(Radiographics. 2001;21:737-757.)
© RSNA, 2001
Fibrosing Mediastinitis1
Santiago E. Rossi, MD,
H. Page McAdams, MD,
Melissa L. Rosado-de-Christenson, Col, USAF, MC,
Teri J. Franks, MD and
Jeffrey R. Galvin, MD
1 The opinions and assertions contained herein are solely the private views of the authors and are not to be construed as official nor as representing those of the Departments of the Air Force or Defense.
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Abstract
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Fibrosing mediastinitis is a rare benign disorder caused by proliferation of acellular collagen and fibrous tissue within the mediastinum. Although many cases are idiopathic, many (and perhaps most) cases in the United States are thought to be caused by an abnormal immunologic response to Histoplasma capsulatum infection. Affected patients are typically young and present with signs and symptoms of obstruction or compression of the superior vena cava, pulmonary veins or arteries, central airways, or esophagus. There may be two types of fibrosing mediastinitis: focal and diffuse. The focal type usually manifests on computed tomographic (CT) or magnetic resonance (MR) images as a localized, calcified mass in the paratracheal or subcarinal regions of the mediastinum or in the pulmonary hila. The diffuse type manifests on CT or MR images as a diffusely infiltrating, often noncalcified mass that affects multiple mediastinal compartments. CT and MR imaging play a vital role in the diagnosis and management of fibrosing mediastinitis.
Index Terms: Mediastinitis, 67.2053, 67.273 • Mediastinum, fibrosis, 67.273
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LEARNING OBJECTIVES FOR TEST 5
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After reading this article and taking the test, the reader will be able to:
- Enumerate the varied radiologic manifestations of fibrosing mediastinitis and the specific imaging features that allow a confident prospective diagnosis.
- List the differential diagnostic considerations and pitfalls in the pathologic diagnosis of fibrosing mediastinitis.
- Define the use of radiologic imaging in the diagnosis and treatment of fibrosing mediastinitis.
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Introduction
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Fibrosing mediastinitis is an uncommon benign disorder characterized by proliferation of dense fibrous tissue within the mediastinum (1). This entity is also known as sclerosing mediastinitis and as mediastinal fibrosis. Affected patients are typically young and present with signs and symptoms related to obstruction of vital mediastinal structures, such as central systemic veins, the esophagus, airways, and pulmonary arteries or veins. The precise cause and pathogenesis of fibrosing mediastinitis in most cases is unknown, and links to infectious and noninfectious causes remain speculative. Recently, Flieder and colleagues (2) proposed the term idiopathic fibroinflammatory lesion of the mediastinum to replace the present term fibrosing mediastinitis. In doing so, they emphasized that, in most cases, a definite cause cannot be established with certainty and that there is substantial variability in the histopathologic appearance of the lesions. Whether this proposed term will eventually replace the present term is unclear.
In this article, we review the current understanding of fibrosing mediastinitis with regard to potential causes and pathogenesis as well as its typical histopathologic, clinical, and radiologic features.
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Causes and Pathogenesis
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Despite extensive investigation, the precise cause and pathogenesis of fibrosing mediastinitis remains elusive. Many, if not most, cases in the United States have been linked to Histoplasma capsulatum infection (1,3–8). This association is based on several observations. First, most cases of fibrosing mediastinitis occur in regions of the United States where H capsulatum infection is endemic. Second, many affected patients have positive skin tests to H capsulatum antigens. Third, residua of granulomatous inflammation are occasionally demonstrated in affected tissues. Fourth, H capsulatum organisms are sometimes identified in histopathologic specimens.
Considerable controversy surrounds the association of fibrosing mediastinitis and histoplasmosis, however. Definitive histopathologic proof of infection—demonstration of organisms within affected tissues—is absent in many cases. Also, histoplasmosis is an exceedingly common infection in endemic regions of the United States, but fibrosing mediastinitis affects only a small fraction of potentially exposed individuals. For these reasons, many authors believe that fibrosing mediastinitis results not from direct infection of the mediastinum by H capsulatum organisms, but rather from an abnormal immunologic reaction to H capsulatum antigens. Furthermore, this fibroinflammatory response to H capsulatum antigens is believed to occur in only a small group of genetically susceptible individuals (1,4,9).
