There are a number of diagnostic imaging modalities used to stage melanoma.
Staging is the process by which your doctor finds out if the melanoma is confined to one place or whether it has spread. This is very important information for planning treatment and working out your prognosis.
These include Ultrasound, CT scans, MRI scan and PET scan. Each of these scans give slightly different information and you will be advised which is appropriate for your situation. Plain x-rays are seldom useful in the management of melanoma. Very occasionally your doctor will recommend a bone scan.
Lymphosyntigrapy or lymph node mapping is discussed in the section on sentinel node mapping.
This technique uses high frequency sound waves to create an image of specific body parts. A gel is placed on the patient’s skin and the ultrasound transducer is then moved across the area to obtain an image. It is mostly used to examine the lymph nodes in the neck, axilla (armpit), or groin. Sometimes it will used to enable accurate biopsies of a node. (Ultrasound guided fine needle aspiration). The examination is painless and usually doesn’t take long. There is no radiation involved and the procedure is safe in pregnancy.
Ultrasound of lymph node
CT or CAT scan stands for “computed axial tomography”. This is the commonest modality used in to stage melanoma. It gives your doctor a series of x-ray slice pictures of your body or parts of your body. These can be viewed from different directions to give a 3D picture of specific organs. It is particularly useful for looking at solid organs like the brain and liver, but also is excellent for the lungs. It can only pick up abnormalities that are around a centimetre in size and may miss smaller lesions. The scan is performed with the patient on a narrow bed that passes through the CT scanner. In most cases the radiology doctor will insert a small needle into the patient’s arm and give them intravenous contrast which helps to outline the organs being looked at. This is the only uncomfortable part of the procedure, which is otherwise painless. It involves the use of radiation and can’t be performed if the patient is pregnant.
CT image of the chest
Magnetic Resonance Imaging (MR)
Magnetic resonance imaging is a relatively new technique which utilises the energy from large magnets to create slice and 3D images of the body and specific organs. Unlike CT scanning it involves no radiation. The patient lies on a bed that passes through the scanner. The machine is very loud and patients wear earphones and listen to music during the procedure. It is quite slow and you may have to hold your breath for short periods of time. Before the scan you will be asked about any metal you may have in your body such as piercings. Also if there is a risk you could have metal fragments in your eyes for example from metal grinding you will need to have an X-ray first. This is because the powerful magnets in the scanner could potentially move the metal around and cause you an injury. Sometimes the radiology doctor will insert a needle to give contrast which helps outline specific structures.
MRI image of the brain
Positron emission tomography (PET) is a scan that picks up emissions from a radioactive tracer. This is commonly a type of sugar which is injected into the patient via a needle. Cancer cells like those of melanoma avidly use any free sugar in the blood stream thus concentrating the radioactive tracer in any areas that cancer is growing. PET scanning is an extremely useful technique to look for evidence that melanoma has spread around the body. It is also used to confirm that an abnormality seen on another type of scan is in fact melanoma. When it is combined with a CT scan at the same time, (CT PET scan), it enables your doctor to see exactly where in your body an abnormal area is located. This can allow for very accurate surgical treatment of melanoma disease. There are now two PET-CT scanners in Auckland at the Mercy and Ascot hospitals (approx. $2500).
PETCT image of the body