Overview of Papillary Necrosis

Renal papillary necrosis (RPN) is a pathological condition that is characterized by the destruction of the pyramids and papillae within the medullary cavity of the kidney as a result of hypoperfusion in a specific area of kidney tissue. Typically due to some conditions or toxins that cause a deficiency of blood in the kidney, part of it dies (necrosis). The condition can be further complicated depending on how much blood supply is compromised, what other comorbidities the patient may have if there are bilateral kidneys, and the extent of renal involvement.

RPN may have grave consequences. Gangrened kidney tissue is at risk of infection and may form calculi or embolize into the ureter, obstructing urine outflow. In cases of more extensive necrosis, such tissue fragments may also become lodged in the calices of the kidney or the junction between the kidney and the ureter.

With regards to the more key participation of both kidneys and/or distressing occlusion of the urinary tract, RPN may result in loss of renal function. The infections that RPN induces are more harmful in individuals with associated illnesses, especially in diabetic patients. They must be treated to prevent more serious outcomes.¹

Overview of Flank Pain 

Flank pain is a frequently encountered symptom that exists in many degrees of severity in different medical disciplines, from primary health care to specialist urology. This symptom has numerous etiologies, particularly kidney-related ones.

A useful strategy to evaluate the potential causes of flank pain in patients is to examine them concerning the kidneys, as follows: 

• Non-Kidney related Causes: Some causes involve issues such as muscles or bones of the back or side
• Parenchymal problems: These are conditions that concern the kidneys themselves, such as infections or inflammation
• Non-parenchymal problems: These are conditions in which urine or any fluid cannot be properly drained out of the kidney

When a patient presents with flank pain, the range of possibilities is wide. A thorough and sufficient history and physical examination help in reducing the number of possible causes. After this, certain laboratory tests or imaging studies, such as CT scans, are done to ascertain the cause. This systematic methodology indeed assists the physician in countering the cause of flank pain promptly, potentiating its treatment effectively.² 

Etiology

Renal Papillary Necrosis occurs when the structures of the renal system known as the renal papillae, which are located in the medullary region of the kidney, undergo necrosis following ischemia. Many disease processes can lead to this condition, including analgesic abuse. In some instances, it has been observed following interventional procedures, such as stenting of mesenteric arteries. Renal papillary necrosis is a bilateral or unilateral kidney disease that may be diffuse or segmental within the kidney.

In the early stages of the disease, the kidneys may function well and remain normal in size. However, over time, kidney function can decline, and in advanced stages, the disease may lead to kidney failure. 

With the mnemonic "POSTCARDS," it is convenient to remember the causes of renal papillary necrosis.

• Pyelonephritis
• Obstruction
• Sickle cell disorder
• Tuberculosis
• Chronic liver disease
• Analgesics overdose
• Renal vein occlusion
• Diabetes
• Systemic vasculitis

These are commonly associated clinically with this type of renal injury.³

Pathology of Renal Papillary Necrosis (RPN)

RPN is a condition that arises due to ischemic necrosis of renal papillae. Necrosis of renal tissue could be due to the following mechanisms:

• Occlusion of vessels: Sickle cell disease can occlude the small blood vessels of the kidney
• Vascular compression: Conditions such as pyelonephritis, which is an infection of the kidney, can extend and compress the renal blood vessels due to inflammation
• Vascular disease: In certain conditions such as diabetes, there can be vasculitis involving the renal blood vessels

If the blood flow to the kidney papilla isn’t restored, it can lead to permanent damage or even complete tissue death (necrosis) in that area. The necrotic papilla can break off (slough) and form cavities that connect to the kidney's drainage system. These cavities can trap contrast dye during imaging tests, making the damage visible.

When looking at the kidney in a more detailed examination (gross pathology), you might see parts of the kidney's outer layer (cortex) shrinking while the papilla shows different stages of tissue death and breakage.⁴

Signs and Symptoms 

The most common indication of papillary necrosis can involve hematuria (the presence of blood in the urine) and flank pain. If the papilla breaks off, it can block the kidney's drainage system, either in the renal pelvis or ureter. This can cause the pain to move from the flank to the groin. If the broken papilla blocks the flow of urine and the other kidney isn’t working properly, it can lead to kidney failure. Blockage at the bladder or urethra can also cause serious problems with urine flow and kidney function.⁵

Radiologic Findings in Renal Papillary Necrosis

In early RPN, an ultrasound may show bright, ring-like structures and fluid in the kidney's medulla, indicating necrotic papilla, sometimes mimicking an enlarged drainage system (pelvicalyceal dilatation). As the condition worsens, cyst-like cavities may form, and the kidney's drainage structures (calyces) may appear blunted. Sloughed papilla can appear as bright spots of debris.

