Renal Cyst: Clinical Guidelines

List of Abbreviations

BP — blood pressure

AH — arterial hypertension

MSCT — multislice computed tomography

CT — computed tomography

MRI — magnetic resonance imaging

Ultrasound — ultrasound examination

EH — essential hypertension

Urolithiasis — urolithiasis

CDFI — color Doppler flow imaging

LDH – lactate dehydrogenase

ESR – erythrocyte sedimentation rate

LoE – level of evidence

GoR – grade of recommendation

BMI – body mass index

GFR – glomerular filtration rate

CM – Contrast media (agents) ATC code – V08

Terms and Definitions

Disease – a disorder of body function, working capacity, and the ability to adapt to changing environmental and internal conditions arising from the impact of pathogenic factors, accompanied by a simultaneous alteration of the body's protective-compensatory and protective-adaptive reactions and mechanisms.

Instrumental diagnostics – diagnostics utilizing various devices, apparatus, and instruments for patient examination.

Laboratory diagnostics – a set of methods aimed at analyzing test material using various specialized equipment.

Syndrome – a cluster of symptoms sharing a common etiology and pathogenesis.

Condition – changes in the body arising from the impact of pathogenic and/or physiological factors and requiring medical care.

Level of evidence – reflects the degree of certainty that the estimated effect of a medical intervention is true.

Grade of recommendation – the degree of certainty in the validity of an intervention's effect and that following the recommendations will do more good than harm in a specific situation.

Surgical intervention – an invasive procedure that may be used for diagnostic purposes and/or as a method of treating diseases.

Surgical treatment – a method of treating diseases through the division and joining of tissues during a surgical operation.

Disease recurrence – the return of a disease after an apparent complete recovery.

Disease outcome – any possible result arising from the impact of a causative factor, prophylactic or therapeutic intervention, and all established changes in health status occurring as a consequence of the intervention.

1. Brief information on the disease or condition

1.1 Definition of the disease or condition

Acquired renal cyst (synonyms: simple, solitary, serous, true, cortical cyst) – a benign, thin-walled, volumetric lesion developing from the renal parenchyma and containing, as a rule, serous fluid produced by the cyst lining itself. Of all proposed naming options, the term "simple cyst" is the most appropriate, as it emphasizes the benign clinical course of the disease, which represents the main characteristic of these neoplasms [1, 2, 3, 4, 5].

1.2 Etiology and pathogenesis of the disease or condition (group of diseases or conditions)

The main theories of renal cyst pathogenesis include:

• Retention-inflammatory – the cyst develops as a result of obstruction and inflammation of the tubular and urinary ducts during embryonic development.

• Proliferative-neoplastic – the cyst arises due to excessive proliferation of the renal epithelium (urothelium).

• Embryonic – the cyst develops due to a defect in the connection between the filtration and secretory parts of metanephrons and the excretory tissue of the mesonephric ducts (Wolffian duct); in these cases, the cyst originates from:

- germinal (primitive) nephron buds;

- embryonic tubules preserved at the cystic stage of development;

- embryonic remnants of ureteral and pelvic cells incorporated into the parenchyma.

One pathogenetic variant is the formation of microscopic dilation of the distal convoluted tubules or collecting ducts as a consequence of unfavorable conditions for urine outflow caused by obstruction and active glomerular secretion above the site of obstruction. This mechanism combines both tubular occlusion (congenital or acquired) and renal tissue ischemia [6].

1.3 Epidemiology of the Disease or Condition

Literature data on the detection rate of simple renal cysts are directly dependent on the diagnostic methods used in patient examination and have changed significantly with the development of diagnostic technologies. Most researchers in the pre-ultrasound era of diagnostics described cystic renal diseases as quite rare, whereas the same authors noted their frequent discovery at autopsies [7, 8, 9]. With the widespread introduction of ultrasound diagnostics and tomographic techniques (CT, MRI) into clinical medicine, cysts began to be detected much more frequently [1, 2, 4, 5, 10, 11].

Among all cystic lesions, the simple cyst is the most common, being diagnosed in 3% of adult patients suffering from urological diseases and found in 50% of autopsies [12]. Simple renal cysts are most frequently encountered at the age of 50 years and older, occurring more often in men than in women with a ratio ranging from 3/2 to 2/1 [3, 13, 14]. With the introduction of CT techniques, cysts are detected in 33% of individuals in the age group over 50 years [15]. The question of whether the number and size of cysts increase remains controversial, but many authors note an increase in both the number and size of cysts with patient age [16, 17, 18, 19, 20].

