Submasseteric Space Infection

Submasseteric space infection is a collection of pus between the masseter muscle and the lateral surface of the mandibular ramus. It is a deep space infection with dramatic trismus and little visible swelling.

The lower third molar is the source in most cases, usually from pericoronitis or caries, and the second molar, a failed extraction or osteomyelitis of the ramus can also be the cause. It is commonly misdiagnosed as a temporomandibular joint disorder.

Pathophysiology. Infection from the third molar region perforates the lateral cortex of the ramus or spreads along the buccal fascia into the space bounded by the masseter laterally, the ramus medially, the zygomatic arch superiorly and the parotid fascia behind.

Pus is confined by the strong masseteric fascia, so swelling stays small while pain and muscle spasm are severe. Chronic infection can cause osteomyelitis of the ramus or spread into the masticator and parotid spaces.

Severe trismus with interincisal opening often under 20 mm, pain at the angle of the mandible on opening and chewing, tenderness over the masseter, fever, malaise and sometimes a brawny swelling over the ramus.

Intraoral findings are subtle: a pericoronal flap over an impacted third molar with pus, limited swelling in the buccal sulcus, and an erythematous retromolar area.

Swelling reaching the orbit, pterygoid region or neck, trismus under 10 mm with dysphagia, drooling or stridor, and sepsis features need immediate admission and airway assessment.

• Clinical diagnosis from trismus, masseter tenderness and the source tooth.
• Panoramic radiograph for the third molar and for osteomyelitis of the ramus.
• Contrast CT of the face when trismus precludes examination, the diagnosis is unclear or spread is suspected. It shows a rim enhancing collection between masseter and ramus.
• Bloods: full blood count, C-reactive protein, glucose, and blood cultures if febrile.
• Culture of pus at drainage.

Differential diagnosis.

• Temporomandibular joint disorder or septic arthritis
• Pterygomandibular space infection
• Masseteric hypertrophy and myofascial pain
• Parotitis or parotid abscess
• Pericoronitis without deep spread
• Osteomyelitis of the ramus
• Tetanus
• Mandibular fracture

• 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 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 5 to 7 days from drainage.
• Surgical drainage with removal or treatment of the source tooth:
  • Intraoral drainage through an incision along the external oblique ridge or anterior border of the ramus, with blunt dissection between the masseter and the bone, for early or small collections.
  • Extraoral drainage through an incision 2 cm below and behind the angle of the mandible, taking care of the marginal mandibular branch of the facial nerve, with blunt dissection to the ramus and a drain left for 24 to 72 hours.
• Early jaw opening exercises after drainage, with a wooden spatula stack or a jaw exerciser, started when pain allows, to prevent fibrosis. Trismus can persist for weeks.
• Analgesia: paracetamol 1 g every 6 hours (maximum 4 g daily) with ibuprofen 400 mg every 8 hours with food, avoided in renal impairment.
• Chronic or recurrent disease needs bone debridement, sequestrectomy and a longer antibiotic course for osteomyelitis.

Special groups. Diabetes and immunosuppression need glucose control and a lower threshold for admission, imaging and surgery.

Monitoring. Review every 12 to 24 hours in hospital for temperature, opening in millimetres, drain output and C-reactive protein. Review at 1 and 4 weeks for trismus and for a residual sinus.

Referral and escalation. Refer urgently to oral and maxillofacial surgery for drainage. Emergency escalation for airway symptoms, orbital or neck extension, or sepsis.