Peritonsillar Abscess
A peritonsillar abscess (PTA), historically called quinsy, is a collection of pus that forms in the peritonsillar space — the anatomical compartment between the tonsillar capsule and the superior pharyngeal constrictor muscle. It is the most common deep space infection of the head and neck in adults and adolescents, with an incidence of approximately 30–40 cases per 100,000 people per year in the United States. Peak incidence falls between ages 15 and 35; the condition is rare in children under 10. Most peritonsillar abscesses evolve from peritonsillar cellulitis — inflammation without pus — and progress to frank abscess formation over 2 to 5 days, often following or during an episode of acute tonsillitis or pharyngitis.
Table of Contents
- What Is a Peritonsillar Abscess?
- Microbiology
- Symptoms and Clinical Presentation
- Diagnosis
- Drainage Procedures
- Antibiotic Treatment
- Complications and Dangerous Spread
- Recurrence and Tonsillectomy Decision
- References & Research
- Featured Videos
1. What Is a Peritonsillar Abscess?
The peritonsillar space is a potential anatomical compartment bounded medially by the tonsillar capsule — the fibrous sheath that envelops the palatine tonsil — and laterally by the superior pharyngeal constrictor muscle. The tonsillar bed can be further subdivided into the peritonsillar space immediately flanking the tonsil and the deeper parapharyngeal space, which lies lateral to the pharynx and is critical in understanding how infection spreads if PTA is not treated promptly.
A key structure implicated in the origin of peritonsillar abscess is Weber's glands — minor salivary glands located in the superior pole of the tonsil. It is hypothesized that these glands serve as the initial nidus of infection: their ducts can become obstructed during episodes of tonsillitis, trapping bacteria and allowing localized suppuration to begin before a full abscess is apparent. This explains why the great majority of peritonsillar abscesses form at the superior pole, in the area of the supratonsillar fossa.
The pathogenesis follows a predictable sequence: local bacterial infection triggers tissue edema and an inflammatory exudate, which accumulates as a loculated pus collection between the tonsillar capsule and the adjacent muscle. The expanding collection displaces the tonsil medially and inferiorly, pushes the soft palate and uvula toward the opposite side, and compresses the adjacent pterygoid muscles — producing the characteristic trismus (jaw stiffness) that distinguishes PTA from simple tonsillitis.
Peritonsillar abscess sits at the most dangerous end of a clinical spectrum. Untreated cellulitis can evolve to abscess; untreated or inadequately drained abscess can spread laterally into the parapharyngeal space, posteriorly into the retropharyngeal space, and ultimately downward into the mediastinum via the fascial planes of the neck — a life-threatening condition known as descending necrotizing mediastinitis, carrying mortality rates of 20–47% even with aggressive surgical and antibiotic treatment.
2. Microbiology
Peritonsillar abscesses are almost universally polymicrobial — cultures grow a mixture of aerobic and anaerobic bacteria, reflecting the flora of the oropharynx and tonsillar crypts. This polymicrobial nature has important implications for antibiotic selection, since no single narrow-spectrum agent will cover the full range of pathogens.
The most frequently isolated aerobic organism is Group A Streptococcus (GAS, Streptococcus pyogenes), which is the most common single organism identified and the same bacterium responsible for streptococcal pharyngitis and scarlet fever. Staphylococcus aureus, including methicillin-resistant strains (MRSA), has become an increasingly important pathogen in peritonsillar abscesses over the past two decades and is associated with more severe disease and a higher rate of treatment failure with standard penicillin-based regimens. Haemophilus influenzae is a less common but relevant aerobic contributor.
The most clinically significant anaerobe is Fusobacterium necrophorum, particularly in young adults. This organism deserves special attention because it is the causative agent of Lemierre's syndrome — a rare but potentially fatal condition in which F. necrophorum bacteremia leads to septic thrombophlebitis of the internal jugular vein and septic emboli to the lungs, joints, liver, and other organs. Any young adult with PTA who develops neck pain or a lateral neck mass alongside systemic sepsis should be evaluated urgently for Lemierre's syndrome. Other common anaerobes include Prevotella species, Peptostreptococcus, and Bacteroides species.
