There are two common head shapes to the Chihuahua breed. The apple head is known for a round dome with bulging eyes and a short muzzle. Deer heads in comparison, have a longer muzzle and the longer slender face resembles the head of a deer, hence the name. The deer head also displays a more refined forehead.
I don't think it is a special breed. Referring to them as dear head chihuahuas has to do with how they look in the head, ears, and face area, they tend to look like a deer in this instance.
The deer head chihuahua is not a special breed of dog but rather a classification of the chihuahua. The chihuahua is the smallest of all the dog breeds.
