This scan of the bilateral kidneys reveals perinephric fluid, worse on the right than the left. Adjacent to the right perinephric fluid there appears to be a dirty shadow artifact with some occasional b-lines, suggesting an air-fluid interface within the fluid cavity. This likely represents a gas forming abscess on the right side, suggesting the possibility of emphysematous pyelonephritis. CT was also performed to stage the patient for drainage, confirming an air-fluid interface in the right perinephric space, as well as left perinephric fluid.
To obtain adequate views of the retroperitoneum, a low frequency transducer such as curvilinear or phased array should be used.
In general, rib spaces are narrower anterior-laterally, and open up slightly posteriorly. Moving posteriorly may improve your renal windows. Moving the patient to a lateral decubitus position can also aid this view.
If ribs continue to inhibit your renal views, consider twisting the probe such that it is parallel to the rib spaces: a hands-in-pocket orientation.
Having the patient take and hold a deep breath can bring the kidneys below the costo-phrenic margin, sometimes dramatically improving renal visualization.
Patients with pyelonephritis who are ill appearing or septic should be considered high risk for having drainable perinephric abscesses. They are more common in immunocompromised patients, especially diabetics.1
The typical sonographic appearance of a perinephric abscess is a relatively hypoechoic rim of fluid surrounding the kidney, but it may contain mixed echoes depending on the echodensity of the purulent material. Ultrasound is the typical first-line imaging technique, but CT would characterize the abscess as well.2
Percutaneous drainage of perinephric abscesses has been shown to be safe and effective, obviating the need for open surgical drainage in most cases.3
This patient was given broad spectrum antibiotics and volume resuscitation in the emergency department. She was admitted to the ICU and had a CT-guided percutaneous drainage of her abscesses. She had an uncomplicated hospital course and was discharged a few days later.
Ko MC, Liu CC, Liu CK. Incidence of renal and perinephric abscess in diabetic patients: a population-based national study. Epidemiology and infection. 139(2):229-35. 2011. [pubmed]
Coelho RF, Schneider-Monteiro ED, Mesquita JL, Mazzucchi E, Marmo Lucon A, Srougi M. Renal and perinephric abscesses: analysis of 65 consecutive cases. World journal of surgery. 31(2):431-6. 2007. [pubmed]
Meng MV, Mario LA, McAninch JW. Current treatment and outcomes of perinephric abscesses. The Journal of urology. 168(4 Pt 1):1337-40. 2002. [pubmed]