Renal papillary necrosis refers to ischemic necrobiosis of the papilla in the medulla of the kidneys (see the images below). A number of conditions may cause renal papillary necrosis; it may be associated with the use of analgesic agents. Renal papillary necrosis may be localized or diffuse and unilateral or bilateral. Earlier in the disease, renal size and function are preserved. Function may deteriorate; in the later stages of the disease, renal failure may occur.
The mnemonic “postcards” is commonly used regarding the causes of renal papillary necrosis
Sickle cell disease
Renal vein thrombosis
Excretory urography in a patient with diabetes. A film obtained at 5 minutes shows horns from the calices, ring shadows, and an egg-in-a-cup appearance (ring sign) characteristic of renal papillary necrosis.
Excretory urography in a 53-year-old man with analgesic-induced nephropathy. A film obtained at 15 minutes after administration of contrast shows a wavy renal outline with tracks of contrast extending from fornix, ring shadows caused by the sloughing of papillae, and an egg-in-a-cup appearance characteristic of renal papillary necrosis. Note the bamboo spine, characteristic of ankylosing spondylitis.
Excretory urography in a patient with renal papillary necrosis and pyeloureteritis cystica. Note the bilateral loss of the renal mantle with contrast tracking from the renal fornix in the lower pole of the right kidney. Note also the multiple smooth filling defects in the ureter, caused by ureteritis cystica.
Plain radiographs demonstrate calcification in a sloughed papilla, which is characteristically ring shaped; such calcification may be the only abnormal radiologic finding in necrosis in situ. Calcification is common in patients with analgesic-induced papillary necrosis, but it has not been reported in cases of renal papillary necrosis associated with hemoglobinopathy.
On excretory urography, persistent streaking of contrast from the fornix at the upper and lower poles is almost diagnostic of renal papillary necrosis. Necrosis in situ is difficult to diagnose because the necrotic tissue does not slough.
Retrograde pyeloureterograph images are sensitive, especially in the presence of renal impairment or when urographic findings are inconclusive.
Ultrasonography is a noninvasive technique that is frequently used to assess the urinary tract. Findings are nonspecific for papillary necrosis.
Computed tomography (CT) scan findings are not diagnostic but may be useful in assessing urinary tract obstruction, hemoglobinopathies, and cirrhosis; these conditions are recognized causes of papillary necrosis.
Magnetic resonance imaging (MRI) findings are nonspecific in cases of papillary necrosis, although MRI may be useful for patients who are allergic to iodinated contrast medium because gadolinium may provide a useful alternative. Gadolinium-enhanced MRI is a useful alternative for patients with renal failure. Gadolinium-based contrast agents have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). NSF/NFD has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness.
Radioisotope scanning provides a sensitive index of renal function.
Limitations of techniques
On plain radiographs, necrotic papillae may occasionally demonstrate a ring of calcification.
On excretory urography, the ulcerated papillae may be observed. Sloughed papillae may cause filling defects within the calyx, pelvocalyceal system, or ureter.
Retrograde pyelography may be helpful when the renal collecting system opacifies poorly or when renal insufficiency is present.
On ultrasonography, sloughed papillae may appear as echogenic material within the collecting system; this is a nonspecific finding. Correlation with clinical and laboratory findings help distinguish renal papillary necrosis from other renal abnormalities that have similar features on ultrasound and that are associated with areas of increased echogenicity (eg, nephrocalcinosis).
No major role exists for CT and MRI in the evaluation of renal papillary necrosis. The usefulness of reformatted multislice spiral CT has yet to be determined. CT findings are not diagnostic but may be useful for patients with poor renal function in whom intravenous urogram radiographs are of poor resolution. Findings of a medullary cavity and calcification are nonspecific. MRI is an expensive tool, but it may be useful for patients with poor renal function and for those who experience hypersensitivity to iodinated contrast media.
Radioisotope studies play a significant role in evaluating renal function, but they provide little anatomic information on the location of lesions.