Severe Right Pulmonary Artery Stenosis Due to Fibrosing Mediastinitis

Abstract

INTRODUCTION: Fibrosing mediastinitis is a rare condition characterized by proliferation of fibrous tissue in the mediastinum, resulting in compression of vital airways and blood vessels. It is thought to result from a hypersensitivity fibrotic reaction secondary to antigenic stimulation, most commonly from previous Histoplasma capsulatum infection. Patients may present with dyspnea or hemoptysis relating to stenosis of the bronchi, however, involvement of the main pulmonary arteries is rare and is associated with significant morbidity and mortality. We present the case of a young woman with profound exercise intolerance and pulmonary hypertension due to fibrosing mediastinitis causing stenosis of the right main pulmonary artery. CASE PRESENTATION: A 24 year old woman from the Ottawa Valley was referred for assessment of dyspnea. She was previously healthy and did not use any regular medications. She developed a respiratory infection 3 months earlier, followed by progressive cough, dyspnea and retrosternal chest discomfort. There was no history of constitutional symptoms, occupational exposures or smoking. She underwent pulmonary function testing, which revealed mild restriction and diffusion impairment. A chest x-ray was normal, with the exception of a small calcified nodule in the left upper lung zone. At this time, the differential diagnosis included pulmonary vascular disease (pulmonary embolism and pulmonary arterial hypertension), valvular heart disease, cardiomyopathy, and interstitial lung disease. She underwent a ventilation-perfusion scan of the thorax, which revealed marked reduction in perfusion to the right lung, with preserved ventilation. A computed tomography scan ruled out a pulmonary embolism, but instead showed extensive calcification surrounding the right main pulmonary artery, with significant luminal narrowing. An exercise echocardiogram was completed for assessment of pulmonary hypertension. With Stage III exercise, the right ventricular systolic pressure (RVSP) rose from 29 mmHg to 88 mmHg and she developed intense fatigue and dyspnea. Her right ventricle was normal in size and systolic function at rest. Given her progressive functional limitation and pulmonary hypertension, she was referred for endovascular stenting of the right main pulmonary artery to restore perfusion to the right lung. Following the procedure, there was subjective improvement in dyspnea and objective improvement in peak exercise RVSP. DISCUSSIONS: The majority of patients diagnosed with fibrosing mediastinitis (FM) are young and present with signs and symptoms of airway or vascular obstruction. Vascular obstruction usually presents with exertional dyspnea. The specific pathogenesis of FM has not been identified, however, this condition has mainly been linked with histoplasma, aspergillus and cryptococcus infection, radiation therapy and autoimmune disease. Systemic treatment has been attempted with corticosteroids, antifungals and immunosuppressive medications, but unfortunately, no definitive benefit has been demonstrated. There has, however, been some reported benefit with endovascular stenting in FM patients who have main pulmonary arterial and venous involvement. In a published case series, one of four bed-bound patients with bilateral pulmonary venous involvement was successfully stented with subsequent complete resolution of symptoms, lasting 4.5 years. While improvements can be dramatic with endovascular stenting, achieving patency of the blood vessel does not always produce clinical and hemodynamic improvement. This may be due to irreversible vascular changes, induced by chronic vascular obstruction. CONCLUSION: Fibrosing mediastinitis should be considered in the differential diagnosis for vascular obstruction in the mediastinum and pulmonary hypertension. While there is no effective medical therapy, endovascular stenting can achieve sustained symptomatic and subjective hemodynamic improvements. Prognosis is variable in these patients, any may depend on the baseline degree of pulmonary hypertension after endovascular stenting.