Question:  You are seeing a 6 year old girl in your clinic for a neck mass.  Her mother has observed a roughly grape-sized mass that fluctuates in size at the angle of the mandible for the last year, but thinks she may have had it for her whole life.  She adds that the area turned red once 3 months ago, but resolved with a short course of antibiotics.  You observe a tiny depression overlying it without surrounding skin changes.  Palpation expresses a small amount of straw-colored fluid without foul odor.  What is your leading differential diagnosis?

[Answer will be posted with next week's new question]

Answer to last week's question, Nose Candy (Feb 23, 2015): 

Cocaine.  Topical 4% cocaine is commonly used for diagnostic and therapeutic procedures in the nasal cavity.