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Emphysematous Pyelonephritis: A Diagnosis Not To Be Missed On POCUS – Renal.PlatoHealth.ai

The aim of this post is twofold: 1. To remind that air appears white on ultrasound, and 2. To underscore the importance of identifying emphysematous pyelonephritis, a diagnosis of critical importance across various medical specialties including nephrology, internal medicine, and critical care. This case was shared by Dr. Joaquín Martínez, @JMMR83 on Twitter (X).

Here are images of the left kidney obtained from a middle-aged patient with type 2 diabetes mellitus and associated complications, including neurogenic bladder, who presented with sepsis and pyuria. The images reveal hyperechoic foci accompanied by acoustic shadowing. At first glance, particularly when using a low-quality ultrasound device, these may be mistaken for kidney stones by an inexperienced user. However, upon closer examination, it becomes evident that the shadowing is not consistently clean but rather “hazy.” Additionally, the hyperechoic foci exhibit movement and are accompanied by hyperechoic vertical artifacts resembling lung B-lines (ring-down artifact). In the setting of a urinary infection in a diabetic patient, these dynamic echogenic foci suggest the presence of emphysematous infection.

Below is an image from the same patient demonstrating the intelligent utilization of a linear transducer to capitalize on its higher resolution, better illustrating the mobile air in the collecting system.

Strictly speaking, if the foci are limited to the collecting system, it is termed emphysematous pyelitis, whereas involvement of the renal parenchyma qualifies as pyelonephritis. Nevertheless, pyelonephritis is primarily a clinical diagnosis (& potentially life-threatening) and should not be ruled out just because you didn’t notice parenchymal air on POCUS. In this case, air is predominantly observed in the collecting system, but there appears to be involvement of the parenchyma, particularly adjacent to the calyces. In patients where ultrasound suggests emphysematous pyelonephritis, a non-contrast CT scan is warranted to confirm the diagnosis and provide detailed information regarding the extent of infection (? Peri-renal spread). Some cases are associated with obstruction and need percutaneous nephrostomy. Severe cases may necessitate nephrectomy.

We have previously shared a similar case in CEN (click here), but the images above provide the most illustrative depiction, once again, thanks to Dr. Martínez.

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