Epstein-Barr virus (EBV) plays a special role in the adolescent age group. Infectious mononucleosis is complicated by peritonsillar abscess in approximately 1–3% of cases, and conversely, any adolescent presenting with PTA should have a monospot test or EBV serology performed. The distinction is clinically important: aminopenicillins such as amoxicillin and ampicillin provoke a diffuse maculopapular rash in up to 90% of patients with active EBV infection — a well-known and uncomfortable drug interaction that must be avoided. When mononucleosis is suspected, penicillin plus metronidazole, clindamycin, or azithromycin are preferred.
3. Symptoms and Clinical Presentation
The clinical presentation of peritonsillar abscess is highly characteristic and, in most cases, allows confident diagnosis at the bedside without imaging. The cardinal symptom is severe, predominantly unilateral throat pain — disproportionately worse on the affected side compared to simple tonsillitis. Pain typically progresses over several days to the point where the patient cannot swallow solids, then liquids, and eventually struggles to manage their own saliva, leading to drooling. Fever is almost universal. The combination of severe unilateral sore throat, fever, and trismus in an otherwise healthy young adult is highly specific for PTA.
Trismus — involuntary limitation of mouth opening caused by spasm of the medial pterygoid muscle in response to adjacent inflammation — is one of the most diagnostically useful signs. It is typically absent in uncomplicated tonsillitis and absent or mild in peritonsillar cellulitis, making its presence a reliable marker for abscess formation. The degree of trismus often reflects the severity of the collection. Patients with significant trismus may be unable to open their mouth wide enough for adequate examination, which can complicate both diagnosis and drainage.
The characteristic "hot potato" voice — a muffled, thick-sounding speech quality as though the patient has a potato in their mouth — results from distortion of the soft palate and oropharyngeal anatomy by the expanding abscess, combined with pain-related reduction in palatal movement. This voice change is a reliable clinical marker and often alerts the experienced clinician before formal examination confirms the diagnosis. Referred otalgia (ear pain on the same side as the abscess) is common, transmitted via the glossopharyngeal and vagal nerves, and halitosis reflects the anaerobic bacterial flora of the pus collection.
On intraoral examination, the affected side shows a bulging, erythematous soft palate with the uvula displaced to the contralateral (opposite) side — one of the most reliable signs of PTA. The tonsil is displaced medially and inferiorly. The swelling is typically fluctuant at the superior pole. Ipsilateral tender cervical lymphadenopathy — particularly the jugulodigastric (tonsillar) lymph node — is almost invariably present. In contrast, bilateral symmetric tonsillar swelling without uvular deviation suggests infectious mononucleosis with tonsillar enlargement rather than PTA.
4. Diagnosis
The diagnosis of peritonsillar abscess is primarily clinical, based on the characteristic history and physical examination findings described above. In straightforward cases with the triad of unilateral throat pain, fever, trismus, and contralateral uvular deviation, no imaging is required before proceeding to drainage. However, limited mouth opening from trismus frequently restricts the clinical examination, and distinguishing PTA from peritonsillar cellulitis or a deeper space infection can be genuinely difficult.
The key differential diagnoses to consider include: peritonsillar cellulitis (inflammation without abscess — no fluctuance, minimal or no uvular deviation, treat with antibiotics first; may resolve without drainage); parapharyngeal abscess (deeper, causes swelling at the angle of the jaw rather than the tonsillar area, requires CT for diagnosis and typically surgical drainage under general anaesthesia); retropharyngeal abscess (most common in children under 5, presents with posterior midline bulge of the posterior pharyngeal wall, neck stiffness, stridor, and restricted neck extension); and epiglottitis (distinguished by stridor, severe dyspnoea, drooling, the characteristic "tripod" posture, and the "thumb sign" on lateral neck radiograph — epiglottitis is a true airway emergency and must never be approached for examination without anaesthetic support).
Contrast-enhanced CT of the neck is the gold standard imaging modality when clinical examination is equivocal, when deep space extension is suspected, or when surgical planning for drainage requires anatomic definition. CT reliably demonstrates a ring-enhancing fluid collection with surrounding inflammatory changes and can distinguish cellulitis (diffuse enhancement without a discrete fluid collection) from abscess (central low attenuation, peripheral rim enhancement). CT also identifies extension into the parapharyngeal or retropharyngeal spaces, or into the neck vasculature in cases of Lemierre's syndrome.
