Renal Papillary Necrosis – Stages and Imaging findings

Normal kidney showing vasculature on color doppler USG

Longitudinal color Doppler US image shows blunting of the upper polar calices (arrows), which are bordered by arcuate vessels (arrowheads)

Early Ischemic Change in the Medullary Pyramid

Renal papillary necrosis is the consequence of an ischemic process in the renal papillae. Infection that causes inflammation of the interstitium also may lead to compression of the medullary vasculature and thus predispose the vessels to ischemic change. Perfusion compromise as a consequence of vasculitis in diabetes mellitus, tuberculosis, or the curtailment of flow observed in hemoglobinopathy, analgesic nephropathy, or acute urinary obstruction, also sets the stage for ischemic changes in the medullary pyramid (1)

Urographic findings during this period of early ischemic change are usually normal. Ischemic changes of the medulla are identified more often and localized more accurately with multi–detector row CT than with IV urography or ultrasonography (US)

Reversible stage ischaemic changes . Contrast-enhanced parenchymal phase CT image shows multiple poorly marginated, hypoattenuated lesions (arrowheads) in the papillary regions and the excretion of contrast material into the renal pelvis (arrow)

EARLY STAGE PAPILLARY NECROSIS

Necrotising papillitis resulting in papillary necrosis as shown by hypoattenuating medullary lesions indicating papillary necrosis and swollen kidney

ADVANCED PAPILLARY NECROSIS

In the advanced stage of necrosis, clefts originate from the fornices and extend into and dissect the medullary pyramids and papillae, ultimately causing the papillae to slough. Caliceal deformities in renal papillary necrosis occur in three forms: medullary, papillary, and in situ

a.normal, b.papillary , c.medullary d.sloughed papillae

PAPILLARY FORM

IVU showing Papillary form CECT showing papillary form in excretory phase imaging

MEDULLARY FORM

IVU showing medullary form

CT showing medullary form cleft arising from fornix and forms medullary pattern

SLOUGING PHASE

Can result in blunted cavity if 1.slough passed out or 2. scarring & calcification if slough retained. The The calcification of necrotic papillae is common in patients with analgesic nephropathy.

Medullary cavity communicating with calyces after sloughing off

Calcification due analgesic nephropathy

HEALING PHASE

During the healing phase, the papilla may epithelialize, and its tip may take on a blunted appearance. In addition, shrinkage of the kidney may occur with reduction of parenchymal thickness. This common sequela of renal papillary necrosis has been attributed to the secondary atrophy of nephrons caused by necrosis of the loops of Henle, which pass deeply into the medulla. Moreover, the loss of renal cortex and associated hypertrophy of the Bertin columns result in a typical irregular wavy renal outline

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