Atrophied Kidney
An atrophied kidney is a kidney that has become smaller than normal, usually with thinning of its outer functional tissue (the renal cortex) and reduced function. It can affect one or both kidneys and results from a wide range of underlying causes, including chronic obstruction, reduced blood flow (renal artery narrowing), long-standing infection or scarring, congenital abnormalities, and progression of chronic kidney disease. An atrophied kidney is often identified incidentally on imaging, but it can also present with reduced kidney function, high blood pressure, or symptoms related to the underlying cause. Evaluation combines imaging, kidney function testing, and, when needed, evaluation of the underlying cause.
What is it?
The kidneys are two bean-shaped organs located in the upper back part of the abdomen, one on each side of the spine. They filter waste and excess fluid from the blood to produce urine, help regulate blood pressure, balance electrolytes, activate vitamin D, and produce hormones that support red blood cell production and bone health. A normal adult kidney is typically about 9 to 12 centimeters long, though the exact size varies with body size, age, and other factors. An atrophied kidney is one that has become smaller than expected, often with a thinned renal cortex (the outer functional layer of the kidney).
Atrophy can affect one or both kidneys. Unilateral atrophy (of one kidney) is often related to a localized cause such as chronic obstruction, reduced blood flow from renal artery narrowing, or long-standing infection or scarring on that side. Bilateral atrophy (of both kidneys) is more commonly seen in advanced chronic kidney disease from any cause, including diabetes, high blood pressure, glomerular diseases, and other conditions. Small kidneys on both sides typically indicate longstanding kidney damage rather than an acute problem.
The causes of an atrophied kidney are diverse. Chronic urinary obstruction (from stones, strictures, tumors, or congenital abnormalities of the urinary tract) can lead to a condition called obstructive uropathy and, over time, to shrinkage of the affected kidney. Renal artery stenosis (narrowing of the artery supplying the kidney), most commonly from atherosclerosis or fibromuscular dysplasia, reduces blood flow and can lead to gradual atrophy—a pattern called ischemic nephropathy. Chronic pyelonephritis (long-standing kidney infection or scarring, often from childhood urinary reflux) can produce a characteristic scarred and atrophied kidney. Vesicoureteral reflux (backward flow of urine from the bladder to the kidney), particularly in childhood, can cause reflux nephropathy with kidney scarring and atrophy. Renal vein thrombosis, radiation therapy, and certain toxins or medications can also lead to kidney atrophy. Congenital hypoplasia describes a kidney that was smaller than normal from birth and can be difficult to distinguish from acquired atrophy without a history of prior imaging.
Progression of chronic kidney disease from any cause can lead to bilateral kidney atrophy, particularly in the later stages. In these situations, the kidneys typically appear small and echogenic (bright) on ultrasound, reflecting long-standing damage.
Symptoms of an atrophied kidney depend heavily on the underlying cause and on whether kidney function overall is affected. Many patients have no symptoms specifically from the atrophy itself, particularly when only one kidney is affected and the other functions normally. In these cases, the finding is often identified incidentally on imaging done for other reasons.
When symptoms are present, they may include high blood pressure (which is common with unilateral atrophy from renal artery stenosis or scarring, and can sometimes be difficult to control), symptoms related to the underlying cause (recurrent urinary tract infections, symptoms of obstruction such as flank pain, symptoms of stones, or symptoms of vascular disease), and, when overall kidney function is significantly reduced (particularly with bilateral atrophy or a single atrophied kidney), symptoms of chronic kidney disease such as fatigue, swelling, changes in urination, itching, nausea, or, in advanced stages, more severe symptoms.
Diagnosis is typically made through imaging. Kidney ultrasound is often the first-line test and can show kidney size, shape, cortical thickness, echogenicity, and features that suggest the underlying cause (such as hydronephrosis from obstruction, or specific scarring patterns from chronic pyelonephritis). CT and MRI provide more detailed anatomical information. Specialized imaging studies may be needed depending on the suspected cause: renal artery imaging (CT angiography, MR angiography, or Doppler ultrasound of the renal arteries) evaluates for renal artery stenosis; nuclear medicine scans (such as MAG3 or DMSA scans) can assess the function of each kidney separately (split renal function), which is helpful when planning treatment; and voiding cystourethrography evaluates for vesicoureteral reflux, particularly in children or young adults with a history of urinary tract infections.
