Renal Scarring
Renal scarring refers to focal areas of thinning or contour irregularity of the kidney caused by permanent damage to areas of kidney tissue. It is an end result of a variety of processes—most commonly prior kidney infection (particularly pyelonephritis or reflux nephropathy from childhood urinary reflux), reduced blood flow (as with segmental infarction from vascular problems), and prior surgery, trauma, or radiation. Renal scarring is often identified incidentally on imaging in adulthood and typically causes no symptoms in the short term. However, extensive or bilateral scarring can contribute to high blood pressure, protein in the urine, and, over time, reduced kidney function. Evaluation and long-term care focus on identifying the underlying cause, protecting the remaining kidney tissue, and monitoring for complications.
What is it?
Renal scarring refers to focal areas of permanent damage to the kidney, typically appearing on imaging as areas of thinning of the kidney’s outer layer (the cortex) with corresponding indented outline of the kidney and, often, associated changes in the underlying collecting system (such as blunting or dilation of the calyces). Scarring is the end result of a process in which normal functioning kidney tissue has been replaced by fibrous tissue that does not function. Depending on the underlying cause and the amount of tissue affected, scarring may involve one focal area, multiple areas, or larger portions of the kidney.
Renal scarring differs from generalized kidney shrinkage or atrophy in that scarring typically produces focal or patchy changes with characteristic patterns that reflect the underlying cause. Extensive scarring can lead to a smaller, distorted kidney that overlaps with the appearance of an atrophic kidney.
Several conditions can produce renal scarring, and the pattern on imaging often provides clues to the underlying cause.
Reflux nephropathy is one of the most common causes of focal kidney scarring in adults. It results from prior vesicoureteral reflux (backward flow of urine from the bladder to the kidneys), typically during childhood, often complicated by episodes of pyelonephritis. Reflux nephropathy characteristically produces focal scars that preferentially affect the upper and lower poles of the kidney, with corresponding blunting of the underlying calyces. Both kidneys may be affected in patients with bilateral reflux, though one side is often more affected than the other.
Chronic pyelonephritis (long-standing kidney infection or scarring from repeated infections) can produce scarring even without a history of reflux, though the two conditions are often intertwined. Chronic pyelonephritis may be associated with obstruction, stones, or other conditions.
Segmental infarction (loss of blood supply to a portion of the kidney) produces a characteristic wedge-shaped area of scarring or focal atrophy that reflects the blood supply of the affected segment. Causes include emboli (blood clots from the heart or aorta traveling to the kidney), local thrombosis of a segmental renal artery, prior renal artery stenosis with treatment, vasculitis (inflammation of blood vessels), and other vascular processes.
Prior kidney surgery or trauma can leave focal scars at the site of prior injury or intervention. Prior partial nephrectomy (surgical removal of part of the kidney for cancer, stone, or other reasons), prior renal artery embolization, prior tumor ablation, or prior significant kidney trauma can all leave characteristic changes on imaging.
Prior radiation therapy to the kidney (either intentional or as an incidental effect of radiation to nearby structures) can produce scarring in the affected portion of the kidney.
Prior severe pyelonephritis, kidney abscesses, or other severe infections can leave scars at the sites of prior involvement.
Less commonly, scarring can result from other processes such as granulomatous diseases (such as tuberculosis), certain autoimmune conditions, prior hemorrhage into the kidney, and other conditions.
The clinical significance of renal scarring depends on the extent of scarring, whether one or both kidneys are affected, whether the underlying process is still active, and the patient’s overall kidney health. Small focal scars with normal overall kidney function typically cause no symptoms and require only long-term monitoring. Extensive scarring, particularly when bilateral, can contribute to reduced kidney function, high blood pressure (which may develop in younger adults or with significant bilateral scarring), protein in the urine, and, over time, chronic kidney disease.
Many patients with renal scarring are identified incidentally on imaging done for unrelated reasons—such as evaluation of abdominal pain, kidney stones, or other conditions. In some patients, scarring is identified during evaluation of high blood pressure at a young age, protein in the urine, recurrent urinary tract infections, or reduced kidney function.
Diagnosis is based on imaging. Kidney ultrasound is often the first-line test and can identify many kidney scars, though it may miss subtle changes. CT with and without contrast provides detailed anatomical information and can identify scars, characterize their pattern, and look for underlying causes such as vascular problems, stones, or obstruction. MRI provides similar information without ionizing radiation and can be useful in specific circumstances. DMSA (dimercaptosuccinic acid) renal scan is a nuclear medicine study that is particularly sensitive for detecting kidney cortical scarring and is considered the gold standard in specific settings, particularly for identifying scarring from reflux nephropathy.
When renal scarring is identified, evaluation may include assessment for underlying causes if they are not already known. This may include vascular imaging to evaluate for renal artery stenosis or other vascular problems, evaluation for ongoing infection or obstruction, cardiac evaluation for possible embolic sources, and, in specific cases, evaluation for autoimmune or granulomatous conditions.