Intraoral ultrasound is an increasingly used point-of-care technique in emergency departments that can safely and rapidly distinguish abscess from cellulitis without radiation. Using a curved intraoral probe placed gently on the peritonsillar area, the abscess appears as a hypoechoic fluid collection. Studies report sensitivity of approximately 89% and specificity approaching 100% in experienced hands, and ultrasound can guide needle aspiration in real time. Blood tests should include a full blood count (typically showing leukocytosis), CRP, and blood cultures if systemic sepsis is suspected. A monospot test and EBV serology are recommended in adolescents and young adults. Throat culture and, when MRSA is a concern, an MRSA swab should be obtained before antibiotic administration.
5. Drainage Procedures
Surgical drainage is the definitive treatment for peritonsillar abscess and distinguishes it from peritonsillar cellulitis, which may resolve with antibiotics alone. Three drainage approaches are in clinical use, each with specific indications and technical considerations. All require adequate local or general anaesthesia and careful attention to avoid the carotid artery, which lies just lateral to the peritonsillar space — typically 2–2.5 cm lateral to the tonsillar fossa.
Needle aspiration is the most widely used first-line procedure in cooperative adults. An 18-gauge needle on a 10 mL syringe is inserted at the point of maximal fluctuance — almost always the superior pole of the tonsil, just lateral to the uvular base — after infiltration of the mucosa with 1% lidocaine with epinephrine. Aspiration of frank pus confirms the diagnosis and achieves immediate decompression. Success rates are reported at 85–90%. A key technical rule: the needle must always be directed medially, never laterally — the carotid artery lies a centimetre or less lateral to the tonsillar fossa and inadvertent carotid puncture is a catastrophic complication. Needle aspiration may need to be repeated if the abscess reaccumulates, but repeat aspiration is well-tolerated. The technique can be performed at the bedside with only topical and local anaesthesia, making it particularly suitable for the emergency department setting.
Incision and drainage (I&D) is performed using a scalpel to make a controlled incision at the site of maximal fluctuance, followed by blunt dissection with a curved haemostat to open the cavity and evacuate the pus completely. This approach achieves more thorough drainage than needle aspiration and is preferred for large collections, for cases where aspiration has failed to yield pus, or when the anatomy suggests a multiloculated collection. The same anatomical landmarks apply and the same precaution against lateral needle/scalpel placement is essential. I&D can generally be performed under local anaesthesia in cooperative adults; children and highly anxious patients may require general anaesthesia and operating room conditions.
Quinsy tonsillectomy — immediate tonsillectomy performed while the abscess is still acute — simultaneously drains the collection and permanently removes the tonsils, eliminating future recurrence risk. However, tonsillectomy in acutely inflamed tissue carries a higher intraoperative and postoperative bleeding risk than elective (interval) tonsillectomy, and requires general anaesthesia. It is therefore reserved for specific indications: recurrent peritonsillar abscess, immunocompromised patients, patients who cannot cooperate with awake drainage, tonsillar hypertrophy causing obstruction, or when the abscess anatomy makes needle/I&D unfeasible. The quinsy tonsillectomy approach is more commonly used in some European countries than in the United States, where needle aspiration followed by interval tonsillectomy is the predominant model.
6. Antibiotic Treatment
Antibiotics are a necessary adjunct to drainage and are given to eradicate residual bacteria, prevent spread into adjacent deep spaces, and reduce the risk of recurrence. Empirical antibiotic selection must cover the polymicrobial flora of PTA — Group A Streptococcus, Staphylococcus aureus, and the anaerobic organisms including Fusobacterium — while accounting for the possibility of EBV infection in younger patients.
Amoxicillin-clavulanate (oral; 875/125 mg twice daily × 10–14 days) is a widely used outpatient first choice, providing coverage against GAS, MSSA, and many anaerobes. The combination of penicillin plus metronidazole is an effective and cost-efficient alternative that pairs excellent streptococcal coverage (penicillin V or amoxicillin) with robust anaerobic activity (metronidazole). Clindamycin is the preferred option in penicillin-allergic patients and provides excellent coverage of both GAS and anaerobes; it also offers some activity against MRSA, making it useful when community-acquired MRSA is a concern. For documented or strongly suspected MRSA infection in a hospitalised patient, intravenous vancomycin is the agent of choice; outpatient MRSA coverage can be achieved with TMP-SMX or doxycycline, though neither covers Group A Streptococcus reliably, necessitating combination. If mononucleosis is suspected or confirmed, amoxicillin and ampicillin must be strictly avoided because of the near-universal rash they provoke in active EBV infection.
