Definition and Overview

The kidneys are some of the most important internal organs in the human body as their main task involves removing waste products of metabolic processes. They are also responsible for regulating the urinary system, maintaining the electrolyte levels in the body, filtering the blood and diverting water-soluble wastes from the bloodstream into the bladder for disposal. The overall importance of the kidney to the functions of the body makes the presence of masses or cysts originating or surrounding this organ extremely alarming. Renal masses can be the first sign of kidney cancer, which is one of the most common cancers in the world.

Research shows that 50per cent of individuals around the world who are over the age of fifty will have a renal mass or fluid-filled sacs known as cysts. It is important for the renal specialist, with the help of a qualified radiologist, to immediately evaluate these masses to determine if they have the potential to cause further health problems for the patient.

The evaluation of kidney mass involves a range of diagnostic and imaging procedures designed to determine if they are benign or malignant. Following the evaluation is the formulation of a treatment plan that can restore the functions or structures of the kidney.

Who Should Undergo and Expected Results

In most cases, renal masses are discovered when the patient undergoes evaluation for other conditions or symptoms. Many patients find out that they have a mass originating or surrounding their kidneys from their primary care physician, who orders a computerized tomography (CT) or ultrasound scan when they complain about abdominal pain.

The expected results of this procedure are the following:

  • Determining if the mass is benign or malignant, and how it will affect the patient’s kidney functions and overall health
  • Determining the best course of action to treat the renal mass

How is the Procedure Performed?

The procedure is typically performed when the patient’s primary care physician detected renal masses following an imaging procedure such as CT or ultrasound scan. The patient will then be referred to a renal specialist, who can then order additional procedures, such as a biopsy, to determine if the mass is benign or malignant or a symptom of a more serious medical condition, such as cancer.

Cysts are common in patients over fifty years old, and most of them are easily identified by the radiologist performing the imaging procedures. Simple cysts do not require medical intervention, and in most cases, the renal specialist will not require the patient to undergo further follow-up consultations or observations. Complex cysts, on the other hand, might require periodic imaging (such as CT, ultrasound and magnetic resonance imaging) to monitor any changes in size or characteristics.

Cysts are categorised based on the Bosniak Classification System:

  • Category I cysts are simple and benign with a thin wall. They do not have calcifications, solid components, or a septum. Density is also low. In most cases, these cysts have a water-like density.

  • Category II cysts are also benign, but they may have one or more septa and mild calcifications.

  • Category IIF cysts appear like Category II cysts, but around 5per cent of them are malignant. They require follow-up imaging before the patient is given a clean bill of health.

  • Category III cysts are those with thick, irregular stems. Roughly 50per cent of these cysts are malignant.

  • Category IV cysts are 100per cent malignant, requiring follow-up imaging procedures and careful monitoring before the renal specialist and the patient decide on the best course of medical or surgical intervention.

Solid masses are easily distinguishable from cysts, and the radiologist can immediately inform the renal specialist and the patient whether the mass discovered is solid or not. Solid masses are cancerous around 80per cent of the time and typically require a biopsy for further evaluation.

Renal biopsy is often guided by imaging equipment such as CT or ultrasound and is an important factor that is highly considered in designing further treatment or therapy for the patient. In some cases, the biopsy must be repeated several times to arrive at a definite diagnosis. If, on the other hand, the solid mass proves to be cancerous or suggests the presence of cancer, the renal specialist can immediately recommend surgery or ablation of the mass without performing a biopsy.

Possible Risks and Complications

The evaluation process itself is generally safe when performed by a qualified and experienced team of radiologists and renal specialists. However, if the patient is not satisfied with the evaluation process, he or she can go to another specialist for a second opinion.


  • Washington University School of Medicine in St. Louis: “Kidney (Renal) Mass”
  • American Urological Association
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