Understanding kidney cyst and its major causes, symptoms and treatment

Kidneys are one of the most crucial organs of human body that helps in detoxification. Humans generally have a pair of kidney, but it has been medically proven that people can survive on a single kidney. The size of each kidney is about 4-5 inches and weighs around 150 grams. The kidneys function as a filter, purifying the blood and working as waste removal system in our body. The blood passes through the kidneys around 12 times in an hour and in one day the kidneys purify around 200 liters of blood. The kidneys also produce 1-2 liters of waste as urine. Erythropoietin, Renin and active vitamin D are the important hormones produced by kidneys with different function like erythropoietin that helps in the production of RBC, Renin that controls the blood pressure level and Vitamin D that stimulates the absorption of calcium.

Just like other human organs, kidneys can also have a cyst, most of which are benign. But having a kidney cyst requires urgent medical attention as they may be a symptom of other medical condition. Read on to know what are kidney cysts, their causes, signs and treatment.

Major causes of Kidney Cyst

There are no particular causes for the sac like outgrowth or kidney cyst. Studies indicate that Kidney cyst may be caused by the obstruction of tubules. The tubules are the tiny structures present within the kidneys which collects urine. The deficiency of blood supply definitely plays a major role in the formation of Kidney cyst. Diverticula is also said to be another reason for Kidney cyst where the sacs formed on the tubules detach and become Kidney cyst.

Signs and symptoms kidney cyst

It is true that most of the kidney cysts hardly present a symptom, but kidney cyst pain is associated to these sacs. People who suffered from the urinary tract infection are prone to Kidney cyst. The symptoms of a simple kidney cyst observed are:
●Urinary tract infection
●Pain, generally concentrated in upper abdomen area
●High Fever
●Severe Pain in back and hips
●Chills

In case of complex kidney cyst the symptoms observed when the cyst grows in size are:
●Tendency of frequent urination
●Severe abdominal pain
●Blood in urine causing hematuria
●High blood pressure
●Headache, fever with pain in lower portion of back
●Serious signs causing sepsis and hemorrhage

Polycystic kidney disease

Polycystic kidney disease is defined as the formation of numerous cysts on the surface of kidneys. Polycystic kidney disease is a genetic cystic disorder leading to the enlargement of kidneys which ultimately reduce the kidney functions and cause kidney failure. There are two major forms of polycystic kidney diseases which are:
●Autosomal dominant polycystic kidney disease: Common as 90% of the people suffers from this disease in the age of 40-50.

●Autosomal recessive polycystic kidney disease: Rarely inherited and can begin in the early stages of life.

Effects of cyst on kidney

There are many effects that are caused by cyst on kidney which mainly includes:

●Deformed size of kidneys due to the formation of abnormal blisters

●Kidney failure

●Reduced Kidney function

●Kidney stones

How to treat Kidney Cyst Pain

The treatment of Kidney cyst pain can be done by determining the cause of the pain which are mainly caused by infection, expansion or bleeding of cysts. Removal of cysts by surgical operations mainly by laparoscope is also a solution to Kidney cyst pain. Medicines such as antibiotics can also reduce the Kidney cyst pain.

Cystic Diseases of the Kidney

Background

One third of people older than 50 years develop renal cysts. Although most are simple cysts, renal cystic disease has multiple etiologies. Broad categories of cystic disease include the following:
●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)

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.

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. 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.

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.[1] 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. 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.

Epidemiology

Frequency
United States
MCDK has an incidence of 1 per 1000-4000 live births.
ADPKD has an incidence of 1 per 400-1000 persons among whites and accounts for 8-10% of all cases of end-stage renal disease (ESRD).
ARPKD has an incidence of 1 per 6000-55,000 live births, with a heterozygous carrier frequency of 1 per 70.
JNPHP affects 1 per 5000 persons.
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 1 per 10,000-50,000 persons, and 20-25% of these patients have renal cysts.
VHLS has an incidence of approximately 1 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. Following initiation of therapy, 10-20% of patients have acquired cystic renal disease after 3 years of dialysis, 40-60% after 5 years, and more than 90% after 10 years.
MSK has an estimated incidence of 1 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 less than 1% of RCC cases.

