Descending Necrotizing Mediastinitis: A Potential Consequence of Odontogenic Infection

What is mediastinitis?

The term mediastinitis refers to either acute or chronic inflammation of the tissues within the middle thoracic cavity (mediastinum). The mediastinum contains important anatomical structures such as the thymus gland, the pericardial sac, the heart, aorta, oesophagus, trachea and major blood vessels. The mediastinum is continuous with fascial spaces in the neck. This anatomical relation explains the possibility of spread of infection from the fascial spaces of the neck into the chest, particularly from the parapharyngeal, prevertebral and retropharyngeal (danger) spaces.⁵

Figure 1 shows the anatomical location of the mediastinum (highlighted in blue) via a 3D reformat of high resolution computed tomography (CT).⁶

The four most common aetiological causes of mediastinitis include:⁷

Mediastinitis ranges in severity, and often requires treatment with antibiotic therapy in an outpatient setting.⁸ Approximately 20% of mediastinitis cases progress to DNM.¹ DNM results from an infection within the oropharyngeal anatomy, spreading down the neck through cervical fascial tissue spaces into the mediastinum.

DNM results from a diffuse multi-organism infection,⁹ including both anaerobes and aerobes. Beta-haemolytic oral Streptococcus is the most commonly isolated microorganism from DNM pathological samples;¹⁰ however Prevotella, Peptostreptococcus, Fusobacterium, Veillonella, Actinomyces, Bacteroides, Staphylococcus and also alpha-haemolytic Streptococcus are frequently found.¹⁰ The virulence of these organisms and secretion of gas and enzyme products (including fibrinolysin, coagulase, hyaluronidase, collagenases and proteases) break down fascial plane boundaries by causing tissue ischaemia, encouraging spread of infection down the neck into the mediastinum.^11,12 Patient factors, such as diabetes and immunodeficiency, can also propagate the spread of infection caused by anaerobic organisms, as these conditions lower tissue oxygen and create a favourable environment in which these pathogens can replicate. The body's natural defence mechanism against progression of DNM is not helped by gravity, respiration and the negative pressure effect in the mediastinum that acts to pull the infection downwards. Once established, DNM creates an area of dead space beneath the sternum in which pus can collect and cause decreased motility of mediastinal structures.¹²

The mortality rate of those patients diagnosed with DNM was reported as 17.5% by a systematic review in 2016.¹ Historically, the rate has been significantly higher at 50%.¹³ The prognosis of DNM is significantly increased if patients have an early CT scan diagnosis, early surgical interventions, appropriate antibiotic therapy and management within an intensive care unit setting.^14,15 For these reasons, early referral of any suspected case by a dental professional could make a significant difference in the outcome for the patient.

As previously mentioned, DNM usually occurs as a complication of either an odontogenic infection or peritonsillar abscess (otherwise known as a quinsy), when the infection has progressed through the neighbouring fascial neck spaces inferiorly into the thoracic cavity.¹⁶ The risk of DNM is greatest in infections occupying the retropharyngeal danger space.⁵ Clinical features of severe cervicofacial infection are detailed in Table 1. Odontogenic infections, particularly those associated with lower third molars, are responsible for approximately 40–60% of DNM cases.^17,18

Case report

We present the case of a fit and well, 21-year-old male. This patient attended a local accident and emergency department with a short history of throbbing dental pain radiating from the lower right quadrant and large submandibular swelling. On further questioning, the submandibular swelling had been present for approximately 48 hours prior to presentation, and the patient had not sought treatment for this swelling before arriving in the accident and emergency department. Clinical examination revealed a large right-sided submandibular swelling, a raised floor of mouth on the right side and trismus (<1-cm mouth opening). The patient had no notable voice changes and did not have signs of acute respiratory distress or stridor; however, observations revealed he was pyrexic and tachycardic. Figure 2 shows the panoramic radiograph taken on initial presentation, with carious lower first permanent molar teeth and extensive peri-apical pathology around the lower right first permanent molar.

