It's also called as pleural capping and it is generally common in old ages,but not more than 5mm on CT scan
. High Resonance CT scan is the best modality to diagnose plural thickening. other causes of plural thickening are pleural effusions, empyema
can be used to detect pleural thickening and distinguish it from plural effusions.
if you are 50+ then it could be normal, so just relax. and if not then try ultrasonography of chest or CT chest(HRCT
good luck. bye.