AKT-1512

A 2-year-old girl is presented to the GP by her mother who has noticed a peculiar lump on her neck. The mother is uncertain about the duration of the lump. The lump is situated in the anterior triangle, just in front of the sternocleidomastoid muscle, and has a soft texture. The lump is mobile but doesn’t transilluminate.

After a biopsy, cholesterol crystals are discovered in the extracted fluid. What is the probable underlying diagnosis?