A 45 year old man presented to the emergency department with a suspected “allergic reaction”. He described facial and neck swelling, progressive inspiratory difficulty and pain on swallowing during the previous seven hours. On further questioning he said that swelling had begun one hour after a prolonged dental extraction for a right lower molar tooth abscess. The procedure had entailed several local anaesthetic injections and the use of an air turbine drill. After the procedure he had started a course of oral penicillin V. He had no known allergies. On general examination, he was alert, well perfused and did not have afebrile. Swelling was noted in the submandibular region, the anterior part of the neck and the supraclavicular fossa (fig 1). His trachea was central and there was no clinical evidence of airway obstruction or ventilatory compromise. Pulse, blood pressure and heart sounds were normal. Subcutaneous crepitus was palpable over the neck, chest and right cheek. An anteroposterior chest radiograph showed extensive subcutaneous emphysema of the soft tissues of the chest and neck, with a pneumomediastinum (fig 2). Prophylactic intravenous cefuroxime and metronidazole were prescribed and the patient was admitted for observation under maxillofacial surgery. The patient's cervical and thoracic symptoms subsided and he remained afebrile and systemically well during the following three days and he was discharged.

Surgical emphysema is a recognised complication of dental treatment. It is important in the emergency department because almost 10% of cases are misdiagnosed as “allergic reactions”, which may lead to errors in treatment.¹ Air may be introduced into the mediastinum via the fascial spaces of the neck using high speed air turbine drills or through an incision or empty socket after extraction.² Approximately one third of cases are secondary to extractions of the mandibular third molar. The differential diagnosis in patients presenting with a combination of face and neck swelling after dental procedures includes pneumothorax, expanding haematoma, infection in the fascial planes of the neck, anaphylaxis, local allergic reaction and angioneurotic oedema.

Complications of cervical emphysema and pneumomediastinum after oral surgery may include mediastinitis, cardiac tamponade and airway obstruction. In addition they may be associated with simple and tension pneumothorax and with pneumoperitoneum. Hence although the condition is not usually life threatening antibiotic prophylaxis is recommended and patients are admitted for observation. The importance in the emergency department is that misdiagnosis as allergic reaction may lead to errors in treatment and adverse outcome.

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Figure 1

Facial appearance on presentation (top) and two months after discharge (bottom).

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Figure 2

Chest radiograph showing pneumomediastinum.