Comprehensive article on atelectasis at:
http://www.emedicine.com/med/topic180.htm Atelectasis
You may want to consult a pulmonologist for advice.
Sounds like at a minimum it needs periodic followup x-rays.
Ellis
Atelectasis is an area of the lung that is not receiving air. This is often referred to as a collapsed area of the lung. Generally this is due to something blocking the airway in that area of the lung. Linear atelectasis is collapsed areas of the lung that have a horizontal appearance. These areas look like a CD, viewed from the side. This may also be called plate atelectasis. Most instances of linear atelectasis are of no consequence to your health.
You will need further testing for the cause of the atelectasis to be found. You should have another chest x-ray in a month, 3 months, and 6 months. If the atelectasis persists, a chest CT scan is the most appropriate next step. It will show more detail than the chest x-ray. If the radiologist has any doubt that this is just linear or plate atelectasis, you should have a chest CT scan now.