Pneumonia with Pleurisiry prognosis

i have been treated for atypical pneumonia with pleurisy with erythromycin and have responded well i believe. The treat was for 10 days of antibiotic. The question is can there be damage to the lung from atypical pneumonis, such as scar tissue or scarring on the lung. On my followup xray it show an are on the left lower lung approx 3 by 4 inches that is white which was explained to me that that part of the lung is not getting oxygen. I am scheduled for a ct scan but the first thing the doctor talked about was a mass that could be cancerous. Which of course scarded me. I am 56 year old male and have not smoked for 2 1/2 years. Have not had any trouble with lungs other than this. Actually this is the sickest I have been my whole life.
I am wondering what other causes could there be for this area of my lung not getting oxygen other than cancer.
Thank You.

[National Jewish]

Most atypical pneumonias are caused by viruses.  They seldom damage the lung.  The most important thing about any pneumonia is that the follow-up chest x-ray is completely clear.  When the chest x-ray doesn