The relationship between fibrosing mediastinitis and the so-called mediastinal granuloma is also controversial. The latter term is commonly used in the setting of a focal mediastinal mass that results from direct infection of lymph nodes by H capsulatum organisms (Fig 1). At resection or biopsy, the mediastinal granuloma is found to be composed of enlarged, matted lymph nodes that contain either caseous or fibrous material (1). The lesion is typically well encapsulated without local invasion or diffuse mediastinal fibrosis. There is usually no involvement of airways, pulmonary arteries, or pulmonary veins. Although most patients with mediastinal granuloma are asymptomatic, a few present with signs and symptoms related to compression of the superior vena cava or esophagus. Some authors believe that mediastinal granuloma is the precursor lesion to mediastinal fibrosis. According to this theory, rupture of a mediastinal granuloma releases antigen into the mediastinum, resulting in either localized or diffuse fibrosis (10). Dines and colleagues (11) at the Mayo Clinic concluded that 34% of 31 patients with mediastinal granulomas in their series eventually developed fibrosing mediastinitis. In theory then, some authors have suggested that mediastinal granulomas should be resected when discovered to prevent evolution to fibrosing mediastinitis. However, Loyd et al (1), in an exhaustive review of the English-language literature on the subject including cases seen up to 1988, reached a different conclusion. They found no evidence that mediastinal granulomas progressed to fibrosing mediastinitis, and they concluded that the two lesions were most likely distinct and separate entities with, perhaps, the same cause (histoplasmosis). Thus, they suggested that resection of mediastinal granulomas should be performed only for diagnosis or relief of symptoms.
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Figure 1a. Mediastinal granuloma due to histoplasmosis in a 30-year-old man with chest pain. (a) Posteroanterior chest radiograph shows a calcified right paratracheal mass (arrowhead). (b) CT scan (mediastinal window) shows the focal paratracheal mass with a low-attenuation center and extensive calcification (arrowhead). Note the mass effect on the trachea (T). A noninvasive, well-encapsulated mass containing viable H capsulatum organisms was found at resection.
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Figure 1b. Mediastinal granuloma due to histoplasmosis in a 30-year-old man with chest pain. (a) Posteroanterior chest radiograph shows a calcified right paratracheal mass (arrowhead). (b) CT scan (mediastinal window) shows the focal paratracheal mass with a low-attenuation center and extensive calcification (arrowhead). Note the mass effect on the trachea (T). A noninvasive, well-encapsulated mass containing viable H capsulatum organisms was found at resection.
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To confound the issue further, some cases of fibrosing mediastinitis are clearly not related to histoplasmosis. In these rare cases, other infections, including tuberculosis (12), aspergillosis, mucormycosis, blastomycosis (13), and cryptococcosis (14), are implicated. Fibrosing mediastinitis has also been reported in the setting of autoimmune disease (14), Behçet disease (15), rheumatic fever, radiation therapy (16), trauma, Hodgkin disease, and drug therapy with methysergide maleate (14). In addition, fibrosing mediastinitis can occur in association with other idiopathic fibroinflammatory disorders such as retroperitoneal fibrosis, sclerosing cholangitis, Riedel thyroiditis, and pseudotumor of the orbit (17–27).
In a relatively large radiologic series, Sherrick and colleagues (28) noted two distinct patterns of mediastinal involvement on CT scans. In 82% of affected patients, they observed relatively localized mediastinal disease most commonly affecting the right paratracheal and subcarinal regions. This pattern was frequently (63% of cases) associated with stippled calcification, and affected patients typically had evidence of prior granulomatous infection, either histoplasmosis or tuberculosis. In a minority of patients (18%), they observed a diffusely infiltrating, noncalcified mass that affected multiple mediastinal compartments. These patients did not have evidence of prior granulomatous infection, and half had other associated conditions such as retroperitoneal fibrosis.
Taken together, these various evidentiary threads suggest that there are, in all likelihood, at least two types of fibrosing mediastinitis. The first type, which is the most common in the United States, is probably caused by a fibroinflammatory response to H capsulatum antigens in a genetically susceptible population. This type usually results in relatively focal mediastinal or hilar fibrosis with extensive calcification. The second, and much less common, type of the disease is probably not caused by histoplasmosis, but occurs idiopathically and is related to other fibroinflammatory lesions such as retroperitoneal fibrosis. This second type results in diffuse, multicompartmental fibrosis and does not usually calcify.
For the remainder of the article, we use the term fibrosing mediastinitis to refer to both types of this disease interchangeably. Most prior treatments of this subject do not make this distinction, nor do they always carefully distinguish mediastinal granuloma from mediastinal fibrosis.
