What is the probable diagnosis of a well-defined, high-signal T2 lesion in the retropharyngeal space in a patient with a history of pharyngitis or tonsillitis?

What is the probable diagnosis of a well-defined, high-signal T2 lesion in the retropharyngeal space in a patient with a history of pharyngitis or tonsillitis?

Retropharyngeal abscess or effusion