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Renal cysts can be benign or malignant, congenital or acquired, one-sided, or involve both kidneys at once. The vast majority of these changes, as much as 90-93%, are mild. What are the causes and symptoms of a kidney cyst? What are the types of cysts and how are they treated?

Renal cystsare fluid spaces within their parenchyma. They can be benign or malignant, congenital or acquired, one-sided, or involve both kidneys at the same time.

The vast majority of these changes, in as much as 90-93%, are mild.

There are some of the most common diseases in which kidney cysts are observed.

Acquired kidney cysts are:

  • simple cysts
  • acquired cystic kidney disease

Congenital cysts include:

  • spongy medullary kidney
  • polycystic renal dysplasia

In contrast, genetically determined kidney cysts include:

  • autosomal dominant polycystic kidney degeneration
  • autosomal recessive polycystic kidney disease
  • nephronophthosis
  • medullary renal cystic disease

Each diagnosed change requires periodic ultrasound control, because it may lead to the development of a malignant neoplastic process.

The most common complications of kidney cysts include cyst bleeding, urinary tract bleeding, cyst infection, and kidney cancer.

Simple kidney cysts

Simple kidney cysts are limited fluid spaces, most often located in the renal cortex, less often in the pelvic region, in the medulla.

These are benign kidney tumors that can be single or multiple in one or both of the kidneys. Cysts are usually detected by chance during routine ultrasound of the abdomen or urinary tract.

  • Simple kidney cysts: structure

Simple cysts are made of fibrous connective tissue that builds up the cyst wall. On the inside, it is lined with a cubic epithelium, and inside it is liquid.

  • Simple kidney cysts: epidemiology

In people over 50, the presence of cysts is found in about 50% of respondents, inmen 2 times more often than women.

It has been proven that the size of simple cysts increases with age, initially they measure from a few millimeters, even up to several centimeters in diameter.

The presence of changes in younger people and children should initiate a more detailed diagnosis to exclude other pathological changes in the urinary system, similar to the ultrasound image.

  • Simple kidney cysts: symptoms

Usually, simple cysts of the kidneys are asymptomatic, while large fluid spaces can cause pain, discomfort in the lumbar and sacral regions and in the abdominal cavity, as well as hematuria and hypertension.

Due to the lack of characteristic symptoms, simple kidney cysts are most often detected accidentally during diagnostic imaging examinations, which include ultrasound (USG), computed tomography (CT) and magnetic resonance imaging (MRI) of the abdominal cavity.

  • Simple kidney cysts: diagnosis

The most frequently used method in the diagnosis of simple cysts within the kidneys and the differentiation between solid lesions and fluid-containing lesions is ultrasound due to its high availability.

In a correct ultrasound image, cysts should be sharply demarcated from the surrounding tissues, with a thin wall and smooth outlines, single-chamber, oval-shaped and anechoic.

During computed tomography examination, the typical feature of a simple cyst is the lack of enhancement after intravenous administration of a contrast agent.

The discovery of unusual changes within the cyst, which include calcifications, the presence of internal echoes, or an irregular outline of the wall, should worry the doctor performing the examination.

In this case, it is recommended to deepen the diagnosis with more advanced and more accurate imaging methods, because cysts that do not meet the criteria of a simple cyst require differentiation from other cystic kidney diseases, as well as kidney cancer.

In case of any doubts regarding the detected lesion, the patient should be ordered to undergo a CT scan as it is the method of choice in detecting, differentiating and assessing the severity of kidney tumors.

  • Simple kidney cysts: treatment

Pharmacological or surgical treatment of asymptomatic simple small kidney cysts is not practiced.

Large diameter lesions that cause pain or discomfort shouldbe removed during surgery performed by a specialist urologist by laparoscopic or open method, if the doctor decides so.

Another method of invasive treatment is puncture of the cyst to aspirate and remove the fluid, and sclerotization, which consists in injecting 95% ethanol into the lumen of the cyst.

