What is hydronephrosis?

Hydronephrosis is a condition associated with the abnormal swelling and stretching of one or both kidneys when urine is unable to drain properly. It usually results from some type of obstruction that can be located in the ureter (which connects the kidney to the bladder), the bladder itself, or the urethra (which allows the urine to drain out of the bladder). Urine then backs up towards the kidney, causing swelling and stretching.¹ 

Hydronephrosis is relatively frequent, occurring in about 1% of adults at some point within their lifetime. Left untreated for a prolonged period of time, an obstruction can unfortunately lead to infections and irreversible damage to the kidneys. Early diagnosis and treatment drastically improve prognosis and increase the chances of kidney function recovery after the obstruction has been removed. Older adults are more prone to hydronephrosis, men in particular, as it is common for the prostate to become enlarged, increasing the risk of hydronephrosis.¹

How ageing affects the urinary system

How does the urinary system work?

One of the main functions of the kidneys is to filter blood by removing waste products and excess fluid. These waste products, along with the excess fluid, form the urine in the tubular system of the kidneys. Urine then exits the kidneys through the ureter and accumulates in the bladder until it is emptied via the urethra.

Age-related changes in the urinary system

As people get older, changes occur in the urinary system. Some of these changes include the following:

• Decrease in bladder capacity: Clinical studies have shown that with age, bladder capacity tends to decrease. It can become more difficult to fully empty the bladder when urinating, suggesting a weakening of the bladder muscles²
• Prostate enlargement: Common in older men, this condition is generally benign. However, it can sometimes obstruct urinary outflow, increasing the likelihood of hydronephrosis^1,2
• Uncontrolled bladder contractions: These are more likely with increasing age, suggesting changes in neural control of the bladder²
• Overall decline in kidney function: It is important to note that as we get older, kidney function declines through various structural and physiological changes. There is wide variability between individuals as to the rate of decline³

Why do these changes matter?

These changes are particularly relevant in older adults as they increase the likelihood of urinary retention and obstruction, both potential causes for hydronephrosis. Because renal function might already be reduced in older individuals, it is essential to rapidly treat any obstruction in order to avoid long-term damage that would further decrease kidney function. 

What causes hydronephrosis in adults?

Mechanical blockages

• Kidney stones: These are small mineral clusters that form in the kidneys and can lodge themselves somewhere in the urinary system, creating an obstruction. These are generally more common in older individuals, and overall, one of the most common causes of hydronephrosis⁴
• Prostate enlargement: Formerly called benign prostatic hyperplasia (BPH), it can obstruct urine outflow. Delayed treatment of BPH can lead to complications, including hydronephrosis^1,2
• Ureteral strictures: These are abnormal narrowings of the ureter, which transports urine from the kidneys to the bladder. In some instances, these can result in a mechanical blockage of the ureter, preventing urine from reaching the bladder.¹
• Tumours: Whether within the urinary tract or pressing from the outside, a pelvic or retroperitoneal tumour is one of the more common causes of hydronephrosis in older individuals¹

Functional or neurological causes

• Neurogenic bladder: A condition where nerve damage can affect bladder function. Damages to the nervous system can interfere with the bladder's ability to function properly. When the brain or nervous system, especially the parts that regulate involuntary bodily processes, are impaired, it can lead to urine retention and an increased risk of lower urinary tract infections. These complications increase the risk of hydronephrosis. This is a particularly relevant issue for individuals living with Alzheimer’s disease or other forms of dementia²
• Bladder dysfunction: With ageing, it is not uncommon to experience weakening of the muscles of the urinary bladder, making it more difficult to fully empty the bladder. In some cases, this can lead to increased back pressure towards the kidneys due to the retained urine^1,2

Causes for hydronephrosis can also broadly be classified as intrinsic or extrinsic. Intrinsic causes refer to an obstruction within the urinary tract system, such as kidney stones. Conversely, extrinsic causes refer to an obstruction due to an element outside of the urinary tract system, such as a tumour putting pressure, and possibly, blocking the passage of urine.^1,2

How is hydronephrosis detected

When urine flow is obstructed, patients usually experience a dull pain in their side or lower back. Sharp, more severe pain can also occur due to muscle contractions when the body attempts to move the urine down the urinary tract, past the blockage. Some individuals experience nausea, vomiting, and the frequent urge to urinate.¹ 

