Alveolitis is inflammation of the smallest of airways/airspace in your lungs (at the alveoli). Alveolitis can be related to an infection like a viral or bacterial pneumonia or could be caused by an irritant or other immune response. The list is long but these are the most common causes. Alveolitis usually goes away within an order of days to weeks once the cause is resolved. There is no real literature to definitively support when alveolitis should be followed-up so I defer this to what you doctor thinks is most appropriate. It really depends widely on the appearance but ranges from a month to a year.
AV malformations are congenital variations in the pulmonary blood vessels that a certain percentage of the population have. Instead of blood vessels connecting from artery to capillary and then vein, what happens is the artery connects directly to the vein, bypassing the capillary. It can get more complicated than this but that is roughly what a pulmonary AV malformation basically is in simplest form. The reason for following these AV malformations is to make sure they don't get too big because they can bleed and cause problems if you ever develop any blood clots in your vessels. Please refer to this article for more information - http://ajrccm.atsjournals.org/cgi/content/full/158/2/643
In that article it was cited that "In one study, follow-up with CT scan one or more years after embolotherapy showed that 96% of PAVM were either undetectable or reduced in size (reference #107 from article)." Reference: Remy, J., M. Remy-Jardin, L. Wattinne, and C. Deffontaines. 1992. Pulmonary arteriovenous malformations: evaluations with CT of the chest before and after treatment. Radiology 182: 809-816 [Abstract/Free Full Text].
Hope this helps!