The task of alcohol is to destroy the epithelium that lines the inside of the cyst. Thanks to this procedure, the cyst will reduce its dimensions. Unfortunately, the recurrence rate of simple cysts after fluid aspiration and sclerotization is about 90%.

  • Simple kidney cysts: complications

The most common complications associated with simple renal cysts are episodes of hematuria, infection of the cyst contents, and transient pyuria.

If you experience symptoms such as fever accompanied by abdominal pain or pyuria, contact your primary care physician.

  • Simple kidney cysts: control

Periodic kidney imaging is recommended, as simple cysts can degenerate into neoplasms, but this is very rare.

In the case of asymptomatic simple cysts, it is recommended to perform an ultrasound once a year.

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Complex kidney cysts

Complex kidney cysts are cysts which, on radiological examinations, show features that prevent a doctor from classifying them as simple cysts.

They have calcification in their structure, are limited by thick walls, and may strengthen after the administration of intravenous contrast during a CT scan.

The detection of such a cyst during tests requires a more detailed diagnosis and the exclusion of the development of a neoplastic process.

Classification of Bosnian cystic masses in the kidneys

Classification of Bosnian kidney cystic lesions (other than simple cysts) can be divided into 4 categories. It is based on the presence of the characteristic features of cysts described during imaging using computed tomography with the use of intravenous contrast agent.

The scale is particularly useful for determining the risk of malignancy of the detected lesion, the need for treatment or further oncological diagnostics.Category I - simple, thin-walled kidney cyst

  • no ventricular partitions
  • no calcification
  • do not contain any content
  • are not strengthened after intravenous contrast agent administration in CT
  • cysts with such characteristics norequire treatment and further oncological diagnostics

Category II - Thin-walled benign cyst

  • contains 1 or 2 thin ventricular partitions
  • may contain slight calcifications within the walls or partitions
  • ventricular septa do not strengthen after intravenous contrast medium administration in CT
  • cysts with such characteristics do not require further oncological diagnostics

Category II F (follow up) - the cyst contains numerous thin septa

  • may contain minor calcifications within the walls or partitions
  • ventricular septum discreetly strengthened after the administration of intravenous contrast in CT
  • no tissue elements in the cyst lumen
  • intrarenal non-contrast enhancing high density cysts>=3cm that are well demarcated from surrounding tissue
  • cysts with such characteristics require periodic control imaging examinations (every 3-6 months)

Category III cysts with a thickened, irregular or smooth wall

  • numerous ventricular septa which are strengthened after intravenous contrast agent administration in CT
  • close observation is recommended, more than 50% of lesions are malignant
  • they mostly require surgery

Category IV - cystic masses with the characteristics of Category III cysts with the presence of soft tissues inside, which strengthen after the administration of intravenous contrast agent in CT

  • surgery is recommended, most lesions are malignant

Acquired cystic kidney disease

Acquired cystic kidney disease is a condition that occurs in patients who suffer from chronic renal failure.

Characterized by the presence of more than 4 cysts in each kidney, excluding polycystic renal degeneration.

The etiology of cyst formation is unknown, but it has been observed that their number increases with the advancement of the underlying disease (kidney cysts are diagnosed in more than 90% of dialysis patients for a minimum of 10 years).

Usually, patients do not report any symptoms, occasionally they report the presence of hematuria, chronic pain in the lumbar region or renal colic. Acquired cystic kidney disease does not require treatment if it is asymptomatic and without complications.

Polycystic kidney degeneration (cystic kidney disease)

Polycystic kidney disease is also calledoften with polycystic kidney disease (PKD).

It is a genetic condition characterized by the presence of numerous cysts in the cortex and the renal medulla.

There are 4 types of disease - adult cystic disease, childhood cystic disease, cystic renal dysplasia and spongy renal medulla.Potter's classification of renal cystic disease based on the image of the kidneys in ultrasound

  • Potter type 1 - childhood polycystic kidney disease (ARPKD)
  • Potter type 2 - polycystic kidney dysplasia
  • Potter type 3 - adult polycystic kidney disease (ADPKD), spongy renal medulla
  • Potter type 4 - obstructive polycystic kidney degeneration

Adult kidney cystic disease

Adult cystic kidney disease (autosomal dominant polycystic kidney disease, ADPKD) is the most common genetically determined kidney disease, with a frequency of 1: 1000 births in the population.

