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What is a Renal Cyst?

A renal cyst is a fluid-filled sac that forms on or in the kidneys, often discovered during imaging tests for other conditions. While generally benign and asymptomatic, some cysts can cause discomfort or complications. Intriguingly, their formation and impact vary, raising questions about kidney health and management. Curious about how these cysts might affect you? Let's explore their mysteries together.
Mary McMahon
Mary McMahon
Mary McMahon
Mary McMahon

A renal cyst is a small pocket filled with fluid and located in the kidneys. Also known as kidney cysts, many renal cysts are benign, and people can live out their entire lives without any knowledge of a cyst. In other cases, they are a cause for concern, and a doctor may recommend follow up treatment which can include surgery to remove the cyst when one is identified in the course of a medical examination and medical testing.

Classically, renal cysts are identified on ultrasound, MRI, or another type of medical imaging study. In the case of a simple cyst, the cyst shows up as a fluid-filled pocket, and if the cyst is aspirated, it can contain clear to yellowish fluid, sometimes mixed with blood. Complex cysts, on the other hand, have irregularities such as calcification, meaning that there is solid material inside the cyst, or they develop internal walls. A complex renal cyst is a cause for concern because it can be associated with the development of kidney cancer.

An example of a healthy kidney and one with lots of cysts.
An example of a healthy kidney and one with lots of cysts.

Some people have one or more cysts on the kidneys at birth. In other cases, a cyst develops as a result of an obstruction somewhere in the kidney. Lymphatic obstructions and vascular disease can both contribute to the development of this type of cyst. Patients can also have a condition called polycystic kidney disease (PKD), a genetic condition in which numerous cysts develop in the kidneys, causing damage to the kidneys and surrounding organs.

And MRI scan can identify a renal cyst.
And MRI scan can identify a renal cyst.

In some cases, this type of cyst can cause flank or back pain, especially if it becomes enlarged. Patients can also experience more generalized abdominal pain or discomfort. Other cysts are asymptomatic, and may only be identified by accident or after a patient dies a natural death. When a cyst is identified, a doctor may recommend additional testing to determine the nature of the cyst and determine whether or not it is an issue. If the cyst is dangerous, it can be removed surgically, or monitored to see if it grows or causes complications for the patient.

An ultrasound is used for a renal doppler.
An ultrasound is used for a renal doppler.

Tapeworms can also cause renal cysts. If a patient has a tapeworm infection which is not addressed in a timely fashion, a doctor may recommend additional testing to determine whether or not the patient has complications such as cysts on the kidneys. Cysts caused by tapeworms can also appear in other organs of the body, and they are classically associated with a decline in organ function.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a TheHealthBoard researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a TheHealthBoard researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...

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Discussion Comments


I kept getting kidney infections (not bladder infections), along with a lot of pain in my left flank. I got one after another and finally I went to a specialist. I had a CT scan which showed a 10 cm cyst inside my kidney. They also told me they don't cause pain. However, I got to the point where I couldn't walk ! I had the cyst drained and it came back within a few weeks. Now I'm looking to have it removed.

Two things you need to know: If it ruptures on its own, it can kill the kidney. so have it taken care of! Second: When you have it drained have them put you under. I did not and it was like having a baby! Do your research and take charge of your health!


I went to the ER with my parents due to chronic (three months) moderate to severe back pain in the location of my left kidney (unable to sleep on that side due to the pain, the pain radiated down into my hip and pelvis making it difficult to walk upright or normally for the last month.) At the hospital I was given a wheelchair to be pushed around in. I told the ER doctor, "It feels like a soft walnut is trying to force itself out of my back where my left kidney is."

I have a surgical history of large fibroids and ovarian and renal cysts and had similar pain then, so I told him to specifically check my left kidney for a cyst or mass. After it became clear the doctor was simply going to discharge me with yet more painkillers and magnesium citrate for constipation, my mother demanded an MRI or a CT. The doctor said he couldn't do the MRI without primary doctor's approval and it was too late to get one (it was 6 p.m.) but he could do the CT with contrast. After the CT was done, he reported there was nothing abnormal with either of my kidneys but to follow up with my primary care doctor to order an MRI to rule out a herniated disc, etc. and to drink the bottle of magnesium citrate.

