare with 14 cases reported so far in our literature review. We report the first case of ureteric stone containing gas along with a literature review and discuss its pathogenesis, implications of these findings.

A fifty-six-year-old diabetic male presented with abdominal distention, fever, and reduced urine output. On evaluation, he had generalized abdominal distention, along with high creatinine of 5.2 mg/dL, neutrophilic leucocytosis of 30,000/dL and pyuria. Non-contrast CT scan showed bilateral perinephric stranding (but no gas in the pelvicalyceal system or renal parenchyma), a small right kidney and a stone in the right ureter containing air within it (Figure 1). He required meropenem (for pyelonephritis) along with bilateral double J (DJ) stenting, after which sepsis settled, counts normalized and abdominal distention reduced. Intraoperative finding of turbid urine efflux from both ureteric orifices was noted during cystoscopy at the time of DJ stenting. The urine culture of this turbid urine showed E. coli sensitive to meropenem which was continued for 14 days. He settled clinically with antibiotics and DJ stenting but nadir creatinine remained at 3.8 mg/dL after 2 weeks. At that time, a functional study with a renal scan showed a right renal split function of 12%. He underwent a right ureteroscopy with stone fragmentation along with left DJ stent removal. During fragmentation, once the stone was fragmented with a holmium laser, the inner hollow part of the stone was exposed (Figure 2, Figure 3). The stone was rather soft easily breakable only with jaws of the ureteroscopic grasper. Stone analysis showed predominant calcium oxalate monohydrate stone (Figure 4). Stone culture corresponded to the urine culture. He had an uneventful recovery and the stent was removed after 2 weeks. Creatinine however remained 3.3 mg/dL after a period of 2 months of follow-up and urine culture became negative.

Gas in the kidney (without any prior instrumentation or communication to the bowel) occurs due to gas-producing infection in the kidney (emphysematous pyelonephritis). A cumulative 14 cases of pneumourolithasis so far are reported including a series of 5 cases in the last 15 years, which are summarised in Table 1 [1] - [10]. Current case is the first case of ureteric stone containing gas to be best of our knowledge. (Rapport has mentioned ureteric stones containing gas in the abstract, but in the full-text article review, the stones in the kidney were containing gas, not ureteric stones)

In presence of obstruction by stone and emphysematous pyelitis, gas formed will not be cleared quickly and will be incorporated inside the stone as it is being formed. Pneumourolithiasis without emphysematous infection of the kidney can also be explained by the bacteria within the stone producing gas, as gas is not seen in the rest of the renal pelvicalyceal system in the imaging in the cases reported. Looking at the cases cited in Table 1, we are of the opinion that if the stones are of matrix composition, then both these theories may be implicated in the formation of gas within the stone. But in the case, the stone is made up of

calcium oxalate, as in our case, the possibility of the bacteria forming the gas within the stone is more likely. As in our case, E. coli is the most common infection which ferments sugar, but Klebsiella is not uncommon. Importantly urine culture does not always correlate to stone culture in the majority of cases in the review of earlier cases [5] [6]. Diabetes is the most common risk factor for infection (EPN) as high sugars will aid in the formation of sugars. Other factors reported in addition to sarcoidosis, hyperparathyroidism and gout.

Radiologically, it may be possible to see gas within the stone on a plain Xray [2]. But it is best seen in CT scans and characteristically, these stones tend to float in the renal pelvis, which can be appreciated in a CT scan done in the supine and prone position [2].

These stones are soft stones due to infection playing a role in playing its formation [5]. Stone analysis in earlier cases shows those stones to be hydroxyapatite, matrix and uric acid stones. Again calcium oxalate monohydrate in the analysis in our case is less commonly reported. As compared to a standard calcium oxalate stone, we feel the stone was softer (very easily breakable with only a ureteroscopic grasper after initial breakage with a laser). This may be due to gas being present in the scaffolding of the stone [5].

Clinically, the detection of pneumourolithasis has many implications. Even in absence of emphysematous infection in the kidney, aggressive treatment should be initiated as mortality in pneumourolithiasis without EPN is reported [6]. Stone culture should be sent routinely in such cases, as they do not always respond to urine culture [5]. Stone culture may be a better guide to antibiotic selection for any possible postoperative urosepsis [5]. Since the stones are soft, endourologic treatment options may be preferred to options like pyelolithotomy as there will be a high chance that stone may break down into fragments during removal and intact removal will be difficult [5].

Gas-containing stones are very rare and we report the first case of ureteric stone containing gas. It occurs due to gas-producing bacterial infection within the stone or the gas being incorporated into the stone during the emphysematous infection. Most commonly, these stones are found in diabetic patients. Finding gas within stone should prompt us to start aggressive antibiotic therapy guided by the stone culture which may be different from urine culture. Surgical therapy, initially DJ stenting and later definitive stone removal should consider the softness of the stones in decision making. Probably, endourologic options may be better than options like pyelolithotomy.

Permissions were taken from the patients prior to the publication of case report.

The authors declare no conflicts of interest regarding the publication of this paper.

Valsangkar, R., Jog, S., Date, J. and Shivde, S. (2022) Ureteric Stone Containing Gas: First Case Report with Review of Cases of Urolithiasis with Gas within the Stone and Its Clinical Implications. Open Journal of Urology, 12, 203-208. https://doi.org/10.4236/oju.2022.124020