Kidney cysts are often discovered by chance during routine medical exams. A patient recently inquired about a kidney cyst they found during their check-up and wondered whether it was dangerous or why it appeared when it had not been present before. As people age, the prevalence of kidney cysts increases, so it’s not unusual to discover them later in life. Let’s take a closer look at what kidney cysts are and why they occur.
What is a Kidney Cyst?
A kidney cyst, also known as a renal cyst, is a round or oval-shaped sac inside the kidney that contains abnormal fluid. The size of kidney cysts can range from as small as 0.2 mm to several centimeters, and they can appear as a single cyst or as multiple cysts. According to studies, simple renal cysts are the most common type and are frequently found as people age.
Simple Renal Cysts (Simple Kidney Cysts)
Over 70% of kidney cysts discovered in individuals are simple renal cysts, which are generally benign (non-cancerous). According to autopsy studies, simple renal cysts can be observed in 50% of individuals over the age of 40. By the age of 60, the incidence increases to 33%. These cysts tend to be few in number, typically 2 or fewer. However, if 3 or more cysts are found, it may suggest a condition called polycystic kidney disease (PKD), which requires further evaluation.
What Causes Kidney Cysts?
The exact cause of simple renal cysts remains unclear, but they are commonly considered a part of the natural aging process. They are more common after the age of 20, and the frequency of occurrence increases with age.
Risk Factors for Kidney Cysts:
- Age: The risk increases with age.
- Gender: Men may have a higher incidence of kidney cysts.
- Kidney Disease: People with a history of kidney disease or hypertension are at higher risk.
- Hypertension: High blood pressure can exacerbate kidney cysts.
How Are Kidney Cysts Diagnosed?
Kidney cysts are typically diagnosed using ultrasound, which can identify the cyst with 98% accuracy. In cases where the cyst is more complex, additional imaging tests such as contrast-enhanced CT or MRI may be necessary to rule out other conditions, including malignancies.
While ultrasound can usually confirm simple cysts, complex cysts require further tests to determine their structure, size, and whether they are benign or potentially malignant.
Conditions to Rule Out:
- Bacterial Infections
- Tuberculous Abscesses
- Tumors
Symptoms of Kidney Cysts
Most kidney cysts are asymptomatic, and many individuals with kidney cysts experience no symptoms at all. However, in some cases, complications or rapid growth of the cyst can lead to the following symptoms:
- Flank pain
- Abdominal discomfort
- Palpable masses
- Hematuria (blood in the urine)
A study conducted in South Korea showed that:
- 86% of kidney cyst cases were asymptomatic.
- 10% of cases presented with mild, intermittent pain.
- 2% had visible blood in the urine.
The likelihood of symptoms increases with cyst size. Larger cysts can also obstruct urine flow, causing additional complications.
Complications of Simple Kidney Cysts
Although rare, simple kidney cysts can develop complications:
- Bleeding: Occurs in 6% of simple cysts, often due to trauma or cyst growth.
- Infection: Infections occur in 2.5% of cases, with symptoms like fever and tenderness. Diagnosis may require aspiration and culture of cyst fluid.
- Rupture: Cysts may rupture due to trauma, infection, or increased internal pressure.
In addition, kidney stones are commonly associated with kidney cysts and may require intervention.
Treatment for Kidney Cysts
- Asymptomatic Cysts: If the cyst is small (less than 1 cm), asymptomatic, and benign, no treatment is needed. These cysts are typically monitored with routine ultrasound exams every 6 to 12 months.
- Symptomatic Cysts: In cases where cysts cause pain, obstruction, or other complications, treatment options include:
- Aspiration: Removing fluid from the cyst using a needle.
- Sclerotherapy: Injecting a solution (usually alcohol) into the cyst to cause it to harden and prevent further fluid buildup.
- Surgical Removal: In cases where the cyst is large (greater than 6 cm) or if it is causing significant symptoms, surgical removal may be necessary.
Are Kidney Cysts Malignant?
Kidney cysts are usually benign, but in some cases, they may indicate the presence of malignant tumors. To determine whether a cyst is benign or malignant, doctors use the Bosniak Classification System, a global standard for categorizing cysts.
- Bosniak I & II: These cysts are benign, and no further testing or follow-up is needed.
- Bosniak IIF: These cysts are mostly benign, but about 11-15% may show malignant characteristics in follow-up tests. These require ongoing monitoring.
- Bosniak III: Cysts in this category have a significant chance of being malignant (50-100%). Surgical removal may be recommended, depending on the patient’s health status and age.
- Bosniak IV: These cysts are highly likely to be malignant and require immediate surgical removal.
Conclusion
Most kidney cysts are benign and asymptomatic, requiring minimal intervention. However, if complications such as pain, infection, or obstruction occur, further treatment may be necessary. For patients with complex cysts or those showing symptoms, additional imaging tests and careful monitoring are essential to rule out malignancy. If you have a family history of kidney disease or are over the age of 60, regular check-ups and imaging exams are important for maintaining kidney health.