Fatty hump at base of neck, what is this?

Lump for how long? There is a great deal of information that must be learned before you can better understand your specific neck mass. If you are having difficulty breathing, swallowing, or speaking, or if it is very painful, you should seek urgent medical attention. Otherwise, masses in general may be benign or cancerous. A long-standing, unchanging, non-painful fatty mass may be a benign tumor called a lipoma.
Brown fat. If it's in back at the base of your neck, chances are its a collection of brown fat. Brown fat differs from regular white fat in that it's rich in mitochondria and metabolically active. While the role in adults is unclear, it may have a function in regulating body weight. Thanks for trusting HealthTap!