A week later, after the follow up, I had the MRI done and lo and behold, the "incidental finding" was of a 3.2 cm high density renal cyst on my left side "as first imaged and unchanged from previous CT scan." After reviewing the ER CT scan and the MRI with a radiology consultant at the same hospital, the only way the ER doctor could have missed seeing the renal cyst was if he hadn't even looked at the images at all.

So don't believe doctors who try to make you think the pain's just in your head, or just a patient looking for a next drug fix, or tell you renal cysts can't cause severe pain, or don't even look at your scans exactly where you tell them to before saying your kidneys have nothing wrong with them. Renal cysts are common, but when they're causing months of excruciating pain to the point where you can't even walk to your mailbox to get your mail or drive to the grocery store, then they needed to be treated!


In my ultrasound yesterday, here are the impressions: small nephrolithiasis, Left 5.1 mm. Small renal nodule, Left 12.5x12.5x14.1 mm. Normal right kidney and urinary bladder ultrasonically. The ureters are not dilated. The urinary bladder is unremarkable.


I have had a lot of lower right back pain for about six months. I have had a CT on my lumbar/back, an MRI on my lower pelvic and kidney. They found a mass they thought, but they think it is a cyst on my left kidney measuring 3.9cm. So, I have an appointment with a urologist tomorrow. I had blood in my urine only one time, and have had no pain in my left kidney.


I am a 24 year old girl. I had my first surgery for my right kidney cyst in 2008, in 2012 I had the right kidney cyst again and again. The doctor removed because it was big.

And now it's there again and big (about 6cm). I'm very worry, if it keeps coming back after each year I might be dead of cancer from the CT scan I have to take after each surgery but not because of the kidney cyst itself.

I thought of removing the whole right kidney but what if the cyst appears on my left kidney?


I am a 50 year old man with a simple renal cyst on my left kidney. I am now awaiting an appointment with my urologist to have it removed. I agree, anon92167: doctors will tell you that these cysts don't cause pain, but they do! After it is drained, I immediately feel better. I start feeling the pain again in about three years. In fact, mine fills up every three years. I can feel it and actually know when its time to get it aspirated. I have had it aspirated three times now--each time it was three years after it was drained. I get a dull pain and numbness on left side. Yes, it is bothersome and painful. I also get a cramping sensation. I guess I am just another "asymptomatic" patient. I am going to have it surgically removed this time.


I am a 54 year old white female having left flank and kidney constant-dull-throbbing pain. I've had this for two months, with chills and disorientation. I have had nausea, but no burning or odor when urinating, but I see a film in my urine. I am bloating and a heating pad not helping.

My stool today was black. I do exercise regularly with weights and I do not drink any sodas, but add crystal lite into water bottles just to add color. I drink a lot of water with lemon as well. I'm considering seeing a doctor, but would like other comments and suggestions. --Dawn H.


I'm in my 40th and started to have a weird sensation of pressure on the left side between ribs and hips. Sitting was quite uncomfortable. It progressed into a constant pressure or pain that comprised the left flank now.

An ultrasound was performed and a single simple cyst (8 cm) was discovered in my left kidney. I am also very surprised by the fact that most literature states that simple renal cysts are asymptomatic. I disagree strongly.

I will see an Urologist next week and see what the future plan is. --Jackie


Can a renal cyst cause numbness from pinching a nerve? I was diagnosed with a right renal kidney cyst and have recently been dealing with UTI's and numbness in part of my foot.


I was wondering if anyone out there can tell me what needs to be done. I have had pain under my right rib and right flank for two years. They've had me on pain killers all this time. I've been to the hospital six times in two years.

They say of an ultrasound I had last week, that a 5cm complex cyst just appeared on my right kidney, so they sent me for a CT scan Friday. I dad to drink some white stuff and they also hooked me up to an IV dye and did a CT also. So is this serious? Am I going to have to have surgery? What kind of approach should they take? I hope someone can help me with these questions. -- Daniel


To follow up, my right kidney was aspirated today, surprisingly just 70mL was drawn off, but I am very pleased it is also now done.

