Pyonephrosis

 Longitudinal ultrasound image of the right kidney shows moderate right hydroureteronephrosis (arrows) with internal debris.

Longitudinal image of the right ureter (arrows) shows a stone (arrowhead) in the distal ureter causing proximal hydroureter. 

Facts:

• Bacterial infection of urine associated with ureteral obstruction, AKA infected hydronephrosis. Accumulation of pus in the renal pelvis and calices of the kidney
• Common causes are ureteric obstruction by stone and ureteropelvic junction (UPJ) obstruction
• Septic patients with high fever, flank pain and tenderness
• Any febrile patients with hydronephrosis should be suspected of having pyonephrosis
• Ultrasound: echogenic urine and debris in the hydronephrotic kidney
• Prompt drainage essential 

Reference:

Hodler J, Von Schulthess GK, Zollikofer ChL. Diseases of the abdomen and pelvis 2010-2013