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Localized Fibrosing Mediastinitis Causing Pulmonary Infarction: A Case Report

Fibrosing mediastinitis is a rare benign disorder that is characterized by deposition of dense fibrous tissue throughout the mediastinum and hilar regions (1). Resultant infiltrative or compressive effects on vital mediastinal organs such as central systemic vein, airway, and pulmonary vessels, could increase morbidity and in rare circumstances even mortality (2). We reported a rare case of fibrosing mediastinitis causing pulmonary infarction by encasing pulmonary artery that was detected on chest computed tomography (CT).


INTRODUCTION
Fibrosing mediastinitis is a rare benign disorder that is characterized by deposition of dense fibrous tissue throughout the mediastinum and hilar regions (1). Resultant infiltrative or compressive effects on vital mediastinal organs such as central systemic vein, airway, and pulmonary vessels, could increase morbidity and in rare circumstances even mortality (2). We reported a rare case of fibrosing mediastinitis causing pulmonary infarction by encasing pulmonary artery that was detected on chest computed tomography (CT).

CASE REPORT
A 44-year-old female patient visited the emergency room (ER) of a tertiary referral university hospital due to acute hemoptysis and right chest wall pain of 2 months duration. Her chest pain was refractory to prior conservative treatment in a local clinic.
The patient was a nonsmoker and had no particular medical history. On laboratory tests, serum erythrocyte sedimentation rate was mildly elevated but other parameters were within normal limits. Plain chest radiograph demonstrated patchy increased opacity in left lower lung zone and small amount of left pleural effusion (Fig. 1). Considering the refractory nature of her chest pain and the acute onset of hemoptysis, post-contrast chest CT was immediately conducted in the ER. Chest CT revealed soft tissue mass at the left hilar region, which showed homogenous enhancement and was encasing and provoking near total occlusion of left inferior pulmonary artery ( Fig. 2A).
There was no visible calcification within the mass. Wedgeshaped subpleural consolidation was seen in the left lower lobe, which was the corresponding vascular territory of the encased A 44-year-old female patient visited our emergency room for hemoptysis and refractory chest wall pain of 2 months duration. She had no history of smoking or other medical conditions. Chest CT scan showed homogenously enhancing soft tissue mass without calcification at the left pulmonary hilum. Encasing and compression of the left lower pulmonary artery by the mass had resulted in pulmonary infarction in the left lower lobe. Laboratory tests for tuberculosis, fungus, and vasculitis were all negative. The patient underwent surgical biopsy and resection of infarcted left lower lobe that was histopathologically confirmed as fibrosing mediastinitis. Herein, we reported a rare case of surgically confirmed and treated localized fibrosing mediastinitis causing pulmonary infarction. Gross examination of resected specimen revealed firm white fibrous tissue surrounding the left hilum (Fig. 3A). Histopathologically, the mass consisted of dense fibrosis surrounding and infiltrating pulmonary vasculature with extension into the lung parenchyme (Fig. 3B). Occasional chronic necrotizing granulomas were seen within the dense fibrosis (Fig. 3C). Polymerase chain reaction (PCR) for tuberculosis was negative and Gomori methenamine silver (GMS) stain for fungal study was also negative. Consequently, the final diagnosis was fibrosing mediastinitis. The patient underwent follow-up for 3 years and was free from symptom and recurrence on imaging.

DISCUSSION
Fibrosing mediastinitis is a benign progressive non-neoplastic disease characterized by infiltration of excessive fibrous tissue within the mediastinum mediated by abnormal immune  Fibrosing mediastinitis is most commonly associated with histoplasma infection in North America (5). Other possible triggers of fibrosing mediastinitis are reportedly tuberculosis, fungal infections, and sarcoidosis (6). However, if certain identifiable cause is absent, the disease is categorized as idiopathic (6).
In many cases, no specific microorganism is identified and thus categorized as idiopathic (7). In our case, laboratory examination and elastin stain for vasculitis were negative and investigation for immunoglobulin G4-related disease was also negative.
In addition, PCR test for tuberculosis and non-tuberculosis mycobacterium were negative, as well as GMS tests for fungal study.
Therefore, our case could be categorized as idiopathic fibrosing mediastinitis. The treatment of fibrosing mediastinitis is controversial. The effect of systemic antifungal or antituberculous therapy is reported in cases with confirmed causative microorganism (9). However, in cases of granuloma or fibrosis causing compression of mediastinal organ, surgical resection of affected tissue is necessary (10). In our case, the patient suffered from chest wall pain and blood tinged sputum as a result of pulmonary infarction.
Surgical resection was necessary for symptom relief as well as histopathologic diagnosis. Consequently, the patient's symptoms were completely resolved for the following 3 years follow up period.
Our case demonstrated the rare occurrence of fibrosing mediastinitis with pulmonary artery occlusion and implication of surgical resection for local disease control.