Corticosteroids have become a widely accepted adjunctive therapy in peritonsillar abscess management. A single dose of dexamethasone 10 mg intravenously significantly reduces pain intensity, time to pain resolution, degree of trismus, and time to discharge compared with placebo in randomised controlled trials. Dexamethasone does not impair local immunity sufficiently to promote abscess recurrence when adequate drainage and antibiotics are provided concurrently. The evidence base is now sufficiently robust that dexamethasone is recommended as routine adjunct therapy by many ENT and emergency medicine guidelines.
Adequate analgesia — typically a combination of NSAIDs (ibuprofen) and paracetamol (acetaminophen), escalating to opioids for severe uncontrolled pain in the acute phase — is essential because uncontrolled pain and trismus impair oral antibiotic and fluid intake. Intravenous fluids are required for patients who cannot maintain adequate oral hydration due to severe odynophagia. Indications for hospital admission include: systemic sepsis or high fever with rigors, trismus preventing adequate awake drainage, CT-confirmed parapharyngeal or retropharyngeal extension, airway compromise (rare), immunosuppression, age under 10 years, or inability to tolerate oral intake after drainage.
7. Complications and Dangerous Spread
When peritonsillar abscess is recognised and treated promptly, serious complications are uncommon. However, delayed presentation, inadequate drainage, or host immunosuppression can allow the infection to spread along the fascial planes of the neck into progressively deeper and more dangerous anatomical compartments. Understanding this spread pattern is essential for every clinician who treats sore throat.
Parapharyngeal space extension occurs when infection tracks laterally through the superior pharyngeal constrictor muscle into the parapharyngeal space — the fat-filled compartment lying between the pharynx medially and the mandible, parotid, and pterygoid muscles laterally. Clinically, parapharyngeal abscess presents with jaw angle swelling, fever, and trismus but without the visible fluctuance and uvular deviation typical of PTA; the abscess lies too deep for intraoral aspiration. Contrast CT is required for diagnosis, and treatment requires surgical drainage, usually under general anaesthesia. The carotid artery, internal jugular vein, and multiple cranial nerves (IX–XII) all traverse the parapharyngeal space, putting them at risk from severe parapharyngeal infections.
Retropharyngeal extension — spread into the space between the posterior pharyngeal wall and the prevertebral fascia — creates a retropharyngeal abscess. Although this is the most common deep neck infection in children under 5, it can complicate PTA in adults when infection tracks posteriorly. Symptoms include neck stiffness, restricted neck extension, dysphagia, and stridor if the airway is compressed. Retropharyngeal abscess is particularly dangerous because the retropharyngeal space is continuous with the "danger space" (prevertebral space extending from the skull base to the diaphragm), providing a direct pathway for infection to reach the mediastinum. Descending necrotizing mediastinitis (DNM) — the result of mediastinal spread — is the most feared complication of deep neck infection, carrying mortality rates of 20–47% despite aggressive surgical debridement and intensive care. CT of the chest is mandatory if mediastinal extension is suspected.
Lemierre's syndrome must be recognised in any young adult with PTA who develops a painful neck mass (from jugular vein thrombosis), persistent or worsening sepsis after adequate drainage, or pulmonary infiltrates (septic emboli). Fusobacterium necrophorum bacteraemia seeds the internal jugular vein, causing suppurative thrombophlebitis with embolic seeding of the lungs, liver, joints, and brain. Treatment requires prolonged intravenous antibiotics (beta-lactam/metronidazole combination for 4–6 weeks); the role of anticoagulation remains controversial but is used in many centres; surgical ligation or excision of the internal jugular vein is reserved for refractory cases. Mortality with appropriate treatment is approximately 5%, but the condition is frequently missed because it presents after apparent improvement of the initial throat infection.
