Chest X-ray

I recently had a base line colonoscopy. The anesthesia used was propofol. I ended up with aspiration pneumonitis. My chest xray showed that the lingular pneum had resolved. I had a ct scan of the chest that showed a 4mm pleural based soft tissue- of right costophrenic recess. My question is could this have been from the anesthesia and should this have showed up on the chest xray. The scan was taken 5 weeks after the incident. Thank you....