Hi. For the condition you have explained about the possibility of retropharyngeal abscess along with known Hashimoto s thryroiditis, you need an urgent investigations and treatment,. I would advise you in such a situations the following: - Report to ER or Hospital immediately as the retropharyngeal abscesses grow very fast and can cause airway obstruction and are life threatening. - Investigations - Ultrasonography, putting in a needle to aspirate to reduce the pressure as well as to get a sample of pus for gram staining, culture and sensitivity. - Start on broad spectrum intravenous antibiotics, anti-inflammatory and supportive treatment. - You may need an emergency surgery of drainage of the abscess. - Intravenous fluid. I hope this tells you the proper way of diagnosis and treatment.