Peritonsillar Abscess

A collection of pus in the potential space between the tonsillar capsule and the superior constrictor muscle. It is the commonest deep neck space infection, with an incidence of around 30 per 100000 in adults, peaking between 20 and 40 years.

Pathogenesis

Two mechanisms are recognised.

• Progression from acute tonsillitis with spread of infection through the tonsillar capsule into the peritonsillar space, forming a cellulitis, that is peritonsillitis, which then suppurates.
• Infection of the Weber glands, a group of 20 to 25 minor salivary glands in the supratonsillar space that drain through ducts into the tonsillar surface and clear debris from the crypts. Obstruction and infection of these glands produces an abscess in the supratonsillar position, which is why the great majority of abscesses are found superior and lateral to the tonsil. This mechanism explains why peritonsillar abscess occurs in patients who have had tonsillectomy and in those with no preceding tonsillitis.

Anatomy that determines drainage technique and its hazards

The abscess lies between the tonsillar capsule medially and the superior constrictor laterally, most often in the superior pole. Lateral to the superior constrictor lies the parapharyngeal space, which contains the carotid sheath. The internal carotid artery lies approximately 2 to 2.5 cm posterolateral and deep to the tonsil, and closer in children and in patients with a tortuous or medially displaced vessel. Needle aspiration and incision must therefore be directed in a strictly sagittal or slightly medial direction and must not be angled laterally, and depth must be controlled by using a needle guard or by exposing only 1 cm of the blade.

Microbiology

Polymicrobial, with a mixture of aerobes and anaerobes.

• Streptococcus pyogenes, which is the most frequently isolated single aerobe.
• Fusobacterium necrophorum, which is disproportionately common in adolescents and young adults and which carries the risk of Lemierre syndrome.
• Streptococcus milleri group, Staphylococcus aureus, Haemophilus influenzae.
• Anaerobes: Prevotella, Porphyromonas, Peptostreptococcus, Bacteroides.

• Severe unilateral sore throat, which is markedly worse on one side and which typically follows several days of tonsillitis.
• Odynophagia progressing to inability to swallow saliva, with drooling.
• Trismus, from irritation and spasm of the medial pterygoid muscle, which is present in around two thirds and which is a key discriminating sign from simple tonsillitis.
• Muffled hot potato voice, from soft palate swelling and reduced palatal movement.
• Referred otalgia on the affected side.
• Fever, rigors, malaise and dehydration.
• Neck pain and torticollis, with the head tilted toward the affected side.
• Foetor oris.

Examination

• Marked unilateral swelling of the soft palate and the supratonsillar region, with the tonsil displaced medially and inferiorly.
• Contralateral deviation of the uvula, which is the classical sign.
• Erythema and fullness of the anterior pillar, often with a visible point of maximal bulge.
• Trismus, which may make examination difficult and which is itself diagnostic information.
• Ipsilateral cervical lymphadenopathy.
• Assess hydration, airway patency and ability to handle secretions.

Red flags requiring escalation beyond simple drainage

• Stridor, respiratory distress or inability to lie flat, indicating airway compromise.
• Neck swelling, induration or crepitus, indicating extension into the parapharyngeal space or necrotising infection.
• Torticollis with severe neck pain and neck stiffness, indicating parapharyngeal or retropharyngeal extension.
• Rigors with unilateral neck tenderness along sternocleidomastoid and pulmonary symptoms, indicating Lemierre syndrome.
• Failure to improve after adequate drainage and antibiotics, which requires imaging for a second collection or deep neck extension.
• Bilateral swelling, which is uncommon and should raise the possibility of lymphoma or another diagnosis.
• Immunocompromise or diabetes, which predisposes to rapid deep extension and necrotising infection.

Clinical in most cases. The combination of unilateral peritonsillar swelling, uvular deviation and trismus is sufficient to proceed to drainage.

• Distinguish peritonsillar cellulitis from abscess. Cellulitis produces swelling without a drainable collection and responds to antibiotics alone; abscess requires drainage. Aspiration is the practical test.
• Intraoral ultrasound with an endocavity probe, which distinguishes cellulitis from abscess with good accuracy and can guide aspiration, and which is particularly useful where trismus limits examination. Transcervical ultrasound is an alternative where intraoral access is impossible.
• Contrast enhanced computed tomography of the neck, indicated where there is trismus preventing examination, suspected deep neck space extension, failure to respond to drainage, an immunocompromised patient, a child in whom examination is limited, or any airway concern. It defines the collection, identifies parapharyngeal and retropharyngeal extension, and shows vascular complications.
• Full blood count, C reactive protein, urea and electrolytes, and blood cultures where systemically unwell.
• Pus culture at drainage for aerobic and anaerobic organisms.
• Monospot or Epstein Barr virus serology, since peritonsillar abscess can complicate infectious mononucleosis and the management differs, with a greater risk of airway obstruction and a strong reason to avoid amoxicillin.
• Human immunodeficiency virus testing where clinically indicated.
• Contrast computed tomography with venous phase and chest imaging where Lemierre syndrome is suspected.

Differential diagnosis

• Peritonsillar cellulitis.
• Severe acute tonsillitis, which is bilateral without uvular deviation or trismus.
• Parapharyngeal and retropharyngeal abscess, which produce neck signs and are defined on imaging.
• Infectious mononucleosis with marked tonsillar hypertrophy.
• Dental infection with a masticator space abscess, which produces trismus with a normal oropharynx.
• Tonsillar or oropharyngeal malignancy, particularly lymphoma, which may present with unilateral swelling. Persistent asymmetry after resolution requires biopsy.
• Internal carotid artery aneurysm presenting as a pulsatile peritonsillar mass, which is rare but which is the reason to look and palpate before incising.

