Can I Get A Unilateral Orchiectomy Does A Bilateral Contract Become A Unilateral Contract Once The Promise Of Something Is Fulfilled?

Does a bilateral contract become a unilateral contract once the promise of something is fulfilled? - can i get a unilateral orchiectomy

I am a contract online class, and asked me what exactly is the difference between bilateral and unilateral contract? There is a difference, although it is very thin, and I studied, the courts are not really hard to distinguish, or is fighting for this type of contract, but is always useful to know for the class.
Thanks