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Practice Essentials

One third of people older than 50 years develop cysts in their kidneys. Although most are simple cysts, renal cystic disease has multiple etiologies. Broad categories of cystic disease include the following^[1]:

Developmental – Multicystic dysplastic kidney (MCDK)
Genetic – Autosomal recessive polycystic kidney disease (ARPKD), autosomal dominant polycystic kidney disease (ADPKD), juvenile nephronophthisis (JNPHP), medullary cystic kidney disease (MCKD), glomerulocystic kidney disease (GCKD)
Cysts associated with systemic disease – Von Hippel-Lindau syndrome (VHLS), tuberous sclerosis (TS)
Acquired – Simple cysts, acquired cystic renal disease, medullary sponge kidney (MSK)
Malignancy – Cystic renal cell carcinoma (RCC); accounts for < 5% of all RCCs

The most common larger cysts include acquired cysts, simple cysts, and cysts associated with ADPKD. Smaller cysts characterize ARPKD, JNPHP, MCKD, and MSK. In adults, renal angiomyolipomas and RCC may also have cystic components.

The presentation and workup in patients with renal cysts varies with the underlying disease. Treatment is aimed at symptom control. In general, therapy is reserved for pain, hypertension, infection, renal salt wasting, and nephrolithiasis.

Pathophysiology

Cysts develop from renal tubule segments and most detach from the parent tubule after they grow to a few millimeters in size. Cyst development is generally attributed to increased proliferation of tubular epithelium, abnormalities in tubular cilia, and excessive fluid secretion.

Developmental cystic renal disease

MCDK represents abnormal development or formation of the kidney and may involve part, or all of, one or both kidneys. This condition is thought to be secondary to dysfunctional genetics, abnormal differentiation of the metanephros or in utero ureteral obstruction. Patients are observed unless complications arise directly from the kidney or its associated conditions.

Inherited cystic renal disease

ADPKD is due to mutations in the genes PKD1 and PKD2, which encode polycystin proteins. Mutations in these genes can be inherited in autosomal dominant or recessive forms, with varying levels of penetrance. The genetic mechanism of cyst development requires a "second hit," a somatic mutation of the normal PKD allele, which accounts for the onset of ADPKD, usually in those aged 30-50 years.

Symptoms primarily include pain, hypertension and renal failure. The goal of treatment is to control blood pressure and to slow the onset of renal failure. ADPKD is associated with involvement of other organs, particularly intracranial aneurysms, which have an asymptomatic prevalence of 8% overall and 23% in patients 60-69 years old.^[2]

ARPKD is due to mutations in PKHD1, a large gene that encodes fibrocystin/polyductin, which plays critical roles in collecting-tubule and biliary development. This disease carries a high neonatal mortality rate, and many individuals who survive eventually require renal transplantation. Symptoms include hypertension and liver disease. Diagnosis is often made in utero. Treatment is supportive in severe cases but otherwise is similar to that for ADPKD.

GCKD is often confused with ADPKD, as it is common in individuals with a family history of ADPKD. This disease is distinguished histologically and symptoms and treatment are similar to those in ADPKD.

JNPHP and medullary cystic disease are two diseases that some consider a disease complex.^[3]They share similar pathologic features but are due to different genetic mutations and have different inheritance patterns. JNPHP is inherited in an autosomal recessive manner and presents in childhood, while MCKD is inherited autosomal dominantly and affects adults. Both diseases present with symptoms of salt wasting and polyuria.

Systemic disease with associated renal cysts

TS is caused by mutations in the suppressor genes TSC1 and TSC2, which encode hamartin and tuberin, respectively. Mutations of TSC2 are much more frequent than mutations of TSC1 and are associated with more severe disease.^[4] Renal cysts and angiomyolipomas are part of a syndrome that includes seizures and dermatologic findings.

VHLS is due to mutations in the VHL gene, which increases the risk for malignancy, including RCC. Affected individuals develop cysts in multiple organs, including the kidney, pancreas, liver, and epididymis.

Acquired cystic renal disease

The exact cause of this disease is not known. It occurs exclusively in patients on dialysis. The severity of disease is directly related to the duration of therapy. Typically, acquired cystic renal disease is asymptomatic but it is known to subsequently increase the risk of RCC.

