Pterygomandibular Space Infection

Pterygomandibular space infection is infection in the space between the medial surface of the mandibular ramus and the medial pterygoid muscle. It causes trismus and pain on swallowing with little external swelling.

Impacted or infected lower third molars are the usual source, and the second molar, a contaminated inferior alveolar nerve block, tonsillitis and parotid disease are less common causes. Spread to the parapharyngeal and masticator spaces is the main risk.

Pathophysiology. The space contains the inferior alveolar nerve and vessels, the lingual nerve and the sphenomandibular ligament. It is bounded by the ramus laterally, the medial pterygoid medially, the lateral pterygoid superiorly and the parotid behind, and it communicates with the parapharyngeal space.

Infection from a third molar spreads along the lingual cortex or from the pericoronal tissue. The medial pterygoid goes into spasm, causing trismus and swallowing pain.

Progressive trismus, severe pain on swallowing, deviation of the jaw, fever, malaise and ear or throat pain. External swelling is minimal, but the soft palate, anterior tonsillar pillar and uvula are swollen and displaced towards the midline.

The patient may have a muffled voice and difficulty opening the mouth for examination, so the pharynx is often not visible.

Uvula deviation, medial displacement of the tonsil, neck swelling, voice change, drooling, stridor, orbital signs, and sepsis features suggest spread to the parapharyngeal or masticator space and need emergency assessment.

• Airway assessment, interincisal distance in millimetres and examination of the pharynx where possible.
• Contrast CT of the face and neck shows a collection medial to the ramus with displacement of the medial pterygoid, and detects lateral pharyngeal, retropharyngeal and carotid sheath spread.
• Panoramic radiograph for the third molar and bone changes.
• Bloods: full blood count, C-reactive protein, glucose, blood cultures when febrile.
• Culture of pus at surgery.

Differential diagnosis.

• Peritonsillar abscess
• Submasseteric and masticator space infection
• Lateral pharyngeal space infection of other origin
• Temporomandibular joint disorder
• Tetanus
• Pericoronitis without deep spread
• Parotid abscess
• Tumour of the oropharynx or infratemporal fossa

• Antibiotics: benzylpenicillin 1.2 g intravenously every 6 hours (or amoxicillin 1 g every 8 hours) with metronidazole 500 mg intravenously every 8 hours. Penicillin allergy: clindamycin 600 mg intravenously every 6 to 8 hours. Convert to oral amoxicillin 500 mg to 1 g three times daily with metronidazole 400 mg three times daily after improvement to complete 7 to 10 days from drainage.
• Surgical drainage and removal of the source tooth:
  • Intraoral approach: vertical incision along the anterior border of the ramus (medial to the external oblique ridge), blunt dissection medially to the pterygomandibular raphe, and a small drain. Take care of the lingual and inferior alveolar nerves.
  • Extraoral approach through a submandibular incision when the infection extends into the neck or the intraoral route is inadequate.
• Early jaw exercises after drainage to restore opening. Trismus can persist for weeks.
• Airway protection with senior anaesthetic input when trismus and pharyngeal swelling reduce access, with awake fibreoptic intubation when needed.
• Analgesia: paracetamol 1 g every 6 hours (maximum 4 g daily) and ibuprofen 400 mg every 8 hours with food, avoided in renal impairment. Hydration and glucose control.

Special groups. Children need weight based dosing and paediatric anaesthetic expertise. Immunosuppressed patients are at higher risk of spread and need early imaging and surgery.

Monitoring. Daily temperature, interincisal opening, swallowing, drain output and C-reactive protein, and repeat imaging if there is no improvement in 48 to 72 hours. Review at 1 and 4 weeks for trismus.

Referral and escalation. Refer urgently to oral and maxillofacial surgery. Emergency escalation for airway threat, lateral pharyngeal or retropharyngeal spread, internal jugular vein thrombosis or sepsis.