What is pyonephrosis, and what are its CT and MRI features?
Pyonephrosis is the presence of pus within an obstructed collecting system and is considered to be a urologic emergency. It requires early diagnosis and early treatment with decompression/drainage and antimicrobial therapy to prevent rapid development of urosepsis and its associated complications.
On CT and MRI, hydronephrosis or hydroureteronephrosis upstream to an obstructive urothelial lesion is seen, sometimes containing complex-appearing fluid, layering debris, or foci of intraluminal gas. Inflammatory thickening of the renal pelvic wall or ureter may also be seen, and associated findings of acute pyelonephritis as previously described are also commonly present.