Etiology

The etiology of renal cysts includes the following:

Developmental cystic renal disease
Inherited cystic renal disease
Systemic disease with associated renal cysts
Acquired cystic renal disease
Unilateral renal cystic disease

Developmental cystic renal disease

Multicystic dysplastic kidney (MCDK) is thought to arise from abnormal development of the metanephros. This may be a genetic effect or may reflect a defect in the ampullary bud (inducer tissue) or the blastema (responder tissue), with resultant poor nephron induction.^[5]Additionally, in utero obstruction has been identified as a possible cause, leading to urinary stasis and cyst formation. Many patients, however, have normal renal development despite obstruction.

Inherited cystic renal disease

The etiology of inherited cystic renal diseases includes the following:

Autosomal dominant polycystic kidney disease (ADPKD)
Autosomal recessive polycystic kidney disease (ARPKD)
Glomerulocystic kidney disease (GCKD)
Juvenile nephronophthisis (JNPHP)
Medullary cystic kidney disease

The exact mechanism of genetically induced cyst formation has yet to be fully defined. Similarities between cystic diseases, however, reveal common pathologic pathways. The vast majority of mutations affect the primary cilia of the tubular epithelium, indicating that disruption of this structure relates to disease development.^[6]Additionally, dedifferentiation and increased proliferation of tubular epithelium, along with abnormal fluid secretion, appear to be common elements in cystic disease.

Autosomal dominant polycystic kidney disease

Inheritance of ADPKD is autosomal dominant, with close to 100% penetrance. PKD1 (chromosome 16p13) encodes for the transmembrane protein polycystin-1 (PC1), which is responsible for cell-to-cell and cell-to–extracellular matrix binding.^[6]Mutations in this gene are responsible for 85-90% of cases. Mutations in polycystin-2 (PKD2, chromosome 4q21), a calcium channel important for PC1 localization and function, account for the remaining 10-15%.^[7]

Interestingly, while ADPKD is a genetic disease that affects every cell in the kidney, cysts involve only 1-2% of the nephrons or collecting ducts, supporting the hypothesis that a "second hit," or mutation of the abnormal allele, must occur.^[3]Five to 8% of cases do not involve a family history and are the result of spontaneous mutations.

Autosomal recessive polycystic kidney disease

All cases of ARPKD are caused by mutations in PKHD1, a large gene that encodes fibrocystin/polyductin, which appears to be related to the polycystin complex and controls epithelial proliferation, secretion, and structure and development of the renal tubules and biliary ducts.^[8]The genetic defect is located on chromosome 6p21.1-p12.

In both ADPKD and ARPKD, epidermal growth factor (EGF) has been identified as an important stimulus for proliferation of cystic epithelium.^[7]

Glomerulocystic kidney disease

GCKD is a rare disease that is transmitted in an autosomal dominant manner. The involved gene has not been identified, and both familial and sporadic forms exist.^[9]

Juvenile nephronophthisis

JNPHP is inherited in an autosomal recessive manner and is due to mutations in the NPHP genes (NPHP1-NPHP5), which are located on multiple different chromosomes and encode nephrocystins and inversin. All of the gene products are found in the primary cilium.^{[10, 7, 11]}Ten to 20% of cases are associated with retinal disease and are termed Senior-Loken syndrome.

Genes involved in JNPHP are as follows:

NPHP1 is located on chromosome 2q12-13 and encodes nephrocystin
NPHP2 is found on chromosome 9q22-31 and encodes inversin
NPHP3 is found on chromosome 3q21-22 and encodes nephrocystin-3
NPHP4 is located at chromosome 1q36 and encodes nephrocystin-4
NPHP5 (chromosome 3q13.33-21.2) encodes nephrocystin-5 and is found only in cases associated with Senior-Loken syndrome

Medullary cystic kidney disease

MCKD is due to mutations in the MCKD1 (chromosome 1q21) and MCKD2 (chromosome 16p12) genes. It is inherited in an autosomal dominant manner.^[7]

Systemic disease with associated renal cysts

Tuberous sclerosis (TS) is inherited in autosomal dominant fashion, with variable penetrance. Approximately 60-70% of cases are due to sporadic mutations. Genetic markers have been identified at chromosome band 9q34 (TSC1, which encodes hamartin) and chromosome band 16p13 (TSC2, which encodes tuberin). TSC2 accounts for two thirds of TS cases.^{[6, 3]}While the functions of these genes are not understood, TSC2 is adjacent to the PKD1 gene, which is involved in the most common form of ADPKD. In some cases, a contiguous gene syndrome has been described, involving large deletions that affect both TSC2 and PKD1.

