Clinical diagnosis, based on history and physical exam.
CT face with contrast will help delineate area of infection
Only necessary to obtain imaging if diagnosis is in question - imaging should not delay emergent airway management or transfer to OR for definitive care
Be aware of possibility of respiratory distress/airway compromise with laying flat for CT scan
CBC
Chem
Lactate
Blood Cultures
Only necessary to obtain imaging if diagnosis is in question - imaging should not delay emergent airway management or transfer to OR for definitive care
Be aware of possibility of respiratory distress/airway compromise with laying flat for CT scan
Ludwig's angina
Streptococcal pharyngitis 
CMV esophagitis
Neisseria gonorrhoeae
Peritonsillar cellulitis
Diphtheria 
Esophageal candidiasis
Bacterial Tracheitis