What could a lump on the back of the neck in the middle be?
Since I am not a Doctor answering your question could do you more harm than good so if it's not too much to ask of you, please go see a Doctor. He or she will be able to answer your question, maybe run a few tests and give you an answer that you won't have to question.
Yes, it could be scar tissue or a muscle knot. A lump on the back could be connected to a severe problem for the entire body. You need to be more descriptive about a lump. This could be a muscle knot or it could be a cancerous growth. Severe or insignificant must be assessed after a proper diagnosis. This requires more info.