Parapharyngeal Abscess

A parapharyngeal abscess (Latin: abscessus parapharyngealis) is a localized collection of pus within the parapharyngeal region of the neck. It is a type of deep neck infection and can be life-threatening because it may spread rapidly and cause severe complications.

This risk is largely explained by anatomy. The parapharyngeal region contains vital structures, including the carotid artery, the internal jugular vein, and cranial nerves IX, X, XI, and XII. If the infection extends, these structures can be affected, and sepsis may develop quickly.

Aetiology and Pathophysiology

The parapharyngeal region lies lateral to the pharynx. It extends from the skull base to the level of the hyoid bone and contains loose connective and adipose tissue. In most cases, infection reaches this space by contiguous spread from nearby inflammatory foci.

Main routes of infection:

• Tonsillar source: This is the most common route. Infection spreads from the palatine tonsil, most often as a complication of acute tonsillitis or a peritonsillar abscess.
• Odontogenic spread: Infection arises from the lower molars, particularly the third molar (wisdom tooth).
• Otogenic source: Infection spreads from ear disease such as otitis media or mastoiditis.
• Salivary gland source: Infection is associated with salivary gland inflammation (sialadenitis).
• Trauma: Infection follows penetrating neck injury or trauma to the pharyngeal mucosa.

These infections are typically polymicrobial. They often involve both aerobic bacteria (e.g., streptococci and staphylococci) and anaerobes.

Clinical significance

Symptoms usually progress rapidly, and patients often appear systemically ill. Diagnosis is based on the characteristic clinical findings. The imaging “gold standard” is contrast-enhanced CT of the neck.

Key features:

• Systemic signs: high fever (39–40°C), chills, and pronounced systemic symptoms.
• Sore throat: usually unilateral, severe, and worse with swallowing.
• Trismus: painful limitation of mouth opening due to spasm of the masticatory muscles. This is one of the key findings.
• Swelling: prominent swelling on the lateral neck beneath the angle of the mandible. On pharyngoscopy, the lateral pharyngeal wall bulges and the tonsil is displaced medially.
• Head posture: the head is often held tilted toward the affected side.

Treatment should be started without delay. It usually involves incision and drainage, most often via a transcervical (external neck) approach, together with high-dose intravenous antibiotics. Importantly, the airway should be assessed and secured as the first priority.

Differential Diagnosis

The main differential diagnosis is a peritonsillar abscess. In peritonsillar abscess, swelling is typically more localized and is most prominent near the upper pole of the tonsil. By contrast, a parapharyngeal abscess more often produces diffuse bulging of the entire lateral pharyngeal wall. Trismus and external neck swelling are also usually more pronounced. Contrast-enhanced CT helps define the location and extent of the collection. It also helps distinguish parapharyngeal abscess from other deep neck infections, such as retropharyngeal abscess and infection of the floor of the mouth, including Ludwig’s angina.