Retropharyngeal Abscess

A collection of pus in the retropharyngeal space, between the buccopharyngeal fascia covering the constrictor muscles anteriorly and the alar layer of the deep cervical fascia posteriorly. It is predominantly a disease of children under 6 years, and it is an airway emergency.

Anatomy that determines behaviour and danger

• The retropharyngeal space extends from the skull base to the tracheal bifurcation at approximately the level of T1 to T2, where the alar and visceral fascia fuse. Infection here can descend directly into the superior mediastinum.
• Posterior to the alar fascia lies the danger space, or space 4, which extends uninterrupted from the skull base to the diaphragm. Infection breaching the alar fascia into this space spreads to the posterior mediastinum with minimal resistance, and this is the anatomical basis of descending necrotising mediastinitis.
• Retropharyngeal lymph nodes, that is the nodes of Rouvière, drain the nasopharynx, adenoids, posterior paranasal sinuses, middle ear and Eustachian tube. These nodes are prominent in young children and atrophy by around 5 years. Suppurative adenitis of these nodes is the mechanism of retropharyngeal abscess in children, which is why the condition is a paediatric disease and why it declines sharply after the age of 6.
• In adults, retropharyngeal abscess arises from penetrating trauma including foreign bodies such as fish bones, from instrumentation, from vertebral osteomyelitis, from tuberculosis of the cervical spine producing a cold abscess, and from extension of other deep neck infections. An adult with a retropharyngeal abscess and no obvious source requires investigation for tuberculosis, malignancy, immunodeficiency and an occult foreign body.

Microbiology

Polymicrobial. Streptococcus pyogenes, Staphylococcus aureus including methicillin resistant strains, Streptococcus milleri group, Haemophilus influenzae, and anaerobes including Fusobacterium, Prevotella, Peptostreptococcus and Bacteroides.

In children

• Preceding upper respiratory infection, pharyngitis or otitis media, typically several days earlier.
• Fever, irritability and malaise.
• Neck pain and refusal to move the neck, with neck stiffness that may be mistaken for meningitis.
• Torticollis, with the head held tilted and rotated, which is a characteristic and readily overlooked sign.
• Refusal to feed, drooling and dysphagia.
• Muffled voice or a cri du canard, that is a duck like cry.
• Neck swelling and cervical lymphadenopathy.
• Stridor, respiratory distress and preference for lying supine with the neck extended, which is the opposite of epiglottitis where the child sits forward. A child who insists on lying flat with the neck extended and who resists sitting up has a retropharyngeal collection until proven otherwise.

In adults

• Severe odynophagia and dysphagia.
• Neck pain and stiffness.
• Fever and systemic upset.
• Dyspnoea and a sensation of throat obstruction.
• A history of foreign body ingestion, instrumentation or recent dental or pharyngeal procedure.

Examination

• Bulging of the posterior pharyngeal wall, which may be unilateral since the space is divided by a midline raphe. This may be subtle and is easily missed, particularly in a distressed child.
• Restricted and painful neck movement, particularly extension.
• Cervical lymphadenopathy.
• Trismus, which is less prominent than in peritonsillar and parapharyngeal abscess.
• Assess the airway carefully but do not provoke a distressed child.

Critical caution: do not perform vigorous oropharyngeal examination or attempt instrumentation in a child with suspected retropharyngeal abscess and airway compromise, since abscess rupture causes aspiration of pus, and distress can precipitate complete obstruction. Examine the airway in a controlled environment with anaesthetic support available.

Red flags

• Stridor, respiratory distress, cyanosis and exhaustion.
• Inability to lie flat, or conversely refusal to sit up.
• Chest pain, dyspnoea and widening of the mediastinum, indicating mediastinal extension.
• Crepitus in the neck, indicating gas forming organisms or oesophageal perforation.
• Rapid progression, hypotension and sepsis.
• Neurological signs, indicating intracranial extension or vertebral involvement.

• Lateral soft tissue neck radiograph taken in true lateral position with the neck extended during inspiration, which is a rapid screening study. Prevertebral soft tissue thickening is abnormal when it exceeds 7 mm at C2 in all ages, or 14 mm at C6 in children and 22 mm at C6 in adults. Air or an air fluid level in the prevertebral space is diagnostic. Films taken in flexion or expiration produce false positive thickening, which is a common source of error.
• Contrast enhanced computed tomography of the neck and chest, which is the definitive investigation. It distinguishes cellulitis and phlegmon from a drainable abscess, defines the extent and the spaces involved, identifies mediastinal extension, and shows vascular complications. A rim enhancing hypodense collection with surrounding fat stranding indicates abscess; homogeneous enhancement without a defined collection indicates cellulitis.
• Include the chest in the imaging whenever mediastinal extension is possible, which is whenever the collection extends below the level of the hyoid.
• Magnetic resonance imaging where vertebral osteomyelitis, discitis or spinal epidural abscess is suspected, which is superior for these.
• Full blood count, C reactive protein, blood cultures, glucose.
• Pus culture at drainage for aerobic, anaerobic, mycobacterial and fungal organisms.
• Tuberculosis testing with an interferon gamma release assay and mycobacterial culture in adults, in the immunocompromised, in those from high prevalence areas, and where the presentation is subacute with a cold abscess and vertebral changes.
• HIV testing.

