Cysts are fluid-filled cavities that can form in almost all tissues and organs of the body. Cysts in the kidney are either acquired renal cysts or congenital or inherited cyst kidneys, which can lead to kidney failure. Both are summarized under the term cystic kidney disease.
Cysts are typically lined with a layer of cells of the surface tissue (epithelium) and surrounded by a capsule of connective tissue. A cyst is usually a harmless and benign process. The fluid content of the cyst often consists of tissue fluid and is mixed with tissue components.
Acquired cystic kidney disease
Simple renal cysts can occur individually or in groups, in only one or in both kidneys. They are usually harmless, do not cause any symptoms and are therefore only discovered by chance. Kidney cysts that are more than the size of a fist can cause pressure pain in the kidney area, abdominal pain or stool irregularities.
Long-term renal insufficiency and dialysis over many years can also be the cause of kidney cysts. They develop in 30 to 90 percent of patients on long-term dialysis and can have serious consequences. For example, they can develop into a complicated cyst and subsequently into a carcinoma.
Inherited and congenital cystic kidney diseases
Cystic kidneys are congenital kidney diseases in which the normal structures of the kidneys are cystically altered. Different forms are distinguished:
The most common is the inherited cystic kidney disease ADPKD (autosomal dominant polycystic kidney disease). Approximately one in four hundred to one in a thousand people suffers from this disease. This form of cystic kidney disease leads to progressive kidney failure from around the age of 40 onwards, requiring dialysis or kidney transplantation.
At the same time, cysts are often found in the liver as well as bulges in the aorta (aortic aneurysm) and blood vessels in the brain (brain-base artery aneurysms). This form of cyst kidney becomes noticeable between the age of 30 and 50, but has existed since birth. In almost half of all patients over the age of 60, the cystic kidneys lead to a permanent functional impairment of the kidneys, renal insufficiency.
Autosomal recessive polycystic kidney disease (ARPKD) is relatively rare. This form of cystic kidney is a part of the so-called Potter’s sequence. It is a combination of several malformations. Autosomal recessive polycystic kidney disease affects one in 20,000 newborns and leads to death in one in three children in the first months of life.
Congenital cystic kidneys also occur as part of other malformations such as the so-called medullary sponge kidney. In some cases they are so severe that the patients die of kidney failure or other complications as early as infancy or childhood.
What symptoms do congenital and inherited cystic kidneys cause?
The symptoms of congenital cystic kidneys depend on the extent of the kidney damage or on complications that have occurred. Flank pain may occur, and in the case of large cysts, the back and abdomen may also be painful. The urine is often coloured bloody red.
Urinary tract infections such as cystitis or pelvic inflammation are common, which manifest themselves with frequent, painful and burning urination and occasionally also with fever. As a further complication, the cysts can tear, causing bleeding and inflammation.
The cystic changes favour the development of kidney stones and high blood pressure.
In the long term, the kidney can become so damaged that it increasingly loses its function. This is known as renal insufficiency, which can end in renal failure. Every second patient with congenital ADPKD needs dialysis at the age of 60. In very rare cases, kidney cysts degenerate and develop into malignant kidney tumours (renal carcinomas, kidney cancer).
How are kidney cysts and cystic kidneys diagnosed?
Renal cysts are often discovered by chance during an ultrasound examination (sonography). Cysts can be distinguished very well from other tissue changes such as renal tumours by ultrasound because they appear as dark, fluid-filled cavities.
Sonography of the kidneys is an examination that is easy to perform and completely painless and without complications for the patient. If the kidneys are greatly enlarged, the doctor can even sometimes palpate them with the hands during the physical examination in the flank area.
Computer tomography or magnetic resonance imaging can also be performed.
During urine examination, red blood cells and proteins in the urine indicate kidney damage. If white blood cells are also found in the urine, there is also inflammation. Blood tests provide information about the current kidney function.
By taking kidney tissue (biopsy) and examining it, the doctor can distinguish between ARPKD and ADPKD, for example. Molecular genetic analyses can help to identify the altered genes.
It is also important to examine patients with cystic kidneys for further cysts in other organs as well as for aneurysms in the aorta and brain vessels.
In patients with cystic kidneys, regular examinations for secondary damage are recommended. These include, above all, the early detection of high blood pressure and its consistent treatment. High blood pressure that is treated poorly or not at all contributes significantly to a rapid loss of kidney function.
Examinations for urinary tract infections are also advisable in order to be able to detect and treat them early.
How are kidney cysts and cystic kidneys treated?
Treatment is not necessary for simple renal cysts that do not cause any discomfort or complications.
Patients with larger cysts or cystic kidneys may need pain-relieving therapy for the pain in the kidney area (so-called flank pain).
If this does not sufficiently relieve the symptoms, it is possible in the case of large cysts to aspirate (puncture) the contents, to obliterate the cysts or, if necessary, to remove them completely (cyst resection). The aim is always to preserve the functional kidney tissue as well as possible and not to damage it. An operation is always necessary if the cysts tear, if they cause severe infections or degenerate malignantly.
The more extensive the operation is, the more complications can occur. This can result in injuries to other organs, nerves and blood vessels, which can cause bleeding and secondary bleeding. Injuries to the urinary organs (for example a ureter) can result in disturbances in urine excretion and urination.
Patients with congenital or inherited cystic kidneys should have their blood pressure checked regularly and aim to normalise their blood pressure in order to slow down the decline in renal function. This is because high blood pressure leads to a more rapid deterioration in kidney function. If the blood pressure is too high, antihypertensive drugs are used in cystic kidneys. Dialysis is necessary for kidney failure. Ultimately, the cystic kidneys can only be cured by a kidney transplant.
What can parents do with cystic kidneys?
Families in which cystic kidneys have appeared should urgently seek genetic counselling if they wish to have children. Every second child whose father or mother has a cystic kidney also develops this disease. In order to be able to recognise and prevent cystic kidneys and their complications at an early stage, it is recommended that children of parents with cystic kidneys undergo appropriate examinations, even if they do not yet have any symptoms.