1.4 Features of Coding the Disease or Condition

N28.1 Acquired renal cyst.

Q61.0 Congenital single renal cyst

Q61.8 Other cystic kidney diseases

1.5 Classification of the disease or condition

More than 20 different classifications of cystic renal lesions have been described in the literature. One of the earliest was the classification by A.Ya. Pytel and Yu.A. Pytel in 1966, according to which all cysts were divided into congenital and acquired [21]. Congenital cysts include polycystic kidney disease, medullary sponge kidney, and simple renal cyst. In addition to the simple renal cyst, the solitary cyst subgroup includes multilocular cysts, parapelvic cysts, and dermoid cysts. Acquired cysts also include parasitic and non-parasitic benign and malignant cystadenomas.

In the classification by A.Ya. Pytel and A.G. Pugachev in 1977, simple renal cysts were divided into groups [22]. According to this classification, a simple cyst can be congenital, acquired; unilateral or bilateral; single or multiple; serous, hemorrhagic, infected; intraparenchymal, cortical, peripelvic, subcapsular, or multilocular. All existing classifications are not without flaws, and many positions remain controversial.

In recent clinical practice, in order to differentiate cysts and cystic tumors based on tomographic criteria, the Bosniak renal cyst classification is used, which was first introduced in 1986, modified in 1994, and updated in 2019 [10, 13, 15, 23]:

Schematic explanation of the introduced clarifying terminology: a – single septa in a quantity of ≤3, multiple – ≥4; b – thin septum or wall with a thickness of ≤2 mm, minimally thickened – 3 mm, thickened – ≥4 mm; c – solid growths along the wall or septa of cystic lesions, shown in gray on the diagram with an acute angle of protrusion, and in black with an obtuse angle.

This classification not only allows cystic kidney diseases to be subdivided into distinct groups, but also determines clinical management strategies, including the most appropriate treatment method. It should be noted that to date, there are no randomized controlled trials regarding the criteria for monitoring and treating cystic renal lesions, and all recommendations are based on expert opinion. Evidence-based criteria exist only for the diagnostic and therapeutic management of category III and IV cystic lesions [5, 10, 11, 15].

1.6 Clinical presentation of the disease or condition

Acquired renal cyst has no pathognomonic clinical signs, and in 70% of patients it is asymptomatic, causing no clinical manifestations for years or even decades. For this reason, it is impossible to reliably diagnose it based solely on clinical symptoms. Often, a simple cyst is accidentally discovered during an examination of a patient for an unrelated disease (pathology of other organs and systems).

Risk factors for the development of acquired renal cysts include the following [14, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33]:

• advanced age,

• male sex,

• urolithiasis,

• smoking,

• arterial hypertension,

• renal dysfunction (azotemia),

• diabetes mellitus,

• gout.

The most characteristic symptoms of a renal cyst are as follows:

• discomfort in the hypochondrium or lumbar region,

• arterial hypertension,

• hematuria.

Pain and discomfort are the most common symptoms that most frequently prompt patients to seek medical attention. A progressive simple renal cyst may in some cases lead to upper urinary tract obstruction, impeding urine flow due to compression of the renal pelvis, calyces, or upper third of the ureter, thereby causing pain. These symptoms should be differentiated from manifestations of other conditions (including urolithiasis, dorsopathy, etc.). When a cyst becomes infected or suppurates, the disease takes an acute course accompanied by high fever and worsening pain.

The combination of a simple renal cyst and transient arterial hypertension occurs in 20% of cases. Arterial hypertension in patients with a simple cyst is of nephrogenic origin and is caused by compression of the renal parenchyma by the cyst followed by renal ischemia. Establishing the simple cyst as the causative factor of hypertension largely determines the choice of treatment method and indications for cyst decompression, regardless of its location. Following cyst aspiration/decompression, blood pressure typically decreases and plasma renin concentration normalizes.

A large uncomplicated renal cyst is generally understood as one with a maximum cross-section exceeding 3 cm. Starting from this size, active surgical management is applicable for this condition. Timely removal or decompression of the cyst helps preserve renal function and eliminate potential symptoms. [34, 35, 36, 37]

2. Diagnostics, medical indications and contraindications for diagnostic methods

Introduction. The diagnosis of acquired renal cyst is associated with certain difficulties due to the absence of clinical manifestations specific solely to this disease, the paucity of subjective symptoms, and, in some cases, a completely asymptomatic course. Furthermore, most clinical symptoms of renal cysts share similar features with renal parenchyma tumors, polycystic kidney disease, dermoid and parasitic cysts, hydronephrosis, and renal abscess.