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Pathologic Characteristics
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Fibrosing mediastinitis is characterized by an ill-defined soft-tissue mass involving the mediastinum in which dense, white fibrous tissue is seen in cut sections. The process may occur as a localized mass or may diffusely infiltrate the mediastinum and, in rare cases, extend into the soft tissues of the neck (29), the posterior mediastinum (30), and the lung (Fig 2).
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Figure 2a. Fibrosing mediastinitis associated with histoplasmosis in a 58-year-old man with a 6-month history of cough. (a) Computed tomographic (CT) scan (lung window) shows an infiltrating, soft-tissue right hilar mass extending into the right lower lobe along bronchovascular bundles. (b) CT scan (mediastinal window) shows the soft-tissue mass (arrowhead) and extensive calcification in the right hilum and subcarinal region. (c) Photograph of the cut surface of the resected specimen shows dense white fibrous tissue in the right hilum extending into the lung parenchyma along bronchovascular bundles (arrows).
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Figure 2b. Fibrosing mediastinitis associated with histoplasmosis in a 58-year-old man with a 6-month history of cough. (a) Computed tomographic (CT) scan (lung window) shows an infiltrating, soft-tissue right hilar mass extending into the right lower lobe along bronchovascular bundles. (b) CT scan (mediastinal window) shows the soft-tissue mass (arrowhead) and extensive calcification in the right hilum and subcarinal region. (c) Photograph of the cut surface of the resected specimen shows dense white fibrous tissue in the right hilum extending into the lung parenchyma along bronchovascular bundles (arrows).
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Figure 2c. Fibrosing mediastinitis associated with histoplasmosis in a 58-year-old man with a 6-month history of cough. (a) Computed tomographic (CT) scan (lung window) shows an infiltrating, soft-tissue right hilar mass extending into the right lower lobe along bronchovascular bundles. (b) CT scan (mediastinal window) shows the soft-tissue mass (arrowhead) and extensive calcification in the right hilum and subcarinal region. (c) Photograph of the cut surface of the resected specimen shows dense white fibrous tissue in the right hilum extending into the lung parenchyma along bronchovascular bundles (arrows).
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Microscopic examination of biopsy specimens from patients with fibrosing mediastinitis reveals abundant, paucicellular fibrous tissue infiltrating and obliterating adipose tissue (Fig 3). The fibrous tissue can contain patchy infiltrates of mononuclear cells. Flieder and colleagues (2), in a study of 30 cases of idiopathic fibrosing mediastinitis, described a histopathologic spectrum of changes for which they established a three-step staging system. Stage I lesions are composed predominantly of edematous fibromyxoid tissue. In stage II disease, the lesions contain glassy bands of eosinophilic hyaline material that encircle and infiltrate mediastinal structures. Obliterative lesions of dense paucicellular collagen characterize stage III disease, and their appearance represents the classic microscopic features of fibrosing mediastinitis (Fig 4). Although Flieder et al found their system useful for describing the variety of histopathologic findings seen in cases of fibrosing mediastinitis, their staging system does not appear to be clinically relevant at this time.
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Figure 3. Fibrosing mediastinitis. Medium-power photomicrograph (original magnification, x25; hematoxylin-eosin stain) demonstrates fibrous tissue (arrows) infiltrating mediastinal adipose tissue.
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Figure 4. Fibrosing mediastinitis. High-power photomicrograph (original magnification, x100; hematoxylin-eosin stain) demonstrates paucicellular, eosinophilic mature collagen, findings typical of fibrosing mediastinitis.
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Because fibrosing mediastinitis is associated with a multiplicity of clinical syndromes and diseases, great care must be exercised when one evaluates open or needle biopsy specimens that demonstrate fibrosis. The histologic differential diagnosis of fibrosing mediastinitis includes localized fibrosis associated with infection, most commonly histoplasmosis (Fig 5) and tuberculosis, and fibrosis occurring in association with a variety of malignancies. The neoplasms that most frequently produce fibrosis and thus must be included in the differential diagnosis include sclerosing non-Hodgkin lymphoma (Fig 6) and the nodular sclerosis variant of Hodgkin disease. Localized fibrous tumors of the pleura and diffuse desmoplastic malignant mesotheliomas should also be considered, although these spindle cell tumors can be readily excluded because of their increased cellularity and the characteristic immunohistochemical staining for CD34 and bcl-2 of the former and keratin of the latter. Metastatic carcinomas with a fibrogenic inflammatory response, thymoma, and thymic carcinoid all show keratin staining of tumor cells. Simple fibrosis, fibromatosis, and low-grade sarcoma are also possibilities in the differential diagnosis. Because all these lesions may exhibit areas of fibrosis, biopsy samples obtained with a percutaneous needle technique may be insufficient to rule out malignancy due to their limited size; an open biopsy with extensive sampling is frequently required to establish a definitive diagnosis (10,14).