Mortality/Morbidity
Cystic renal disease accounts for approximately 10% of all ESRD cases.
ADPKD is 1 of the top 4 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.
Neonatal mortality secondary to ARPKD approaches 25-35% and is usually related to respiratory compromise.
More than 50% of patients with ARPKD require kidney transplant before age 20 years.
JNPHP is the most common cause of genetic ESRD in children.
TSC is associated with a high frequency of angiomyolipoma.
Patients with acquired cystic disease are more likely to develop RCC (5-25%). Additionally, tumors are commonly bilateral, and 15% are metastatic.
Race
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
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
ADPKD has a bimodal distribution of onset, with some cases presenting in infancy or childhood.[3]
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 between the third and fifth decades of life.
Simple cysts are very rare in children but increase in frequency with age.

Guidelines on the management of renal cyst disease

Introduction

Renal cysts are a common finding on routine radiological studies. As such, patients are often referred to urologists for their opinion regarding potential intervention and follow-up.

Autopsy studies in patients over the age of 50 reveal greater than a 50% chance of having at least one simple renal cyst. In 1983, using early computed tomography (CT) scan technology, renal cysts were discovered in 33% of patients in the same age group. Today, ultrasound and cross-sectional imaging studies are frequently used to aid in obtaining the diagnosis of abdominal complaints. With improved technology and newer generation diagnostic equipment, renal masses are more frequently identified than 25 years ago.

Methods

The Canadian Urological Association Guidelines Committee has reviewed the literature using a MEDLINE search of the English language.

Definition

Renal cysts, in general, may be classified as “simple” or “complex.” “Simple” cysts are best defined using sonographic criteria. These include: (1) absence of internal echoes, (2) posterior enhancement, (3) round/oval shape and (4) sharp, thin posterior walls. When all of the criteria are met, the cyst is benign and no follow-up is required. The difficulty arises when cysts do not meet the rigid characteristics of the “simple” definition. Therefore, clinicians need to rely on a rapid, safe and accurate system to identify benign versus malignant masses and ultimately have the guidance on nonsurgical or surgical treatment options.

The Bosniak classification of renal cysts
The Bosniak renal cyst classification system was initially reported in 1986, using CT scan findings.Although other imaging modalities are frequently used in the evaluation of renal masses, such as ultrasound and magnetic resonance imaging (MRI), CT scan (with and without contrast enhancement), remains the primary diagnostic technique.

Ultrasonography is helpful for simple cyst identification, but provides limited information with increasingly complex renal cysts and solid masses. However, MRI can be helpful with increasingly complex cyst identification. Recent developments with MRI scanning allow shorter breath holds and increased contrast resolution with gadoliniumenhanced images. As such, the cysts may be characterized in greater detail, compared with CT scan. The MRI may demonstrate poorly identified septa on CT scan and show enhancements that are not otherwise clearly perceived. Also, MRI may differentiate between hemorrhagic cysts and solid enhancing masses.

The Bosniak system consists of four categories based on triphasic CT findings, ranging from simple to complex cysts . Category I cysts have no malignant potential and, as such, no follow-up is required. However, there is a large difference in potential malignant risk, between category II and category III. These are 0% to 5% and about 50%, respectively. To clarify this further, a subcategory of II was developed, IIF (for “follow-up”). Category IIF identifies the category II cyst which was slightly more complicated, but not necessarily suspicious enough to warrant surgical exploration. Category IIF includes cysts which have multiple thin septa, slight wall-thickening without measurable contrast enhancement. They may have calcification, including thick, nodular or irregular calcification. Ultimately, 95% of category IIF cysts are proven to be nonmalignant.While the importance of calcification has diminished over the years since the original classification, enhancement with CT contrast has not. Any mass studied with CT thin slice scanning, that increases between 10 to 20 Hounsfield units (i.e., Category III and IV), is a renal cell carcinoma until proven otherwise.

Summary

There are no randomized controlled trials with regards to follow-up or management of cystic renal masses, as such, the recommendations are primarily expert opinion.

At this time, category I and II renal cysts, do not require further imaging or follow-up. Patients in Category IIF, because of the approximate 5% malignant risk, do require periodic imaging. (There is no consensus or evidence based interval determined for follow-up imaging.) Combination of ultrasound and MRI should be considered as follow-up for Bosniak IIF and reduces the lifetime radiation dose (once the lesion has been characterized by triphasic CT scan) in patients younger than 50 years. For Category III (50% malignant risk) and category IV (75% to 90% malignant risk), surgical excision is recommended. (Level 3 evidence, Grade B recommendation). Although MRI may add further information, it should be used as an adjunct to CT scans in difficult cases (Level 4 evidence, Grade C recommendation).