Criteria for establishing the diagnosis/condition based on:

1. anamnestic data – cystic or fluid structures in the kidneys previously detected during examinations, and a family history of cystic renal diseases;

2. physical examination – patient complaints of discomfort and pain in the lumbar and hypochondriac regions, elevated blood pressure, and blood in the urine. A palpable, mildly tender mass in the hypochondrium, in the projection of the kidney;

3. ultrasound examination of the kidneys – detection of an echo-negative, thin-walled round or oval formation in the renal projection with clear, smooth, continuous contours and posterior acoustic enhancement;

4. contrast-enhanced computed tomography or magnetic resonance imaging of the kidneys – a round or oval neoplasm of fluid density that does not enhance with contrast agents.

2.1 Complaints and Anamnesis

Complaints and medical history are described in section 1.6 "Clinical Presentation".

Comments: Clinical manifestations of acquired renal cysts are meager and nonspecific. Patients usually do not present with significant complaints. They report periodic or constant aching pain in the corresponding half of the lower back or hypochondrium, without clear radiation. The pain may worsen with physical exertion. Typically, pain sensations subside at rest. Patients occasionally report a palpable mass in the hypochondrium or the sensation of an additional abdominal mass detected during self-examination.

The evaluation begins with a detailed history and assessment of complaints, paying attention to the duration of symptoms, presence of pain or lumbar trauma, as well as blood pressure changes and a history of hematuria. [29, 35, 36].

2.2 Physical Examination

Physical examination most often does not allow for a reliable assessment of the presence of a simple renal cyst.

During physical examination of patients with large renal cysts, an enlarged or downward-displaced kidney can be palpated in the corresponding hypochondriac or flank regions of the abdomen.

In some cases, localized tenderness on palpation and a positive Pasternack's sign (costovertebral angle tenderness) in the lumbar region may be elicited by gently tapping with the hand over the renal projection.

When measuring blood pressure, arterial hypertension is noted in a subset of patients (20%).

Comments: examination of the patient in standing and supine positions in a warm room. Abdominal palpation should be performed not only in the supine position, but also in the lateral position, with the legs drawn up to the abdomen. Percussion and tapping of the lumbar regions should be performed with the patient sitting or standing, applying short, light blows with the ulnar edge of the hand in the area of renal projection (costovertebral angle), alternately on the right and left sides. Blood pressure measurements must be taken alternately on both brachial arteries. Physical examination data make it possible to detect the presence of a mass in the hypochondria, pain in the renal projection, and arterial hypertension.

2.3 Laboratory Diagnostics

Laboratory abnormalities are nonspecific and often completely absent. Nevertheless:

- complete urinalysis – to rule out microhematuria.

- general biochemical blood test – to rule out elevated azotemic parameters (blood creatinine level, glomerular filtration rate).

GCP CLOE 4Grade of Recommendation — C (Level of Evidence — 4)

Comments: microhematuria is a fairly rare symptom of a simple renal cyst, indicating impaired organ blood flow and venous congestion. Assessment of blood creatinine levels, blood urea levels, and calculation of the glomerular filtration rate allow for the evaluation of signs of concomitant renal failure.

2.4 Instrumental Diagnostics

The introduction of modern diagnostic imaging methods (ultrasound, CT, MRI) into clinical practice makes it possible to establish an accurate diagnosis in the majority of cases.

Ultrasonography

Comments: the current understanding of renal cyst diagnostics primarily relies on ultrasound imaging due to its near-universal availability, high efficacy, lack of side effects, and low cost, which is supported by the results of numerous domestic and international studies over many years. B-mode ultrasound can differentiate between simple and complex cysts [38, 84]. When signs of a complex renal cyst are detected (thickening of the wall, septa, solid component, etc.), computed tomography of the kidneys and upper urinary tract with intravenous bolus contrast enhancement (A06.28.009.001) or magnetic resonance imaging of the kidneys with contrast enhancement (A05.28.002.001) is required, accompanied by a description of the identified changes according to the Bosniak classification [39]. Contrast-enhanced ultrasound can also be used to characterize cystic renal masses according to Bosniak [84, 85].

Computed tomography

The gold standard for diagnosing renal cysts is computed tomography of the kidneys and upper urinary tract with intravenous bolus contrast enhancement. This method allows not only the detection of cystic lesions, but also the differential diagnosis of cysts and cystic tumors.