Additional, rarer complications include airway obstruction from a large bilateral abscess or extensive oropharyngeal oedema (managed with early secured airway — intubation or tracheotomy), aspiration pneumonia from spontaneous rupture of the abscess into the pharynx, and carotid artery pseudoaneurysm — an extremely rare but catastrophic erosion of the carotid wall by adjacent infection presenting with massive oropharyngeal haemorrhage.
8. Recurrence and Tonsillectomy Decision
Peritonsillar abscess recurs in a meaningful proportion of patients managed conservatively. Published recurrence rates after needle aspiration are approximately 10–15%; after incision and drainage, 5–10%; and after quinsy tonsillectomy, near zero. This gradient drives ongoing debate about when to recommend interval (delayed) tonsillectomy after a successfully treated episode of PTA.
The case for interval tonsillectomy — performed electively 4–6 weeks after complete resolution of the acute infection — rests on eliminating the anatomical substrate for recurrence and preventing future episodes of PTA, which become progressively more technically difficult to drain as peritonsillar scar tissue accumulates. Accepted indications for interval tonsillectomy include: two or more episodes of PTA; recurrent tonsillitis meeting the Paradise criteria (typically 5–7 or more tonsillitis episodes per year for at least 1–2 years); tonsillar hypertrophy causing obstructive sleep apnoea or significant swallowing difficulty; and patient preference after counselling on recurrence risk.
The value of tonsillectomy after a single lifetime episode of PTA is genuinely debated. UK national guidelines, following the 2014 Powell et al. multicentre study, suggest that most adults with a first episode of PTA can be managed with watchful waiting rather than automatic interval tonsillectomy, given that approximately 85–90% will never have another episode. Patients at higher recurrence risk — smokers, those with diabetes or immunosuppression, and those with a prior history of recurrent tonsillitis — have a stronger indication for interval tonsillectomy even after a single PTA episode. Children are generally considered for tonsillectomy at a lower threshold than adults, both because recurrence risk in childhood is higher and because recurrent PTA significantly impacts school attendance and quality of life.
Technical factors deserve emphasis: tonsillectomy performed in the interval (at least 4–6 weeks after the acute episode) is significantly safer than quinsy tonsillectomy. Peritonsillar scar tissue from PTA can create adhesions that make the tonsillar bed more adherent and technically demanding to dissect, slightly increasing bleeding risk even in the interval setting. The overall tonsillectomy complication rate (bleeding 2–4% of cases, particularly in the first 24 hours and again at day 5–10 when the eschar separates) should be discussed explicitly with patients as part of the shared decision-making process. Post-tonsillectomy haemorrhage is the primary serious risk, and patients should be counselled to seek emergency care immediately for any throat bleeding after the procedure.
9. References & Research
- Galioto NJ. Peritonsillar abscess. Am Fam Physician. 2008. PMID 18481571.
- Johnson RF, Stewart MG. The contemporary approach to diagnosis and management of peritonsillar abscess. Curr Opin Otolaryngol Head Neck Surg. 2005. PMID 15761280.
- Spires JR et al. Treatment of peritonsillar abscess. Arch Otolaryngol Head Neck Surg. 1987. PMID 3579149.
- Klug TE et al. Incidence and clinical presentation of peritonsillar abscess. Eur J Clin Microbiol Infect Dis. 2014. PMID 24402656.
- Powell J et al. UK peritonsillar abscess study. J Laryngol Otol. 2013. PMID 23360760.
- Marom T et al. Peritonsillar abscess microbiological changes. J Clin Microbiol. 2010. PMID 20089748.
- Mehanna HM et al. Peritonsillitis: a prospective randomized study to compare medical vs surgical management. Clin Otolaryngol. 2002. PMID 12383300.
- Costantino TG et al. Ultrasound-guided aspiration of peritonsillar abscess in the ED. Am J Emerg Med. 2012. PMID 22717192.
- Ozbek C et al. Comparison of needle aspiration versus incision and drainage in the treatment of peritonsillar abscess. J Laryngol Otol. 2004. PMID 15086953.
- Windfuhr JP et al. Intraoperative complications in 8915 tonsil cases. Laryngoscope. 2012. PMID 22972558.
- Sowerby LJ et al. Lemierre syndrome. J Otolaryngol Head Neck Surg. 2018. PMID 28786347.
- Chau JK et al. Evidence-based practice: management of peritonsillar abscess. Otolaryngol Clin North Am. 2012. PMID 22498247.
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