Blood tests including creatinine and estimated glomerular filtration rate (eGFR) assess overall kidney function. Urine tests for protein, blood, and other findings help evaluate the type and severity of kidney damage. Additional testing depends on the clinical context and may include tests for specific glomerular diseases, autoimmune conditions, or other underlying causes.
Identifying the underlying cause is important because it may be treatable in some cases and because it affects the risk of further kidney damage over time.
Important to Know
Management of an atrophied kidney depends on the underlying cause, the presence and severity of symptoms, overall kidney function, and the patient’s other medical conditions. Care is typically coordinated by primary care clinicians and nephrologists (kidney specialists), with involvement from urologists, vascular specialists, radiologists, and other specialists as needed.
For patients with an incidentally identified atrophied kidney with normal overall function and no identifiable treatable cause, management typically focuses on general kidney protection and periodic monitoring. This includes regular check-ups 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 depends on the specific findings and other risk factors.
Blood pressure control is one of the most important aspects of care. High blood pressure can cause further damage to the remaining functional kidney tissue and is often more difficult to control in patients with unilateral atrophy or bilateral kidney disease. Medications that both control blood pressure and provide direct kidney protection—such as ACE inhibitors or angiotensin receptor blockers (ARBs)—are often preferred, particularly when protein is present in the urine. In some situations (such as bilateral renal artery stenosis or a single kidney with renal artery stenosis), these medications require careful monitoring, as they can affect kidney function.
For renal artery stenosis identified as an important contributor to atrophy or difficult-to-control hypertension, treatment options include optimal medical therapy (blood pressure control, statins, and other measures), and, in selected patients, procedures such as angioplasty with or without stent placement. Not all patients with renal artery stenosis benefit from procedures, and the decision is individualized based on the pattern of disease, blood pressure response to medications, and kidney function.
For urinary obstruction, treatment focuses on relieving the obstruction when possible. Options depend on the specific cause and may include removal of stones, procedures for strictures, treatment of tumors, or, in some cases, drainage procedures such as ureteral stents or nephrostomy tubes. Relieving obstruction may improve or preserve function in some patients, particularly when the obstruction has been present for a relatively short time.
For chronic pyelonephritis or reflux nephropathy, treatment focuses on preventing further infections (through antibiotics when needed, sometimes preventive antibiotics in specific situations, and, in children, evaluation for vesicoureteral reflux), and management of blood pressure and kidney function over time.
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.
Avoidance of medications and substances that can harm the kidneys is important. Nonsteroidal anti-inflammatory drugs (NSAIDs, such as ibuprofen and naproxen) can affect kidney blood flow and function and should generally be limited in patients with kidney atrophy 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; these decisions are made in consultation with clinicians. 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.
In rare cases, an atrophied kidney may need to be surgically removed (nephrectomy) if it causes severe complications such as difficult-to-control high blood pressure (in specific circumstances), recurrent severe infections, or malignancy. This decision is highly individualized and involves careful evaluation of the risks and benefits.
For patients with congenital or long-standing unilateral atrophy who have normal function of the other kidney, care approaches parallel those for having a single functioning kidney (see also our Absent Kidney page), with attention to protecting the functional kidney over the long term.
Care is typically coordinated by primary care clinicians and nephrologists, 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, and warning signs of complications all contribute to better outcomes.
Red flag symptoms include severe flank or back pain, significant decrease in urine output, blood in the urine, foamy or dark urine, severe swelling of the face or legs, severe or difficult-to-control hypertension, symptoms of severe electrolyte abnormalities (severe weakness, muscle cramps, irregular heartbeat), signs of urinary tract infection with fever, severe abdominal pain, or rapid clinical deterioration. These warrant prompt or urgent medical evaluation, as they may indicate acute injury or dysfunction of the kidney, obstruction, infection, or other serious problems.