Welcome! Thanks for asking your question. My name is***** am a licensed veterinarian and I will be assisting you today. First I need to ask you a few questions so that I can be well informed and give you the best advice.
1- How long has he had the lump?
2- How big is it?
3- Is it bothering him?
1- Do you feel comfortable in saying that this came on in the last day or so?
Thank you for answering my questions. Please give me a few minutes to type your answer.
Friend, if the lump you are seeing came about in the last few days this is very likely inflammation. Possible causes are: An abscess (infection), cyst, hematoma, soft tissue swelling, etc. But, if it has been there for a long time and you just recently noticed this could be a tumor, which then the question is: Is it a malignant or benign type mass? Unfortunately, on history or physical exam alone we can not determine the exact type of lump, I am sorry. To determine the exact nature of the lump I would recommend you speak to your family veterinarian about doing an FNA (fine needle aspirate); this is a very quick test where your vet will collect a sample of the cells with a needle. Requires no anesthesia, inexpensive when compared to a biopsy and can be done within minutes during an office examination. Your vet will most likely submit the sample to a lab to be evaluated under the microscope for a definitive diagnosis. The decision of benign neglect or complete surgical removal should be made based on FNA results if this is a mass. But, if it is an abscess then your vet will drain it and start him on antibiotics. So, treatment will depend on the exact underlying type of lump.
My goal is to provide you with excellent service - I hope I've provided the information you were seeking, if you feel you have received anything less, please reply back as I am happy to address follow-up questions. Kindly rate me when you are done.