Hypermetabolic on PET scan means that the tissue lights up or is hotter because it is more active then the background tissues. PET scans most commonly use a glucose molecule attached to a radioactive molecule which is then distributed throughout the body. Cells which use more glucose are then called hypermetabolic.
What does hypermetabolic look like on PET scan?
Hypermetabolic appears hotter or brighter then the surrounding tissues. This means that the tissue is processing glucose more then usual. This is abnormal and can mean there is inflammation, infection, trauma, or cancer. Hypermetabolic on PET scan therefore does not give us a diagnosis.
Since PET scans are most commonly done for cancer, we look for Hypermetabolic activity to detect it. We use PET scans to look for spread or recurrence of cancer. We look at tissues to see if there are areas that are hotter then usual. This may indicate cancer.
One example would be hypermetabolic areas in the liver. In the setting of cancer, this would be concerning for cancer spreading to the liver. We will often see masses on a CT scan that correspond to the hypermetabolic or hot spots. This means that the cancer in the liver uses more glucose then the background liver.
Hypermetabolic on PET scan can also be used for a primary cancer. One common example is for lung cancer. Lung cancer in its early stages will look like a round spot in the lung. PET scan can help us distinguish benign spots from those which are cancerous. The cancerous spots will be hypermetabolic or hot. There is however overlap with benign abnormalities and cancer.
What else can look hypermetabolic other then cancer?
Hypermetabolic on PET scan can also refer to inflamed or infected tissues. Some tissues which are hypermetabolic or hot on PET scan can look cancerous but are really inflamed or infected. Even tissues that are bruised after trauma can be hypermetabolic. These tissues also use more glucose then the surrounding.
Often we can not tell from the pet scan alone whether a hypermetabolic tissue is cancerous. We need other imaging and even biopsy in some cases. The degree of hypermetabolic activity can also help us. If the tissue is very hypermetabolic and hot, then it is more likely to be cancerous.
Having prior scans and clinical information helps us with hypermetabolic abnormalities on PET
Having more clinical information and prior imaging tests is also very helpful in telling us what the hypermetabolic abnormality may be on PET scan. For example, a hypermetabolic lung nodule which has appeared rapidly in a patient with symptoms like fever may be a fungal infection. A slower growing nodule which is hypermetabolic is more likely to be cancer.
Hypermetabolic on PET scan tells us that the cells and tissue uses more glucose then the surrounding tissues. This looks hot or bright on the scan. It tells us nothing about the diagnosis. Having prior scans and more clinical information helps us reach a more confident diagnosis. More testing may be needed when we encounter hypermetabolic abnormalities.