Comments: CT of the kidneys and upper urinary tract with intravenous bolus contrast enhancement is the most valuable and effective diagnostic method for cystic renal lesions, provided the patient has no contraindications to the procedure.

CT techniques with intravenous bolus administration of contrast agents (ATC V08), introduced into urological practice in 1972, are currently the "gold standard" in the evaluation of patients with cystic renal lesions. The efficacy of CT for acquired renal cysts reaches 100%. The Bosniak working classification of cysts was developed precisely on the basis of CT diagnostic results. Modern information processing and digitalization techniques, three-dimensional and multiplanar reconstructions, and virtual endoscopy provide qualitatively new information [39, 41]. In addition to determining cyst characteristics, CT of the kidneys and upper urinary tract with intravenous bolus contrast enhancement makes it possible to assess the topographic and anatomical relationships of renal lesions with the elements of the pelvicalyceal system, renal hilum, vascular structures, and adjacent organs.

The main difficulty lies in the diagnosis of complex renal cysts and cystic masses, which most often represent malignant cystic tumors. Cystic renal tumors on a series of CT scans of the kidneys and upper urinary tract with intravenous bolus contrast enhancement are characterized by nodular areas in the wall or thickened cyst septa, which, according to computed tomography data, enhance with contrast agents (ATC V08); these structures are most often the site where cancer is detected.

For renal cell carcinoma (RCC) and benign cysts, the mean attenuation in the pre-contrast phase is approximately similar, being 31.5 and 32.4 HU, respectively. Meanwhile, renal cell carcinoma demonstrates significantly higher values in the corticomedullary phase—112.9 versus 59.8 HU, respectively. A formula has been developed to differentiate renal cell carcinoma. According to this formula, if the difference between the radiological attenuation in the corticomedullary phase and the attenuation in the pre-contrast phase is equal to or greater than 42 HU, the lesion under investigation is most likely RCC. This technique has a sensitivity of 97.1% and a specificity of 85.7% [39, 40].

Renal and urinary tract scintigraphy

Comments: According to several studies, renal cyst growth can lead to renal parenchyma atrophy and a decrease in the GFR of the cyst-affected kidney [43, 44, 45, 46]. While the volume of the renal parenchyma and the volume of the cyst cavity can be calculated using segmentation methods based on CT data of the kidneys and upper urinary tract with intravenous bolus contrast enhancement, renal and urinary tract scintigraphy is used to determine the function (GFR) of the cyst-affected kidney and indications for surgical treatment of the renal cyst. The loss of 20% of the renal parenchyma may be considered an indication for renal and urinary tract scintigraphy, since the loss of one-fifth of the renal parenchyma volume increases the likelihood of a significant decrease in GFR by more than 10 times [34].

Magnetic resonance imaging

Comments: Contrast-enhanced MRI of the kidneys is a highly sensitive and specific method for diagnosing renal cysts, and this method can be used in pregnant women as well as in patients with allergies to iodinated radiocontrast agents (ATC V08A). According to the literature, when using this method to diagnose complex renal cysts, its sensitivity is 71% and specificity is 91% [48]. It is worth noting that when analyzing CT images, massive calcification can mask the soft tissue component; to rule this out, MRI can be used as a method with higher sensitivity for detecting areas of contrast enhancement, including those not discernible against the background of calcifications on CT. Renal MRI makes it possible to visualize septa that are poorly identifiable on computed tomography; furthermore, it helps differentiate complex renal cysts from hemorrhagic cysts and renal hematomas [49].

2.5 Other Procedures

Laboratory and morphological studies of cyst walls and cystic fluid

Comments: The cavity of simple cysts is usually filled with serous fluid. In some cases, hemorrhagic cyst contents may be present, but true "hemorrhagic" cysts account for only 0.4–0.6%. Cytological examination of the renal cyst contents (cyst content sediment) reveals epithelial cells without signs of atypia, and occasionally lymphocytes and macrophages. In cystic renal tumors of Bosniak categories III and IV, atypical cells in cyst aspirates are detected in 50% of cases. A number of clinical cases have shown that in the majority of instances, this result turns out to be false-negative [52, 53].