Inheritance of von Hippel-Lindau syndrome is autosomal dominant, with variable penetrance. The genetic defect has been localized to chromosome band 3p25.

Biochemical analyses^{[12, 13]}have identified a protein (mammalian target of rapamycin [mTOR]) that may be part of a common pathway in several of the genetic forms of cystic disease. Activity of mTOR is related to cell growth, proliferation, apoptosis, and differentiation. Increased levels of mTOR have been found in cyst epithelium. Under normal conditions, PC1 (mutated in ADPKD) and TSC2 (mutated in TS) suppress or inactivate mTOR. Mutations in these genes, as well as in others that relate to the primary cilia, result in dysregulation of mTOR activity, possibly allowing cyst formation.

Acquired cystic renal disease

The exact cause of cyst formation has not been identified. One theory suggests that the development of cysts in acquired renal cystic disease (ARCD) is secondary to obstruction of the tubules by fibrosis or oxalate crystals. Another hypothesis invokes the accumulation of growth factors and stimulatory chemicals (uremia), including EGF, which leads to the development of cysts.^[3]The disease occurs in patients on all types of dialysis and appears to regress after transplantation.

Unilateral renal cystic disease

This is a rare disease characterized by multiple cysts with intervening normal parenchyma in one kidney. It looks similar to ADPKD on both imaging and pathologic examination. Patients may present with hematuria, pain, or a flank mass. This is a benign entity and is not associated with cysts or malformations in other organs.^[14]

Epidemiology

The epidemiology of disorders associated with renal cysts is as follows:

MCDK has an incidence of one per 1000-4000 live births^[5]
ADPKD has an incidence of one per 500-1000 persons, affecting 12.5 million worldwide, and accounts for 8-10% of all cases of end-stage renal disease (ESRD) and 5-10% of renal transplants^[15]
ARPKD has an incidence of one per 6000-55,000 live births, corresponding to one per 70 unaffected carriers in the general population
JNPHP affects one per 5000 persons^[10]
JNPHP and MCKD account for 10-20% of children with chronic renal failure and for 1-5% of all patients undergoing dialysis or transplantation
TS has an incidence of one per 10,000-50,000 persons, and 20-25% of these patients have renal cysts^[16]
VHLS has an incidence of approximately one per 39,000 persons, and two thirds of these individuals develop renal cysts
In acquired cystic renal disease, cysts are present in 8-13% of patients with chronic renal failure prior to dialysis, in 10-20% of patients after 3 years of dialysis, in 40-60% after 5 years, and in more than 90% after 10 years^[17]
MSK has an estimated incidence of one per 5000 persons and is found in approximately 20% of patients with nephrolithiasis
Simple cysts are the most common cystic renal lesions; they are present in 5% of the general population, increasing in frequency to 25-33% of patients older than 50 years, and account for 65-70% of renal masses
Cystic RCC accounts for fewer than 1% of RCC cases

ADPKD is found throughout the world in all racial and ethnic groups. Acquired cystic renal disease is most common in white men and African Americans.

Sex-related demographics of disorders associated with renal cysts are as follows:

Multicystic dysplastic kidney is more common in males than in females
Symptomatic progression of ADPKD appears to be more rapid in men
VHLS affects men and women with equal frequency
Acquired cystic renal disease is more common in men
MSK has a male-to-female ratio of 2:1

Age-related demographics of disorders related to renal cysts are as follows:

ADPKD has a bimodal distribution of onset, with some cases presenting in infancy and 2% presenting before the age of 15 years ^[10]
ARPKD presents in infancy, childhood, or adolescence
VHLS typically presents in the third or fourth decade of life with visual or central nervous system symptoms
MSK typically presents in the third to the fifth decades of life
Simple cysts are rare in children but increase in frequency with age

Prognosis

Bilateral multicystic dysplastic kidney (MCDK) is incompatible with life. More typically, the disease is unilateral or segmental and is discovered on prenatal sonogram.

