Peritonsillar abscess (Quinsy) is a deep neck infection resulting from accumulation of purulent material in the peritonsillar space between the palatine tonsil capsule and the superior pharyngeal constrictor muscle. It is the most common deep neck abscess in young adults (15-35 years) and usually develops as a complication of acute tonsillitis. CT shows a rim-enhancing hypodense collection with medialized tonsil, surrounding fat stranding, and reactive cervical lymphadenopathy. It is a condition requiring emergent drainage; if delayed, it can lead to life-threatening complications such as airway obstruction, parapharyngeal/retropharyngeal spread, carotid artery erosion, and jugular vein thrombophlebitis (Lemierre syndrome).
Age Range
15-45
Peak Age
25
Gender
Equal
Prevalence
Common
Peritonsillar abscess usually develops as a complication of acute tonsillitis. The infection crosses the tonsil capsule and spreads to the peritonsillar space — a potential space filled with loose areolar tissue between the tonsil capsule and the fascia of the superior pharyngeal constrictor muscle. The infection initially begins as peritonsillar cellulitis (phlegmon) and progresses to abscess formation through suppuration. The abscess wall is formed by a pyogenic membrane surrounded by granulation tissue and fibrin — rim enhancement on CT reflects this vascularized abscess wall. The purulent material within the abscess is protein-rich fluid and necrotic debris — low CT density and diffusion restriction on DWI result from this protein-dense, viscous content. Inflammatory edema and vasodilation in surrounding fat are seen as fat stranding on CT. Tonsillar medialization results from the abscess pushing the tonsil medially. Infection can track along fascial planes to parapharyngeal, retropharyngeal, and even mediastinal spaces — evaluation of these compartments is therefore mandatory. Due to proximity to the carotid sheath, vascular complication risk is high.
A rim-enhancing hypodense collection in the peritonsillar space is the pathognomonic CT finding of peritonsillar abscess. The collection displaces the tonsil medially and the soft palate anteriorly, creating the characteristic asymmetry.
Contrast-enhanced CT shows a rim-enhancing hypodense collection in the peritonsillar space. The abscess wall shows smooth or irregular rim enhancement with thickness of 2-4 mm. Abscess content is hypodense at 10-30 HU reflecting purulent material. The tonsil is markedly medialized and enlarged. Surrounding soft tissue edema and fat stranding are present. Palatopharyngeal muscles may be thickened and enhanced. Cervical reactive lymphadenopathy accompanies.
Report Sentence
A rim-enhancing hypodense collection measuring approximately ...x... mm is noted in the left peritonsillar space, consistent with peritonsillar abscess; the tonsil is medialized and the airway is narrowed.
DWI shows marked diffusion restriction (high signal) in the abscess lumen with corresponding low ADC value. The high viscosity of purulent material and density of cellular debris restrict water molecule movement. This feature is critically important in distinguishing abscess from cystic/necrotic tumors — tumor necrosis generally does not show diffusion restriction. The combination of rim enhancement + DWI restriction has high specificity for abscess diagnosis.
Report Sentence
Marked diffusion restriction and low ADC values are noted in the peritonsillar collection on DWI, interpreted in favor of abscess.
The abscess pushes the tonsil medially, narrowing the oropharyngeal airway. The ipsilateral tonsil is significantly enlarged and medialized. The uvula may deviate to the contralateral side. Airway width is a critical assessment parameter — severe narrowing may require emergent airway intervention.
Report Sentence
The left tonsil is markedly medialized, narrowing the oropharyngeal airway; the uvula is deviated to the right.
Proximity to the carotid sheath is a critical assessment parameter in peritonsillar abscess. Abscess collection crossing parapharyngeal fat planes to reach the carotid sheath increases the risk of internal carotid artery erosion and internal jugular vein thrombophlebitis. CT should evaluate whether the fat plane between the carotid artery and abscess is preserved, filling defect in the jugular vein (thrombus), and vessel wall irregularity.
Report Sentence
The peritonsillar abscess collection extends to parapharyngeal fat planes but the fat plane between the carotid sheath is preserved; no thrombus was detected in the internal jugular vein.
Intraoral US shows a hypoechoic/anechoic collection in the peritonsillar region. Internal echogenicities due to debris and thin lines due to septa may be seen. Peripheral increased Doppler vascularity reflects the vascularized granulation tissue of the abscess wall. US can also be used for localization and guidance during drainage.
Report Sentence
Intraoral US demonstrates a hypoechoic collection with internal debris in the left peritonsillar region, consistent with peritonsillar abscess.
Criteria
Not yet suppurated, diffuse soft tissue edema/enhancement
Distinct Features
No collection, diffuse enhancement; treated with antibiotics; drainage not required
Criteria
Organized purulent collection, rim enhancement
Distinct Features
Drainage mandatory (aspiration or incisional); DWI restriction marked
Criteria
Parapharyngeal/retropharyngeal spread or vascular complication
Distinct Features
Multi-compartment involvement; carotid/jugular complications; emergent surgical drainage
Distinguishing Feature
Lymphoma is a solid homogeneous mass with no rim enhancement or collection; abscess is a rim-enhancing hypodense collection
Distinguishing Feature
SCC shows solid mass + central necrosis with invasive margins; abscess is a fluid collection with acute clinical presentation
Distinguishing Feature
Hypertrophy is bilateral symmetric, solid homogeneous, no collection; abscess is unilateral collection + clinical inflammation
Urgency
emergentManagement
interventionalBiopsy
Not NeededFollow-up
specialist-referralPeritonsillar abscess is a condition requiring EMERGENT drainage. Needle aspiration or incisional drainage + IV antibiotics is the standard treatment. Carotid sheath involvement, airway compromise, and descending mediastinitis are life-threatening complications. CT findings determine drainage indication and approach.
Peritonsillar abscess is a condition requiring emergent drainage. If untreated, it can lead to life-threatening complications such as airway obstruction, carotid artery erosion, jugular vein thrombophlebitis (Lemierre syndrome), and mediastinitis.