Intermediate bronchial fistula formation caused by mediastinal drainage tube compression and fungal infection is rare. The major risk factor for fungal infection is immunodeficiency including transplantation, AIDS, prolonged therapy with corticosteroids and malignancy et.al. Uncontrolled diabetes mellitus could results mildly immunosuppression and increases the risk of bacterial infection. In our case, the combination of mediastinal drainage tube compression and destroy effect of fungal infection contribute to bronchial fistula formation.
Imaging findings are crucial for the diagnosis. From the lung window of chest multi-slice CT, the connection of intermediate bronchus and mediastinal drainage tube tract was observed. The specific finding of fungal infection is pseudomembrane. Fungal infection would bring completely demolished mucosa, transmural bronchial necrosis and pseudomembranes. The biopsy results depicting numerous fungal hyphae. Based on the evidence above, the diagnosis of benign intermediate bronchial fistula was made.
Early diagnosis and antifungal treatment may significantly improve the outcome. Arguder and colleagues reported a case of pseudomembranous aspergillus tracheobronchities, which caused tracheal perforation [1]. The patient was unsuitable for any invasive procedure because of very large perforation and died of respiratory failure. In our case, due to the fistula in intermediate bronchus, the lung function is not affect obviously. After the diagnosis of fungal infection from pathology was made, antifungal drug was given.
The treatment strategies of benign tracheobronchial fistula including surgery and endobronchial stenting. Considering the general condition of our patient, endobronchial stenting as a minimally invasive was developed. Small diameter silicon stent placement was the first choice in our case, but it is not available in our hospital, only metallic stent can be used. Although FDA warning uncovered metallic stenting in benign tracheal stenosis due to granulation hyperplasia. The application of covered metallic stent benefit many patients with tracheal fistula and stenosis [2,3,4]. The obstacles of the early years of metallic stent implantation involved the limitations of stent sizes. Ill-matched stent including undersized stent and oversized stent may cause undue friction and pressure, result in excessive granulation tissue formation [5]. To minimize the complications of granulation tissue formation after metallic stent placement, we ordered an individualized covered metallic stent to match the diameter of bronchus. Post-stent 40 days, sputum retention was observed through bronchoscopy, no stent migration and severe granulation hyperplasia happened.
Thus, we conclude that: 1. Tracheobronchial fistula caused by the combination of mediastinal drainage tube compression and fungal infection is rare. It is characterized by pseudomembranous formation on the wall of airway. 2. Uncontrolled diabetes mellitus could results mildly immunosuppression and increases the risk of bacterial infection. 3. Timely stenting could boost the healing of fistula via granulation tissue proliferation.