On the day of presentation, the patient started broad spectrum empirical intravenous (IV) antibiotics and underwent urgent general anaesthetic for examination, dental extractions and incision and drainage of the submandibular abscess under the care of oral and maxillofacial surgeons (OMFS).

Microbial culture of the pus, and a sample of tissue from the urgent surgical debridement grew Streptococcus sanguinis, Staphylococcus epidermidis, Granulicatella adiacens, Streptococcus anginosus and Streptococcus constellatus, all of which are Gram-positive facultative anaerobes. Following these results, the antibiotic regimen was consolidated to IV meropenem following microbiology advice on best targeting these specific micro-organisms.

Although this patient had no known risk factors for developing such extensive pathology, it was important to rule out underlying health conditions. These included the investigation of blood-borne diseases, such as HIV, hepatitis B and C, and ruling out diabetes.

Three days following his initial admission to hospital, the patient's condition deteriorated. Further washout of his submandibular abscess via an extra-oral approach was completed under general anaesthetic. It was during this operation that the extension of the abscess into the retrosternal region became apparent. Surgical intervention behind the sternum requires cardiothoracic input, therefore the patient's care was escalated to a tertiary unit with thoracic support available immediately via ambulance. At this point, plain film radiographs of the patient's neck and chest were taken, which showed a widened mediastinum (Figure 3). These radiographic signs are relatively late indicators of DNM. Further signs that could be found in such cases may be subcutaneous emphysema and pleural effusions.

The patient remained intubated in an intensive care unit (ICU). As a complication of the mediastinitis, he developed acute respiratory distress syndrome (ARDS) and required periods of prone ventilation. Prone ventilation (ie mechanically ventilating the patient positioned on their stomach) reduces the mortality of patients with ARDS¹⁹ by improving oxygenation and perfusion of the lungs and increasing drainage of fluid. A CT investigation highlighted extensive pulmonary abnormalities compatible with ARDS and pulmonary interstitial fluid overload (Figure 4). Figure 4 shows the extensive fluid collections on CT, and also demonstrates the value of this 3D imaging modality in surgical planning. CT scans with contrast are highly accurate and able to evaluate infection spread easily to aid surgical management of DNM. The use of CT scans to monitor disease progression and recovery has been advocated for patients with DNM^20,21 and is now considered to be a routine standard of care. During his time in the ICU, the patient underwent two further general anaesthetics for debridement of his submandibular space abscess and deep neck infection.

This young patient spent a total of 15 days in hospital as a direct result of his odontogenic infection, and required four general anaesthetics in quick succession. Not only will this experience undoubtedly have long-term physical repercussions for the patient, psychological sequelae are also likely, including the possibility of ICU-related post-traumatic stress disorder and the exacerbation of dental anxiety.²²

Relevance to dental professionals

It is unlikely that dental professionals in primary care would diagnose a patient as having mediastinitis, owing to the lack of access to appropriate clinical imaging and diagnostics. However, the general dentist will have an awareness of the clinical signs of systemic infection and the risk of sepsis, and should be cognisant of the potentially very severe consequences of spreading neck infection. Much like necrotizing fasciitis, or Ludwig's angina, DNM requires urgent aggressive surgical management²³ and must be referred to the nearest accident and emergency department without delay.

In addition to sending the patient to the accident and emergency department, urgent phone referral to ‘bleep’ the oral and maxillofacial surgery department will alert the team to the inbound clinical scenario, which may expedite the patient's admission.

It is possible that dental professionals may come into contact with patients who have experienced inpatient care as a result of dental abscesses, dental-related sepsis or complications, such as mediastinitis. The understanding of how these experiences may have affected patients and their relationship with dental care should be considered. Severe complications of dental infections are stressful for patients and their families, and in some cases can result in negative psychological association for patients. Patients who have experienced life-threatening infections and required urgent inpatient management may require additional support from their dentist and GP after discharge.

Conclusion

Mediastinitis is a rare but severe complication of odontogenic infection. The clinical case described in this article highlights a patient with no other known medical risk factors, and as such illustrates that although rare, mediastinitis is a risk for any patient with extensive odontogenic infection, and patients with infections extending into the neck should be referred for urgent evaluation.