Kidney Stones Vanished into Thin Air: Distinguishing Emphysematous Pyelitis from Renal Calculi on Ultrasound

Abstract

Emphysematous pyelitis (gas within the excretory system) is a rare infection with a mortality of 20%. Although, it may resolve with antibiotics alone, the presence of gas within the kidney must be detected and clearly distinguished from uncomplicated pyelonephritis or calculi. Acoustic shadowing on ultrasound (i.e. the drop in echo strength under a highly reflective or attenuating structure) can be useful in this situation. This can distinguish calcification (clean shadowing) or bone (partial shadowing) and gas (dirty shadowing). To highlight the importance of the correct interpretation of this imaging artifact we describe the course of a 64 years old woman who presented with fever, left flank pain and dysuria. The renal tract ultrasound was initially reported to show multiple renal calculi. However, on re-review it was noted that the appearance of the acoustic shadowing was more consistent with air. The diagnosis of emphysematous pyelitis was confirmed by computed tomography.