The technique used to perform the aspiration is similar to ultrasound-guided vascular procedures. The only difference is that a high-frequency (5-10 MHz) curved array endocavity probe is used to guide the aspiration of peritonsillar abscess because its shape allows placement in the posterior pharyngeal space. The procedure is typically performed freehand, but a needle guide can be attached to the endocavity transducer to perform the aspiration. However, it adds significant costs to the procedure and also limits the distance the needle can be inserted into the oropharynx. The manual dexterity needed to manipulate the endocavity probe while performing aspiration requires some practice. Generally, the procedure is performed by one operator, holding the probe with one hand and performing the aspiration with the other hand, while making appropriate adjustments of the probe to visualize the needle. Prior studies have clearly demonstrated the ability of the emergency physicians to effectively use bedside ultrasound for both the diagnosis of peritonsillar abscess and real-time guidance for needle aspiration (3, 4, 5).

Adequate systemic analgesia should be given to the patient prior to performing the procedure. Topical anesthetic should be sprayed into the posterior pharyngeal area to avoid gagging and overcome trismus. After placing gel over the tip of the endocavity probe, it should be covered with a sheath or condom. The endocavity probe is then inserted into the oral cavity and advanced into the pharyngeal region. The peritonsillar area is scanned systematically in both long and short axes. The presence of the peritonsillar abscess should be confirmed, which can have variable appearances on ultrasound. Often, a peritonsillar abscess is visualized as a hypoechoic or complex cystic mass, typical of most abscesses (Fig. 25.1). The depth of the abscess cavity from the mucosal surface
should be noted, and the length of the needle required to enter the abscess cavity should be determined prior to aspiration. The carotid artery and its relationship to the abscess cavity should be assessed. It is visualized as an anechoic tubular structure along the posterolateral aspect of the tonsil, generally within 5 to 25 mm of an abscess cavity (Fig. 25.1). Color Doppler can help identify the carotid artery. The relationship of the tonsillar tissue, abscess cavity, and carotid artery is best assessed in transverse axis. The transducer should be held horizontally, and the fluid collection should be localized. Once the abscess is localized, an 18-gauge 2-inch needle attached to a 5- to 10-mL syringe is inserted lateral to the tip of the transducer (Fig. 25.2). Alternatively, a 14-gauge needle can be used if purulent material appears too thick. The needle should be placed in the middle of the tip of the transducer, exactly in the same plane as the ultrasound signal. As with vascular access procedures, real-time guidance should be used. The same principles should be employed to track the entire course of the needle. The needle should be advanced slowly under direct visualization with ultrasound. If the needle tip is not seen at any point, no further advancement should be made. Once the needle penetrates the abscess cavity, aspiration should be performed under real-time guidance (Fig. 25.3). Reduction in the size of the abscess cavity should be seen on ultrasound (Fig. 25.4). Occasionally, saline injection into the abscess cavity might be necessary to break up the loculations and facilitate aspiration (Fig. 25.5).