Surgery this summer?

My 13 year old son was born with transposition of the great arteries and had an arterial switch to correct it.  6 months later he had another unexpected emergency heart surgery.  He has had a leaky aortic valve (minor problem) since then and has developed a dilated aortic root.  An MRI in 2008 showed a measurement at the sinuses of 34mm.  In 2009 there was an increase to 38.5 mm.  My son's physical activities have been restricted, which has been a little harder than we anticipated for a child as active as mine.  We will be seeing the cardiologist next week for an Echo/Ekg and office visit but am unsure of the questions I should ask.  This cardiologist is great, however not very forthcoming with details or what to expect.  His response was that this is unchartered territory with an arterial switch patient.  I don't know what procedures or medications will correct his current problem.  At what point do they decide that it's time to operate and what does it involve?  Any information will be greatly appreciated!