Parapharyngeal Abscess

A collection of pus in the parapharyngeal space, an inverted cone extending from the skull base at the sphenoid to the greater cornu of the hyoid, which contains critical neurovascular structures and communicates freely with every other deep neck space.

Anatomical compartments, which determine both presentation and hazard

The styloid process and the fascia running from it, that is the aponeurosis of Zuckerkandl and Testut, divide the space into two compartments.

• Prestyloid, or muscular, compartment: contains fat, the internal maxillary artery, the inferior alveolar, lingual and auriculotemporal nerves, and the deep lobe of the parotid. Infection here produces trismus from medial pterygoid irritation, medial displacement of the tonsil and lateral pharyngeal wall, and prominent external neck swelling at the angle of the mandible.
• Poststyloid, or neurovascular, compartment: contains the carotid sheath with the internal carotid artery, internal jugular vein and vagus nerve, plus cranial nerves IX, XI and XII, and the cervical sympathetic chain. Infection here produces cranial neuropathies, Horner syndrome, internal jugular vein thrombosis and carotid complications, with little or no trismus and less obvious pharyngeal bulging. Poststyloid infection is therefore more dangerous and less clinically obvious.

Communications

The parapharyngeal space communicates with the retropharyngeal, submandibular, masticator, parotid, peritonsillar and carotid spaces, and inferiorly with the mediastinum through the carotid sheath. It is the central crossroads of the deep neck, which is why infection here spreads in every direction.

Sources

• Tonsillar and peritonsillar infection, which is the commonest.
• Odontogenic infection, particularly of the lower third molars, spreading through the masticator space.
• Pharyngeal infection.
• Salivary gland infection, particularly parotid and submandibular.
• Foreign body and penetrating trauma.
• Extension from other neck spaces.
• Intravenous drug use with neck injection, which produces carotid space infection directly.
• Branchial cleft anomaly infection.
• Petrous apicitis and mastoiditis, tracking inferiorly.

Microbiology

Polymicrobial with a predominance of anaerobes: Prevotella, Porphyromonas, Fusobacterium, Peptostreptococcus and Bacteroides, together with Streptococcus pyogenes, the Streptococcus milleri group, Staphylococcus aureus, Klebsiella pneumoniae particularly in diabetics, and Eikenella corrodens in odontogenic infection.

• Fever, rigors and systemic upset, frequently with sepsis.
• Severe odynophagia and dysphagia.
• Trismus, which is often marked in prestyloid infection and which limits examination.
• Neck swelling and induration at the angle of the mandible and along the anterior border of sternocleidomastoid, which is the characteristic external finding and which distinguishes this from peritonsillar abscess.
• Torticollis with the head tilted toward the affected side.
• Medial displacement of the lateral pharyngeal wall and the tonsil, without the uvular deviation and supratonsillar bulge of peritonsillar abscess.
• Muffled voice.
• Referred otalgia.
• Dyspnoea and stridor where the airway is compromised.

Signs of poststyloid involvement, which change urgency entirely

• Horner syndrome with ptosis, miosis and anhidrosis, from sympathetic chain involvement.
• Hoarseness and aspiration from vagal involvement.
• Dysphagia and loss of the gag reflex from glossopharyngeal involvement.
• Tongue deviation from hypoglossal involvement.
• Shoulder weakness from accessory nerve involvement.
• Swelling and tenderness along the internal jugular vein, indicating thrombophlebitis.
• Any of these findings mandates urgent contrast imaging with vascular assessment.

Red flags

• Airway compromise.
• Sepsis and haemodynamic instability.
• Crepitus in the neck or skin discolouration, indicating necrotising infection.
• Chest pain and dyspnoea, indicating mediastinal extension.
• Sentinel haemorrhage from the mouth, nose or ear, which precedes carotid rupture and which requires immediate angiography.
• Rigors with pulmonary symptoms in a young patient, indicating Lemierre syndrome.
• Diabetes, immunocompromise and intravenous drug use, all of which predict rapid deterioration and unusual organisms.

• Contrast enhanced computed tomography of the neck and chest, which is the essential investigation. It defines the space involved, distinguishes cellulitis from a drainable collection, identifies the prestyloid or poststyloid location, demonstrates extension to other spaces and to the mediastinum, and shows internal jugular thrombosis, carotid narrowing and pseudoaneurysm. Include the chest whenever the collection extends inferiorly.
• Computed tomography angiography where carotid involvement, pseudoaneurysm or sentinel bleeding is suspected, and magnetic resonance angiography as an alternative.
• Magnetic resonance imaging for skull base involvement and where soft tissue detail is needed.
• Full blood count, C reactive protein, renal function, glucose and HbA1c, coagulation screen, blood cultures, lactate.
• Pus culture at drainage for aerobic, anaerobic, mycobacterial and fungal organisms.
• HIV testing and diabetes screening in all patients.
• Orthopantomogram or dental assessment where an odontogenic source is possible, which it frequently is.
• Echocardiography where endocarditis is a concern, particularly in intravenous drug users.