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Figure 5a. Histoplasmosis. (a) Medium-power photomicrograph (original magnification, x50; hematoxylin-eosin stain) of a hilar lymph node specimen shows a caseating granuloma composed of a rim of epithelioid histocytes (arrowheads) surrounding central caseous necrosis (N). Note peripheral lymphoid infiltrate (L). (b) Oil immersion photomicrograph (original magnification, x500; Grocott methenamine-silver stain) shows small oval-shaped yeasts of H capsulatum. Note the rare budding forms (arrowhead).
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Figure 5b. Histoplasmosis. (a) Medium-power photomicrograph (original magnification, x50; hematoxylin-eosin stain) of a hilar lymph node specimen shows a caseating granuloma composed of a rim of epithelioid histocytes (arrowheads) surrounding central caseous necrosis (N). Note peripheral lymphoid infiltrate (L). (b) Oil immersion photomicrograph (original magnification, x500; Grocott methenamine-silver stain) shows small oval-shaped yeasts of H capsulatum. Note the rare budding forms (arrowhead).
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Figure 6a. Sclerosing diffuse large B-cell lymphoma. (a) High-power photomicrograph (original magnification, x400; hematoxylin-eosin stain) demonstrates hypercellular atypical lymphoid infiltrate. (b) High-power photomicrograph (original magnification, x400) of a specimen stained with immunohistochemistry for CD20 (B-cell marker) shows positive cytoplasmic staining.
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Figure 6b. Sclerosing diffuse large B-cell lymphoma. (a) High-power photomicrograph (original magnification, x400; hematoxylin-eosin stain) demonstrates hypercellular atypical lymphoid infiltrate. (b) High-power photomicrograph (original magnification, x400) of a specimen stained with immunohistochemistry for CD20 (B-cell marker) shows positive cytoplasmic staining.
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Clinical Features
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Patients with fibrosing mediastinitis are typically young at presentation, although the disease is reported to occur over a very wide age range (Table 1). It affects males and females in roughly equal proportions. A recent study suggested that African-American patients are disproportionately affected (2), but this predilection has not been reported in other series.
Most patients present with signs or symptoms related to obstruction or compression of vital mediastinal structures such as the central airways, superior vena cava, pulmonary veins, pulmonary arteries and esophagus. The heart, pericardium, coronary arteries, aorta, and aortic branch vessels are much less frequently involved (1,14,22,23, 31–33). The most common presenting complaints include cough, dyspnea, recurrent pulmonary infection, hemoptysis, and pleuritic chest pain (Table 1). Patients present with systemic signs such as fever and weight loss less often (1,2,5,6,14,28).
Fibrosing mediastinitis has been reported to be the most common benign cause of the superior vena cava syndrome (1). However, this syndrome is unusual in many series of patients with fibrosing mediastinitis, particularly when cases of mediastinal granuloma are excluded. In fact, some authors have concluded that superior vena cava syndrome more typically results from compression of the superior vena cava by a mediastinal granuloma and that superior vena cava obstruction in cases of fibrosing mediastinitis is comparatively rare (1).
Obstruction of the central airways is fairly common in patients with fibrosing mediastinitis and typically manifests with cough and dyspnea. Affected patients can also present with a history of recurrent or persistent pneumonia or exhibit atelectasis in the lung distal to the occluded airway.
Patients with pulmonary venous occlusion can present with progressive or exertional dyspnea as well as with hemoptysis. This pattern of symptoms has been called the "pseudo-mitral stenosis syndrome." Long-standing pulmonary venous occlusion can also result in secondary pulmonary arterial hypertension and cor pulmonale—one of the most important causes of morbidity and mortality in patients with fibrosing mediastinitis (34,35). Pulmonary venous occlusion can also lead to pulmonary infarction (36,37). Pulmonary arterial stenosis or occlusion less frequently results in pulmonary hypertension (38).
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Treatment and Prognosis
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Fibrosing mediastinitis often has an unpredictable course, with both spontaneous remission or exacerbation of symptoms being reported. Loyd et al (1) reported a mortality rate of greater than 30%, which is much higher than that reported in other studies. Causes of death are usually recurrent infection, hemoptysis, or cor pulmonale. The mortality rate among patients with subcarinal or bilateral mediastinal involvement may be higher than that among patients with more localized mediastinal or hilar fibrosis (1). There are three possible avenues for treatment: systemic antifungal or corticosteroid treatment, surgical resection, and local therapy for complications.
