Introduction
The development of pneumomediastinum in general may result from one or more disruption of anatomic structures [
1]: (1) direct air leak from rupture of trachea, bronchus, or esophagus into the mediastinum; (2) perforation of a hollow abdominal viscus with subsequent dissection of air into the mediastinum via the diaphragmatic hiatus or (3) air may reach the mediastinum through and along the potential spaces and fascial planes of the neck, (4) tears in the pulmonary parenchyma resulting in leakage of air into the pulmonary interstitium: air can further dissect along the fascial sheaths and the adventitia of blood vessels and bronchi to the hilum and eventually into the mediastinum (“Macklin Effect”).
Case report
A 56-year-old man presented spontaneously to the Emergency Department complaining of facial and neck edema after assumption of nonsteroidal anti-inflammatory drugs (NSAIDS). The triage nurse assigned the patient to Accident & Emergency (A&E) doctor as probable allergic reaction to NSAIDS. The patient was a heavy smoker and was treated with sodium oxybate for alcoholic and with antidepressants and benzodiazepines for depression. The vitals at admission were stable, blood pressure (BP) 150/100 mmHg, heart rate (HR) 95 bpm and O2 saturation 100% in room air. At examination the murmur was slightly decreased but bilaterally present, the patient was eupnoeic, without wheezing or chest tightness, and there were no signs of bronchospasm. There was an extensive facial and neck edema with a mild rash in absence of throat and mouth swelling. To avoid a deterioration of the clinical stability, therapy with salbutamol and beclometasone nebulization as well as i.v. steroids and antihistamine was initiated and the patient was admitted for observation. The following day his vitals were still stable and the patients remained eupnoeic, however, the diffuse edema and swelling were increased despite therapy. At examination the murmur was clearly decreased in both sides, more evident in the left. Diffuse crepitation was now palpable over the chest, neck and face, consistent with subcutaneous emphysema. The patient was asked if have had recent trauma and he finally remembered an accidental fall three days earlier, while he was alone, with left blunt thoracic trauma. The following day because of the left chest pain he took NSAIDS. An urgent chest X-ray (CXR) revealed a huge subcutaneous chest and neck emphysema without clearly visible pneumothorax (Fig. 1). Subsequent chest CT scan showed a small left pneumothorax and a large amount of air in the mediastinum (24 cm × 15 cm × 11 cm). No rib fractures were documented (Fig. 2). The radiology resident misinterpreted the image as a huge pneumopericardium. However, the patient was hemodynamically stable and electrocardiogram (ECG) did not show any alteration. The cardiothoracic attending surgeon correctly interpreted the CT scan as a huge pneumomediastinum and ordered a bronchoscopy to rule out tracheobronchial injuries. Bronchoscopy was negative and the patient was conservatively treated without inserting any chest drain. His conditions improved in the following days and the patient was discharged home 6 days after the admission.
Discussion
The differential diagnosis from drug-induced allergic asthma was deceptively hard in this case. Spontaneous pneumomediastinum is rare in these cases but may occur after alveolar rupture and air penetration into the pulmonary interstice, followed by air penetration toward the hila and into the mediastinum [
2,
3]. Pneumomediastinum was reported in up to 10% of patients with severe blunt chest trauma [
4].
The pathophysiology of pneumomediastinum was first described by Macklin in 1939 [
5]. The “Macklin effect” involves alveolar ruptures with air dissection along bronchovascular sheaths to the mediastinum; these alveolar ruptures are either isolated or confluent and then result in pulmonary lacerations [
6]. In case of a pneumothorax, a concomitant tear of the parietal pleura may allow the free pleural air to enter the mediastinal compartment. Finally, subcutaneous emphysema created by rib fractures (in association with a pneumothorax or not) may progress along fascial sheaths and extend into the mediastinum. Conversely, a pneumomediastinum may dissect along fascial sheaths to create a cervical or thoracic subcutaneous emphysema [
7].
The Macklin effect may also be involved in various other conditions other than trauma, such as asthma crises, neonatal respiratory distress syndrome, positive-pressure mechanical ventilation and Valsalva maneuvre.
Treatment of subcutaneous emphysema is primarily directed at treating the underlying cause. Inspiration of 100% oxygen helps to promote subcutaneous air reabsorption [
8]. Pneumomediastinum may resolve spontaneously with proper rest and observation.
The deceiving clinical presentation of the patient at his arrival to the Emergency Department represents the genuine peculiarity of this case. In fact, facial and neck edema was initially misinterpreted as common drug allergic reaction related to recent assumption of NSAIDS. A&E doctors did not suspect any subcutaneous emphysema since the patient did not have signs of bronchospasm and no mention of recent thoracic blunt trauma was reported. Only after 24 h subcutaneous emphysema became palpable. Fortunately, the diagnostic delay had no consequences since the patient was conservatively managed.
Each emergency physician should suspect this rare occurrence visiting a patient with facial and upper trunk edema. Accurate physical examination is mandatory.
Compliance with ethics guidelines
Salomone Di Saverio, Kenji Kawamukai, Andrea Biscardi, Silvia Villani, Luca Zucchini, and Gregorio Tugnoli declare that they have no conflict of interest. Additional informed consent was obtained from all patients for whom identifying information is included in this article.
Higher Education Press and Springer-Verlag Berlin Heidelberg
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