Pneumomediastinum and subcutaneous emphysema complicating a patient with a lung abscess

Abstract

Pneumomediastinum and subcutaneous emphysema are conditions that carry significant morbidity. They are uncommonly seen as complications of lung abscess formation and prompt recognition and treatment is necessary. We present a 59-year-old male patient who complained of shortness of breath and chest pain for 2 weeks. Computed tomography (CT) of the thorax showed a left lower lobe lung abscess. This was associated with leucocytosis and raised C-reactive protein. Ultrasound-guided drainage revealed viscous pus requiring manual aspiration for adequate drainage. The patient later developed extensive pneumomediastinum and subcutaneous emphysema involving the pretracheal space, without evidence of pneumothorax. Left lower lobectomy was performed to control sepsis. The patient achieved a complete recovery following his surgery and antibiotic treatment, with interval resolution of pneumomediastinum and subcutaneous emphysema. We present the radiological and clinical features leading to the diagnosis of pneumomediastinum and subcutaneous emphysema.

INTRODUCTION

Lung abscess is a condition that carries significant morbidity and mortality. It is uncommonly complicated by pneumomediastinum and subcutaneous emphysema, conditions that could cause airway compromise. There are few case reports regarding such complications in the current literature. We report a patient with a lung abscess complicated by the development of pneumomediastinum and subcutaneous emphysema, the subsequent treatment, and the associated clinical and radiological features.

CASE REPORT

A 59-year-old male smoker with a background history of diabetes, dyslipidaemia and hypertension was admitted with a 2-week history of shortness of breath, left-sided and central pleuritic chest pain, and generalized malaise. There was no fever. On admission, the patient was haemodynamically stable, afebrile, and dyspneic with an oxygen requirement of 4 L/min. Clinical examination revealed reduced breath sounds, increased vocal resonance, and dull percussion notes at the left hemithorax.

Investigations revealed neutrophilic leucocytosis with a white cell count of 30.5 × 10⁹/L, and a C-Reactive Protein level of 302.9 mg/L. Chest X-ray (CXR) showed patchy infiltrates predominantly over the bilateral lower zones, with a left lower zone consolidation (Figure 1A). No definite air-fluid levels or pneumomediastinum were noted on the initial chest radiograph. Computed tomography (CT) of the thorax was arranged showing multi-lobar pneumonia, with a dominant abscess in the left lower lobe basal subpleural region with smaller abscesses within the consolidated left lower lobe (Figures 2A, B). The same CT images also illustrate the extent of contact between the mediastinal space and the lung parenchyma involved by the abscess and pneumonia.

FIGURE 1. Serial CXRs taken during the patient's admission: (A) CXR on admission, (B) CXR after abscess drainage and drain insertion, (C) CXR upon complaint of increased shortness of breath, chest pain and rhinolalia, (D) CXR after left lower lobectomy, and (E) CXR prior to discharge

FIGURE 2. CT Thorax films: (A) On admission - Soft tissue window in contrast phase, showing rim enhancement of left lower lobe lung abscess. (B) Lung window of image A. (C) CT film showing bilateral extensive subcutaneous emphysema and pneumomediastinum.

Intravenous piperacillin-tazobactam and metronidazole were started. Ultrasound-guided drainage to the left lower lobe lung abscess with a 12-French catheter was done (Figure 1B), yielding 270 ml of frank pus. Despite initial improvement, the patient deteriorated within 1 day of drainage, with an increased oxygen requirement of up to 5 L/min, associated with recurrence of pleuritic chest pain radiating to the back, shortness of breath and occurrence of a high-pitched, nasal voice. Repeated CXR showed pneumomediastinum and subcutaneous emphysema. CT thorax confirmed pneumomediastinum without pneumothorax (Figures 1C and 2C). The abscess drainage catheter was checked to be patent at the time and there was no air leak noted in the drainage bottle.