In autosomal dominant polycystic kidney disease (ADPKD), renal insufficiency typically develops in people older than 30 years, and 50% of patients progress to end-stage renal failure by the age of 60 years. One third of patients die secondary to renal failure, one third die due to complications from hypertensive nephropathy, and 6-10% die secondary to subarachnoid hemorrhage.

Neonates presenting with autosomal recessive polycystic kidney disease (ARPKD) often die within 6 weeks secondary to pulmonary disease and renal failure. Neonatal mortality secondary to ARPKD approaches 25-35% and is usually related to respiratory compromise.^[6] If patients survive this first period, they have an 80% chance of living to 15 years. For patients presenting in infancy, approximately one third progress to severe renal insufficiency at age 5 years and nearly 100% progress by age 20 years.

In juvenile nephronophthisis (JNPHP) and medullary cystic kidney disease (MCKD), patients typically progress to renal failure within 5-10 years of presentation. In von Hippel-Lindau syndrome, as many as 40% of patients develop renal cell carcinoma, which is the leading cause of death.

Acquired cystic renal disease is progressive while the patient remains on dialysis. The disease often regresses after transplantation, but associated tumors may become more aggressive because of the patient's immunosuppression.^[17]

Medullary sponge kidney carries an excellent prognosis and is typically nonprogressive.

In many forms of cystic renal disease, morbidity and mortality is secondary to end-stage renal disease (ESRD) and renal cell carcinoma (RCC).

End-stage renal disease

Rates of ESRD are as follows:

Cystic renal disease accounts for approximately 10% of all ESRD cases
ADPKD is one of the top four causes of ESRD and is the etiology of renal failure in 5-10% of patients undergoing dialysis
ARPKD accounts for 5% of ESRD in children
More than 50% of patients with ARPKD require kidney transplant before age 20 years ^[8]
JNPHP is the most common cause of genetic ESRD in children ^[11]

Malignancy

Risk of RCC in cystic diseases of the kidney is as follows:

Tuberous sclerosis: RCC occurs in a small percent of patients with TS (< 5%)
Von Hippel-Lindau syndrome: 70% of patients with VHLS who survive to age 60 years develop RCC; the tumor is frequently bilateral and multicentric
Patients with acquired cystic disease are more likely to develop RCC (5-25%); additionally, tumors are commonly bilateral, and 15% are metastatic ^[17]

Although a causal relationship between acquired renal cystic disease (ARCD) and RCC has not been established, the incidence of RCC is 30 times greater in people with ARCD than in the general population, 4-7% over a 7- to 10-year period. Notably, this rate is much higher in men than women (male-to-female ratio, 7:1) and in patients with cysts that enlarge the kidney outside the normal range.

Cancer incidence in patients receiving renal transplants for polycystic kidney disease (PKD) was 48% higher than that expected in the general population, in a study of 10,166 renal transplant recipients with PKD and 107,339 transplant recipients without PKD; but after adjustment for age and other factors, cancer incidence was lower in PKD transplant recipients than non-PKD recipients^[18]

Other morbidity

Multicystic dysplastic kidney

Concerns in MCDK include the following:

Cyst rupture
Infection
Calcification
Malignancy

Inherited cystic renal disease

If a patient experiences persistent pain, consider the possibility of renal infection, tumor, or nephrolithiasis. Ten to 20% of patients have urate or calcium oxalate nephrolithiasis. One third to one half of patients experience renal infection, including infected cyst and pyelonephritis (women are affected more frequently than men). Perinephric extension with abscess is a potential sequela and has a 60% mortality rate. Berry aneurysms often are stressed by concomitant hypertension, and they bleed in 5-10% of patients.

Acquired renal cystic disease

Patients with ARCD may have cyst rupture and hemorrhage, although fewer than 14% of patients experience episodes of hematuria. With cyst rupture, hemorrhage into the pelvis or retroperitoneum can occur.

