Ultrasound highly sensitive but moderately specific for detection of peritonsillar abscess

One of the most common head and neck infections is PTA. It has an estimated incidence between 10 and 40 cases per 100,000 annually and about 63,000 emergency department (ED) visits in the US annually.

PTA refers to the purulent collection between the palatine tonsil and its capsule, developing from initial tonsillitis or pharyngitis.

The complications of PTA include airway obstruction, aspiration pneumonitis, mediastinal extension, and carotid sheath erosion.

Distinguishing peritonsillar abscess (PTA) from peritonsillar cellulitis using clinical assessment is challenging. Many features overlap for both conditions and physical examination is only about 75% sensitive and 50% specific for diagnosing PTA. The primary objective of this systematic review was to determine the test characteristics of Ultrasound for diagnosing PTA when compared to a reference standard of computed Tomography or acquisition of pus via needle aspiration or incision and drainage. The systematic review followed PRISMA-DTA guidelines.

The results of the study could be summarised as:

• 18 studies met the inclusion criteria.

• Final analysis had 17 studies with 812 patients

• 541 patients had Peritonsillar abscess.

• Pooled bivariate sensitivity, specificity, LR+ and LR- was 86%, 76%, 3.51and – 0.19 respectively.

• The radiology-performed Ultrasound had a sensitivity and specificity of 89% and 71% on subgroup analysis, compared to POCUS, having sensitivity and specificity of 74% and 79%.

• Comparing the two different techniques, the sensitivity specificity of intraoral and transcervical was 91%, 75% and, 80%, 81%, respectively

Concluding further, they said this is the first systematic review and meta-analysis determining the diagnostic importance of Ultrasound for PTA. Computed Tomography has accuracy, but it increases patient exposure to ionizing radiation and intravenous (IV) contrast.

Researchers finally reported that Ultrasound has a high sensitivity for ruling out PTA, but the specificity is moderate for establishing the diagnosis. Ultrasound is an acceptable alternative to CT, they said.

Further reading:

Daniel J. Kim MD et al. Test characteristics of Ultrasound for diagnosing peritonsillar abscess: A systematic review and meta-analysis. First published: 10 January 2023 https://doi.org/10.1111/acem.14660