An Unexpected Neighbor

Question:   You are evaluating a patient with a biopsy proven right sided tonsil squamous cell carcinoma which is HPV positive.  He has a single cystic lymph node in the right neck in level III.  Looking through his CT scan, you also note an cystic 1 cm mass medial to the internal carotid artery and just below the level of the palate.  What does this finding most likely represent?     [Answer will be posted with next week's new question]

Answer to last week's question, Colliding at Dizzying Speed (December 21, 2015): 

Labyrinthine concussion.