A.In early ischaemic stage :During the early ischemic stage of renal papillary necrosis, corticomedullary or parenchymal phase multi–detector row CT shows a poorly marginated area of decreased enhancement at the tip of the medullary pyramid.
.1. Pyelonephritis also may be visible as a circumscribed area of reduced enhancement at CT during the corticomedullary and parenchymal phases, but the lesions in pyelonephritis are typified by lobar or segmental involvement instead of being limited to the medullary pyramid.
2.Moreover, during the late parenchymal phase, the margins of the lesions show the intense venous hyperemia that characterizes inflammatory disease.
3.Attenuation coefficients and locations may help differentiate ischemic lesions from cysts, abscesses, and hematomas.
B.In cases of advanced disease: causes of cystic lesions in the areas of renal medullae or sinuses should be considered in the differential diagnosis. Other possible causes include
2. congenital megacalices
3. parapelvic cyst
In particular, the location of the arcuate artery relative to cystic lesions may be helpful for differentiation
Cavities produced by renal papillary necrosis can be differentiated from those in hydronephrosis by an irregular cavity contour and by extension of the cavity to arcuate arteries. Moreover, in hydronephrosis all calices are blunt tipped, whereas in papillary necrosis one or more calices may extend beyond the levels of others
Arrowheads indicating arcuate arteries
Like the cavities in renal papillary necrosis, pelvocaliceal diverticula may manifest as contrast material–filled fluid collections adjacent to calices. However, these two entities can usually be distinguished on the basis of location: Pelvocaliceal diverticula are not found in papillae but, rather, adjacent to the caliceal fornices or, less commonly, to an infundibulum or the renal pelvis