Differential diagnosis

• Epiglottitis, in which the child sits forward, drools and has a normal neck, and where the airway obstruction is supraglottic.
• Croup, with a barking cough and inspiratory stridor with a normal pharynx.
• Meningitis, which shares neck stiffness but not the pharyngeal findings.
• Cervical adenitis without abscess.
• Parapharyngeal abscess, which produces lateral rather than posterior pharyngeal wall bulging and more marked trismus.
• Cervical spine osteomyelitis and Pott disease, with vertebral destruction on imaging.
• Foreign body with perforation.
• Retropharyngeal haematoma after trauma or in an anticoagulated patient, which can also obstruct the airway.
• Neoplasm, including lymphoma and metastatic disease.

Airway first, then imaging, then antibiotics and drainage.

Airway management

• Assess airway urgency immediately. Involve senior anaesthetic and, in children, paediatric intensive care support at the point of suspicion, not after imaging.
• Keep the child calm and with a parent. Do not distress them with repeated examination, cannulation or lying them flat against their will.
• Give humidified oxygen.
• Where intubation is required, it should be performed by the most experienced anaesthetist available in theatre with surgical airway equipment and an otolaryngologist present, using an inhalational induction with maintained spontaneous ventilation. Abscess rupture during intubation with aspiration of pus is the specific hazard.
• Nebulised adrenaline 1 mg/kg of 1 in 1000 to a maximum of 5 mL, and intravenous dexamethasone 0.6 mg/kg, may be used as temporising measures for airway oedema, though they do not treat the collection.

Antibiotics

• Intravenous therapy from the outset, with broad spectrum cover including anaerobes and staphylococci.
• Co amoxiclav 30 mg/kg every 8 hours in children, or 1.2 g every 8 hours in adults.
• Alternatively ceftriaxone 50 mg/kg every 12 hours in children, or 2 g every 12 hours in adults, plus metronidazole 7.5 mg/kg every 8 hours in children or 500 mg every 8 hours in adults.
• Add clindamycin 10 mg/kg every 6 to 8 hours in children, or 600 mg every 6 hours in adults, or vancomycin with a target trough of 15 to 20 mg/L, where methicillin resistant Staphylococcus aureus is prevalent. Clindamycin also suppresses toxin production in streptococcal disease.
• Piperacillin with tazobactam 4.5 g every 6 to 8 hours, or a carbapenem, for severe disease, mediastinal extension and immunocompromise.
• Narrow to culture as available. Continue intravenously until afebrile and improving, then complete a total of 2 to 3 weeks, and 4 to 6 weeks for osteomyelitis or mediastinitis.

Conservative management

A trial of intravenous antibiotics without drainage is reasonable in a child with a small collection, generally under 2 to 2.5 cm in maximum diameter, without airway compromise, without sepsis, and with the capacity for close monitoring. Around half of such children resolve without surgery. Reassess clinically at 24 and 48 hours, and repeat imaging if there is no improvement. Any deterioration, airway concern or failure to improve within 24 to 48 hours mandates drainage.

Surgical drainage

Indications:

• Airway compromise.
• Abscess larger than 2 to 2.5 cm.
• Failure to improve within 24 to 48 hours of intravenous antibiotics.
• Sepsis or systemic deterioration.
• Mediastinal extension.
• Immunocompromised patient.
• Diagnostic uncertainty requiring tissue.

Technique:

• Transoral drainage for midline and paramedian collections confined to the retropharyngeal space above the level of the hyoid. Performed under general anaesthesia with a secured airway, using a Boyle Davis gag, with the patient in Trendelenburg position and with suction immediately available so that pus is not aspirated. Make a vertical incision in the posterior pharyngeal wall over the point of maximal bulge, aspirate first with a needle to confirm and to reduce the risk of a sudden gush, then incise and break loculations with forceps. Avoid lateral dissection, since the carotid sheath lies laterally.
• External transcervical drainage through an incision along the anterior border of sternocleidomastoid for collections extending laterally into the parapharyngeal space, extending below the hyoid, or descending toward the mediastinum. This approach permits complete drainage and placement of a drain.
• Mediastinal extension requires thoracic surgical involvement with thoracotomy or video assisted thoracoscopic drainage, since descending necrotising mediastinitis has a mortality of 20 to 40 percent and cannot be adequately drained from the neck alone.
• Repeat imaging and re drainage where the patient fails to improve.

Complications

• Airway obstruction and asphyxia.
• Abscess rupture with aspiration pneumonia and lung abscess.
• Descending necrotising mediastinitis, pericarditis and empyema.
• Extension to the parapharyngeal space with carotid sheath involvement, internal jugular vein thrombosis and carotid artery erosion.
• Sepsis and multi organ failure.
• Cervical vertebral osteomyelitis and spinal epidural abscess with cord compression.
• Atlantoaxial subluxation, that is Grisel syndrome, presenting with persistent torticollis after resolution and requiring imaging and orthopaedic or neurosurgical involvement.

Follow up

Repeat imaging where recovery is slow. Investigate adults for an underlying cause including foreign body, tuberculosis, malignancy, diabetes and immunodeficiency. Persistent torticollis after resolution requires cervical spine imaging.