Welcome! My name isXXXXX am a UC Davis graduate, and currently, a Medical Director of a veterinary hospital.
I am sorry to hear about this concern.
My primary concerns for a acute onset fluid filled swelling include:
1. Seroma Seroma
They can form even with no evidence of trauma on the surface of the skin, and can form due to allergic reactions (i.e. insect bite or sting).
2. Abscess (infection)
3. A benign cyst is still possibleCysts
Antibiotics is very important to continue, and if it is an abscess, it may even be necessary to open it and drain it later.
If a seroma, then it was a good choice to start some type of anti-inflammatory reaction.
I would imagine it is possible this occurred as a result of an injury or a insect bite or sting reaction.
Sorry to hear about this concern for Toby. Please let me know if there is anything I did not cover for you. I hope that information has been helpful.
Please remember to select Reply to Expert, if for any reason you need further clarification, have more questions, or were expecting a different type of answer. Please, hold off providing your feedback rating until you have asked all your questions.
My goal is to try and provide you the best answer possible.