A computed tomography (CT) scan is an imaging tool that your oncology team may use to help diagnose kidney cancer. Sometimes, doctors will order a biopsy of your kidney if a CT scan or other imaging tests show signs of cancer. In a biopsy, healthcare providers use a needle to take a small sample of kidney tissue to be studied in a lab.

In this article, we’ll talk about how CT scans work, what results tell your doctors, and how accurate they are. We’ll also cover when a biopsy might be recommended.

If your healthcare provider has ordered a CT scan for kidney cancer, here’s what you need to know.

How Do CT Scans Work?

A CT scan is like a high-tech upgrade to a standard X-ray. While a regular X-ray takes a flat, 2D picture, a CT scan takes many X-ray images from different angles as the scanner moves around your body. A computer then combines these images into detailed cross-sectional pictures, sometimes called “slices,” of your internal organs.

CT scans are usually read by radiologists (doctors who specialize in imaging tests).

Before the CT scan begins, you’ll lie on a flat table. A technologist will slide that table into a ring that looks like a large doughnut. The parts of the CT scanner that take the images are in that ring.

The technologist may ask you to change positions or move slightly so they can get the best possible pictures of your kidneys and the surrounding organs. To get even more detailed images of your kidneys, your doctors may want to use an IV dye, also called contrast dye. For CT scans, this dye is usually iodine-based and helps certain areas stand out more clearly on the images.

However, this dye can cause problems for some people whose kidneys aren’t working well. Your healthcare team will check your kidney function before the test. If it’s not safe to use the dye, they may order another imaging test, such as an MRI or an ultrasound instead.

How Is a CT Scan Used To Diagnose Kidney Cancer?

Doctors use CT scans to get images that may show whether a kidney mass is more or less likely to be cancer.

Different types of kidney cancer may appear differently on CT scans. In general, doctors are checking for masses that look solid and that take up a lot of the contrast dye. They may look for other, more specific, characteristics if they suspect a particular type of kidney cancer that shows up differently on a CT scan.

Sometimes, kidney cancer is found during a CT scan for something else, such as a stomachache or a sports injury. If this happens, you may need to have another CT scan for kidney cancer to get more information specifically about the tumor.

How Accurate Are CT Scans for Kidney Cancer?

CT scans are highly accurate at detecting masses in the kidneys, with some research showing accuracy rates above 99 percent for renal mass detection. In many cases, CT findings give doctors enough information to strongly suspect or diagnose kidney cancer without a biopsy.

However, CT scans can’t always tell whether a mass is cancer or benign (noncancerous) or identify the exact type of kidney cancer.

What Do CT Results Tell Doctors About Kidney Cancer?

A CT scan acts like a high-definition road map for your doctors. Instead of guessing, they can see detailed images of what’s happening inside your body.

CT scans give healthcare professionals quite a bit of information about any tumors in your kidneys, including:

• Information to help them decide if any masses are cancerous or benign
• The exact location of the tumor or tumors, including whether a tumor is inside the kidney or growing outside it
• The size of the tumor
• How far the cancer has metastasized (spread), including whether it has reached nearby lymph nodes (small immune system glands) or other parts of the body

After you’ve been diagnosed, they may also use CT scans to:

• Help plan for surgery
• See if kidney cancer treatment is working
• Check to see if the cancer has returned

If your doctor orders a CT scan, they should tell you why they’re doing it so you know what kind of results you might get.

If your doctors are concerned about how kidney tumors might be affecting blood vessels in your kidneys, they may ask for a special CT scan, called a CT angiography. This type shows blood vessels in more detail.

Kidney Biopsy

A kidney biopsy involves taking a sample of tissue from a kidney mass that may be cancerous. Doctors usually do this by inserting a thin, hollow needle into the part of your kidney where the tumor is. Most of the time, imaging — such as a CT scan or ultrasound — is used to guide the needle.

Once they have a sample, they’ll send it to a lab for analysis. At the lab, a pathologist (a doctor who studies cells and tissue) can look at the tissue under a microscope and do tests to get more information about your kidney cancer.

Not everyone with a kidney tumor needs a biopsy. If the CT scan gives your doctor enough information to diagnose or strongly suspect kidney cancer, they might skip this step and go straight to treatment.

However, if the imaging results are unclear or your doctor needs more information before recommending treatment, a biopsy may help.

When Do Doctors Order Biopsies To Diagnose Kidney Cancer?

Health experts have different thoughts on when a biopsy is necessary to diagnose kidney cancer.

Some may recommend a biopsy when imaging shows a kidney mass but doctors need more information before choosing a treatment. Others note that kidney cancer CT scan images alone are often enough to make a diagnosis, which can help you get treatment faster. This may depend on factors including:

• Which type of kidney cancer is suspected
• How much the cancer may have spread
• Where the tumor is located in your kidney
• How large the tumor or tumors are

The decision usually comes down to what will help your healthcare team choose the safest and most effective treatment plan for you.

In general, doctors may recommend a biopsy when:

• The results of your CT scan or other imaging test aren’t clear, the mass looks unusual, or doctors need to know whether it is cancer or a harmless growth.
• Surgery isn’t a good option for you, either because of the features of the kidney mass or for other reasons.
• You have small tumors that may need only monitoring, also called active surveillance.
• Doctors are considering a treatment other than surgery, such as ablation (using heat or cold to destroy cancer cells), or they need more information before recommending treatment.

If your healthcare team can diagnose kidney cancer based on a CT scan alone, they often recommend surgery instead of a biopsy. They may also decide to do surgery based on the location of the tumor and the way it’s affecting your kidneys.

If they decide to go straight to surgery, a pathologist will examine the tumor tissue after it is removed rather than through a biopsy.

Analyzing a Tissue Sample

Getting a kidney tumor sample is an important part of the diagnosis process, whether your cancer care team obtains it through surgery or a biopsy. Examining tumor cells can:

• Confirm your kidney cancer diagnosis
• Determine the grade of your kidney cancer (how abnormal the cancer cells look under a microscope)
• Show what type of kidney cancer you have

The lab results tell the doctor if it’s clear cell renal cell carcinoma, papillary renal cell carcinoma, or another type of kidney cancer. This information helps doctors choose the treatment plan that best fits your diagnosis.

Talking to a Doctor About Kidney Cancer

All of this information helps your cancer care team determine your prognosis (outlook) and recommend what treatment options may be right for you.

Since different options work better for different types, stages, and grades of kidney cancer, it’s important to have as much information as possible before making decisions about treatment plans.

It’s important to remember that you aren’t just a passenger in this process — you’re a key member of the team. This is called shared decision-making. Your doctor brings the medical expertise, but you bring your own goals and preferences.

Your kidney cancer specialist will talk you through the potential benefits and risks of each treatment option, and you’ll be able to share your goals and preferences. Together, you and your doctor can make decisions about the treatment plan.

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How did your oncology team use CT scans to diagnose kidney cancer? Let others know in the comments below.