Differential diagnosis

• Peritonsillar abscess, which produces uvular deviation and supratonsillar swelling without significant external neck swelling.
• Retropharyngeal abscess, with posterior wall bulging and neck extension.
• Submandibular space infection and Ludwig angina, which involves the floor of mouth with tongue elevation.
• Masticator space abscess from a lower molar, with severe trismus and swelling over the ramus.
• Suppurative parotitis and lymphadenitis.
• Infected branchial cleft cyst.
• Neoplasm: parapharyngeal space tumours including pleomorphic adenoma of the deep parotid lobe, paraganglioma and schwannoma, which present as a slowly growing painless mass with medial tonsillar displacement and no infective features. A pulsatile parapharyngeal mass must never be aspirated or incised without imaging, since paraganglioma and carotid aneurysm present this way.
• Tuberculous cold abscess.

Airway, resuscitation, broad spectrum intravenous antibiotics, and drainage. Parapharyngeal abscess should be managed as a surgical emergency in a unit with anaesthetic and critical care support.

Airway management

• Assess and secure the airway before anything else. Trismus, swelling and distortion make these among the most difficult airways in surgical practice.
• Involve the most experienced anaesthetist available. Awake fibreoptic intubation is often the technique of choice, and tracheostomy under local anaesthesia should be planned as a fallback with the surgeon scrubbed and the neck prepared before induction.
• Do not attempt routine laryngoscopy in a patient with significant trismus and swelling.
• Avoid sedation outside a controlled environment.

Resuscitation

• Intravenous access, fluid resuscitation with 0.9 percent sodium chloride, and management of sepsis according to standard sepsis pathways with early antibiotics, cultures, lactate, urine output monitoring and vasopressors where required.
• Optimise glycaemic control with an insulin infusion in diabetics, since hyperglycaemia both drives and results from the infection.
• Correct coagulopathy.

Antibiotics

• Empirical intravenous therapy covering streptococci, staphylococci and anaerobes: co amoxiclav 1.2 g every 8 hours, or ceftriaxone 2 g every 12 hours plus metronidazole 500 mg every 8 hours.
• Piperacillin with tazobactam 4.5 g every 6 to 8 hours, or meropenem 1 g every 8 hours, for severe disease, sepsis, diabetes, immunocompromise or mediastinal extension.
• Add clindamycin 600 mg every 6 hours for streptococcal toxin suppression in severe or necrotising disease, and vancomycin with a target trough of 15 to 20 mg/L where methicillin resistant Staphylococcus aureus is a concern.
• Children: co amoxiclav 30 mg/kg every 8 hours, or ceftriaxone 50 mg/kg every 12 hours plus metronidazole 7.5 mg/kg every 8 hours, with clindamycin 10 mg/kg every 6 to 8 hours added as indicated.
• Narrow to culture. Continue intravenous therapy until afebrile and clinically improved, completing 2 to 3 weeks in total, and 4 to 6 weeks for mediastinitis, osteomyelitis or jugular thrombophlebitis.

Surgical drainage

Indicated for any drainable collection, for failure to improve within 24 to 48 hours of antibiotics, for airway compromise, and for sepsis.

• External transcervical approach, which is the standard for parapharyngeal abscess. A horizontal or oblique incision two fingerbreadths below the mandible along the anterior border of sternocleidomastoid, taking care to preserve the marginal mandibular branch of the facial nerve by keeping the incision low and by identifying and retracting the branch superiorly. Dissect bluntly between the submandibular gland and the sternocleidomastoid, retract the carotid sheath posteriorly, and enter the space with a finger or blunt forceps, breaking loculations. Place a corrugated or suction drain and leave the wound partly open.
• Transoral drainage is appropriate only for a limited prestyloid collection bulging medially, in a patient with no trismus, and where the carotid has been shown on imaging to be well posterior. It provides inadequate drainage for most parapharyngeal collections and risks carotid injury, so it should be used selectively.
• Combined transoral and transcervical drainage for extensive disease.
• Drain all involved spaces, since infection has usually spread beyond the parapharyngeal space by the time it is diagnosed. Failure to drain a contiguous space is the commonest cause of persistent sepsis.
• Extract the causative tooth or drain the source at the same operation.
• Mediastinal extension requires thoracic surgical involvement, since transcervical drainage alone is inadequate for descending necrotising mediastinitis.
• Repeat computed tomography and re exploration where the patient fails to improve within 48 hours.
• Tracheostomy where prolonged airway support is anticipated.

Complications and their management

• Airway obstruction.
• Descending necrotising mediastinitis, with a mortality of 20 to 40 percent, requiring thoracic drainage.
• Internal jugular vein thrombophlebitis, that is Lemierre syndrome, with septic pulmonary emboli. Prolonged intravenous antibiotics with anaerobic cover, drainage of metastatic abscesses, and a case by case decision on anticoagulation with haematology input.
• Carotid artery erosion and pseudoaneurysm, presenting with sentinel bleeding from the mouth, nose or ear, or with an expanding pulsatile mass. Requires immediate computed tomography angiography and endovascular management with covered stent or occlusion, with carotid ligation as a last resort carrying a substantial stroke risk.
• Necrotising fasciitis of the neck, requiring urgent radical debridement, often repeated, with critical care support.
• Cranial neuropathies, which may recover partially.
• Horner syndrome.
• Sepsis, disseminated intravascular coagulation and multi organ failure.
• Empyema, pericarditis and lung abscess.

Follow up

Continue imaging surveillance where there was vascular or mediastinal involvement. Address the underlying source definitively, including dental extraction and interval tonsillectomy where indicated. Screen for diabetes, HIV and immunodeficiency in every adult with a deep neck space infection, since these are common and frequently first identified in this setting.