Odontogenic Infection of the Infratemporal Fossa: A Diagnostic Challenge

The infratemporal fossa (IF) is a wedge-shaped space (Figure 1). It is bounded laterally by the medial surface of the ramus of the mandible, medially by the lateral pterygoid plate, superiorly by the greater wing of the sphenoid on the mesial aspect and temporal fossa on the lateral aspect. Posteriorly, it is bounded by the tympanic plate and styloid process and anteriorly by the posterior surface of maxilla (Figure 2). Its contents include the muscles of mastication, the pterygoid venous plexus and several nerves including mandibular and lingual nerves.

The clinical significance of the IF is that infection can arise or spread into it, and spread from it to the bony barriers present anteriorly, medially and posteriorly within the fossa. It communicates with other deep neck spaces, including the masticator and parapharyngeal spaces.^2,3 Trismus, loss of taste sensation, compression of the mandibular nerve and numbness of the tongue are symptoms that can arise as a result.¹

Case report

A 48-year-old female presented to the emergency department with complaints of a progressively worsening sore throat and jaw stiffness. She gave a 3-day history of sudden onset of pain in the right side of her throat, difficulty in mouth opening and swallowing. The pain was severe, interfered with her sleep and she could only manage fluid intake. She had no underlying medical conditions and had a known allergy to penicillin and codeine.

Examination showed significant trismus, sharp radiating pain on palpation of the right side of her face, and pyrexia. There was no swelling of the floor of the mouth nor any extra-oral swelling. Blood tests showed significantly raised inflammatory markers and an elevated white cell count. She was referred to ENT for suspected quinsy. Initial treatment was empirical with clindamycin, intravenously. Twenty-four hours after commencement of antibiotic therapy, there was no improvement in her symptoms or blood test results, and in addition, she had developed a subtle right temporal swelling. She was subsequently referred to the maxillofacial department to rule out a dental source of infection.

History of toothache in the lower right quadrant was elicited, for which the patient unfortunately could not access dental services at the time because she was unregistered. Further examination by the maxillofacial team revealed tender swelling of the right temporal region and localized right buccal swelling extending to the right submandibular region, as well as persisting trismus. The lower right third molar and second premolar (LR8 and LR5) were grossly carious and tender to percussion. A panoramic radiograph (Figure 3) was taken to check for any other pathology. An urgent head and neck CT scan was conducted, and an abnormality in the right temporal and infratemporal fossa, with inflammation and oedema, was identified (Figure 4).

A diagnosis was made of right infratemporal space abscess from the LR8 spreading into the parapharyngeal space. This necessitated incision and drainage of the right infratemporal space and extractions of the carious LR8, LR5 and retained roots of the UR6 under general anaesthesia. Copious pus was released from the LR8 socket. Gas was also expelled from the infratemporal region. An extra-oral drain was placed in right infratemporal fossa and two intra-oral drains into the right buccal and parapharyngeal spaces. The microbiology result showed mixed respiratory flora and the patient continued to receive intravenous clindamycin.

At 48 hours post-operatively, there was still increasing pain and trismus. A repeat CT identified the presence of a 1 x 2 x 5-cm intramuscular abscess extending from the right mandibular angle up into the right temporal muscle, anterior to the lateral pterygoid and deep to the masseter muscles (Figure 5). The patient was subsequently returned to theatre for further washout and through and through drainage of the right infratemporal fossa into the mouth. She was commenced on IV clarithromycin and metronidazole on the advice of the microbiology team.

The patient recovered well, with the drains being removed 4 days post-operatively. She was discharged with oral antibiotics. At the 1-month review, she complained of intermittent headaches and residual trismus. On examination, the right temple swelling had resolved and the skin incision had healed well. We believed inflammation of temporalis and masseter was causing restricted mouth opening and tenderness. Regular analgesia was advised, and jaw exercises prescribed to encourage mouth opening.

Discussion

The presentation of an infratemporal fossa abscess is related to the specific anatomy involved.⁵ The clinical symptoms commonly reported are pain, fever and trismus.⁶ Extra-oral swelling and oedema are usually late presentations.⁷ Trismus develops as the temporalis and pterygoid muscles lying within the IF are commonly involved.⁶ There has been one reported case of inferior alveolar nerve involvement and numbness to lower lip on the affected side.⁸

IF abscesses can develop from odontogenic or sino-nasal infections. IF abscesses of dental origin can arise from the spread of infection through the cortical bone and periosteum into adjacent tissues. Additionally, iatrogenic infections from needle injections, for example a mandibular block, can result in microbial contamination of the infratemporal fascia.⁹ Leventhal and Schwartz report an aetiology of maxillary nerve block and multiple injections for anaesthetizing prior to a dental procedure.¹⁰

Sino-nasal causes are more commonly associated with maxillary sinus fractures and sinusitis, resulting in direct microbial access into the IF space.⁶ Untreated odontogenic infections usually spread through buccal, submandibular or sublingual spaces (or a combination of these).¹¹ Although the primary cause of IF abscess originates from mandibular molars, odontogenic infections rarely spread to the infratemporal fossa.^9,12

IF abscess is a diagnostic challenge because of the non-specific symptoms, especially during the early stages of infection, as seen in our case.⁵ The lack of familiarity with IF abscess can lead to delays in diagnosis and treatment.³ These delays in treatment can lead to potentially life-threatening complications, including mediastinitis, pericarditis and cavernous sinus thrombosis owing to the anatomy closely linked to the IF space.^10,12,13

The first line imaging modality in diagnosing IF abscess is contrast-enhanced CT, and should be used when feasible.⁶ CT scanning is the most effective method of diagnosing IF infection because it can differentiate between cellulitis and abscess clearly.³ MRI can also help the diagnosis of infratemporal infection cases, particularly if a neoplasm is also suspected. MRI provides more information on perineural infiltration and intracranial involvement when compared to CT.¹⁴

Antimicrobial therapy should initially be broad spectrum owing to the variability of micro-organisms.^2,6 The definitive treatment of IF abscesses is surgical incision and drainage, with either an extra- or intra-oral approach, or a combination of both.⁶ Most cases of IF abscess reported show a slow recovery process, particularly with regard to mouth opening. Diacono and Wass reported only a 50% improvement in mouth opening after 1 year.⁷ Owing to the extent of the inflammation and involvement of the muscles of mastication, we recommend early follow-up and provision of rehabilitation to improve mouth opening where indicated.

Conclusion

Infratemporal abscesses of odontogenic origin are rare and can be misdiagnosed. It can be a life-threatening infection and requires urgent referral to the maxillofacial team. Thorough history and examination, as well as relevant radiographic investigations, are all important in prompt diagnosis and management of an infratemporal infection. Timely access to dental services will go a long way in reducing the risk of spread of dental infection.