What is a "right frontal hypodense subdural collection"? in the brain?

The information you gave us is just a little piece of an entire picture. With this, I can tell you that it could be seen in chronic subdural hematoma, higroma, trauma and other diagnoses and long words. Really, NOT meaningful to you because I don’t have anything else related to your patient. The best is to ask the Neurologist who is in charge to explain. I’m sure he/she will be happy to do.

Presumably you didn't just wander into a CT facility and make an impulse purchase. Your doctor ordered the CT for a reason. What was the reason? The CT isn't the patient, you are. Test results by themselves are meaningless. What does your doctor say? If you haven't asked your doctor, please state why not.