Very strange. My wife was diagnosed with a left pulmonary artery aneurysm
on December 14, 2009, almost the same time as you. Same thing - none of the cardiologists had ever seen one. We were sent to Mayo Clinic for a consult. She had another MRI
and about a dozen other tests. In the end, they said to come back every 6 months for follow up MRI's to make sure it does not grow. If it grows, they'll develop a surgical procedure for it. Good news is that it is on the low pressure side of the heart, there is less stress
on that area.