Blood tests including creatinine and estimated glomerular filtration rate (eGFR) assess overall kidney function. Urine tests for protein, blood, and infection help evaluate the type and severity of kidney damage. Blood pressure measurement is essential.
Important to Know
Management of renal scarring focuses on protecting the remaining functioning kidney tissue over the long term, monitoring for early signs of complications, and treating any underlying processes that may be active. Care is typically coordinated by primary care clinicians and, when needed, nephrologists (kidney specialists), urologists, and other specialists.
For patients with focal renal scarring identified incidentally with normal overall kidney function and no underlying active process, management typically focuses on general kidney protection and periodic monitoring. This includes regular clinical assessment with blood pressure measurement, periodic blood tests (creatinine and eGFR), and periodic urine tests for protein and blood. The frequency of monitoring is individualized and may range from annual to less frequent visits in stable patients without additional risk factors.
Blood pressure control is one of the most important aspects of long-term care. High blood pressure is common in patients with extensive kidney scarring and can worsen kidney function over time. ACE inhibitors or angiotensin receptor blockers (ARBs) are often preferred because they both lower blood pressure and provide direct kidney protection, particularly when protein is present in the urine. In some situations (such as bilateral renal artery stenosis or scarring in a solitary kidney), these medications require careful monitoring, as they can affect kidney function.
Management of protein in the urine (proteinuria) is important because it is both a marker of kidney injury and a factor that can worsen kidney function. ACE inhibitors and ARBs are the primary treatments for proteinuria in patients with renal scarring, and newer options (such as SGLT2 inhibitors) may be considered in specific circumstances. Reduction in dietary sodium may also be helpful.
Avoidance of medications and substances that can harm the kidneys is important. Nonsteroidal anti-inflammatory drugs (NSAIDs) can affect kidney blood flow and function and should generally be limited in patients with significant kidney scarring or reduced function. Careful attention to medication dosing based on kidney function is important, and certain contrast agents used in imaging may require special consideration. Avoiding smoking and limiting alcohol also support kidney health.
Management of other health conditions that affect the kidneys is essential. Diabetes should be well controlled to reduce the risk of further kidney damage. Cardiovascular risk factors, obesity, and other conditions should be addressed. A generally healthy diet, adequate hydration, and regular physical activity all support overall kidney and general health.
Management of urinary tract infections is important. Symptomatic infections should be promptly evaluated and treated with appropriate antibiotics. In patients with a history of reflux nephropathy or recurrent infections, further evaluation may be appropriate to identify contributing factors. Long-term preventive antibiotics are not routinely used in adults but may be considered in specific circumstances.
Treatment of underlying processes is important when they are still active. This may include treatment of renal artery stenosis (in selected patients when it is contributing to hypertension or reduced function), treatment of ongoing infections or obstruction, treatment of active autoimmune or granulomatous conditions, and management of embolic sources.
For patients with reduced overall kidney function (chronic kidney disease), management follows established principles: blood pressure control, control of diabetes when present, protein management as recommended by nephrology, careful attention to medications, management of complications (anemia, bone and mineral disorders, electrolyte disturbances), cardiovascular risk reduction, and, in advanced stages, preparation for kidney replacement therapy (dialysis or transplant) when needed.
Care during pregnancy in patients with significant renal scarring requires special attention. Kidney function, blood pressure, and protein in the urine should be monitored more closely, and urinary tract infections should be promptly evaluated and treated. Coordination with obstetrics, nephrology, and, when appropriate, maternal-fetal medicine is important.
For patients with a solitary functioning kidney with scarring, care approaches parallel those for having a single functioning kidney (see also our Absent Kidney page), with attention to protecting the functional tissue over the long term.
Care is typically coordinated by primary care clinicians and, when needed, nephrologists and urologists, with involvement from other specialists as needed. Imaging and laboratory findings are interpreted alongside the patient’s symptoms, examination, family history, and broader clinical context rather than in isolation.
Patient education plays an important role. Understanding the diagnosis, the underlying cause when identified, the rationale for recommended monitoring and treatment, the importance of medication choices and lifestyle recommendations, warning signs of complications, and, when relevant, the meaning for pregnancy or family members all contribute to better outcomes.
Red flag symptoms include severe flank or back pain, high fever with chills (particularly with signs of severe urinary tract infection or possible kidney infection), significant decrease in urine output, blood in the urine, severe swelling, severe or difficult-to-control hypertension, symptoms of severe electrolyte abnormalities (severe weakness, muscle cramps, irregular heartbeat), severe abdominal pain, sudden neurological symptoms (which could suggest embolic events), or rapid clinical deterioration. These warrant prompt or urgent medical evaluation, as they may indicate acute infection, worsening kidney function, embolic events, or other serious problems.