EPN is a life-threatening and acute severe necrotizing infection, involving the renal parenchyma, collecting system, and/or perinephric tissue by gas-producing uropathogens. E. coli has been isolated from pus or urine cultures in approximately 75% of EPN cases, and other pathogens, such as Klebsiella and Proteus, have also been reported [1]. Its risk factors include DM (up to 95% of patients), female gender, reduced host immunity, chronic urinary tract infections, and genitourinary obstruction [1, 2]. Mortality in EPN has been attributed to patients with disturbed consciousness, thrombocytopenia, and septic complications [1, 3].

Abdominal CT is currently the preferred radiographic modality for diagnosing EPN and staging its severity, which is correlated with its management [4]. EPN is classified into four classes: Class 1 indicates gas confined to the collecting system; Class 2 indicates gas confined to the renal parenchyma without extension to extrarenal space; Class 3A indicates extension of gas or abscess to perinephric space-as in our patient; Class 3B pertains to extension of the gas or abscess to the pararenal space; and Class 4 refers to bilateral EPN or a solitary kidney with EPN [5]. According to this classification, our patient was had Class 3B EPN.

Venous gas is a rare complication of EPN and, to our knowledge, there have been only 15 previously reported cases of EPN with venous gas (Table 1) [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]. Of these cases, 13 (87%) of patients were diabetic, and 12 (80%) were female. E. coli were the most common bacteria identified (11/15, 73%). The portal vein (7/15, 47%) and the inferior vena cava (5/15, 33%) were the most common blood vessels involved. To our knowledge, there have been no previous reports of EPN with venous gas in the uterine vein. Thrombosis is another rare complication of EPN. According to our knowledge, there have been only three previously reported cases of EPN with venous thrombosis (Table 1) [21,22,23]. All three cases were female, and unlike venous gas, the renal veins were the most common blood vessels involved by EPN with venous thrombosis.

However, the precise mechanisms of venous air bubble formation in EPN have not been determined. Sebastià et al. [24] proposed three possible mechanisms for the pathogenesis of portomesenteric vein gas associated with infectious abdominal disease: (1) sepsis in the mesentery and portal vein branches; (2) increased intracavitary fermentation of carbohydrates caused by bacteria; and (3) perforation of a mesenteric abscess in the mesenteric lumen, which separates between the peritoneal lobules of the mesenteric membrane to enter the mesenteric vein. It was previously reported that infected bubbles enter the bloodstream and can form seeds in various organs, leading to the spread of infection [12]. In this patient, we speculate that the uterine vein gas was caused by sepsis in the uterine vein, because she had septic shock and a high blood sugar level on admission. The high plasma glucose level serves as a favorable environment for Enterobacteriaceae’s mixed acid fermentation to produce gas, the main components of which are carbon dioxide and hydrogen. The precise mechanisms of venous thrombosis in EPN have also not been determined. Similar to Jignesh et al., we speculate that it was likely provoked by an infectious, and therefore hypercoagulable state [21].

Of 15 patients with venous gas, 5 were treated with nephrectomy, 5 underwent PCD, 3 were treated with antibiotics and general management alone, and 1 patient underwent exploratory operation. Two patients died. One patient, with air in the renal vein and septic emboli in the lungs, died of cardiac arrest within hours of admission. One died because of cardiovascular collapse resulted from septic shock, endogenous air emboli, or a combination of both. Of 3 cases with thrombosis in EPN, one was treated with nephrectomy, one underwent PCD, and one was treated with antibiotics and general management alone. All three patients achieved an improved clinical outcome. However, the incidence of venous gas and thrombosis in patients with EPN may be underestimated, especially in patients with poor prognosis, because venous gas and thrombosis may be overlooked on radiological images of EPN, especially in patients without enhanced abdominal CT.

In Class 3 EPN (based on the Huang and Tseng classification) [5], basic resuscitation and PCD should be performed in conjunction with good glycemic control. Nephrectomy or open drainage should be performed if there is no response to these measures [1]. The clinical presentation in our patient was typical: a diabetic with inadequate glycemic control, vomiting, and disturbance of consciousness. The clinical evolution and CT (Stage 3) led us to perform PCD. The PCD treatment was ineffective, and the EPN was successfully treated by open drainage.

A high degree of clinical suspicion, immediate CT scan, and corresponding medical or surgical treatment, are the basis for successful EPN management. At higher stages (3/4), PCD should be performed as soon as possible, and nephrectomy or open surgery should not be delayed if the PCD is ineffective [3].

In conclusion, EPN requires urgent attention as complications of sepsis can be life-threatening. Venous air bubbles are a rare but potentially fatal complication of EPN, requiring early diagnosis and treatment. Awareness of this disease may lead to early CT scan for diagnosis and staging of disease severity, and may prompt physicians to implement effective antibiotic therapy, PCD or operation to achieve good clinical outcomes.