Approaches to the Diagnosis of Peritonsillar Abscess with Point-of-Care-Ultrasound

Ilana Rosner, DO
Published Jan. 02, 2021

Probetrotters | Medical Education

Ultrasound (US) is an important modality in differentiating, diagnosing and treating peritonsillar abscesses in the emergency department (ED). Peritonsillar abscesses (PTAs) are the most common deep neck infections, and 80% of cases are found in patients aged 10 to 40.8 The diagnosis is usually made clinically with a physical exam and confirmed by needle aspiration of purulent material at the time of drainage.8Incision and drainage or needle aspiration are the definitive treatment options in order to protect the patient from complications such as airway obstruction, abscess rupture, and extension to the deep tissues of the neck, carotid sheath, or posterior mediastinum.3 However, physical exam alone is unreliable in distinguishing between PTAs and peritonsillar cellulitis (PTC), with a sensitivity of 78% and specificity of 50%.7 Treatment typically consists of blind needle aspiration, aiming at the superior pole where 70% of PTAs occur.8 This is in contrast to PTC in which there is no role for drainage. This method has a false negative rate of 10 to 24% when done by experienced ENTs.1 Other drawbacks of blind aspiration include multiple insertions due to loculated abscesses or unknown locations, pain, and the close proximity of the internal carotid artery.8

Diagnostic Imaging

CT scan has a sensitivity of 100% and specificity of 75% for diagnosing PTA.2,6 MRI can also be used for diagnosis, with less radiation than CT.8 However, neither of these have a role in treatment. Ultrasound is a quick and inexpensive modality that can not only differentiate PTA from PTC, but can also guide needle drainage.7 Both intraoral ultrasound (IOU) and transcutaneous ultrasound (TCU) are good options. On ultrasound, a PTA will typically appear as enlarged tonsils with heterogeneous or cystic appearance.8 Any fluid collection adjacent to the tonsil and with tonsillar distortion is suspicious for PTA.5 Using color doppler can also aid in identification. A PTA should be hypoechoic, however it may have surrounding inflamed tonsillar tissue which can appear as a circumferential hyperechoic ring. Lack of color flow confirms it is not a vascular structure, while structures with flow are likely to be blood vessels or inflamed tonsillar tissue. There are two approaches to using US to diagnose PTAs. There is an intra- oral approach using an endo-cavitary probe or the superficial approach using a high frequency linear probe.

Fig. 1 Color doppler showing inflamed tonsillar tissue (white arrow) next to an abscess (black arrow) lacking color flow

Intraoral Approach

The intraoral approach can typically be done efficiently after practicing on 3-4 patients, and small studies have shown a sensitivity of 89 to 95%.8 One study found that compared to using landmarks, IOU diagnosed 100% of PTA vs 64% from landmarks.8It also led to a 7-fold decrease in subspecialty consults.8Importantly, given that the posterior wall of the abscess is on average 9mm from the carotid artery, it can aid in the safety of needle aspiration.8 Using an intracavitary transducer, place the probe on the tonsil, and orient it in the transverse plane.8

Fig. 2 Endocavitary Probe for IOU
Fig. 3 Positioning for IOU approach


  1. Anesthetize the area with topical gel, spray, or injection.

  2. A tongue blade can be used to visualize the pharynx. Alternatively, a miller blade can be used and can be held by the patient for their comfort.

  3. Use a clean endocavitary probe with a cover.

  4. Insert the endocavitary probe, starting on the contralateral side of the mouth. Begin with the probe in the transverse orientation.

  5. Identify the PTA and measure it in two planes to estimate its volume.

  6. Determine the depth from the surface.

  7. Locate the internal carotid artery, which is 5-25mm posterior to the abscess, in order to avoid puncturing it as you’re attempting aspiration. Using color flow can help in visualization.

  8. Drainage can then be done dynamically or statically with direct visualization of the needle into the abscess, or visualizing the general area of the abscess and then performing drainage statically after removal of the probe.

