Kidney masses, or tumors, are growths that develop on the kidney. They can be cancerous or benign. In some cases, they may indicate an infection.

Doctors can diagnose a mass on the kidney using imaging tests such as ultrasound, MRI, or CT scans. The treatment will vary depending on the type of growth.

One type of mass that doctors can find on the kidney is renal cell carcinoma (RCC), which is a type of cancer. Doctors can diagnose RCC in the early stages, which usually results in a better outlook.

Keep reading to learn more about finding a mass on the kidney and how doctors treat these tumors.

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A mass or tumor on the kidney refers to an abnormal growth on this organ.

Most growths that develop in the kidney are not cancerous. However, they might still require medical intervention.

Doctors will describe kidney masses as solid or cystic. Solid masses comprise tissue, whereas cystic masses contain air, fluid, pus, or other material.

Different types of kidney masses exist, and their causes, symptoms, and treatments will differ. For example, a cyst on the kidney will likely indicate an infection.

Doctors will consider the size of the tumor, among other factors, to help them determine whether it is a cause for concern. They may use different imaging techniques to determine the size of the mass. Generally, research shows that:

  • tumors less than 3–4 centimeters (cm) across are less likely to be malignant
  • up to 40% of 2-cm kidney masses are benign, with only 10% being high grade RCC
  • nearly 30% of masses that are 4 cm or larger are high grade cancer

Due to this, doctors may perform further tests on people with larger kidney masses, as they carry a higher risk of being malignant.

The main concern for solid kidney masses is RCC, which is the most common form of kidney cancer, accounting for 9 in 10 cases.

Other cancers of the kidney include:

  • clear cell RCC
  • non-clear cell RCC
  • transitional cell carcinoma
  • nephroblastoma
  • renal sarcoma

Some benign, or noncancerous, tumors of the kidney are:

  • angiomyolipoma
  • oncocytoma
  • metanephric adenoma

Staging kidney cancer

After confirming a diagnosis of kidney cancer, doctors will determine the cancer’s staging.

Staging allows doctors to know how much the cancer has spread. Using the TNM system, stage 1 is the least serious form of cancer, while stage 4 describes advanced cancer.

The TNM system involves checking the following:

  • Tumor size: Doctors will determine the size and extent of the main tumor.
  • Nodes: They will check whether the tumor has spread to nearby lymph nodes.
  • Metastasis: Imaging tests can reveal whether the tumor has spread to other parts of the body, such as the bones or lungs.

Learn more about kidney cancer staging.

A mass on the kidney may occur for different reasons.

For kidney carcinoma — a type of cancer — smoking is a major cause. Other causes of kidney carcinoma include:

Some genes may also contribute to kidney mass formation. Polycystic kidney disease is a medical condition that results from gene mutations. People living with polycystic kidney disease develop many cystic masses on their kidneys.

Von Hippel-Lindau syndrome is another rare disease that can cause growths in the kidneys. People living with von Hippel-Lindau syndrome have many cysts and tumors in different body organs, such as the kidneys.

Birt-Hogg-Dubé syndrome is another genetic disorder that causes kidney tumors, among other symptoms.

A mass on the kidney rarely causes symptoms initially. However, in the advanced stages, they may sometimes cause some symptoms.

People may have pain between the ribs and the hip and notice blood in the urine. Sometimes, doctors can feel the tumor when carrying out a physical examination.

Some signs and symptoms that may indicate a mass on the kidney include:

Symptoms are not a reliable way to diagnose kidney masses. If people experience any of these symptoms or notice these changes, they should consult a doctor.

Physical exams of the kidneys will not detect a mass. Doctors also cannot diagnose masses on the kidneys by analyzing the signs and symptoms alone.

Instead, they need to use imaging techniques such as ultrasound, MRI, or CT scans.

The decision to use a specific imaging technique depends on the type of tumor and certain clinical characteristics of the person.

CT scan

CT scans are appropriate when doctors need a quick image of the kidney. They will use CT scans to detect a mass if a person cannot have an MRI. For example, people with metallic implants cannot undergo MRI scans.

Using a CT scan, doctors can tell the exact location, size, and shape of a tumor. To see the kidneys, imaging technicians may need to inject an intravenous dye. CT scans also reveal whether the cancer has spread to other parts of the body.

An additional test called a biopsy sometimes takes place with CT scans. Biopsies involve using a needle to take a sample of tissue from the tumor and checking it for cancer cells.

MRI scan

MRI scans may be the preferred option when detecting small kidney masses because, unlike CT scans, they do not use radiation for imaging. People allergic to the IV contrast dye that healthcare professionals use in CT scanning may require an MRI to detect a mass on the kidney.

If kidney cancer has grown into major blood vessels in the belly, MRI scans provide better images.

Ultrasound

Doctors can also see kidney masses using ultrasound. This type of imaging can show whether a mass is solid or fluid-filled or contains air. Ultrasound images of kidney masses can also show differences between benign tumors and cancers that have spread.

As with CT scans, doctors can use a biopsy needle to take a sample from a mass in the kidney.

Urine and blood tests

Although urine and blood tests cannot diagnose kidney masses, they can provide clues that the kidney is not working as it should.

Doctors can sometimes find blood and cancer cells in urine samples.

The treatment for kidney masses depends on the diagnosis.

For masses that doctors diagnose as infections, they may prescribe antibiotics.

For kidney cancer, the treatment options can depend on:

  • the person’s age and overall health
  • the size and shape of the tumor
  • the person’s preferences
  • previous treatments

Biopsies, surgery, and thermal ablation are possible treatments for kidney cancer. With thermal ablation, doctors use heat to destroy the tumor.

Complications can sometimes occur from the treatment of kidney masses. These may include:

  • infections
  • bleeding
  • kidney failure

Learn more about the different types of treatment for kidney cancer.

Active surveillance

Sometimes, rather than treating smaller masses — typically those smaller than 3 cm — doctors will perform frequent checkups using imaging tests. This is called active surveillance. Its main aim is to prevent the tumor from being able to cause issues for the person.

Some experts agree that checking the mass through medical imaging every 3–6 months for the first year is appropriate. Once the doctor has determined how the mass is changing over time, they may adjust the time between checkups.

According to experts, the incidence of kidney masses has increased over the past few decades. However, it is likely that improved imaging techniques are better able to detect abnormal growths, resulting in more diagnoses.

The outlook for people with incidentally small renal masses is good. The 5-year survival rate has improved steadily in recent years because of new treatments and earlier detection.

Experts estimate that the survival rate for stage 1 and 2 RCC is greater than 90%. However, in the advanced stages of RCC, this falls to below 15%.

A mass on the kidney may indicate cancer, but these tumors are often benign.

Doctors use imaging tests to diagnose kidney masses and determine their stage. This information allows them to create the best possible treatment plan for the person. When a person receives treatment for RCC in the early stages, the outlook is generally good.