ADPKD is caused by a mutation in the genes PKD 1 (located on chromosome 16) and PKD 2 (located on chromosome 4).

The disease may affect one or both of the kidneys, which enlarge with age and become enormous.

  • Adult cystic kidney disease: symptoms

The first symptoms of the disease usually appear after the age of 30. In the initial phase, patients report pain in the lumbar region, recurrent urinary tract infections, polyuria and the need to urinate at night, the appearance of arterial hypertension, and symptoms of renal colic.

With the development of the disease, intense pains in the lumbar region or abdominal pain, hematuria, enlarged abdominal circumference and headaches are observed. In end-stage renal cystic disease, renal failure develops.

  • Adult renal cystic disease: diagnosis

The test used to diagnose polycystic kidney disease is ultrasonography.

The typical features of this disease entity are the presence of numerous cysts of different dimensions in both kidneys, as well as the significant enlargement of the dimensions of these organs, which become lumpy.

Based on the image of the kidneys in the USG examination, the criteria for the diagnosis of ADPKD were developed according to Ravin. This classification is based on the assessment of 3 features: patient age, family history and the number of renal cysts.

Family interviewNumbercysts required for the diagnosis of ADPKD
Under 3030.-60. year of lifeOver 60 years of age
Positive>=2 cysts in one or both kidneys together >=2 cysts in each kidney >=4 cysts in each kidney
Negative>=5 cysts in one or both kidneys together >=5 cysts in each kidney >=8 cysts in each kidney

Supportive examinations include scintigraphy and urography, but in case of diagnostic doubts, it is recommended to perform renal arteriography, computed tomography or magnetic resonance imaging.

Cysts can occur not only in the kidneys but also in other organs such as the liver, spleen, pancreas and lungs.

The diseases accompanying cystic kidney disease include arterial hypertension, nephrolithiasis, and aneurysms of the arterial circle of the brain (Willis), which are found in up to 10% of patients.

  • Adult kidney cystic disease: treatment

Treatment options for adult kidney cystic disease are limited. It is recommended to lead a sparing lifestyle and avoid injuries to prevent the cyst from rupturing.

Treatment is symptomatic, water and electrolyte management, blood pressure control and avoidance of urinary tract infections.

Surgical treatment is used in exceptional life-threatening situations. In the event of end-stage renal failure, dialysis therapy is instituted and a decision should be made regarding a possible kidney transplant.

Childlike cystic kidney disease

Autosomal recessive polycystic kidney disease (ARPKD) is a genetically determined disease that is very rare in society (1: 6000-1: 40,000 births).

ARPKD is caused by a mutation in the PKHD 1 gene located on chromosome 6.

The disease is diagnosed in newborns, and it may be suspected in utero based on the image of the kidneys in prenatal ultrasound.

Renal cystic disease is characterized by an abnormal structure of the collecting tubes within the kidneys, which undergo cystic dilatation.

The ultrasound image shows a significant, even two-fold enlargement of the dimensions of the kidneys with an uneven, lumpy surface, obliterated cortical structurespinal and increased echogenicity.

Very numerous cysts of small dimensions (about a few millimeters) are visible using a specialized high-frequency ultrasound head.

It is worth extending the diagnosis to include imaging of the lungs, pancreas and liver, because in the course of this type of polycystic kidney disease, cystic changes often occur in other organs.

As a rule, the disease affects both kidneys at the same time, and only in 7% of newborns one organ is affected by the disease. In the case of bilateral kidney involvement, the prognosis is very serious and unfavorable, 75% of children die in the first two years of life.

The only possible treatments for advanced disease in which end-stage renal disease develops are dialysis and kidney transplantation.

Polycystic renal dysplasia

Multicystic dysplastic kidney (MCDK) is one of the more common causes of a tumor in the abdominal cavity in a newborn.

