What can this mean .... fdg uptake in the medistinial nodes is indeterminate ?

Uncertainty: When a test result comes back as indeterminate, it means "inconclusive." In other words, the degree of uptake into the mediastinal nodes was neither conclusively normal nor abnormal Therefore the conclusion is uncertain or indeterminate. It seems unfair to put you in this medical limbo but your doctor can do further tests to ascertain if the lymph nodes are overactive metabolically.

Sarcoid?: It means that there is a slight uptake of radiolabeled sugar (glucose) in the middle of your chest. This may be normal, or may be nothing, or maybe sarcoidosis, or something else. Bronchoscopy with ultrasound maybe useful. Or maybe there is nothing to worry at all. Discuss with your doc what is next.