Comments: macroscopically, the cyst wall has a smooth, thin, shiny surface, clearly demarcated from the renal parenchyma. Microscopically, the cyst wall is represented by a connective tissue capsule lined with flattened or single-layer columnar epithelium. Chronic inflammatory infiltration may be observed in the cyst wall, with a cellular composition represented by lymphocytes and plasma cells, as well as macrophages containing hemosiderin. At the cellular level, the paracystic zone of the renal parenchyma shows tubular atrophy, interstitial sclerosis, glomerular hyalinosis, and signs of chronic inflammation [56]. When performing a pathomorphological examination of the renal biopsy (surgical) material (examination of the excised wall) (A08.28.005), its malignant potential must be ruled out. A Russian study showed that malignant neoplasms after surgical excision of category I, II, and IIF cysts were detected in 0%, 2.7%, and 15.1 of cases, respectively [57]. Renal cysts of Bosniak category II and higher have varying malignant potential, although referring to cyst transformation as "malignant degeneration" is incorrect. Malignant cysts are usually early-stage tumors with a low histological grade [58]. Bosniak category IV renal cysts most commonly represent a cystic variant of renal cell carcinoma. Most renal cell carcinomas are solid, but 4–7% are cystic and correspond to Bosniak category IV [59].

3. Treatment, including drug and non-drug therapies, diet therapy, and pain management

Introduction. Most asymptomatic simple renal cysts require only active surveillance, monitoring both cyst characteristics and trends in clinical symptoms, the course of arterial hypertension, and renal function. Given the availability and safety of ultrasound diagnostics and the growth rate of cysts, the most rational approach is to perform renal ultrasound every 6 months for the first year, followed by annual monitoring thereafter.

Indications for surgical treatment include:

• presence of intractable pain syndrome (after ruling out other causes of these symptoms), leading to a persistent decrease in the patient's quality of life and working capacity,

• deformation of the pelvicalyceal system of the affected kidney causing urodynamic impairment due to cyst compression on the renal pelvicalyceal system,

• decreased renal function (GFR) according to dynamic nephroscintigraphy results,

• patients with a cyst in a solitary kidney and decreased renal function,

• persistent uncorrectable arterial hypertension, after ruling out other causes for its occurrence,

• the patient's persistent desire to be rid of this condition.

3.1 Conservative Treatment

There are no conservative or pharmacological treatments for acquired renal cysts.

3.2 Surgical methods of treatment

3.2.1 Puncture methods of treatment

Percutaneous cyst puncture with aspiration of contents and sclerotherapy of the cyst cavity is an effective and reasonably safe treatment method (A11.28.004.001 puncture and aspiration from a renal cyst or renal pelvis under ultrasound guidance). The advantage of this surgical method is its minimally invasive nature, which is why it is actively used in elderly and comorbid patients as it can be performed under local anesthesia. Furthermore, this method is one of the most common procedures for treating simple cysts due to its high cost-effectiveness, low complication rate, possibility of performance without general anesthesia, and extremely rapid patient rehabilitation.

Comments: The efficacy of puncture treatment ranges from 84 to 96% [62]. However, the recurrence rate with this method can reach 30–54% [63]. With every 3 cm increase in cyst size (4–7 cm / 7–10 cm / > 10 cm), the recurrence rate increases by 3.5 times [64]. The most frequently used sclerosing agent is 95% #ethanol, as it does not require dilution, lacks significant systemic toxic effects, and is rapidly eliminated from the body [60, 61]. The exposure time of the drug for complete sclerotherapy of the cyst walls ranges from 5 minutes to 4 hours. However, there is no difference in achieving a positive therapeutic effect between 2- and 4-hour sclerotherapy protocols [65]. The volume of the sclerosing agent should be 20%–25% of the cyst volume, but should not exceed 100 ml due to the high risk of complications. For large cysts greater than 10 cm, it is advisable to drain them for 2–3 days with repeated episodes of sclerotherapy. If there is no discharge during the specified period, the drain is removed. Complications of the technique are associated with both the technical difficulty of the puncture and the increase in the volume of the administered drug, accounting for about 11.2% [66]. Puncture drainage and sclerotherapy of the renal cyst (A16.28.089) is a safe and effective first-line therapy for symptomatic simple renal cysts, although it is inferior in efficacy to laparoscopic renal cyst excision (A16.28.071.001) due to a higher risk of disease recurrence [67, 68, 69, 70, 71].

3.2.2 Video-endosurgical methods of treatment

Extrarenal marsupialization (A16.14.002) with cystoscopy and wide resection or incision of the cyst wall using various types of energy and its communication with the perirenal adipose tissue under endoscopic guidance is an experimental treatment method with a high percentage of complication risks. A cyst cavity communicated with the pelvicalyceal system differs very little from a hydrocalyx or calyceal cyst (diverticulum). This method is not applicable in routine clinical practice for patients with renal cysts [72, 73].

