There are a number of possibilities: lymphoid tissue, sebaceous cyst, pustule, etc. Usually just lancing these will solve the problem, and if this is a solitary fluid-filled lesion without inflammation/pain/redness then that would be my first course of action.
If however it appears to be a firm mass, then I would biopsy. If there is inflammation/redness/pain, then antibiotic therapy would also be indicated.
On occasion these resolve spontaneously, and was just likely reactive lymph tissue. See your veterinarian for further information and treatment.
Dr. Van Lienden
Dr. Raymond Van Lienden DVM
The Animal Clinic of Clifton
12702 Chapel Road, Clifton
Virginia, U.S.A. 20124