Ultrasound Exam

Position the ultrasound system just behind and lateral to the patient to allow the operator a direct view of the screen while performing the examination. Advance a cleaned and covered high-frequency (8-5 MHz), intra-cavitary probe into the patient’s mouth with the indicator pointing to the patient’s right (Pic. 2).

Always examine the unaffected tonsil first by fanning in a cephalad-to-caudad direction. Visualize both the lateral and superior aspect of the unaffected tonsil to ensure that you are familiar with normal sonographic anatomy. The unaffected/normal tonsil should be oval, have a central hyperechoic hilum and a hypoechoic periphery (as compared to adjacent muscle tissue). A more experienced sonographer can employ color power Doppler or color Doppler to detect the classic central flow of lymphatic tissue. Recognizing the normal sonographic appearance of the unaffected tonsil is critical in differentiating a peritonsillar abscess from peritonsillar cellulitis⁵ (Pic. 3).

After clearly visualizing the normal tonsil, repeat the examination for the affected tonsil. Again, look closely for any hypoechoic areas adjacent to the tonsil (most commonly located either superiorly or laterally). Similar to abscesses seen under the skin surface, the sonographer should look for a discrete hypoechoic cavity with disorganized purulent material. Novice sonographers can easily mistake a cellulitic tonsil for an abscess, and a clearly defined hypoechoic/anechoic pocket of fluid should be identified (Pic. 4 and Pic. 5). Finally, identification of the carotid artery allows the clinician to assess the proximity of the vessel in relation to the abscess cavity (commonly 3-4 cm behind the posterior pharynx)^2–4 (Pic. 6).

Peritonsillar Drainage

Although real-time, ultrasound guidance for needle drainage of peritonsillar abscess has been described, we recommend a pre-procedural marking technique. Because of the limited space in the posterior pharynx, concurrent real-time ultrasound needle visualization and abscess drainage can be technically challenging. We use ultrasound to diagnose and locate the abscess cavity, then remove the ultrasound and perform the needle drainage.

After the patient is comfortable, and the abscess has been identified, use a Macintosh laryngoscope (size 3 or 4) to expose and illuminate the target peritonsillar aspiration site. We recommend placing a 3.5 inch 18-20 g spinal needle on a 10 ml syringe with the distal 2 cm of the needle cover cut to limit the risk of inadvertent carotid artery puncture. The length of the spinal needle allows for the operator’s hand to maneuver freely outside the mouth during aspiration (Pic. 7). With the patient’s head supported, the operator should aspirate as the needle tip enters the abscess cavity.