Laparoscopic excision of renal cysts (A16.28.071.001 laparoscopic excision of renal cyst) is a safe and effective surgical treatment method and is considered as a second-line therapy for renal cysts or as a first-line method in the presence of significant risk factors for disease recurrence [74].

Comments: The efficacy of laparoscopic renal cyst excision based on postoperative instrumental characteristics reaches 96%, and based on clinical criteria assessing the regression of pain syndrome, it is 95% [70]. For laparoscopic excision of renal cysts, transperitoneal or retroperitoneoscopic approaches can be used, depending on the location of the cyst, with no significant difference in efficacy and safety between them [77]. It is possible to use a drainless modification of the surgery, early removal of the urinary catheter, and patient mobilization to achieve higher patient satisfaction with the surgery [78]. No significant differences were noted between percutaneous puncture and laparoscopic treatment methods regarding the overall complication rate, but economic costs for laparoscopic technologies exceed puncture methods by more than twofold.

Considering comparative studies regarding the two techniques, it can be concluded that in young, non-debilitated patients with low surgical risks, patients with large cysts, and those with a high risk of recurrence, laparoscopic decortication of the renal cyst is indicated. Meanwhile, in comorbid patients with renal cysts up to 5 cm in size, percutaneous cyst aspiration followed by sclerotherapy is recommended with a high probability of success and the possibility of repeated sessions if necessary [70, 71, 76, 79].

Partial nephrectomy using a laparoscopic or robot-assisted approach is applicable for Bosniak type III and IV renal cysts, given the high probability of diagnosing renal cell carcinoma (RCC) [48, 50, 89]. Depending on the clinical situation, the patient may undergo nephrectomy.

Comments: when performing these surgical techniques, the main objectives are to achieve oncological radicality, including tumor removal within healthy tissue, reducing warm ischemia time during surgical stages, preserving as much normal renal parenchyma as possible, and preserving the intrarenal arterial vascular tree necessary for the recovery of renal function. Robot-assisted surgical procedures are certainly effective; however, due to the need for accessible special expensive equipment and extremely high economic costs, these techniques are impractical for uncomplicated Bosniak category I, II, and IIF cysts. Nevertheless, they are of great practical value for cystic formations of Bosniak categories III and IV [80, 81, 82].

4. Medical Rehabilitation and Sanatorium-Resort Treatment

There are no rehabilitation and sanatorium-resort treatment methods for renal cysts, and they are not recommended for use.

5. Prevention and Dispensary Observation

There is no specific prevention for renal cysts. Preventive measures are based on risk factors and come down to timely and effective treatment of urolithiasis, management of diabetes mellitus and gout, as well as smoking cessation. For screening of this disease, renal ultrasound is the most accessible method.

Follow-up is performed every 6–12 months for uncomplicated category I and II renal cysts to evaluate cyst growth dynamics [24]. Careful monitoring is also required for patients with a cyst in a solitary or solely functioning kidney [83].

Any complicated cystic formations (categories IIF, III, IV) are considered to be potentially malignant and require further evaluation and active treatment. Contrast-enhanced renal MRI can provide valuable information, but in complex situations, it is used in diagnostics as an adjunct to computed tomography of the kidneys and upper urinary tracts with intravenous bolus contrast enhancement [11, 15].

Comments: Annual renal ultrasound is a mandatory method for monitoring cyst growth and changes in their characteristics. Renal ultrasound is also indicated in the follow-up of patients who have undergone puncture or surgical treatment in order to timely detect disease recurrence.

6. Organization of Medical Care

Indications for hospital admission to a medical organization:

1. puncture treatment of a renal cyst. Planned hospital admission

2. laparoscopic treatment of a renal cyst. Planned hospital admission;

3. renal resection using a laparoscopic or robot-assisted approach. Planned hospital admission;

4. cyst infection with purulent-septic complications. Emergency hospital admission

Indications for discharging a patient from a medical organization:

1. restoration of the patient's satisfactory well-being and cyst drainage after puncture treatment, 1–2 days post-surgery;

3. restoration of the patient's satisfactory well-being and activity, elimination of the cyst after laparoscopic renal cyst excision, exclusion of the risk of delayed bleeding, thromboembolic complications, and intestinal paresis, 1–2 days post-surgery;

4. restoration of the patient's satisfactory well-being and activity, elimination of the cyst after surgical treatment, exclusion of the risk of delayed bleeding and intestinal paresis, timely and uncomplicated postoperative course, timely healing of the postoperative wound, 5–7 days post-surgery;

