Retropharyngeal abscesses are deep neck space infections that can pose an immediate life-threatening emergency, with potential for airway compromise and other catastrophic complications.
For an optimal understanding of deep space infections, knowledge of the anatomy of the fascial planes of the neck is necessary. Superficial and deep fascia layers are found in the neck. Although fascia is typically adherent to adjacent structures, potential spaces can be created when an infection intercalates between the fascial layers and creates a real space, with rapid spread of inflammation and pus in the space between the fascial planes.
The retropharyngeal space is located immediately posterior to the pharynx (nasopharynx, oropharynx, and hypopharynx), larynx, and trachea. The visceral (buccopharyngeal) fascia, which surrounds the pharynx, trachea, esophagus, and thyroid, forms the anterior border of this space. Bounded posteriorly by the alar fascia, the retropharyngeal space is bounded laterally by the carotid sheaths and parapharyngeal spaces. It extends superiorly to the base of the skull and inferiorly to the mediastinum at the level of the tracheal bifurcation (see the image below).
Two other potential spaces (the danger space and prevertebral space) are in close proximity to the retropharyngeal space. The danger space is formed anteriorly by the alar fascia and posteriorly by the prevertebral fascia. The prevertebral space is bounded anteriorly by the prevertebral fascia and posteriorly by the longus colli muscles of the spine.
The danger space extends down the mediastinum to the level of the diaphragm, whereas the prevertebral space continues to the insertion of the psoas muscles. These anatomic relations can allow an infection of the retropharyngeal space to spread to the mediastinum, leading to potentially fatal mediastinitis.
The retropharyngeal space can become infected in either of the following two ways:
Infection can spread from a contiguous area
The space can be directly inoculated from penetrating trauma
The "classic" retropharyngeal abscess observed in pediatric patients occurs when an upper respiratory infection (URI) spreads to retropharyngeal lymph nodes, forming chains in the retropharyngeal space on either side of the superior constrictor muscle.
Sources of infection can include pharyngitis, tonsillitis, adenoiditis, adenitis, otitis, sinusitis, and other infections (ie, nasal, salivary, dental). Degeneration or suppuration of these nodes leads to abscess formation. Infectious sources (eg, osteomyelitis of the spine) also can spread directly anteriorly from the prevertebral space.
Of specific interest is the group of lateral retropharyngeal nodes at the base of the skull that bear the name of French anatomist Henri Rouviere. These Rouviere nodes are typically not of great clinical interest, but as the primary lymphatic drainage of the nasopharynx, they can become significant in cases of nasopharyngeal cancer. They are also pertinent to the discussion of retropharyngeal abscess, in that they can suppurate and lead to a retropharyngeal abscess.
Penetrating trauma can also be involved in retropharyngeal space infection. Accidental lacerations are not uncommon in children who run and fall down after they have placed a sharp object in their mouths. Foreign bodies (for example, fishbones) have been implicated in penetrating trauma to the retropharyngeal space. Iatrogenic causes of inoculation to this space include instrumentation with laryngoscopy, endotracheal intubation, surgery, endoscopy, feeding tube placement, and dental injections and procedures.
Complications of retropharyngeal abscess arise from mass effect, rupture of the abscess, or spread of infection. The most urgent complication is expansion of the abscess against the pharynx or trachea, causing airway compression. Rupture of the abscess can cause aspiration of pus, leading to asphyxiation or pneumonia. Spread of infection can lead to inflammation and destruction of adjacent tissues.
Spread of infection to the mediastinum can result in mediastinitis, purulent pericarditis and tamponade, pyopneumothorax, pleuritis, empyema, or bronchial erosion. Lateral spread of infection can involve the carotid sheath and cause jugular vein thrombosis or carotid artery rupture. Posterior spread of infection can result in osteomyelitis and erosion of the spinal column, causing vertebral subluxation and spinal cord injury. The infection itself can evolve into necrotizing fasciitis, sepsis, and death.
Hence, accurate and prompt treatment and intervention for presumed retropharyngeal abscess is crucial to prevent significant untoward sequelae.
Most retropharyngeal space infections arise from drainage to the retropharyngeal nodes from nasopharyngeal infections. The resulting lymphadenitis can lead to a cellulitis, which can then suppurate and become an abscess. Possible predisposing infections can include pharyngitis, tonsillitis, otitis, adenitis, adenoiditis, sinusitis, and nasal, salivary, and dental infections. Retropharyngeal infections are also spread from contiguous spaces, such as the parapharyngeal space (eg, abscesses), submandibular space, or prevertebral space (eg, osteomyelitis).
The retropharyngeal space can also be directly inoculated secondary to penetrating trauma. Running and falling down with a sharp object in the mouth is not unusual in children. Because parents may be unaware of these predisposing events, diagnosis is even more elusive. Foreign bodies (for example, fishbones) can become lodged in the posterior pharynx. Although this can happen in the pediatric age group, a foreign body lodged in the posterior pharynx is also a cause of abscess formation in adults.
Deep-space infections can be iatrogenic secondary to instrumentation of the upper respiratory tract. All of the following can predispose to abscess formation:
Feeding tube insertion
Head and neck surgery
Risk factors may include low socioeconomic status, poor oral hygiene, and immune dysfunction (eg, from HIV, diabetes, or immunosuppression).
Bacteria are often polymicrobial, with gram-positive organisms and anaerobes predominating, but gram-negative bacteria have also been isolated. The source is usually oropharyngeal flora. The most common cause is group A beta-hemolytic streptococci. Other nonhemolytic streptococci can be present. Staphylococcus aureus is also fairly common. Abdel-Haq et al noted an increasing incidence of methicillin resistance in Staphylococcus isolates (24% of all cultures, 64% of Staphylococcus- positive cultures). 