Drainage plus antibiotics plus analgesia plus rehydration. Antibiotics alone treat cellulitis but not an established abscess.

Drainage

• Needle aspiration is the first line procedure. Topical anaesthesia with lidocaine spray followed by infiltration with lidocaine 1 or 2 percent with adrenaline. Use an 18 gauge needle on a 10 mL syringe, with the sheath of a needle guard or with the plastic needle cover trimmed to expose only 1 cm, preventing deep penetration.
• Aspirate at the point of maximal bulge, usually superolateral to the upper pole, directing the needle in the sagittal plane, parallel to the sagittal axis and never laterally. If no pus is obtained, redirect slightly inferiorly and then at the middle pole, but do not go deeper or angle laterally.
• Incision and drainage under local anaesthesia is an alternative and achieves more complete evacuation. Use a number 11 blade with all but 1 cm of the blade wrapped in tape, make a 1 cm incision at the point of maximal bulge, then spread with Tilley or artery forceps to break loculations.
• Have suction ready and position the patient sitting upright leaning forward, so that pus is not aspirated.
• Both techniques have similar success rates of around 90 percent. Aspiration is less painful and is repeatable; incision provides more sustained drainage.
• Reaccumulation occurs in around 10 to 15 percent and requires repeat aspiration.

Indications for drainage under general anaesthesia

• Children, and uncooperative adults.
• Severe trismus preventing intraoral access.
• Failed local anaesthetic drainage.
• Airway compromise.
• Suspected extension into the parapharyngeal space requiring external drainage.

Antibiotics

• Intravenous therapy for patients requiring admission: co amoxiclav 1.2 g every 8 hours, or benzylpenicillin 1.2 g every 6 hours plus metronidazole 500 mg every 8 hours.
• Clindamycin 600 mg every 6 hours intravenously in penicillin allergy, which covers streptococci and anaerobes well.
• In children, co amoxiclav 30 mg/kg every 8 hours, or benzylpenicillin 25 mg/kg every 6 hours plus metronidazole 7.5 mg/kg every 8 hours.
• Convert to oral therapy when swallowing improves and the patient is afebrile, usually within 24 to 48 hours, completing a total of 10 days with co amoxiclav 625 mg three times daily or clindamycin 300 to 450 mg four times daily.
• Cover Fusobacterium adequately in adolescents and young adults, since Lemierre syndrome arises from inadequately treated peritonsillar infection.
• Do not use amoxicillin alone where infectious mononucleosis has not been excluded.

Corticosteroid

A single dose of dexamethasone 10 mg intravenously in adults, or 0.6 mg/kg to a maximum of 10 mg in children, reduces pain, trismus and fever and shortens the time to symptom resolution. It is a reasonable adjunct in most cases.

Supportive care

• Intravenous fluids with 0.9 percent sodium chloride, correcting the deficit, since these patients are usually significantly dehydrated.
• Regular intravenous paracetamol 1 g every 6 hours plus a nonsteroidal anti inflammatory drug where tolerated, with opioid titration for severe pain.
• Topical benzydamine.
• Airway observation. Involve anaesthetics early where there is any airway concern.

Tonsillectomy

• Interval tonsillectomy, performed 6 weeks or more after resolution, is indicated for a second episode of peritonsillar abscess, for a first episode in a patient with a significant history of recurrent tonsillitis, and for patients with airway obstruction from tonsillar hypertrophy.
• After a single episode in a patient with no history of tonsillitis, the recurrence rate is only around 10 to 15 percent, and routine tonsillectomy is not justified.
• Quinsy tonsillectomy, that is tonsillectomy during the acute episode, achieves drainage and definitive treatment in one procedure and avoids a second admission. It carries higher intraoperative bleeding and is more technically demanding but does not carry a materially higher complication rate in experienced hands. It is indicated where drainage cannot be achieved under local anaesthesia, where there is airway compromise, in children requiring general anaesthesia anyway, and where recurrent tonsillitis already justifies tonsillectomy.

Complications

• Airway obstruction.
• Aspiration of pus, particularly if drainage is performed with the patient supine.
• Extension to the parapharyngeal, retropharyngeal and prevertebral spaces, and descending mediastinitis, which carries high mortality and which requires urgent contrast imaging of the neck and chest with surgical drainage.
• Lemierre syndrome with internal jugular thrombophlebitis and septic pulmonary emboli, treated with prolonged intravenous antibiotics with anaerobic cover for 4 to 6 weeks, drainage of metastatic collections, and a case by case decision on anticoagulation.
• Necrotising fasciitis of the neck, particularly in diabetic and immunocompromised patients, requiring urgent radical debridement.
• Carotid artery erosion and pseudoaneurysm, presenting with sentinel bleeding, which requires immediate angiography.
• Sepsis and streptococcal toxic shock syndrome.

Follow up

Review at 4 to 6 weeks to confirm resolution and to reassess tonsillar symmetry. Persistent unilateral tonsillar enlargement after an abscess has settled requires tonsillectomy with histology, since lymphoma and carcinoma present in this way and are sometimes discovered only after an apparent abscess fails to resolve completely.