5. elimination of the purulent infection focus. 7–10 days, provided complete resolution of the acute inflammatory process;

7. Additional Information

The prognosis for renal cysts is favorable. The standard method for detecting renal cysts is ultrasound. To differentiate the diagnosis and clarify the Bosniak cyst type, it is necessary to use computed tomography of the kidneys and upper urinary tracts with intravenous bolus contrast enhancement (A06.28.009.001). As alternative methods for the differential diagnosis of complex cysts (types III–IV) and in the presence of contraindications to CT of the kidneys and upper urinary tracts with intravenous bolus contrast enhancement, renal ultrasound or contrast-enhanced magnetic resonance imaging of the kidneys (A05.28.002.001) should be used. Ultrasound-guided renal biopsy (A11.28.001.001) of complex renal cysts is not recommended. Follow-up is indicated for patients with small cysts that show no tendency to grow, classified as Bosniak categories I, II, and IIF. Patients with cysts in an anatomically or functionally solitary kidney require special attention and monitoring due to the risk of developing renal failure. In the presence of symptoms, elevated blood pressure, or asymmetric decrease in renal function, surgical treatment of the renal cyst should be considered. As a first-line therapy, puncture drainage and sclerotherapy of the renal cyst (A16.28.089) are indicated for patients with small cysts (volume less than 100 ml) without septa, as well as for comorbid and elderly patients. In case of disease recurrence, in non-debilitated patients, or when diagnosing large cysts (volume greater than 100 ml) with septa, laparoscopic renal cyst excision is recommended [3, 5, 10, 11, 83].

Criteria for Evaluating the Quality of Medical Care

References

Appendix A1. Working Group Composition

1. Markosyan, Tigran G., D.Sc. in Medicine, Leading Specialist at the Petrovsky National Research Centre of Surgery, Professor at the Department of Rehabilitative Medicine, Balneology and Physiotherapy, Nursing with a Course in Sports Medicine at the Medical-Biological University of Innovations and Continuing Education of the Burnasyan Federal Medical Biophysical Center of the Federal Medical-Biological Agency of Russia;

2. Shpot, Evgeny V., D.Sc. in Medicine, Professor at the Research Institute of Uronephrology and Human Reproductive Health at the Sechenov First Moscow State Medical University (Sechenov University);

3. Kharchilava, Revaz R., Ph.D. in Medicine, Director of the Praksi Medica Training Center for Clinical Skills at the Sechenov First Moscow State Medical University (Sechenov University);

4. Malkhasyan, Vigen A., D.Sc. in Medicine, Professor at the Department of Urology at the Russian University of Medicine; Head of the Urological Department No. 67 at the Botkin Moscow City Clinical Hospital of the Moscow Healthcare Department;

5. Sukhikh, Sergey O., Ph.D. in Medicine, Urologist at the Moscow Urological Center of the Botkin Moscow City Clinical Hospital of the Moscow Healthcare Department;

Conflict of interest: none declared.

Appendix A2. Methodology for Developing Clinical Guidelines

Target audience for these clinical guidelines:

1. urologists;

2. pediatric urologists-andrologists;

3. surgeons;

4. general physicians / internists;

5. ultrasound diagnostics physicians;

6. general practitioners;

7. nephrologists;

8. radiologists;

9. medical students and residents in postgraduate education programs.

In these clinical guidelines, all data are ranked by level of reliability (evidence) depending on the quantity and quality of studies on the issue.

Methods used to collect/select evidence: search in electronic databases, analysis of modern scientific developments regarding acquired renal cysts in Russia and abroad, synthesis of practical experience of Russian and foreign specialists.

Methods used to formulate recommendations: expert consensus.

Table 1. Scale for assessing levels of evidence (LE) for diagnostic methods (diagnostic interventions).

Table 2. Scale for assessing levels of evidence (LE) for prevention, treatment, and medical rehabilitation methods, including those based on natural therapeutic factors (preventive, therapeutic, and rehabilitative interventions).

Table 3. Scale for assessing grades of recommendation (GoR) for prevention, diagnostic, treatment, and medical rehabilitation methods, including those based on natural therapeutic factors (preventive, diagnostic, therapeutic, and rehabilitative interventions).

Procedure for updating clinical guidelines.

The mechanism for updating clinical guidelines provides for their systematic revision at least once every three years, as well as upon the emergence of new evidence-based medicine data on the diagnosis, treatment, prevention, and rehabilitation of specific diseases, or in the presence of justified additions/comments to previously approved clinical guidelines, but no more frequently than once every 6 months.