Presuming that many, perhaps most, cases of fibrosing mediastinitis in the United States are related to H capsulatum infection and an ensuing inflammatory reaction, some investigators have treated patients with systemic antifungal agents or corticosteroids. Most of the available data in this regard are based on either case reports or small series; prospective, randomized controlled trials have not been performed (5,6,10). The limited data available suggest that ketoconazole therapy may result in stabilization of the disease process or, in some cases, limited symptomatic improvement (6). However, given the unpredictable nature of the disorder, the significance of these uncontrolled data is not clear (32). Most studies have shown little or no beneficial effect of corticosteroid therapy (10).
If disease is localized, surgical resection of affected tissues may be curative or result in amelioration of signs and symptoms (3,5,10). A complete resection may require extensive vascular or airway reconstruction (39), techniques that are available at only a few centers. Bilateral mediastinal involvement is generally thought to preclude a surgical approach. On the whole, the results of surgical therapy have been disappointing, and resection is often associated with high morbidity and mortality (1).
Increasingly, symptomatic patients are treated with local therapies directed toward reopening occluded or severely stenosed airways, pulmonary arteries, or venae cavae. Laser therapy, balloon dilation, and intravascular or endobronchial stent placement have all been used with some success to treat affected patients (40–42) (Figs 7, 8). Spiral vein grafts to bypass an occluded vena cava have also been used with success (43).
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Figure 7a. Left main bronchus stenosis due to fibrosing mediastinitis treated with laser ablation, balloon dilation, and endobronchial stent placement. The patient also had a history of recurrent left lung pneumonia. (a) CT scan (mediastinal window) shows a wire mesh stent in the left main bronchus, calcified adenopathy (arrow) in the aortopulmonary window, and a subcarinal soft-tissue mass (arrowhead). * = esophagus. (b) CT scan (lung window) shows an outpouching (arrowhead) of the anterior esophageal lumen adjacent to the stent that was confirmed to represent a bronchoesophageal fistula at a barium swallow examination (not shown). Note lingular consolidation, which most likely represents pneumonia. The patient subsequently underwent esophagectomy and anterior gastric interposition.
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Figure 7b. Left main bronchus stenosis due to fibrosing mediastinitis treated with laser ablation, balloon dilation, and endobronchial stent placement. The patient also had a history of recurrent left lung pneumonia. (a) CT scan (mediastinal window) shows a wire mesh stent in the left main bronchus, calcified adenopathy (arrow) in the aortopulmonary window, and a subcarinal soft-tissue mass (arrowhead). * = esophagus. (b) CT scan (lung window) shows an outpouching (arrowhead) of the anterior esophageal lumen adjacent to the stent that was confirmed to represent a bronchoesophageal fistula at a barium swallow examination (not shown). Note lingular consolidation, which most likely represents pneumonia. The patient subsequently underwent esophagectomy and anterior gastric interposition.
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Figure 8a. Superior vena cava syndrome due to fibrosing mediastinitis treated with balloon dilation and endovascular stent placement. (a) Posteroanterior chest radiograph shows enlargement of the right hilum, a right paratracheal mass, and a well-circumscribed right upper lobe nodule (arrow). Note calcification in the right hilum and nodule. (b) Contrast material-enhanced CT scan (mediastinal window) shows the infiltrating soft-tissue mass (solid arrows) with dense calcification in the right paratracheal region. Note obstruction of the superior vena cava, enhancement of multiple mediastinal collateral veins (arrowheads), and the densely calcified pulmonary nodule (open arrow). (c) Frontal superior vena cavagram shows a balloon-tipped catheter traversing a distal stenosis (arrows) of the superior vena cava. Note the mediastinal collateral veins (arrowheads). The patient underwent balloon dilation of the superior vena cava stenosis followed by placement of a metallic mesh stent. (d) Collimated posteroanterior chest radiograph obtained at follow-up shows the metallic mesh stent in the brachiocephalic vein and superior vena cava. The patient experienced marked symptomatic relief following endovascular therapy.
