Etiology

Around 45% of RPAs are the sequelae of an upper respiratory tract infection (e.g., pharyngitis, tonsillitis, sinusitis, dental infections). Most of the time RPAs are polymicrobial irrespective of age of presentation.[9][10] The most common microorganisms implicated are Streptococcus viridans, Staphylococcus aureus, Streptococcus epidermidis, and beta-hemolytic streptococci. Less common causes include Veillonella species, Bacteroides melaninogenicus, Haemophilus parainfluenzae, and Klebsiella pneumoniae. Infections with both methicillin-resistant Staphylococcus aureus and Mycobacterium tuberculosis have also been reported.[11][12] Normal commensals of the upper respiratory tract can become pathologically offending organisms in an RPA.[13][14][15][16] Approximately 27% of RPAs are associated with accidental trauma to the retropharyngeal area from, for example, foreign body ingestion, a child running along with a lollipop in their mouth and falling, or swallowing sharp objects such as chicken bones. The remaining 28% are idiopathic.[13][14][15]

Pathophysiology

The retropharyngeal space is immediately anterior to the prevertebral fascia that continues inferiorly from the skull base for the length of the pharynx. It is in continuity with the parapharyngeal space and the infratemporal fossa. The retro- and parapharyngeal spaces are separated by the alar fascia, which seems to be an ineffectual barrier to the spread of infection. As the retropharyngeal space is in continuity with the superior and posterior mediastinum, it is a potential pathway for spread of infection into the chest.

The retropharyngeal space contains loose areolar tissue and lymphatic chains, the former allowing movement of the pharynx and esophagus on swallowing. The lymph flowing through the space originates from tissues in the nose, paranasal sinuses, eustachian tubes, and adjacent pharyngeal tissues. Pus formation in the retropharyngeal nodes is often well contained, and therefore vertical spread of infection can occur late in the progression of the condition, although this rarely occurs in practice.

Most of the symptoms and signs of RPA relate to the increasing obstruction of the upper aerodigestive tract and irritation of local muscle groups (e.g., sternomastoid and pterygoids).

Classification

Etiologic classification

There is no formal classification of RPAs, but classification can be based on the etiology, which includes:

  • Upper respiratory tract infection

  • Trauma/foreign body ingestion

  • Idiopathic.

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