Fibrosing Mediastinitis with Severe Bilateral Pulmonary Artery Narrowing

Abstract

Although fibrosing mediastinitis is uncommon, it is a devastating sequela of certain granulomatous diseases. The compression of mediastinal structures can lead to severe cardiopulmonary symptoms. We report the case of a 50-year-old woman who presented with severe bilateral branch pulmonary artery compression 6 months after bilateral pulmonary artery stenting. We performed bypass surgery with use of a homograft conduit. Seven months postoperatively, the homograft and stent in the right pulmonary artery were patent, and the patient had resumed activities of daily living, including full-time employment. In addition to reporting this patient's case, we discuss surgery as an alternative to stenting in patients with fibrosing mediastinitis.

Fibrosing mediastinitis is an infrequent but debilitating sequela of fungal and mycobacterial infections. In the United States, Histoplasma capsulatum is the most frequently reported infectious cause.¹ An infiltrating fibrotic mass and mediastinal lymphadenopathy can compress mediastinal structures, including the tracheobronchial tree, esophagus, venae cavae, pulmonary veins, and pulmonary arteries (PAs). The superior vena cava (SVC) is the vessel most commonly obstructed.² Stents have been used with variable success to reconstitute blood flow through native vessels. Stents are typically used to correct SVC obstruction, and they yield good short-term patency. They are considered to be first-line therapy in most situations³; however, few reports of long-term patency are available.

Pulmonary artery involvement in fibrosing mediastinitis is rare. Percutaneous stent placement has been used in the treatment of PA stenoses secondary to fibrosing mediastinitis.^4-6 Thiessen and colleagues⁶ published a report of PA stent patency at 10 years; however, most studies lack long-term follow-up. Bypass procedures with the use of homografts have been performed, mostly in cases of SVC obstruction. Brown and associates⁷ successfully treated PA obstruction, using a porcine valved conduit in 1 patient and aortic homografts in 2 patients for anastomoses from the right ventricle (RV) to a distal branch PA. The patient who received the porcine conduit died perioperatively of respiratory failure after an unrelated procedure; in the other patients, the homografts remained patent without reintervention at 9 and 10 years.⁷ Here, we report the case of a patient with fibrosing mediastinitis who underwent PA bypass surgery after her bilateral PA stents became severely narrowed.

Case Report

In October 2008, a 50-year-old woman presented at our institution with exertional chest pain and worsening dyspnea and hypoxia. Her medical history included fibrosing mediastinitis, rheumatoid arthritis, hypertension, and multiple sclerosis. She had been diagnosed with fibrosing mediastinitis 10 years before our evaluation, when a biopsy for evaluation of an aortopulmonary window mass revealed chronic fibrosis. She had previously had positive Histoplasma titers.

Results of echocardiography were consistent with pulmonary hypertension and RV dysfunction. Right- and left-sided heart catheterization revealed elevated RV and PA pressures of 76/4 and 76/10 mmHg, respectively. Left ventricular contractility appeared to be normal, and there was no notable coronary artery disease. Subsequent catheterization revealed bilateral branch PA stenoses, with a luminal diameter of 2 to 3 mm over a length of 2.2 cm (Fig. 1). The left PA-to-main PA gradient was 70 mmHg (left PA, 11/9 mmHg; main PA, 81/10 mmHg). The right PA-to-main PA gradient was 54 mmHg (right PA, 27/10 mmHg; main PA, 81/10 mmHg). A 27-mm Palmaz® Genesis™ Peripheral Stent (Cordis Corporation, a Johnson & Johnson company; Bridgewater, NJ) was placed in the right PA and a 23-mm Genesis stent in the left PA, and the patient was discharged from the hospital with instructions to take 81 mg of aspirin daily. Her symptoms improved initially; however, she returned 6 months later with dyspnea on minimal exertion and chest pain. Repeat angiography revealed nearly complete occlusion of the left PA stent, and the lesion could not be passed with a guidewire. The main and right PA pressures were 75/12 and 34/12 mmHg, respectively. Results of computed tomographic angiography corroborated these findings. Systemic anticoagulation with warfarin and antiplatelet therapy was initiated, and the patient was referred for surgical intervention.

Fig. 1 Coronary angiogram shows bilateral pulmonary artery stenoses (arrows).

