How to diagnose a peritonsillar abscess

The tonsils are between the anterior and posterior pillars of the throat. A peritonsillar abscess is an abscess in the tonsillar capsule, behind a tonsil. Most peritonsillar abscesses are unilateral, but they can also be bilateral.

The cause of the abscess is usually infection of the tonsil or surrounding structures. Sometimes, this is from untreated tonsillitis. Other times, the abscess formation is unrelated to a tonsil infection.

When we culture the pus after drainage, the content is often polymicrobial. The most common bacteria are group A streptococcus, Staphylococcus aureus, and oral flora anaerobes.

Peritonsillar abscess is uncommon in children under the age of 6. In fact, most abscesses occur in people that are 10 to 30 years old.

Peritonsillar abscess drainage is indicated to prevent airway obstruction, sepsis and other terrible complications such as internal jugular vein thrombophlebitis (Lemierre’s syndrome), necrotizing fasciitis, and mediastinitis.

So, it’s very important to make the diagnosis and treat it early!

There are four key situations where you shouldn’t drain a peritonsillar abscess:

1. Unconfirmed presence of pus collection
2. Coagulopathy
3. Uncooperative patient
4. Severe trismus with inability to open mouth widely

In these cases, the patient should go to the operating room under general anesthesia.

The treatment for peritonsillar abscess is invasive so it’s very important to get informed consent from your patient. While there is no alternative to draining a large abscess, antibiotics and steroids can be administered for early abscess or tonsillar cellulitis, with close follow up.

What are the physical signs of a peritonsillar abscess?

If the patient is experiencing the following symptoms, they may be suffering from a peritonsillar abscess:

• Swelling behind tonsil with off-centered uvula
• Unilateral sore throat
• Swallowing problems
• Fever
• Discomfort and dehydration
• Trismus (the inability to open their mouth wide)
• Altered voice (like they have a hot potato at the back of their throat)

Diagnostic imaging for a peritonsillar abscess

If the diagnosis is not obvious, you have two imaging options for diagnosing a peritonsillar abscess:

1. Ultrasound (most commonly intracavitary probe)
2. Computed tomography, or CT (if the patient has significant trismus)

The advantage of the CT scan is that you can see the location of the carotid artery and depth of the abscess.

For more information on how to use these techniques to diagnose peritonsillar abscesses, see Medmastery’s POCUS Masterclass.

There are lots of other diagnoses that present with sore throat and trouble swallowing. Sometimes, a patient can have unilateral tonsillitis or peritonsillar cellulitis, where there is redness but no pus collection.

As well, young kids don’t get peritonsillar abscesses, but they can get retropharyngeal abscesses. Because the throat looks fine when you examine it, these abscesses can be diagnosed by a CT scan. If you see a normal-looking throat on a sick patient with painful swallowing, you should consider epiglottitis. A lateral soft tissue x-ray can screen for retropharyngeal abscesses.

Great work! Now you know the basics to diagnose and get consent for peritonsillar abscesses.

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