@van333, welcome. Seeing test results before having a chance to talk to your doctor can be worrisome.
Regarding metabolic activity.
"A PET scan (positron emission tomography) works to identify areas of hypermetabolic activity anywhere in the body. A radioactive substance is given to the patient and this attaches to glucose, which is attracted to cells that are hypermetabolic. When the scan is done, these areas "light up." Often, but not always, cancer cells fall into this category of being hypermetabolic. In addition, not everything that is hypermetabolic is cancer."
The scan cannot differentiate between cancer cells or other situations like infection or inflammation that may be causing this activity.

And "indeterminate etiology and significance" means that they couldn't yet identify a cause or origin.

Usually it takes multiple test to determine a diagnosis. Did your doctor order more tests to investigate? What symptoms led to your needing investigation?