Lung X-ray-Cat Scan

What indication when looking at a Cat scan or X-Ray that a spot on the lung is scar tissue verses cancer?  I was first told from an X-Ray it was a benign lymph node which I didn't by so a cat scan was done and deteremined that it is scar tissue in the lung, have a follow up cat scan in 3 months so if they are SURE it's scar tissue why the follow up?

[National Jewish Health]

The radiologic appearance on x-ray or CT scan of a lesion can enable a radiologist to distinguish between a cancer and a scar, with a high degree of probability, especially when age, smoking history, occupational exposures, general well being etc. are also taken into account.  And, many sound medical conclusions are reached on the basis of high probability rather than with absolute certainty.

The recommendation that you have a follow-up CT scan, be it at 3 or even 6 months is intended to address any uncertainty, albeit small, that a tumor might be masquerading as a scar.  The longer the period of radiologic stability of a lesion, 3 months vs 6 months, the greater the likelihood that it is benign.  Two years of stability is considered, by almost all experts, to be almost absolute evidence that a lesion is not a cancer.

Good luck.