Pyonephrosis is a term given to an infection of the kidney which leads to pus in the upper collecting system and can progress to obstruction.
The diagnosis of pyonephrosis is suspected when the clinical symptoms of fever and flank pain are combined with the radiologic evidence of obstruction to the urinary tracts 1.
Usually shows dilatation of the pelvicalyceal system which the following additional features
- echogenic debris in the collecting system: considered the most reliable sign 4
- fluid-fluid levels within the collecting system
- incomplete (dirty) echoes of collecting system gas may be occasionally seen
The presence of clinical signs of infection with hydronephrosis on CT is considered a more sensitive indicator of pyonephrosis than many of the CT findings alone 6. In addition to features of obstruction, CT may demonstrate
- thickening of the renal pelvic wall (>2 mm)
- parenchymal or perinephric inflammatory changes
- dilatation and obstruction of the collecting system
- higher than usual attenuation values of the fluid within the renal collecting system
- layering of contrast material above and anterior to the purulent fluid on excretory studies
A caveat to CT evaluation is that it is often difficult to distinguish simple hydronephrosis from pyonephrosis on the basis of fluid attenuation measurements.
MRI may demonstrate features similar to those seen on CT. Some promising preliminary work has been done with both diffusion-weighted imaging and apparent diffusion coefficient maps in an attempt to distinguish hydronephrosis from pyonephrosis, but these techniques require further investigation 4.
Treatment and prognosis
Emergent insertion of a percutaneous nephrostomy to drain the infected collecting system is usually after review and close collaboration with a urologist.
- 1. Yoder IC, Pfister RC, Lindfors KK et-al. Pyonephrosis: imaging and intervention. AJR Am J Roentgenol. 1983;141 (4): 735-40. AJR Am J Roentgenol (citation) - Pubmed citation
- 2. Colemen BG, Arger PH, Mulhern CB et-al. Pyonephrosis: sonography in the diagnosis and management. AJR Am J Roentgenol. 1981;137 (5): 939-43. AJR Am J Roentgenol (citation) - Pubmed citation
- 3. Yoder IC, Lindfors KK, Pfister RC. Diagnosis and treatment of pyonephrosis. Radiol. Clin. North Am. 1984;22 (2): 407-14. - Pubmed citation
- 4. Craig WD, Wagner BJ, Travis MD. Pyelonephritis: radiologic-pathologic review. Radiographics. 28 (1): 255-77. doi:10.1148/rg.281075171 - Pubmed citation
- 5. Kim SH. Radiology Illustrated: Uroradiology. Springer. (2012) ISBN:3642053211. Read it at Google Books - Find it at Amazon
- 6. Fultz PJ, Hampton WR, Totterman SM. Computed tomography of pyonephrosis. Abdom Imaging. 1993;18 (1): 82-7. - Pubmed citation