High flow oxygen therapy was started for the initial management of the subcutaneous emphysema. The patient soon underwent left lower lobectomy for removal of the infected lung tissue subsequently, and a chest drain was inserted intraoperatively. Intraoperative findings showed a residual left lower lobe abscess involving the apical and posterior basal segments with its walls in contact with the posterior chest wall and mediastinal pleura.

Bacterial culture of the abscess fluid showed Streptococcus constellatus, Prevotella species, and Eggerthia species. Sputum cultures were unrevealing. Dental examination showed multiple caries and dental extraction was done to remove dental sources of sepsis. The patient fully recovered following his operation and completion of a course of antibiotics which were subsequently adjusted to amoxycillin-clavulanic acid based on the abscess fluid culture results. Follow-up chest radiographs also demonstrated resolution of the pneumomediastinum and subcutaneous emphysema (Figures 1D, E).

DISCUSSION

The diagnosis of pneumomediastinum was suspected based on the presenting complaints of central chest pain with radiation to the back, new onset rhinolalia and shortness of breath, which are known signs of pneumomediastinum.¹

We hypothesise that the pathophysiology involved in this case of lung abscess with pneumomediastinum was related to the Macklin effect, with necrosis of bronchiole walls during severe infection resulting in alveolar rupture causing interstitial emphysema, and subsequent dissection of air along the bronchovascular sheath culminating in a pneumomediastinum.² The absence of pneumothorax could be attributable to the air traversing the pleura through the bronchovascular bundles without disruption to the pleural surface. The high flow rate of air from the lungs into the mediastinum could have led to further dissection of air into areas of lower resistance such as the subcutaneous space leading to subcutaneous emphysema. While the case series by Sakai et al. mentioned pneumonia, and not lung abscess as an associated condition of the Macklin effect and pneumomediastinum,² we hypothesise that the mechanism of alveolar rupture remains similar in lung abscesses due to an underlying necrotising infective process.

An alternative possibility that could account for this patient's clinical presentation would be subcutaneous emphysema occurring as a complication of the abscess drain insertion with pneumomediastinum occurring secondarily.³ However, this is considered less likely in the absence of significant air leak from the abscess cavity, as the abscess drainage catheter was checked to be patent upon onset of the subcutaneous emphysema and there was no air leak noted in the drainage bottle.

Pneumomediastinum in the absence of pneumothorax is a rare complication of lung abscess formation. A study by Weber et al. described an incidence of only two cases out of 1119 patients with lung abscesses⁴; therefore, a high index of suspicion is required to diagnose this complication. Recently, pneumomediastinum and lung abscesses were reported in a patient with COVID-19 pneumonia as a case report by Ghalechyan et al.⁵ This could suggest that the development of pneumomediastinum, lung abscesses and severe pneumonia are manifestations along a disease spectrum of growing clinical significance.

In conclusion, the findings from this case and the literature suggest that clinicians should be highly alert for the development of pneumomediastinum in patients with lung abscesses or severe pneumonia, particularly those with involvement of the mediastinal pleural surfaces and multiple bronchovascular bundles. In the absence of complications such as pneumothorax or pneumomediastinum, a trial of conservative management with image-guided drainage of the abscess with intravenous antibiotics should be implemented. However, patients should be closely monitored, and any deterioration in their clinical and biochemical parameters, or lack of response to treatment should prompt early investigation for the development of complications, or persistence of any septic foci requiring further intervention. Early detection of such complications and intervention are necessary to minimize associated morbidity or mortality.

AUTHOR CONTRIBUTIONS

All authors fulfil the criteria of authorship. Christopher Chan drafted the original manuscript. All authors were involved in the care of the patient, contributed to revisions of the manuscript, provided final approval of the version to be published and agreed to be accountable for all aspects of the work.

CONFLICT OF INTEREST

None declared.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

ETHICS STATEMENT

The authors declare that appropriate written informed consent was obtained for the publication of this manuscript and accompanying images.