It is interesting to keep in mind the fluid content doesn't equate in the same ratio of fluid to size because of the effect of volume. In other words, although there is much less fluid, it's still a decent size. Apparently after three weeks, the left has not filled in any significant way. Boy, am I happy just now. --Nick


I have had growing aches and pains on the left and right of my tummy, described in writing to my doctor as the 'kidney area.' I had bloating, abdominal pain and lower back pain and general unwell feelings sometimes feeling a bit sick. After a long wait (even with private care, you need a referral) the tests started. The gastro consultant finally passed me onto a urologist. A CT scan had showed cysts in both kidneys. My left kidney was aspirated two weeks ago (drained) and it contained over 500 mL of fluid. My right side is apparently similar in size, to be done shortly, I hope. The left side pain has gone.

If anyone says kidney cysts don't cause pain and they are qualified, then they ought to be struck off and go back to college. It is also a surprise that doctors don't seem to recognize very accurate descriptions of pain location and description. I feel that mine could have been found much faster and at lower cost if my well described issues of pain and location had been followed up quickly and accurately. I have no experience yet and so cannot comment on if I will suffer refill of the cyst(s). -- Nick


Well, I went into the ER with severe stomach pain so they did a CT scan and blood work. Turns out I have a cyst on my left kidney and a kidney stone as well.

My stone is tiny so they think all the pain is coming from my cyst. They are not always accidentally discovered and some people are very aware that something is wrong with them! I'm having bad pain mostly of my left side and lots of burning.

For everyone reading this, I am very sorry for this strange thing going on with you and I know how you feel. You are not alone! It will be O.K. -- I hope.


To all of those who have kidney cysts: do not take any pain killing medication except tylenol. Otherwise, you can really damage your kidneys. Also, antibiotics can damage your kidneys. I have a renal cyst on my left kidney and constant pain in the right flank. I've seen four doctors who said the pain on the right side has nothing to do with the 8cm cyst on my left kidney. Well, after lots of research, it appears they are wrong.

Don't always listen to doctors. They are not gods and they certainly do not know everything. Thank heavens for the internet.


I am a 50 year old female and for the last few months I have had a sharp pain on right side of body. There are times when I won't have pain for a week or two, then all of a sudden I will urinate and the pain is back. Does anyone know what is causing this?


I am a 31 year old female and they started off treating me for pneumonia, and I still now can't breathe.

A CT scan showed a cyst on my kidney stent, and I have very high fever unbearable pain, and now am swollen 10 times my size and today they drilled a hole beneath my ribs and inserted a drainage tube for all the infection. What is wrong? I am sick of being used.


In August 2009, three months after the birth of my second child, I went to the hospital for severe cramps. During the CT scan, they discovered a 12cm cyst on the outside of my right kidney, pushing against my liver. For the first year and a half, I went from a urologist to a liver specialist. They have since determined after two mri's, another CT scan and a renal ultrasound that it is a simple cyst. It has grown about 1/2" since early 2010 and I will soon have a new scan.

I have also been told by my urologist that my renal cyst would not cause pain and I beg to differ! I don't have a lot of pain, but I have a feeling of fullness in my back and maybe every month or so, I will have some pains there. It is very uncomfortable and sometimes it keeps me down for a bit. I am a 38 year old mother of two and this is very scary!


I am a 27 year old female who is in relatively good health. About a month ago, I went to the hospital for flank pain and side pain and a lot of blood in my pee. They said i had kidney stones and to take these meds and pain killers, that the stones would pass, but the pain never left. The pain killers only damped down the pain to tolerable.

A week later, I went back to the hospital because the pain was so bad it was taking my breath away. They did another ultrasound and said that I had a mass or cyst on my left kidney and it is about the size or a little bigger than a 50-cent piece.

My doctor said now I am going to the urologist Monday. What will they do? I am still having blood in my pee and I'm really scared. My doctor has already told me when I asked what they will do he said probably exploratory surgery. I'm really scared and yes, they do cause pain. I don't care what anyone says.