Fig. 4 Proximity of Internal Carotid (white arrow) to PTA (red arrow)
  • Advantages:

    • Has higher sensitivity compared to transcutaneous approach.8

  • Disadvantages:

    • This approach cannot be used if the patient has severe trismus or is uncooperative.

    • Accessing the tonsil for drainage may be limited due to the size and positioning of the probe.

Transcutaneous Approach

There are limited studies suggesting that TCU diagnosed PTAs 100% of the time IOU could not be used, and led to an increased quantity of aspirate.2If the patient is unable to open their mouth due to trismus or there is not an available endocavitary probe then a linear or curvilinear transducer can be used transcutaneous.4 Place the probe under and medially to the angle of the mandible, with the probe marker facing the patient’s ear.6 Find the internal jugular and carotid artery and fan the transducer cephalad.6Identify the submandibular gland, and the tonsil will be deep to this structure.8

Fig. 5 Linear Probe for TCU
Fig. 6 Positioning for TCU approach


  1. Using a high frequency linear transducer, place it under mandible with the probe marker facing the right of the patient. First evaluate the unaffected side.

  2. Locate the internal jugular vein and carotid artery using color doppler. Then fan cephalad until the pharyngeal tonsil is located.

  3. Once the tonsil is identified, move the probe laterally.

  4. If you come across a hypoechoic structure, this may be an abscess. These can be surrounded by a hyperemic rim from inflamed tonsillar tissue. If there is no flow, it confirms that it is not a vascular structure.

  5. Drainage can then be done dynamically with direct visualization of the needle into the abscess.

Fig. 7 Transcutaneous approach showing tonsil (black arrow) and Internal Carotid (white arrow)


  • When intraoral cannot be used such as when the patient has significant trismus, or when it is a pediatric patient who is uncooperative and won’t tolerate the probe in their mouth.4

  • Higher specificity than IOU.2


  • There is more subcutaneous tissue that needs to be penetrated in order to see the abscess and there may be interference from bone.


Ultrasound is an ideal modality for diagnosis and management of peritonsillar abscesses in the emergency department. It is quick, inexpensive, limits the amount of radiation exposure, and is the only modality that guides needle drainage.

[1] Blaivas M, Theodoro D, Duggal S. Ultrasound-guided drainage of peritonsillar abscess by emergency physician. Am J Emerg Med 2003;21(2):155–8.

[2] Filho, B et al. Intraoral and transcutaneous cervical ultrasound in the differential diagnosis of peritonsillar cellulitis and abscesses,Brazilian Journal of Otorhinolaryngology,Volume 72, Issue 3, 2006, 377-381, doi:10.1016/S1808-8694(15)30972-1.

[3] Froehlich MH, Huang Z, Reilly BK. Utilization of ultrasound for diagnostic evaluation and management of peritonsillar abscesses. Curr Opin Otolaryngol Head Neck Surg. 2017;25(2):163-168. doi:10.1097/MOO.0000000000000338

[4] Halm, Brunhild, Ng, Carrie, Larrabee, Yuna. Diagnosis of a Peritonsillar Abscess by Transcutaneous Point-of-Care Ultrasound in the Pediatric Emergency Department. Pediatr Emerg Care. 2016;32(7):489-492. doi:10.1097/PEC.0000000000000843.

[5] Kew J, Ahuja A, Loftus WK, Metreweli C. Peritonsillar abscess appearance on intraoral ultrasound. Clin Radiol 1998;53:143–6.

[6] Rehrer, Matthew et al. Identification of peritonsillar abscess by transcutaneous cervical ultrasound. The American Journal of Emergency Medicine , Volume 31 , Issue 1 , 267.e1 – 267.e3

[7] Scott PM, Loftus WK, Kew J, Yue V, van Hasselt CA. Diagnosis of peritonsillar infections: a prospective study of ultrasound, computerized tomography and clinical diagnosis. J Laryngol Otol 1999;13:229–32.

[8] Secko M, Sivitz A, Think ultrasound first for peritonsillar swelling, Am J Emerg Med (2015), j.ajem.2015.01.031