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Figure 8b. Superior vena cava syndrome due to fibrosing mediastinitis treated with balloon dilation and endovascular stent placement. (a) Posteroanterior chest radiograph shows enlargement of the right hilum, a right paratracheal mass, and a well-circumscribed right upper lobe nodule (arrow). Note calcification in the right hilum and nodule. (b) Contrast material-enhanced CT scan (mediastinal window) shows the infiltrating soft-tissue mass (solid arrows) with dense calcification in the right paratracheal region. Note obstruction of the superior vena cava, enhancement of multiple mediastinal collateral veins (arrowheads), and the densely calcified pulmonary nodule (open arrow). (c) Frontal superior vena cavagram shows a balloon-tipped catheter traversing a distal stenosis (arrows) of the superior vena cava. Note the mediastinal collateral veins (arrowheads). The patient underwent balloon dilation of the superior vena cava stenosis followed by placement of a metallic mesh stent. (d) Collimated posteroanterior chest radiograph obtained at follow-up shows the metallic mesh stent in the brachiocephalic vein and superior vena cava. The patient experienced marked symptomatic relief following endovascular therapy.
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Figure 8c. Superior vena cava syndrome due to fibrosing mediastinitis treated with balloon dilation and endovascular stent placement. (a) Posteroanterior chest radiograph shows enlargement of the right hilum, a right paratracheal mass, and a well-circumscribed right upper lobe nodule (arrow). Note calcification in the right hilum and nodule. (b) Contrast material-enhanced CT scan (mediastinal window) shows the infiltrating soft-tissue mass (solid arrows) with dense calcification in the right paratracheal region. Note obstruction of the superior vena cava, enhancement of multiple mediastinal collateral veins (arrowheads), and the densely calcified pulmonary nodule (open arrow). (c) Frontal superior vena cavagram shows a balloon-tipped catheter traversing a distal stenosis (arrows) of the superior vena cava. Note the mediastinal collateral veins (arrowheads). The patient underwent balloon dilation of the superior vena cava stenosis followed by placement of a metallic mesh stent. (d) Collimated posteroanterior chest radiograph obtained at follow-up shows the metallic mesh stent in the brachiocephalic vein and superior vena cava. The patient experienced marked symptomatic relief following endovascular therapy.
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Figure 8d. Superior vena cava syndrome due to fibrosing mediastinitis treated with balloon dilation and endovascular stent placement. (a) Posteroanterior chest radiograph shows enlargement of the right hilum, a right paratracheal mass, and a well-circumscribed right upper lobe nodule (arrow). Note calcification in the right hilum and nodule. (b) Contrast material-enhanced CT scan (mediastinal window) shows the infiltrating soft-tissue mass (solid arrows) with dense calcification in the right paratracheal region. Note obstruction of the superior vena cava, enhancement of multiple mediastinal collateral veins (arrowheads), and the densely calcified pulmonary nodule (open arrow). (c) Frontal superior vena cavagram shows a balloon-tipped catheter traversing a distal stenosis (arrows) of the superior vena cava. Note the mediastinal collateral veins (arrowheads). The patient underwent balloon dilation of the superior vena cava stenosis followed by placement of a metallic mesh stent. (d) Collimated posteroanterior chest radiograph obtained at follow-up shows the metallic mesh stent in the brachiocephalic vein and superior vena cava. The patient experienced marked symptomatic relief following endovascular therapy.
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Radiologic Features
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Chest Radiography
The radiologic features of fibrosing mediastinitis are summarized in Table 2. Although chest radiographs of patients with fibrosing mediastinitis usually appear abnormal, the findings can be quite subtle and the extent of mediastinal involvement is frequently underestimated on the basis of these findings (44) (Fig 9). Fibrosing mediastinitis usually manifests on chest radiographs as nonspecific widening of the mediastinum, with distortion and obliteration of normally recognizable mediastinal interfaces or lines. The middle mediastinum is affected most often, particularly the subcarinal and right paratracheal regions (Fig 8). The right side of the mediastinum is more commonly involved than the left (31,45). Less frequently, a focal hilar mass is observed (34) (Fig 10). Calcification within the mediastinum or hila is seen in up to 86% of patients.
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Figure 9a. Idiopathic fibrosing mediastinitis in a 30-year-old man with superior vena cava syndrome. (a) Posteroanterior chest radiograph shows subtle thickening of the right paratracheal stripe and a calcified right upper lobe nodule (arrow). (b) Contrast-enhanced CT scan (mediastinal window) shows an infiltrating soft-tissue attenuation mass in the middle mediastinum. Note encasement and narrowing of the distal superior vena cava (white arrowhead) and right pulmonary artery (black arrowheads) and distention of the azygous vein (arrow). (c) Contrast-enhanced CT scan (mediastinal window) obtained at a more caudal level shows encasement and narrowing of the right superior pulmonary vein (arrowheads). (d) Frontal pulmonary arteriogram shows smooth long-segment narrowing (arrows) of the right main pulmonary artery (M). (e) Frontal superior vena cavagram shows smooth, eccentric stenosis (arrows) of the distal superior vena cava (S).
