Showering gas bubbles within the inferior vena cava detected sonographically can unmask a hidden infection: a case report of a rare presentation in a patient with emphysematous cystitis

Abstract

We present a case of incidentally discovered gas bubbles flowing within the inferior vena cava during a routine abdominal sonographic examination, that subsequently unmasked a previously undiagnosed emphysematous cystitis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40477-022-00673-4.

Introduction

Radiologists are usually aware of the imaging appearance of portal venous gas on both computed tomography (CT) and ultrasound (US), as well as a long list of potential causes. However, sonographic detection of flowing gas within the systemic circulation is an extremely rare phenomenon that many radiologists might not have seen during their career. We present a case of incidentally discovered gas bubbles flowing within the inferior vena cava (IVC) during a routine abdominal sonographic examination that subsequently unmasked a previously undiagnosed emphysematous cystitis.

Case report

A 47-year-old woman with a 5-year history of diabetes mellitus and a 1-year history of hypertension presented to our hospital for elective phacoemulsification eye surgery for cataract. Pre-procedural laboratory results demonstrated abnormal readings of the kidney function test (KFT), particularly the sodium level, which was low at the time of presentation (123 mmol/L). The potassium level was slightly high (5.47 mmol/L), along with urea and creatinine levels (8.5 mmol/L and 104 mmol/L, respectively). The ophthalmologic procedure was postponed, and the patient was referred to a nephrologist for further management. Shortly after this discovery, the patient complained of vague abdominal discomfort, with a few episodes of nausea and vomiting, for which repeated KFT and routine abdominal sonographic examination were ordered. The new KFT revealed a further decrease in sodium level (115 mmol/L), while the US showed flowing echogenic particles within the IVC (Fig. 1, Supplementary file 1). We did not have a reasonable explanation for this imaging appearance at that time based on the available clinical data; hence, an enhanced triphasic CT was performed for further clarification. No similar findings were observed within the IVC on the CT scan, or in any other major venous tributary. However, this led to an unexpected diagnosis of emphysematous cystitis (Fig. 2). Having known the diagnosis aided by the CT scan, we concluded that the flowing echogenic particles observed on the US represented gas bubbles. The CT scan also showed a few extraluminal gas bubbles in the peri-vesical region (Fig. 3), which we presumed to represent the venous access of the showering gas observed on the US through the peri-vesical venous plexus. Repeated US on the same day showed echogenic walls of the urinary bladder (Fig. 4). Subsequently, urine culture was performed and was positive for Escherichia coli, while blood culture was negative. The patient was placed on antibiotic treatment for 10 days (ertapenem), and she was discharged uneventfully.

Fig. 1.

Numerous echogenic particles are observed flowing within the IVC during US exam. IVC inferior vena cava, US ultrasound

Fig. 2.

Multiple gas bubbles are observed throughout the walls of the urinary bladder on CT. CT computed tomography

Fig. 3.

A few extra-luminal gas bubbles that are thought to be within the peri-vesical venous plexus

Fig. 4.

Echogenic walls of the urinary bladder on US. US ultrasound

Interestingly, this patient had a vague abdominal illness 2–3 months before the current presentation, in which she documented fatigue, nausea, and vomiting, and was partially treated with antibiotics for a presumed diagnosis of urinary tract infection. She stated that her current presentation was similar to that of her previous presentation.

Discussion

Flowing echogenic particles within blood vessels detected on US are usually caused by air bubbles. While the use of contrast-enhanced US is gaining more popularity worldwide, radiologists are becoming more familiar with the sonographic appearance of intravenous microbubbles used for this purpose. Furthermore, tiny microbubbles can be observed on US after intravenous injections and were used with echocardiography to detect cardiac shunts [1]. Moreover, some authors have reported cases of continuous air embolism in the IVC in patients receiving positive end-expiratory pressure ventilation which subsided at the end of the illness [2]. However, these clinical scenarios are usually obvious to radiologists when enough clinical data are available, and rarely cause a diagnostic dilemma. These potential causes were excluded from our case. While La Pietra et al. [3] stated that 23% of patients undergoing enhanced CT examinations can have small amounts of air discovered in their venous system, to the best of our knowledge, no such percentage has been established regarding US.

A few case reports have been published describing the sonographic appearance of gas flowing within the systemic circulation. In two of these reported cases, to our knowledge, this incidental discovery led to subsequently unmask a hidden infection [4, 5], one of which was lethal despite appropriate medical and surgical treatments [4]. In another case, septicaemia caused by a gas-forming infection was suggested as a cause for the sonographic appearance [1], although this was not documented pathologically, and the patient died in the hospital without permission for autopsy being granted. Winter et al. [4] presented an interesting case of necrotising soft tissue infection in the left proximal thigh that was unnoticed during the clinical examination; however, it was subsequently detected after performing an abdominal US followed by a CT scan. The sonographic appearance, in their case, is the same as that in our case. However, their patient died a few days after the initial diagnosis of a deadly infection, while our patient survived emphysematous cystitis after antibiotic therapy.

The nature of the gas was theorised by McCabe et al. [6] to be carbon dioxide resulting from bacterial fermentation of glucose. The increase in intravesical pressure and/or bacterial injury of the bladder wall may have contributed to the translocation of gas into the venous system [5]. Organisms most commonly responsible for gas formation in cases of emphysematous cystitis are Escherichia coli and Enterobacter sp., and less commonly, Proteus, Klebsiella, and Streptococci [6]. However, whatever organism caused the gas-forming infection, presence of venous gas per se does not seem to reflect the severity of infection, and air embolisms have not been reported to date [7].

While some case reports only showed a gas bubble within the femoral vein and/or the IVC on CT scan [1, 6, 8], other cases, including ours, did not show any but on US. The reason for this is not fully understood, but we postulate that gas bubbles within a rapidly flowing systemic circulation would be difficult to detect on a CT scan, especially in cases of infection where the systemic circulation would be hyperactive. Conversely, in cases where portal venous gas is present, the blood flow is slower and gas bubbles would be “stuck” in hepatic sinusoids, making them more likely to be detectable by CT.

In conclusion, sonographic detection of flowing gas bubbles within the IVC should prompt a search for a hidden downstream infective process, and radiologists should be familiar with this rare, yet important, and potentially lifesaving imaging phenomenon, to avoid missing a serious hidden pathology.

Supplementary Information

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Declarations

Funding

This article was not funded by the authors’ institution or any other institution.

Conflict of interest

The authors declare the absence of any conflict of interest.

Consent to participate

Informed consent was obtained from the patient in question in this case report.