My husband just had a cyst aspiration done three days ago. It was in half of his left kidney, and the doctor said it shouldn't cause pain, surprise! This is why he went to the urologist. It was the pain, and as soon as the procedure was done and we were walking out of hospital, his pain was gone. Three days later it is now back, the flank pain, and back etc. He said it is the same pain, and it is his kidney.

The doctor's answering service doesn't take calls, the doctor tells the service to tell patients to go to the ER. The biopsy results won't be back for four more days. This is upsetting.


To anon131242: I don't know how long ago you posted, but that is definitely not normal and needs treatment. You need a second opinion from a competent urologist.


I was diagnosed with a 15cm renal cyst over 5 years ago after experiencing severe abdominal pain, which pain killers did not relieve.

I was born with only one right kidney and still had to wait over six months for laparoscopic surgery, even after several trips to the hospital in major pain. I had a recurrence five years later and just had open surgery to remove an even bigger cyst again. My recovery was shorter this time around, but after a recent colonography it seems I have a small renal cyst that will probably grow again.


Doctors are not gods, but some can be real clods - especially when they make callous and sweeping statements such as 'cysts don't cause pain'.

A cyst itself may not be painful, but it can press on sensitive areas and nerves around the site causing pain - particularly if it is a large cyst!

I have a 3cm complex cyst on my right kidney, and my right flank is in continual aching and stabbing pain!


In December 2010 I went overseas to check on my back that is getting worse and is very painful 24/7. No painkiller seems to help me now.

When I explained my symptoms to the back specialist and gave him the MRI i had in 2008 he said he needed a new MRI, for to him, it has gotten worse. I did the MRI and went back to him only to find out that there is an 8cm left renal cyst.

What do you recommend i do because i have chronic pain every day and cannot function properly as a human being. Help. --ycgp


I went to er because after being diagnosed with a uti. i began having significant right flank/side pain--burning and achy sensation. The CT showed "small" cyst or nodule on right kidney. The doctor said they do not cause pain.

What the hell? Is it just coincidence that i am having pain on my right side? I am supposed to go for an ultrasound, however i am frustrated at what the md said. If i am having pain then i am having pain. Anyone have the same issue?


My son, who is six years old, has mild parenchymal disease with renal cyst. I was just worried because I don't want him to undergo surgery. Can anybody explain to me what is Parenchymal Disease, I haven't checked with the pedia-nephro since it's holiday. Please enlighten me. Thank you.


My 14 year old granddaughter has a cyst 20.5cm x 17.5cm x 15cm in her right abdomen and pelvis discovered when having a sport related medical.

She has been suffering from shortness of breath for about six months but no other symptoms. She had an ultra sound, cat scan which showed it coming off her kidney which has all but disappeared. The urologist is sending her for a renal scan and mach3 scan in couple of days. They say it's the biggest they have seen.

Her normally flat stomach is starting to protrude. Hope they hurry up and so something as it is simply so worrying.


I also have a renal cyst on my right kidney. It was discovered 2 yrs ago while I suffered from an unrelated illness. I was fine until i went back to the ER this past summer with right flank pain. Docs discovered the cyst had more than doubled in size, now measuring approx 7 cm. After being sent home and me following up with a urologist I had an aspiration a month later.

Because of the location they were unable to use a sclerosing agent(Alcohol) to decrease the risk if it from coming back. I only missed two days of work, the day of and the day after.

Two and a half months later, i was in pain again and the ultrasound showed the cyst had come back and was now larger. I am scheduled for laparoscopic surgery this month to have the cyst fully removed. Hope all goes well.

The doc was a little concerned about the location of the cyst, the kidney is also draining through the cyst. This, we discovered, is why the cyst refilled so fast.


if anyone has a history of cancer or even melanoma like me, you need to have kidney cysts rechecked. they are usually nothing, but if you've had any kind of cancer, have the cyst rechecked and make sure it stays stable. they found one one my left renal last week. it is stable but because of my melanoma they will keep an eye on it.


I'm a 51 year old male who has been diagnosed with bilateral renal cysts of which the cyst on the left kidney is a complex cyst. There is pain on the left side of my back and blood in the urine every couple of weeks. My urologist tells me the pain and blood are probably not coming from the cyst and that I have no reason to worry nor is there any reason to perform surgery. I'm not overly confident with the assessment.