The most common anaerobes are Bacteroides species. Other causative agents include Haemophilus parainfluenzae and Veillonella, Peptostreptococcus, Fusobacterium, and Eikenella species. The incidence of beta-lactamase production is high. One study noted 22% beta-lactam resistance.
Mycobacterium tuberculosis, Bartonella henselae, and coccidiosis should be suspected in patients who may be predisposed (eg, immunosuppressed individuals or recent immigrants), especially if they are not responding to more conventional therapy.
Another consideration in the evaluation of these patients is the possibility of Lemierre syndrome (septic thrombophlebitis of the internal jugular vein from a head and neck infection, such as a retropharyngeal abscess). This infection is classically associated with Fusobacterium necrophorum, an anaerobic gram-negative rod. 
United States statistics
In an analysis of a large national database of pediatric admissions in the United States,  Lander et al found 1321 cases of retropharyngeal abscess in 2003. A large retrospective review of pediatric head and neck infections at the University of Mississippi Medical Center, published in 2006,  found that of the 1010 documented pediatric head and neck infections, 26 were retropharyngeal abscesses.
In a 2014 study, Novis et al used the Kids' Inpatient Database (KID) to evaluate the incidence, demographics, and outcomes of deep neck space infections in US children between 2000 and 2009.  The incidence of pediatric retropharyngeal abscess increased significantly, but there were no concurrent increases in combined deep neck space infections, peritonsillar abscesses, or parapharyngeal abscesses. Management of retropharyngeal abscesses changed over this period (decreased operative intervention and shorter average hospital stay).
With less access to health care and less availability of antibiotics, deep neck space infection is a more common complication of URI in developing nations. Pathogens not typically seen in the United States are also seen in this population (including tuberculosis) and should be considered.
A tertiary hospital in Freiburg, Germany studied deep neck infections occurring over 8 years.  Of the 234 documented infections, 15 (6.4%) were retropharyngeal abscesses. Although no subgroup analysis was specifically performed for retropharyngeal abscesses, one interesting finding was a higher than expected rate of B henselae infection (catscratch disease) and cervical tuberculosis. The treating physician should thus consider all infectious etiologies when treating and evaluating patients with a suspected infection.
A study from India also described a socioeconomic correlation with deep neck abscesses.  Most patients with retropharyngeal abscesses were of low socioeconomic status, which was theorized to contribute to the incidence of abscesses through poor orodental hygiene and a lack of access to health care.
Age-, sex-, and race-related demographics
Retropharyngeal abscess is almost exclusively a pediatric diagnosis. Most incidents occur in children aged 6 months to 6 years (mean age, 3-5 years). [3, 4, 8, 8] Other deep neck abscesses (eg, parapharyngeal and peritonsillar) are observed more frequently in adults and older children.
In children, a retropharyngeal abscess is usually caused by an infection that spreads to the retropharyngeal lymph nodes, with subsequent cellulitis and abscess formation. Fibrosis and atrophy start in these nodes at age 4 years, and by age 6 years, the retropharyngeal nodes have typically regressed. In older patients, infection of the retropharyngeal space usually occurs from penetrating trauma or direct spread from an adjacent space.
Although no sex predilection has been described in the literature, several studies have noted a higher incidence of deep neck infections in boys. In a large national database, 63% of patients were male. 
No racial predilection has been described in the literature.
In uncomplicated cases of retropharyngeal abscess in a relatively healthy patient, the prognosis for complete recovery without sequelae is excellent. Complicated cases may be associated with significant mortality and morbidity.
In the assessment of a patient with a potential deep neck space infection, airway compromise should immediately be identified and addressed. Evaluation by an otolaryngologist, if possible, should be obtained. Large abscesses can compress the pharynx or trachea, causing suffocation. The abscess also can rupture, causing asphyxiation or aspiration and pneumonia.
Proper positioning and avoidance of unnecessary manipulation are essential. Closely monitor patients with airway compromise, and do not allow these patients to leave the acute care area until deemed sufficiently stable.
Sedation and paralytics should be avoided until an airway assessment is performed because they can relax airway muscles, leading to complete obstruction. Endotracheal intubation is dangerous unless performed under direct visualization. If direct visualization is not possible secondary to trismus or anatomic distortion, consider fiberoptic intubation or a surgical airway (eg, cricothyroidotomy or tracheotomy).
Spread of infection to adjacent structures in the neck can occur in rare cases and can sometime lead to lethal outcomes. If the carotid artery is infected, it can rupture, a complication associated with a 20-40% mortality. Involvement of the jugular vein can result in thrombosis of the jugular vein, which has an associated mortality of 60%; identifying this complication is essential.
Spread of infection to the spine can lead to osteomyelitis and vertebral erosion, which in turn result in subluxation and subsequent spinal cord injury. Atlanto-occipital separation secondary to erosion of the transverse ligament of the atlas has also been reported. Retropharyngeal infections can also spread into the chest, leading to mediastinitis, which has a mortality of 40-50%.
Advise a follow-up appointment for parents or caregivers of children diagnosed with URIs that do not follow an appropriate course of resolution.
Advise parents or caregivers to return immediately if the patient develops clinical manifestations of deep neck space infection, such as difficulty swallowing, swelling in the back of throat or neck, muffled voice, jaw or neck stiffness, or worsening of symptoms (or if symptoms do not resolve after a reasonable period).
Advise parents to remain especially alert for signs of airway compromise, such as shortness of breath, drooling, or noisy breathing.
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