The most common exams for the diagnosis of hydronephrosis are ultrasound, MRI, and CT of the kidneys or abdominal area. Because it is easy, fast, and non-invasive, ultrasound is the recommended method for the initial diagnosis of hydronephrosis.⁵ In over two-thirds of cases, ultrasound imaging will also help determine the cause of the obstruction that led to hydronephrosis.⁶

For most patients, blood and urine tests are often run to check for markers of kidney function and infection. This is important as hydronephrosis can be very damaging to the kidneys when not treated promptly.^1,5

Why is hydronephrosis a concern in older populations?

Older populations are more prone to certain health conditions, including diabetes, cardiovascular disease, prostate enlargement or cancer, tumours in the pelvis or abdomen, and kidney stones. These are conditions that are either potential causes of hydronephrosis or can make it more challenging to treat.⁵ Consequently, these should be closely monitored, particularly in older adults, as they can make the prevention and management of hydronephrosis more difficult.

Diabetes is a known risk factor for BPH and kidney stones. Moreover, the use of antidiabetic medications (e.g., insulin) is likely to increase the risk of BPH and lower urinary tract infections. It is therefore harder to prevent hydronephrosis when managing diabetes.^4,7

Cardiovascular diseases (CVD) have no direct link to hydronephrosis or its causes, but the medications used for CVD have to be carefully considered when treating hydronephrosis. For instance, older patients with CVD who take anticoagulant medications would need to stop them to undergo any surgical procedure (eg, tumour removal, prostate resection, extracorporeal shock wave lithotripsy (ESWL)) where bleeding could be an issue. However, this is not always safe, and alternative treatments may be required.⁸

Even though this is highly variable among individuals, it has been well-documented that the ageing process involves a progressive deterioration of the kidneys, resulting in the decline of renal function. In healthy adults, the kidneys have more working capacity than needed, referred to as the renal functional reserve. Therefore, if some kidney tissue is damaged, the remaining healthy tissue is normally sufficient to perform all the required functions of the kidneys. However, with ageing, this reserve capacity decreases, making older populations more vulnerable to the negative impacts of hydronephrosis.^3,9

Management and treatment options

Proper treatment of hydronephrosis is based on what caused it in the first place and the severity of the situation.

• Kidney stones: In less severe cases, management may involve increased fluid intake and dietary changes. The obstruction is monitored until resolved or until it is determined that removal of the kidney stones is necessary.^1,4 The most common way of removing kidney stones is extracorporeal shock wave lithotripsy (ESWL), a non-invasive method using shock waves to break down the kidney stones into small enough fragments that can pass naturally⁸
• Prostate enlargement: When hydronephrosis is caused by benign prostatic hyperplasia, treatment focuses on removing the obstruction to relieve urine backflow to the kidneys. It may involve placing a catheter to immediately drain the retained urine and avoid renal damage. Another approach is the use of medications to reduce the size of the prostate or surgical removal of the obstructing part of the prostate⁷
• Tumours or masses: Treatment primarily focuses on managing the tumour or mass causing the obstruction. It may include surgical removal, or other treatments such as chemotherapy or radiation for cancerous tumours. If necessary to prevent kidney damage, immediate relief can be achieved by placing a catheter directly into the obstructed area to allow for urine to drain¹

Summary

Hydronephrosis is a condition where one or both kidneys abnormally swell or stretch due to a blockage in the urinary tract system. It is more common in older adults, particularly men, due to age-related conditions such as prostate enlargement, weaker bladder muscles, and a higher risk for kidney stones. Common causes include kidney stones, tumours, ureteral strictures, and neurological or functional bladder issues. Symptoms can range from dull flank pain to nausea and frequent urination. Diagnosis usually involves imaging, with ultrasound being the first-line diagnostic tool, along with blood and urine tests. Hydronephrosis is especially concerning in older adults, who often have other conditions like diabetes or cardiovascular disease that complicate treatment. Additionally, reduced kidney reserve in older populations makes timely management critical. Treatment depends on the underlying cause. It may include medications, catheterisation, or surgical procedures to relieve the obstruction and prevent kidney damage.