The kidney cysts are benign lesions formed by collected of liquid within the kidney. These are real "pockets" of liquid, which represent a very widespread problem in the population. They are often found during radiographic examinations, more often performed for other reasons, constituting a feedback incidental. Various studies have been performed to determine its prevalence, and autopsy studies have estimated that after the age of 50 the chance having cysts in the kidney is greater than 50%.
What are the causes of kidney cysts? The exact mechanism leading to renal cyst formation is not known. It is suspected that at the origin there is a weakening of the structure of the renal tissue, linked to aging and genetic factors, which leads to failure with the development of cysts that fill with liquid and gradually dilate. The cyst is essentially a malformative lesion.
What are the symptoms of kidney cysts? Kidney cysts are almost always asymptomatic. Even very large cysts (up to 10 cm in diameter) can go unnoticed for a long time, as they can cause no discomfort. Cysts can be single, or there may be multiple cysts, both in the same kidney and in both kidneys. Depending on the location in the kidney, cysts can be referred to as kidney cysts cortical if peripheral, renal cysts parapyelic if placed centrally in the kidney. The cyst can also be described as formation exophytic when it has the form of a protrusion from the periphery of the kidney to nearby structures.
Cysts can very rarely become symptomatic. For this to happen they usually have to be large in size. Symptoms of kidney cysts are related to the development of complications:
- compression of nearby structures, such as the ureter, with the development of urinary tract obstruction and colic. Very large cysts can generate a sense of weight.
- superinfection, usually linked to trauma, or to the penetration of infecting organisms in other ways, for example from kidney infections.
- bleeding and hematuria (blood in the urine), if there is bleeding inside the cyst. The walls of the cysts are in fact equipped with blood vessels, which if damaged can bleed. Bleeding within the cyst can cause rapid increase in size because the cyst dilates and fills with blood, pain in the side may be felt.
- break cyst, for example following trauma or a fall, with pain or haematuria (blood in the urine). It is a rare event whose symptoms vary depending on the structures with which the cyst enters into communication after rupturing.
A further possible complication of kidney cysts is malignant degeneration, ie the formation of a tumor starting from inside the cyst. It is a rare complication that is observed only in some types of cysts, called complex.
In fact, renal cysts are defined as simple if they consist solely of a thin wall with homogeneous fluid inside, without an evident vascularization. This type of cysts are the vast majority of cysts observed every day, and have an absolutely zero risk of malignant degeneration. However, they can increase in size over time so they are often subjected to checks.
The complex kidney cysts (which represent the minority of renal cysts), instead they are defined as such because they can have thickened walls, the presence of septa within them, increased vascularization and inhomogeneous content. The risk of malignant degeneration of this type of cyst varies depending on the appearance, according to a 4-stage classification called Bosniak. For stage 4 cysts, the most severe, there is a risk of 80% cancer and surgical removal is recommended.
There diagnosis of kidney cysts it is often an occasional finding when performing radiology tests.
Cysts are often first identified on ultrasound of the abdomen, and may come as a surprise to the patient who was not previously aware of them. As already mentioned above, however, this is almost always a benign finding that should not alarm. On the ultrasound it is possible to correctly evaluate all the characteristics of the cysts: wall thickness, presence of septa, content, size and by means ofecocolorDoppler also vascularization. This allows you to immediately distinguish a simple renal cyst from a complex one. Ultrasound also makes it possible to distinguish renal cysts from angiomyolipoma, a form of benign kidney tumor that does not cause metastasis. The kidney can also be studied by identifying the presence of micro calcifications (renella or kidney sand) or actual kidney stones, which can cause pelvic dilatation with the development of colic. It is therefore not necessary to perform more complex imaging tests if simple renal cysts are found.
In the case of finding a complex cyst, however, the internal structure of the cyst must be studied in more detail. For this reason, depending on the opinion of the attending physician or referring specialist, it may be necessary to perform a magnetic resonance, which allows to see the cyst in greater detail, for example allowing to understand if any inhomogeneity of the contents of the cyst is linked only to hematoma or to the presence of a solid formation suspected for tumor. The resonance, if it identifies a suspicious area, is not alone sufficient to diagnose a tumor with certainty: in these cases it is necessary to proceed with a biopsy, to look for areas of heteroplasia.
The presence of bilateral kidney cysts it may be a sign of a rare inherited genetic disorder, the renal polycystosis, autosomal dominant disease. For this reason it is important for the doctor to know if the patient's parents were suffering from this disease. It is also necessary to evaluate the liver, as patients with polycystic kidney also develop hepatic cysts (in patients not affected by polycystosis the most typical benign lesion of the liver is angioma). Renal polycystosis requires frequent checks and specialist visits as affected subjects, due to the high number of cysts, can evolve towards renal failure, and present other malformative problems.
In patients with multiple and large renal cysts, such as to partially subvert the structure of the kidney, some blood tests, including creatinine, may need to be done to check that the kidney is functioning properly.
They do not exist interventions preventives able to avoid the onset of kidney cysts. There are currently no drugs or medical therapies that allow to treat the kidney cysts.
Being completely asymptomatic, simple renal cysts, even large ones, are left in place and subjected, according to the doctor's judgment, to ultrasound examinations of control to distance a few years. Simple renal cyst almost never requires any kind of therapy. However, the antibiotic treatment in the event that the cysts overinfect, or surgical removal if they cause compression on the urinary tract (we are talking about very large cysts, over 10 cm). For surgery of large simple kidney cysts, different types of surgery can be performed:
- Retrograde intrarenal surgery, a minimally invasive method practiced through the use of a very small endoscopic camera, used to trace the kidney starting from the bladder and ureter. It can only be done in certain types of cysts, which are opened with a laser and thus empty into the urinary tract. A small stent is left in place for a few weeks after surgery to ensure adequate healing.
- Percutaneous kidney surgery, another type of minimally invasive surgery performed by making a small incision through the skin and soft tissues to the kidney. Also in this case an endoscopic video camera is used to open the cyst, perform needle aspiration and subsequently remove the remaining wall. The procedure requires hospitalization.
- Laparoscopy, practiced through three small abdominal incisions, one for the video camera and the other for the introduction of surgical instruments. It is the best technique for removing cortical renal cysts present in abundant numbers or in patients with polycystic kidney.
Complex renal cysts need, due to the risk of malignant degeneration in carcinoma, of closer controls, and may require in addition to ultrasound the execution of further tests already described above. In complex cysts, especially in type 4, treatment can include the removal of the cyst alone and its own alcoholization, also the removal of part or all of the kidney tissue (nephrectomy) which can be invaded by the tumor. This can be done by robotic surgery or with chemoembolization with techniques of interventional radiology.
- Guidelines on the management of renal cyst disease, Thomas FW, Can Urol Assoc J., 2010 Apr; 4 (2): 98–99.
- Israel GM, Bosniak MA. An update on the Bosniak renal cyst classification system. Urology. 2005; 66: 484-8. [PubMed]
- Is it safe and effective to treat complex renal cysts by the laparoscopic approach ?, Pinheiro T, Sepulveda F, Natalin RH et al., J. Endourol, 2011 Mar; 25 (3): 471-6. doi: 10.1089 / end.2010.0254. Epub 2011 Mar 1.