I have a 6 month old heifer calf that had a small fluid sac on the top of her head behind her poll when she was born(about the size of a half dollar). It is filled with fluid and even has hair growing from it and is sensitive to the touch. I have never seen anything like it and have asked several vets and they also do not know what it is. I assumed that it would dry up and fall off sometime before weaning but it is still very intact. Does anybody know what this could be? I've been told it could have something to do with her spinal fluid.