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In the past, the majority of kidney cancers were identified
due to symptoms. These characteristic
symptoms are still seen in a minority of people who present with
larger kidney cancers.
However, today, the majority of kidney cancers are
“incidental findings.” The term incidental finding simply
means that the kidney tumor, which is usually small in diameter,
was found during the evaluation of a separate process. Often, a
sonogram will be ordered for a non-specific complaint and a kidney
mass will be identified.
Today, the reason that the majority of kidney tumors
are discovered while still very small in size is the increased use
of radiologic tests. These tests have become important in identifying
kidney masses as well as in determining if the mass is suspicious
for kidney cancer. Unfortunately, with contemporary radiographic
technology, it remains impossible to determine if the mass is truly
a kidney cancer as opposed to some other non-cancerous growth in
the kidney.
Depending on the size of the mass, the probability
of kidney cancer can be estimated. Smaller kidney masses can be
benign growths 30-40% of the time. In contrast, larger kidney growths
are more commonly kidney cancer (over 90%). Naturally, it would
seem that a small procedure like a biopsy to take a small sample
of the kidney mass tissue would be prudent. However, biopsy
is not usually indicated for several reasons.
The most common radiographic tests that are used to
identify, characterize and stage kidney cancer
are a sonogram IVP, CAT scan, or MRI scan. Each of these tests is
discussed briefly below.
- Kidney sonogram (ultrasound) –
Sonography, also know as ultrasonography uses sound waves outside
the human hearing range that come from a probe. Typically this
probe is placed on the outside of the skin, but probes that are
used within body cavities exist to perform ultrasound during surgery
as well. These sound waves interact with different structures
within the body and bounce back to the probe in different ways.
The ultrasound probe can then interpret the sound waves that have
bounced off of body structures to construct an image. As ultrasound
technology relies on sound waves, there is no radiation exposure
during ultrasound evaluations. However, current ultrasound technology
does not produce the high resolution anatomic images that can
be obtained with other imaging tests such as MRI and CT scans.
Typically, ultrasound evaluation can identify that there is a
problem in the kidney, and another modality such as CT or MRI
is used to more precisely characterize the kidney lesion.
- IVP – An IVP is initials
for intravenous pyelogram. This test consists of the injection
of dye material into the veins. The dye circulates and is absorbed
by the kidney. The kidney then releases the dye into the urine
and the dye follows the normal urinary system. Standard X-rays
are taken and can be used to look
at the kidney as well as the ureters and bladder.
The IVP was historically the test of choice to identify the majority
of kidney problems. Over time, other tests have taken over as
they are more versatile and precise. However, there is still a
role for IVP in contemporary medicine. Like kidney sonography,
the IVP is usually used only to identify that there may be a renal
mass. A CT or MRI scan typically will follow to better characterize
the kidney lesion and to determine if it may be kidney cancer.
The IVP has been supplanted by other tests for a number of reasons.
Primarily, the IVP is a two dimensional representation of the
urinary tract. The IVP also does not characterize the anatomy
around the urinary tract. As such, other tests that provide more
information (eg. CT or MRI scans) are more commonly used in clinical
practice today.
- CT scan – A CT scan is an
acronym for computerized axial tomography. A CAT scan uses standard
X-rays, and therefore does expose the patient to a small amount
of radiation. CT scans are superior to standard X-ray tests as
a computer is used to interpret the X-rays and to reconstruct
a three dimensional representation of the patient’s anatomy.
CT images therefore provide the ability to characterize renal
masses to determine if they are potentially cancerous. Additionally,
the CT image will provide a surgeon with very clear pictures of
the local anatomy to help to determine what type of surgery is
indicated and how this surgery might best be performed.
CT scans can be performed with or without intravenous contrast
material. Intravenous contrast material is a dye which, very much
like the IVP test, spreads around the body through the arteries
and veins. Renal masses, which get a blood supply, are said to
"enhance" and are suspicious for kidney cancer. Kidney
masses that do not "enhance" are not usually suspicious
for kidney cancer and usually do not require surgical intervention.
- MRI scan – The initials MRI
stand for magnetic resonance
imaging. An MRI scan is very much like a CT scan
in that a computer integrates the signal to construct a three
dimensional image of the patient being examined. The MRI scan
differs in that there is no radiation. Instead, the MRI uses a
magnet to create the signals that later become an image of the
patient.
When comparing an MRI to a CT scan in varying clinical settings,
there are different factors to consider. However, both imaging
modalities provide excellent images, which can be used to diagnose
the nature of a renal mass and to help decide on the best form
of clinical management.
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