Medullary sponge kidney

Nephrolithiasis and nephrocalcinosis are common in patients with MSK. MSK is found in 8.5-20% of patients with nephrolithiasis. The dilated collecting ducts may have relatively diminished flow, favoring calcium deposition.

Other common complications of this disease include renal infection and hematuria. A rare complication is renal abscess, which requires a prolonged course of antibiotics and possible surgical drainage.

Simple cysts

A simple cyst can become hemorrhagic or infected. The cause of the hemorrhage is often unclear, but it may be related to trauma, bleeding diatheses, or varices in the cyst wall. Cyst infection may result from disseminated hematogenous infection, ascending urinary tract infection, or urologic instrumentation.

Patient Education

Genetic counseling is important in all of the heritable cystic renal diseases. Individuals with autosomal dominantly inherited diseases (eg, ADPKD) need to be counseled that their offspring have a 50% chance of developing the disease. Those with autosomal recessively inherited diseases (eg, ARPKD) should be counseled that all of their offspring will carry the disease. Parents of children with an autosomal recessively inherited disease should be counseled that subsequent children have a 25% chance of having the disease and a 50% chance of being an unaffected carrier of the gene.

For patient education information, see Kidney Cyst and How Does Polycystic Kidney Disease Affect the Kidneys?

Clinical Presentation

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Media Gallery

Cut surface of a nephrectomy specimen from a patient with a multicystic dysplastic kidney (MCDK).
Nephrectomy specimen from a patient with a large benign simple cyst.
External surface of a nephrectomy specimen from a patient with autosomal dominant polycystic kidney disease (ADPKD).
Cut surface of the same nephrectomy specimen from a patient with autosomal dominant polycystic kidney disease (ADPKD).
Cut section of nephrectomy specimen demonstrating renal cell carcinoma (RCC), with an adjacent simple cyst.
Close-up photograph of the cut surface of the same nephrectomy specimen demonstrating a simple cyst adjacent to a renal cell carcinoma (RCC).
A prenatal sonogram of a fetus with a multicystic dysplastic kidney. The right kidney is appreciated as a large multicystic paraspinal mass. The left kidney and bladder are normal, and a normal amount of amniotic fluid is present.
CT examination of the abdomen of a 70-year-old woman with autosomal dominant polycystic kidney disease (ADPKD) is shown. The kidneys are bilaterally enlarged with multiple cysts.
CT scan of the same patient (70-year-old woman with autosomal dominant polycystic kidney disease [ADPKD]) demonstrating multiple hepatic cysts.
This CT scan demonstrates acquired renal cystic disease (ARCD) in a 70-year-old man who is dialysis-dependent. The CT scan demonstrates bilateral atrophic kidneys with multiple renal cysts.
A CT scan of a 38-year-old man with von Hippel-Lindau syndrome (VHLS). The patient previously underwent resection of multiple bilateral renal cell carcinomas (RCCs). CT scan demonstrates multiple cysts in the kidneys and pancreas, as well as solid renal lesions suggestive of malignancy.

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Table 1. Bosniak Classification of Cystic Renal Masses, Version 2019^[45]

Table 1. Bosniak Classification of Cystic Renal Masses, Version 2019 ^[45]