I'm 25 years old and i have a renal cyst on my left kidney. I'm constantly having pain and the pain killers do not help, they only make me sick. the doctors say that the cyst does not cause pain. but i am the third person i know with this cyst who is always having pain on the left side where the kidney and the cyst is.

I've been dealing with this pain for two years now and I'm sick and tired. medicine does nothing to help because they do not care. i think that maybe renal cysts do, in fact cause pain, so maybe these doctors should take another look at these simple cysts.


renal cysts usually are discovered accidentally on routine investigation for another problem and rarely can cause symptoms. when they are large or cause symptoms, they need follow up.


My 17 year old just got diagnosed with a renal cyst on her left kidney, it's 14mm, which I thought was pretty big. She also has a 3 mm stone in her tube. We go to the urologist today. But is this normal at such a young age?


I'm 36 year old female. I was just diagnosed with a 11cm left renal cyst and was told by the specialist that I need to have it aspirated (they expect 300cc or more) and we will schedule removal surgery in the next month or two. I am assured that the cyst will refill and that this is the only option to completely remove it.

I am scheduled for the aspiration tomorrow morning. I'm not sure what to expect, wondering how painful, how long is recovery, and will I have immediate relief from this aspiration.

I am in so much pain at the moment. My lower back, ribs and entire torso hurt. I'm nervous and not sure really how the procedure is performed It's all been sudden (with the doctors). I have been in pain for months, but thought that I may have pulled a muscle. Went to the ER and after a CT scan was told that it was a cyst. It is not a tumor, no cancer, no kidney stones, just a cyst.


I am 31 years old now and a general practitioner. I have a renal cyst measuring 4cm which was discovered only during our annual examination. I was experiencing back pains which was on and off however i thought it was part of my low back pain syndrome which i was suffering for years (X Ray of LSV- LSV instability).

I know for a fact that most renal cysts are benign however i'm still worried, being a doctor and all. I will follow up with a urologist/nephrologist about it.


"Kidney cysts do not cause any problems."

- anon92167

I'm diagnosed with bilateral symptomatic renal cysts, and I'm in pain 99 percent of the time. But whenever i go to hospital, they say they cannot do anything about it but to just ask me stay on the painkillers. I'm taking tramadol which surprisingly, to a lot of people, doesn't have any effect on me. the pain still continues till today and I'm looking for ways to put a stop to this painful misery I'm going through. Even if i have to go overseas just to have a surgery, I will do it. -shahidah


I have three renal cysts on my right kidney and they were found when I was being checked for my gallbladder. This was in 2007. I had gallbladder surgery and I am still going to have the cysts checked every six months. They have not grown but two of them have some type of lines running through them. I now go back in a year but I do have pain in my back on that right side only so I am wondering if what they is true or not. "Kidney cysts do not cause any problems."


Do renal cysts dissipate by themselves and if so what are the symptoms? My husband has a renal cyst and has had diarrhea for three days. We are wondering if it has burst by itself.


I'm in my late 50's and I was notified today that a renal cyst had been discovered during an MRI for a spine problem! They will do an ultrasound in a few days so the article appears to be accurate.


Kidney cysts are quite common and for the most part do not cause any problems. People are not even aware they have a cyst.

Cysts are usually discovered accidentally by ultrasound, MRI or CT in the process of testing for some other problem.

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    • An example of a healthy kidney and one with lots of cysts.
      By: Alila
      An example of a healthy kidney and one with lots of cysts.
    • And MRI scan can identify a renal cyst.
      By: Mikhail Kondrashov
      And MRI scan can identify a renal cyst.
    • An ultrasound is used for a renal doppler.
      By: Klaus Eppele
      An ultrasound is used for a renal doppler.
    • Renal cysts are commonly found during a kidney ultrasound or another form of diagnostic imaging.
      By: jeff gynane
      Renal cysts are commonly found during a kidney ultrasound or another form of diagnostic imaging.
    • A renal cyst is a small pocket filled with fluid and located in the kidneys.
      By: freshidea
      A renal cyst is a small pocket filled with fluid and located in the kidneys.