Nowadays it is diagnosed during prenatal ultrasound during prenatal ultrasound.

In adults, especially when one kidney is affected by the disease, it is diagnosed accidentally during a follow-up ultrasound examination of the abdominal cavity or the urinary tract.

Typically polycystic dysplasia occurs as a one-sided lesion, although it can also be bilateral, and affect only a part of the organ.

It is characterized by the presence of multiple cysts of various sizes and the absence of a proper calicotropic system. It is a condition that results from abnormal kidney development in the womb.

Due to underdevelopment of the ureter or renal pelvis, the diseased kidney does not have normal tissue in terms of functionality, but only structures indicating the survival of fetal structures and calcified cysts with abnormal parenchyma between them.

When it affects both kidneys, it is fatal.

Ultrasound examination should be used to assess not only the structure of the kidney affected by the disease, but also the entire urinary system, because polycystic dysplasia may be accompanied, among others, by presence of vesicoureteral drainage, obstruction of the ureter in the kidney on the opposite side, and other birth defects in organs such as the heart, intestines and nervous system.

The disease is not common, in the population it occurs with a frequency of 1: 4,300 births.

Spongy medullary kidney - kidneyspongy

Medullary sponge kidney (MSK) is a rare, congenital kidney defect that dilates and softens the collecting tubules located in the renal pyramids. It occurs in 1 in 5,000 people in the population.

As a rule, the disease is asymptomatic, and the first symptoms do not appear until around 40-50. years of age, although the disease develops from birth.

Symptoms such as increased urinary calcium excretion (hypercalciuria), hematuria, sterile pyuria, and renal colic may occur due to an increased predisposition to the formation of medullary calcification, nephrolithiasis, and nephrocalcinosis (nephrocalcinosis).

Imaging tests, such as X-rays of the urinary system, as well as urographic examination, which is the most sensitive, are used to diagnose the sponginess of the renal medulla.

It shows pearly deposits within the kidney papillae and radial strands of contrast agent in the renal medulla.

Ultrasound examination shows numerous small cysts 1-7mm in diameter and numerous calcifications resembling grape clusters.

In samples taken during autopsy, the altered kidney looks like a sponge on the cross-section, hence the name of the disease.

Treatment of spongy medullary kidneys is only symptomatic. Particular attention should be paid to the prevention of urinary tract infections, as they often recur and, together with kidney stones, may cause renal failure.

Cystic renal medulla

Medullary cystic kidney disease (MCKD) is an autosomal dominant genetically determined disease.

Most patients have a mutation in the gene encoding the uromodulin protein (i.e. the Tamm and Horsfall protein), which is a component of the renal tubular basement membrane.

There is a formation of small cysts and fibrosis in the parenchyma of the affected kidneys, which reduces their dimensions.

The most frequently reported disease symptoms are:

  • polyuria
  • increased thirst
  • proteinuria
  • changes in urine sediment
  • renal anemia

The diagnosis of cystic renal medulla is based on family history, clinical symptoms, laboratory tests and a typical ultrasound image of the kidneys.

As the disease progresses, it comes to end-stage renal disease. In these patients, apart from symptomatic treatment, dialysis therapy is introduced.

Nephronophthysis

Nephronophtysis (NPH) is a genetically determined kidney disease inherited in an autosomal recessive manner.

Most patients have mutations in the NPH1 gene (causes loss of nephrocystin protein function) located on chromosome 2, NPH2 (encodes inversin protein) on chromosome 9 or NPH3 (encodes protein nephrocystin 3) on chromosome 3, depending on on the type of disease.

Nephronophthosis can occur in both children and adults, and the first symptoms appear between the ages of 4 and 8.

Symptoms of the disease are similar to those of renal medullary cystic disease, with polyuria, increased thirst, proteinuria, changes in urine sediment and renal anemia, but they appear much earlier.

It is worth mentioning that there are also reports of extra-renal changes, including impaired growth and degeneration of the retina. End-stage renal disease develops as the disease progresses.

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Urology and Nephrology