Category	Description	CT Findings	MRI Findings
I	Benign simple renal cyst requiring no follow-up	Well-defined thin (≤ 2 mm) smooth wall without septa, calcifications, or solid components; homogeneous simple fluid (–9 to 20 HU); the wall may enhance	Well-defined thin (≤ 2 mm) smooth wall without septa, calcifications, or solid components; homogeneous simple fluid (signal intensity similar to cerebrospinal fluid); the wall may enhance
II	Benign renal cyst or likely benign renal mass requiring no follow-up	All six types have well defined thin (≤ 2 mm) smooth wall: 1 -3 hairline-thin (≤ 2 mm) septa; the septa and wall may enhance; may have calcification of any type Homogeneous hyperattenuating masses (≥ 70 HU) on noncontrast CT Homogeneous nonenhancing masses (> 20 HU) may have calcification of any type Homogeneous masses ≤ 20 HU on noncontrast CT Homogeneous masses 21 to 30 HU) on portal venus phase CT Homogeneous low-attenuation masses too small to characterize	All three types have well defined thin (≤ 2 mm) smooth wall: 1 -3 hairline-thin (≤ 2 mm) enhancing septa; nonenhancing septa may have calcification of any type Homogeneous masses markedly hyperintense at T2-weighted imaging on noncontrast MRI Homogeneous masses markedly hyperintense at T1-weighted imaging on noncontrast MRI
IIF	Cystic renal mass follow-up imaging at 6 and 12 months and then annually to assess for morphologic changes	Minimal enhancement and/or thickening (3 mm) of a hairline-thin smooth septum or wall; or ≥ 4 smooth thin (≤ 2 mm) enhancing septa	Two types: Minimal enhancement and/or thickening (3 mm) of a hairline-thin smooth septum or wall; or ≥ 4 smooth thin (≤ 2 mm) enhancing septa Homogeneous masses on unenhanced fat-saturated T1-weighted imaging
III	Cystic renal mass, intermediate possibility of malignancy.	One or more thick (≥ 4 mm width) or irregular (≤ 3 mm obtusely margined convex protrusions) enhancing septa or enhancing walls	One or more thick (≥ 4 mm width) or irregular (≤ 3 mm obtusely margined convex protrusions) enhancing septa or enhancing walls
IV	Cystic renal mass, likely malignant	One or more large enhancing modules (≥ 4 mm obtusely margined convex protrusions or any size convex protrusion with acute margins)	One or more large enhancing modules (≥ 4 mm obtusely margined convex protrusions or any size convex protrusion with acute margins)

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Author

Thomas Patrick Frye, DO Clinical Fellow, Urologic Oncology Branch, National Cancer Institute, National Institutes of Health

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Chief Editor

Bradley Fields Schwartz, DO, FACS Professor of Urology, Frank and Linda Vala Endowed Chair of Urology, Director, Center for Laparoscopy and Endourology, Department of Surgery, Division of Urology, Southern Illinois University School of Medicine

Bradley Fields Schwartz, DO, FACS is a member of the following medical societies: American College of Surgeons, American Urological Association, Association of Military Osteopathic Physicians and Surgeons, Endourological Society, Society of Laparoscopic and Robotic Surgeons, Society of University Urologists

Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Endourological Society Board of Directors<br/>Serve(d) as a speaker or a member of a speakers bureau for: Cook Medical<br/>Received research grant from: Cook Medical.

Additional Contributors

Edmund S Sabanegh, Jr, MD Chairman, Department of Urology, Glickman Urological and Kidney Institute, Cleveland Clinic Foundation

Edmund S Sabanegh, Jr, MD is a member of the following medical societies: American Medical Association, American Society of Andrology, Society of Reproductive Surgeons, Society for the Study of Male Reproduction, American Society for Reproductive Medicine, American Urological Association, SWOG

Disclosure: Nothing to disclose.

Steven Abboud Research Fellow, Medical Research Scholars Program, National Cancer Institute, National Institutes of Health

Steven Abboud is a member of the following medical societies: American Medical Association, American Medical Student Association/Foundation

Disclosure: Nothing to disclose.

Acknowledgements

John M Corman, MD Clinical Associate Professor of Urology, University of Washington at Seattle; Consulting Staff, Department of Urology, Virginia Mason Medical Center

Disclosure: Nothing to disclose.

Alex Gorbonos, MD Assistant Professor, Department of Urology, Loyola University School of Medicine

Alex Gorbonos, MD is a member of the following medical societies: Alpha Omega Alpha, American Urological Association, Endourological Society, and Phi Beta Kappa

Disclosure: Nothing to disclose.

Justin A Siegal, MD Radiologist, Department of Radiology, Virginia Mason Medical Center

Disclosure: Nothing to disclose.

Andrew T Trout, MD Resident Physician, Department of Radiology, University of Michigan Medical School

Andrew T Trout is a member of the following medical societies: American Medical Association, Phi Beta Kappa, Radiological Society of North America, and Sigma Xi

Disclosure: Nothing to disclose.