Dronan sits in the middle of a junction surrounded by potential adds.
The approach passages from North and West have a lot of wanderers who can also join in if you don't clean up thoroughly before you start, so take the time to clear your back.
A static mob on South side of junction can be single pulled but watch out for a wanderer who comes from the South.
So, luckily you ought to get a single add when you pull Dronan but a tough drachnid pet, Fluffy, will spawn immediately too.