Introduction
Simple kidney cysts are fluid-filled pouches that can occur in one or both kidneys. There can be single or multiple kidney cysts. The simple kidney cysts are mostly round or oval. Their size ranges from a pea to a golf ball. It is the most common kidney cyst and is generally non-cancerous or benign. These cysts are generally asymptomatic, but infections can make them symptomatic. They are accidentally detected during the diagnostic radiological examination of the abdomen. Simple kidney cysts are usually harmless; they do not enlarge the kidneys or reduce the kidney function, unlike the cysts in polycystic kidney disease (PKD). Polycystic kidney disease is a genetic disorder that leads to chronic kidney disease.
What Causes Simple Kidney Cysts?
Simple kidney cysts are not hereditary but are acquired. The exact cause of a simple kidney cyst is not known. Males are more likely to get kidney cysts. Their incidence increases with increasing age. The kidneys have very small tubules which collect freshly formed urine. When these tubules get blocked, small pouches may form on them. These pouches may detach and become simple kidney cysts. Certain medical conditions, such as polycystic kidney disease, can cause the cysts to grow in size. Medical conditions that cause simple or complex kidney cysts:
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Chronic Kidney Disease - This disease impairs kidney function leading to kidney damage.
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Medullary Cystic Kidney Disease - This is an inherited condition affecting the kidneys. It leads to scarring and reduced kidney function.
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Autosomal Dominant Polycystic Kidney Disease - This is a genetic disorder with the growth of several cysts within the kidney.
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Von Hippel-Lindau Disease - This is an inherited disorder that causes the growth of tumors and cysts in some parts of the body.
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Tuberous Sclerosis Complex - This is a rare multi-system genetic disease that causes the growth of non-cancerous tumors in the brain, kidneys, heart, eyes, lungs, and skin.
What Are the Symptoms of Simple Kidney Cysts?
Usually, kidney cysts are asymptomatic. Rarely because of infections or other conditions, they enlarge in size, causing:
Hematuria - The presence of blood in the urine.
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The cyst in the upper abdomen or back can become large, cause pain, and press against the bone and other organs.
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Fever and chills.
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Pain.
Hypertension - An increase in blood pressure.
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In case the cyst blocks the ureters (the tube connecting the kidneys with the bladder), difficulty in passing urine is evident.
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Presence of mass in the abdominal area.
What Is the Epidemiology of Simple Kidney Cyst?
Simple renal cysts are very common. Their incidence increases with increasing age. Around 25% of individuals who are forty years or above and around 50% of those who are fifty years or above have simple kidney cysts. Simple kidney cysts can double in size over a period of ten years. They are detected accidentally and are usually asymptomatic. More than one simple kidney cyst is seen in individuals with chronic renal disease who are on dialysis.
How Are Simple Kidney Cysts Diagnosed?
Simple kidney cysts are often detected in radiographic imaging tests to diagnose other conditions. For detecting simple kidney cysts:
Medical History - The doctor will inquire about the medical problems that one had in the past. A detailed history of the development of any symptom is also noted.
Imaging Tests- They help to distinguish between a simple and complex cyst. Tests are:
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Kidney Ultrasound - Ultrasound uses high-frequency sound waves and echoes to create images of the kidney and other organs.
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Kidney CT (computed tomography) Scan - CT scan uses a combination of X-rays and computer technology to produce images of the internal organs. This scan uses dyes or contrast media to differentiate the fluid-filled cysts from the tumors.
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Kidney MRI (magnetic resonance imaging) - This technique uses magnetic fields, radio waves, and computer technology to create images of internal organs. They usually do not use dyes or contrast media.
The radiologist will differentiate between simple and complex cysts with the help of these radiographic images. At times they use the Bosniak CT system to rate the cysts. It divides the cysts into five categories, I, II, II-F, III, and IV. These ranks are based on complexity and possible malignancy. A cyst ranked in the I category does not need any imaging. Kidney cysts that fall into higher categories might need more imaging and treatment. Category IV cysts are most likely linked to cancer. If the diagnosis still remains unclear even after performing the imaging tests, then genetic testing is recommended. It can rule out conditions such as polycystic kidney disease.
Lab tests include
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Urine Test.
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Blood Tests.
How Are Simple Kidney Cysts Treated?
Simple kidney cysts that are asymptomatic do not need any treatment. However, regular ultrasounds are advised to keep a check on the shape and size of the cysts. Cysts causing symptoms, such as pain or blockage of urine flow, should be treated.
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Drainage - Few studies suggest draining or removing the cysts might help individuals with high blood pressure related to simple kidney cysts.
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Sclerotherapy - Sclerotherapy is a procedure where a long needle is inserted through the skin into a cyst with the help of ultrasound used as a guide. It is used to drain a cyst. The cyst is drained with the help of a needle and injected with an alcoholic solution. This solution hardens the cyst. Thus, it cannot fill with fluid again. This procedure is performed under local anesthesia.
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Surgery - In the case of a large cyst, laparoscopic surgery is recommended for removal. Laparoscopic surgery, also called keyhole surgery, is a minimally invasive technique involving several small cuts. It uses a laparoscope, thin tube-like equipment with a small video camera, and tiny instruments. The cyst is drained at first and then removed or burned away. This process is carried out under general anesthesia. The hospital stay is around one or two days.
Conclusion
Simple kidney cysts are small fluid-filled pouches within one or both kidneys. They are quite common. Usually, simple kidney cysts are asymptomatic, but in the presence of other conditions, they become symptomatic. The diagnosis is usually based on radiological findings. Asymptomatic cysts are not treated, while treatment is required for symptomatic cysts. The treatment involves drainage or surgery based on their size. The outlook is excellent after surgery, with very few complications.