The pulmonary outflow tract was reconstructed with use of a 24-mm valved PA homograft (CryoLife, Inc.; Kennesaw, Ga). When the mediastinum was entered, extensive “woody” fibrosis was seen to involve the left and posterior portion of the aorta and PA confluence, and it extended into the left hilum. Cardiopulmonary bypass was initiated with use of bicaval venous cannulae and an aortic perfusion cannula. The heart was arrested by means of antegrade perfusion with cardioplegic solution. Clamping the aorta was difficult because of the extensive, infiltrating fibrotic mass. The left PA could not be bypassed, so the left branch of the homograft was oversewn. A new pulmonary outflow tract was constructed anteriorly by means of a longitudinal arteriotomy in the distal right PA between the SVC and aorta, and by anastomosis of the homograft to the right PA in an end-to-side fashion (Fig. 2). An incision was then made in the pulmonary outflow tract, and the proximal anastomosis was fashioned end-to-side. The graft filled nicely, and the patient was weaned from cardiopulmonary bypass without incident. A GORE-TEX® membrane (W.L. Gore & Associates, Inc.; Flagstaff, Ariz) was sewn to the edges of the pericardium to cover the homograft and prevent impingement on the sternum. The preoperative warfarin was restarted, and the patient was bridged to warfarin anticoagulation with therapeutic doses of enoxaparin. She had an uncomplicated hospital course and was discharged on postoperative day 7.

Fig. 2 Line drawing of the post-surgical anatomy. The pulmonary artery homograft extends from the right ventricular outflow tract to the right pulmonary artery between the aorta and superior vena cava. The left limb was oversewn, and an anastomosis of the right limb was fashioned end-to-side to the right pulmonary artery. The hatched lines indicate fibrosis.

At the 7-month follow-up examination, the patient reported marked symptomatic improvement. She independently carried out activities of daily living, including full-time employment—a substantial improvement in her functional status. She still experienced dyspnea upon moderate exertion. Cardiovascular magnetic resonance imaging showed a patent homograft and patent stent in the native right PA (Fig. 3); however, the left PA remained occluded. The RV was slightly dilated, with mild dysfunction. The left and right ventricular ejection fractions were 0.55 and 0.39, respectively. The patient's cardiac output was 5 L/min, and her cardiac index was 2.9 L/min/m². Systemic anticoagulation (warfarin and antiplatelet therapy) with 81 mg/d of aspirin was to be continued indefinitely. Monitoring was to include yearly cardiac magnetic resonance imaging with 6-month clinical follow-up, and echocardiographic imaging if there was a change in the patient's clinical situation. At 1 year, her symptoms remained stable and she continued to work full-time.

Fig. 3 Magnetic resonance image shows a patent pulmonary homograft (arrow).

Discussion

First described by Nathan Oulmont in 1855,⁸ fibrosing mediastinitis is an uncommon sequela of histoplasmosis. Fibrosing mediastinitis is occasionally asymptomatic but is often associated with substantial morbidity. There is no reliable medical therapy for compression of vascular structures secondary to fibrosing mediastinitis. Historically, surgery has been palliative. Percutaneous stent placement in occluded vessels has become first-line therapy for SVC obstruction.

Although successful PA stenting has been documented in several case reports and case series, long-term outcomes are largely unknown. Our patient presented with severe bilateral PA stenoses and was treated with bilateral PA stents. After initial success, both stents became severely narrowed within 6 months. The stent obstruction appeared to be secondary to extraluminal compression, both on PA angiography and during visual inspection of the PA at the time of operation. Thiessen and colleagues reported 10-year stent patency in a patient who had focal stenosis.⁶ Our patient had stenosis of a length greater than 2 cm bilaterally. The short segmental stenosis in Thiessen and colleagues' patient might have contributed to the long-term patency in that stent, and indeed the extent of inflammation and the affected length of the PA might have been responsible for the varied outcomes in other reported cases. The fibrosis in our patient was quite extensive and aggressive: it infiltrated the soft tissue outside the mediastinum, and it surrounded and infiltrated the great vessels. Of note, because the fibrosis extended far into the left hilum and into the segmental PA branches and extensively involved the aorta, the bypass procedure was effective in restoring blood flow to the right lung only. Hence, the patient's exertional capacity remained limited by single-lung physiology. Regardless, we think that this is an acceptable compromise, in that the unilateral bypass procedure avoided a hazardous dissection around the left hilum. Although we selected a PA homograft, an aortic homograft would also have been an excellent choice. The PA homograft was exactly the proper length and had the appropriate curvature to extend from the RV outflow tract to the right PA between the aorta and the SVC.

As with our patient, most reports of surgical intervention have described early substantial relief of symptoms. However, patients in those cases reported activity restrictions due to exertional symptoms, most commonly dyspnea.⁷ This is most likely due to the progressive nature of fibrosing mediastinitis, in that mediastinal structures invariably become increasingly narrowed with time. Although stent placement is a viable option for symptomatic patients who have substantial comorbidities, bypass grafting should be considered in patients who can tolerate a surgical procedure, in younger patients who are likely to need reintervention, and in patients such as ours, who have experienced failed percutaneous intervention.