Appendix A3. Reference Materials

1. Federal Law No. 323-FZ dated November 21, 2011, "On the Fundamentals of Public Health Protection in the Russian Federation".

2. Order of the Ministry of Health of the Russian Federation No. 562n dated October 31, 2012, approving the Procedure for Providing Medical Care in the Profile of "Urology-Andrology" (Registered with the Ministry of Justice of the Russian Federation on December 17, 2012, Registration No. 26159).

3. Order of the Ministry of Health of the Russian Federation No. 804n dated October 13, 2017, "On Approval of the Nomenclature of Medical Services" (as amended).

4. International Statistical Classification of Diseases and Related Health Problems (ICD-10);

5. Federal Law No. 489-FZ dated December 25, 2018, "On Amendments to Article 40 of the Federal Law 'On Compulsory Medical Insurance in the Russian Federation' and the Federal Law 'On the Fundamentals of Public Health Protection in the Russian Federation' regarding Clinical Guidelines".

6. Order of the Ministry of Health of the Russian Federation No. 103n dated February 28, 2019, "On Approval of the Procedure and Timeframes for the Development and Revision of Clinical Guidelines, Their Template Form, and Requirements for Their Structure, Composition, and Scientific Validity of Information Included in Clinical Guidelines".

Appendix B. Physician Action Algorithms

Appendix C. Patient Information

Acquired renal cyst (synonyms: simple, solitary, serous, true, cortical) is a benign, thin-walled, mass lesion developing from the renal parenchyma and typically containing serous fluid. It is quite common, occurring in approximately 33% of the adult population and up to 7-9% of children.

The disease usually lacks characteristic clinical signs; in 70% of patients, it is asymptomatic and often an incidental finding during examinations for diseases of other organs and systems. The main cause of renal cysts is impaired urine outflow through the collecting ducts, duct obstruction (most commonly sclerotic), and active glomerular secretion above the site of obstruction.

Symptoms

Patients are typically asymptomatic. The most characteristic symptoms of a renal cyst include: dull pain in the hypochondrium or lumbar region; elevated blood pressure; hematuria (blood in the urine).

Diagnostics

The physician examines the patient in standing and supine positions, palpates the abdomen to detect an enlarged kidney or an additional mass, and checks for tenderness in the renal areas. Blood pressure measurement on both brachial arteries is mandatory. Laboratory blood and urine tests generally do not reveal significant changes.

Renal ultrasound is the primary method for initial diagnosis of renal cysts. Combined with color Doppler ultrasonography, the method provides objective information on renal blood flow and detects signs of arterial hypertension associated with compression of the renal parenchyma by the cyst.

For differential diagnosis and determining the cyst type, contrast-enhanced computed tomography (CT) of the kidneys with intravenous bolus injection is used. This method accurately identifies the renal mass, its characteristics, and associated urinary tract abnormalities. In complex, ambiguous cases, suspected malignant cystic tumors, or iodine contrast allergies, contrast-enhanced magnetic resonance imaging (MRI) of the kidneys with intravenous bolus injection is the required diagnostic method.

Treatment

The goal of treatment is to remove the cyst or its contents, thereby reducing the compressive effect of the cyst on the renal tissue. Most asymptomatic renal cysts do not require treatment and need dynamic surveillance only. Indications for surgical treatment are based on cyst characteristics accompanied by escalating clinical manifestations or suspected renal tumor.

Conservative, medical, physiotherapeutic, or spa-resort treatments for renal cysts do not exist.

Several types of surgical interventions are available:

• puncture treatment methods consisting of cyst puncture, evacuation of contents followed by injection of sclerosing chemical agents into the cyst lumen to glue the walls together;

• laparoscopic and robot-assisted surgeries, recommended for disease recurrence or non-debilitated patients, as well as for large cysts (volume > 100 ml) with septations;

Postoperative patient monitoring includes dynamic ultrasound control. The main criteria for successful treatment are a sustained decrease in blood pressure and no cyst recurrence.

Prognosis

The prognosis for renal cysts is favorable. The rate of cyst recurrence and postoperative complications is minimal.

Prevention

Prevention of the disease is not possible. However, adhering to scheduled follow-up examinations by a urologist (physician / general practitioner) allows for timely initiation of treatment if necessary.

Appendix G. Assessment Scales, Questionnaires, and Other Evaluation Tools

Not applicable.