A CT scan without contrast may be normal early on, but later, CT with contrast shows reduced blood flow and scarring in the medulla, highlighting papillary necrosis. Advanced imaging tests like CT urography and intravenous pyelography are most effective, showing dye leaking into damaged areas and detecting sloughed papilla.

Key signs include:

• Lobster claw and goblet signs: Dye around necrotic papilla
• Ball-on-tee sign: Dye outside the calyx due to a sloughed papilla

If a blockage is present, it must be removed. Treatment focuses on pain management and hydration, as there's no way to reverse the necrosis. Transitional cell carcinoma may occur alongside RPN or mimic it.^4,5

Management and Treatment 

The treatment for Renal Papillary Necrosis is mainly supportive. If there is a blockage, it can be treated with a stent to help restore urine flow, except in cases of acute kidney failure. Infection control is crucial, so antibiotics should be started as soon as possible to prevent the need for surgery.⁶

Patients with analgesic nephropathy (kidney damage caused by painkillers) generally don’t handle surgery well, so endoscopic surgery is a safer option. One method involves retrograde ureteric catheterization, which bypasses the blockage. This can be combined with the use of proteolytic enzymes to break down the obstruction in the ureter.

The Dormia stone basket is often used to safely remove impacted renal papillae in the lower ureter. If recovery is slow or there is leftover urine, additional endoscopic treatment can help clear any bladder-neck obstruction.

Even after stopping painkillers, sloughing of the renal papilla can occur months later. In cases of acute papillary necrosis, prompt endoscopic surgery is recommended. This conservative approach clears the blockage and drains the kidney without removing the kidney itself (unlike immediate nephrectomy), which is especially important for patients with only one working kidney. The tissue retrieved using the Dormia basket also allows for histological confirmation and helps preserve kidney function in potential cases of bilateral disease.⁷

FAQs

Can renal papillary necrosis lead to kidney failure?

Of course, if the detached tissue wedges itself somewhere and the other healthy kidney is not working correctly, it would cause kidney failure.

Why is it that renal papillary necrosis is occasionally confused with cancer?

Imaging studies often demonstrate similar defect characteristics of renal papillary necrosis and transitional cell carcinoma, such that differentiating between the two is challenging.

Can sloughed papilla still happen after stopping painkillers?

 Yes, even after stopping painkillers, the kidney can still slough off damaged papillae months later due to lasting damage from previous analgesic use.

Why is endoscopic surgery preferred over removing the kidney in RPN?

 Endoscopic surgery removes the blockage without taking out the entire kidney, which helps preserve kidney function, especially in patients with only one working kidney.

Summary 

Renal papillary necrosis (RPN) is a disease that occurs due to hypoperfusion of the medullary region leading to ischemia and ultimately the death of renal papillae. This can result from several infections, obstructions, or even medication such as analgesics. With the progression of the disease, the occurrence of sloughed papillae can obstruct the urinary tract, resulting in complications as kidney stones, urinary tract infections, and urinary retention. Investigational imaging techniques such as CT-urography and intravenous pyelography assist in the diagnosis of RPN by visualizing the elements such as sloughed papillae and any other renal structures that are compromised. The main aim of treatment is to cure the existing infections and relieve the existing obstructions and or any pain. Sometimes, endoscopic procedures may be required to excise the sloughed papillae, particularly for patients who cannot have more radical procedures.

Flank pain is one of the classic signs of RPN and is usually accompanied by hematuria. As the papilla becomes detached, it may block the renal pelvis or ureter, which in turn causes pain that shifts from the flank to the lower abdomen (groin). This can worsen and result in renal failure if the blockage is too advanced and the other kidney is also not functioning properly. This is especially hazardous in RPN as there are other comorbid conditions such as diabetes that the patient has, and hence, early management is critical to avoid sequelae. Plotting images and supportive handling are vital in alleviating such symptoms and averting renal failure.