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Figure 9b. Idiopathic fibrosing mediastinitis in a 30-year-old man with superior vena cava syndrome. (a) Posteroanterior chest radiograph shows subtle thickening of the right paratracheal stripe and a calcified right upper lobe nodule (arrow). (b) Contrast-enhanced CT scan (mediastinal window) shows an infiltrating soft-tissue attenuation mass in the middle mediastinum. Note encasement and narrowing of the distal superior vena cava (white arrowhead) and right pulmonary artery (black arrowheads) and distention of the azygous vein (arrow). (c) Contrast-enhanced CT scan (mediastinal window) obtained at a more caudal level shows encasement and narrowing of the right superior pulmonary vein (arrowheads). (d) Frontal pulmonary arteriogram shows smooth long-segment narrowing (arrows) of the right main pulmonary artery (M). (e) Frontal superior vena cavagram shows smooth, eccentric stenosis (arrows) of the distal superior vena cava (S).
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Figure 9c. Idiopathic fibrosing mediastinitis in a 30-year-old man with superior vena cava syndrome. (a) Posteroanterior chest radiograph shows subtle thickening of the right paratracheal stripe and a calcified right upper lobe nodule (arrow). (b) Contrast-enhanced CT scan (mediastinal window) shows an infiltrating soft-tissue attenuation mass in the middle mediastinum. Note encasement and narrowing of the distal superior vena cava (white arrowhead) and right pulmonary artery (black arrowheads) and distention of the azygous vein (arrow). (c) Contrast-enhanced CT scan (mediastinal window) obtained at a more caudal level shows encasement and narrowing of the right superior pulmonary vein (arrowheads). (d) Frontal pulmonary arteriogram shows smooth long-segment narrowing (arrows) of the right main pulmonary artery (M). (e) Frontal superior vena cavagram shows smooth, eccentric stenosis (arrows) of the distal superior vena cava (S).
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Figure 9d. Idiopathic fibrosing mediastinitis in a 30-year-old man with superior vena cava syndrome. (a) Posteroanterior chest radiograph shows subtle thickening of the right paratracheal stripe and a calcified right upper lobe nodule (arrow). (b) Contrast-enhanced CT scan (mediastinal window) shows an infiltrating soft-tissue attenuation mass in the middle mediastinum. Note encasement and narrowing of the distal superior vena cava (white arrowhead) and right pulmonary artery (black arrowheads) and distention of the azygous vein (arrow). (c) Contrast-enhanced CT scan (mediastinal window) obtained at a more caudal level shows encasement and narrowing of the right superior pulmonary vein (arrowheads). (d) Frontal pulmonary arteriogram shows smooth long-segment narrowing (arrows) of the right main pulmonary artery (M). (e) Frontal superior vena cavagram shows smooth, eccentric stenosis (arrows) of the distal superior vena cava (S).
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Figure 9e. Idiopathic fibrosing mediastinitis in a 30-year-old man with superior vena cava syndrome. (a) Posteroanterior chest radiograph shows subtle thickening of the right paratracheal stripe and a calcified right upper lobe nodule (arrow). (b) Contrast-enhanced CT scan (mediastinal window) shows an infiltrating soft-tissue attenuation mass in the middle mediastinum. Note encasement and narrowing of the distal superior vena cava (white arrowhead) and right pulmonary artery (black arrowheads) and distention of the azygous vein (arrow). (c) Contrast-enhanced CT scan (mediastinal window) obtained at a more caudal level shows encasement and narrowing of the right superior pulmonary vein (arrowheads). (d) Frontal pulmonary arteriogram shows smooth long-segment narrowing (arrows) of the right main pulmonary artery (M). (e) Frontal superior vena cavagram shows smooth, eccentric stenosis (arrows) of the distal superior vena cava (S).
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Figure 10a. Fibrosing mediastinitis due to histoplasmosis in a 55-year-old man with cough and hemoptysis. (a) Posteroanterior chest radiograph shows a left hilar mass. (b) Coronal T1-weighted (repetition time msec/echo time msec = 870/20) magnetic resonance (MR) image demonstrates the left hilar mass (arrowheads) of heterogeneous low-to-intermediate signal intensity obstructing the left main bronchus (L). Note the subcarinal component of the mass (S). A = aorta, P = pulmonary artery, T = trachea.
