Accurate Diagnosis of Peritonsillar Abscesses Using Relative CT Number Measurements in Low-Density Areas of Contrast CT Images

<b>Objectives</b>: A diagnostic indicator for differentiating peritonsillar abscess (PTA) from peritonsillar cellulitis (PTC) has not been established. Our aim was to define radiological criteria for differentiating PTA from PTC. <b>Methods</b>: We retrospectively extracted low-density areas around the tonsils of PTA and PTC cases from contrast-enhanced CT images between 2021 and 2024. PTA cases were identified as those in which drainage by puncture or incision was observed, while PTC cases were those in which drainage was not observed. A total of 138 cases were finally analyzed (PTA, 111 cases; PTC, 27 cases). The CT attenuation value of a low-density area relative to that of the area surrounding the low-density area was used as the relative CT number, and relative CT numbers were compared between PTA and PTC cases. Using univariate and multivariate analyses, we identified factors that had diagnostic value for differentiating between PTA and PTC. <b>Results</b>: Relative CT numbers for PTA were significantly lower than those for PTC (<i>p</i> < 0.001). The univariate logistic regression analysis showed relative CT number, low-density ROI (region of interest), and surrounding ROI as having predictive value for differentiating PTA from PTC. In multivariate logistic regression analysis, only the relative CT number had predictive value for distinguishing PTA from PTC (odds ratio, 2.28), with a relative CT number of <0.46 being significantly associated with PTA. <b>Conclusions</b>: Low relative CT numbers could potentially be used to identify PTA, and their measurement could provide a diagnostic marker for the accurate diagnosis of abscess formation.