Benign & Cystic Tumors of the Kidney

Background

Causes

Diagnosis & Evaluation

Treatment

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Background

 

A cyst is simply a round fluid-filled mass (much like a water balloon). They can be found in almost every part of the body. The kidney is one of the most common sites for cysts. These are infact so common that about 50% of adults who have a kidney ultrasound will be found to have at least one kidney (or renal) cyst. Nearly all cysts are perfectly benign, of absolutely no threat, and need not be treated or followed. However, rarely a kidney cancer can appear "cystic", although it will have characteristics on imaging that make it obvious it is not a "simple cyst". On the other hand, some perfectly benign cysts can have atypical features. Your urologist will discuss with you the chance of whether your particular cyst is benign or not and discuss with you management options.

There are several other "cystic diseases" of the kidneys, including so-called "polycystic kidney disease" (PCKD). this is usually an inheritable condition of progressive production of many cysts in the kidneys through adult life. The kidneys can literally become replaced with innumerable cysts that lead eventually to kidney failure. There is usually a family history of PCKD, and/or the presence of MANY renal cysts at dianosis, not just 2 or 3 in a kidney.

Cystic tumors may be benign (such as "multilocular cystic nephroma") or malignant. Your urologist will discuss the details of this in you case if he suspects either of these relatively rare conditions.

 

Causes

 

What causes benign simple cysts to occur is still unknown. There is nothing that can be done to prevent them, nor need there be as they are extremely common and non-threatening.

 

Diagnosis & Evaluation

 

An ultrasound usually first demonstrates the presence of one or more renal cysts. If the radiologist is satisfied that the cyst(s) satisfies the criteria of a simple cyst, nothing more is necessary. If there is any doubt, then depending on certain factors it may be recommended that a CT scan be done to decide if the cyst in question is indeed benign or not. Sometimes we will simply follow with another ultrasound in a few months to reassess.

 

Ultrasound and CT are complementary. Ultrasound is very good at establishing the presence of fluid - which is critical in differentiating simple benign cysts from small solid renal masses (some of which are cancerous). CT is not as good for small lesions, but good in defining solid tumors as well as extent of tumor.

 

Treatment

 

Simple cysts require no treatment and usually no followup is necessary. When appropriate imaging is performed and the presence of a simple cyst is confirmed, cancer is not a concern. No matter what their size, simple cysts almost never cause any problems - if you have a simple cyst (especially if it is less than 10 cm) and any kind of symptoms, another cause should be sought. Rarely, problems can arise and include:

 

  1. Symptoms: pain, fullness, bloating. Cysts less than 10 cm are almost never symptomatic. If you have a small cyst and have pain, there is likely another cause.
  2. Bleeding: bleeding can rarely occur within cysts. If not caused by trauma, further evaluation to check for cancer will be arranged.
  3. Hypertension: compression of the kidney parenchyma can rarely cause problems with blood pressure. Because run-of-the mill hypertension (so called essential hypertension) is so common, if you have a cyst and high blood pressure, the cyst is probably not the cause.

 

PCKD is best followed by a nephrologist for prevention and delay of renal failure as well as genetic counselling. A cystic tumor where cancer cannot be ruled out may require surgical removal.

 

In some cases, cysts can be serious. A commonly used classification of cysts is the Bosniak classification system. It is quite good at the extremes where either a benign lesion or malignancy can be specified with good certainty, but in the middle ground, follow-up is sometimes advisable where the diagnosis is uncertain.

 

Class Description Follow-up
I

Benign simple cyst

 

Thin wall (no internal echoes, sharpley defined walls, round or ovoid). No enhancement on CT

None
II

Benign minimally complicated cyst

 

The vast majority of these are non-cancerous. Out of the tens of thousands of Bosniak II renal cysts, there have only been a few case reports of malignancy developing in these cysts. They always have a thin wall. May have any of the following:

  • Thin sepation, no more than a few
  • Thin calcification of the wall
  • 'Hyperdense': high hounsfield units on CT, but no enhancement (can confirm fluid with ultrasound); <3 cm

Usually None

Sometimes repeat imaging

III

Indeterminant Cyst


Some of these can be cancerous. Some of the components may enhance when contrast is given during CT. May have any of the following

  • Thicker wall
  • More than a few septations
  • Irregular calcification of the wall

Sometimes repeat imaging

Usually remove cyst or kidney.

IV

Malignant (cancerous cyst)

 

May have any of the following:

  • Enhances on CT
  • Nodularity
  • Solid components
Usually removal of the cyst or kidney

 

On the Web

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UrologyHealth.org The patient information site of the American Urological Association.