7 month old english mastiff mix developed a growth on the backof his neck

Dog Question: my 7 month old english mastiff mix developed a growth on the backof his neck (seemingly overnight).  it feels like it is fluid filled and moveswhen you touch it. the dog does not shoe signs of pain when you touch it.  it almost seems like a hematoma.  your thoughts?

Hi Whitley,

I could be a cyst or a hematoma among other things.

In either case  your dog would not appear painful. 

I would closely monitor it.  If it gets larger than see your vet.

In most cases it should go down in size over time.

(could it be a spider bite or an insect bite?)