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Figure 10b. Fibrosing mediastinitis due to histoplasmosis in a 55-year-old man with cough and hemoptysis. (a) Posteroanterior chest radiograph shows a left hilar mass. (b) Coronal T1-weighted (repetition time msec/echo time msec = 870/20) magnetic resonance (MR) image demonstrates the left hilar mass (arrowheads) of heterogeneous low-to-intermediate signal intensity obstructing the left main bronchus (L). Note the subcarinal component of the mass (S). A = aorta, P = pulmonary artery, T = trachea.
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As expected, the radiographic findings of fibrosing mediastinitis in an individual patient very much depend on the mediastinal structure or structures involved. Patients with superior vena cava obstruction may have bilateral widening of the superior mediastinum on chest radiographs due to engorged collateral veins (Fig 11). Involvement of the central airways can result in segmental or lobar atelectasis or recurrent pneumonia in the affected portions of lung. Less commonly, actual narrowing of the affected airways is seen (Fig 7). The area of narrowing usually occurs at the level of the carina and in the majority of cases involves both main bronchi (7) (Fig 12). Pulmonary arterial obstruction is typically unilateral and can result in an appreciable diminution in size and quantity of vessels and localized regions of oligemia in the affected portions of lung. Pulmonary venous obstruction manifests radiographically with findings of localized pulmonary venous hypertension: peribronchial cuffing, septal thickening, and localized edema (7) (Fig 13). Pulmonary arterial or venous obstruction can also cause pulmonary infarcts that manifest as peripheral, wedge-shaped areas of homogeneous opacity. Pleural effusions are uncommon (7,44–46).
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Figure 11a. Fibrosing mediastinitis due to histoplasmosis in a 40-year-old man with superior vena cava syndrome. (a) Posteroanterior chest radiograph shows a focal right paratracheal mass (arrowhead). (b) Superior vena cavagram shows marked narrowing (arrows) of the superior vena cava at the level of the mass. Note opacification of multiple collateral veins (arrowhead).
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Figure 11b. Fibrosing mediastinitis due to histoplasmosis in a 40-year-old man with superior vena cava syndrome. (a) Posteroanterior chest radiograph shows a focal right paratracheal mass (arrowhead). (b) Superior vena cavagram shows marked narrowing (arrows) of the superior vena cava at the level of the mass. Note opacification of multiple collateral veins (arrowhead).
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Figure 12. Idiopathic fibrosing mediastinitis in a 38-year-old man with intermittent stridor. Linear tomogram shows diffuse narrowing of the trachea and both main bronchi and a soft-tissue mass encasing the distal trachea.
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Figure 13a. Fibrosing mediastinitis due to histoplasmosis in a 36-year-old woman with dyspnea. (a) Posteroanterior chest radiograph shows volume loss in the right hemithorax and findings of localized edema in the right lower lobe. The right hilum is enlarged. (b) CT scan (lung window) shows marked thickening of interlobular septa (arrows) in the right lung. (c) Contrast-enhanced CT scan (mediastinal window) shows a right hilar and subcarinal soft-tissue mass obstructing the right pulmonary artery (R) and superior pulmonary vein (arrowhead). More caudal images (not shown) demonstrated obstruction of the inferior pulmonary vein. Note punctate subcarinal calcification (arrow). A = aorta, S = superior vena cava. (d) Frontal pulmonary arteriogram shows mild, smooth narrowing of the right pulmonary artery (P) and marked narrowing of the truncus anterior (arrows) and right interlobar pulmonary artery (arrowhead).
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Figure 13b. Fibrosing mediastinitis due to histoplasmosis in a 36-year-old woman with dyspnea. (a) Posteroanterior chest radiograph shows volume loss in the right hemithorax and findings of localized edema in the right lower lobe. The right hilum is enlarged. (b) CT scan (lung window) shows marked thickening of interlobular septa (arrows) in the right lung. (c) Contrast-enhanced CT scan (mediastinal window) shows a right hilar and subcarinal soft-tissue mass obstructing the right pulmonary artery (R) and superior pulmonary vein (arrowhead). More caudal images (not shown) demonstrated obstruction of the inferior pulmonary vein. Note punctate subcarinal calcification (arrow). A = aorta, S = superior vena cava. (d) Frontal pulmonary arteriogram shows mild, smooth narrowing of the right pulmonary artery (P) and marked narrowing of the truncus anterior (arrows) and right interlobar pulmonary artery (arrowhead).
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Figure 13c. Fibrosing mediastinitis due to histoplasmosis in a 36-year-old woman with dyspnea. (a) Posteroanterior chest radiograph shows volume loss in the right hemithorax and findings of localized edema in the right lower lobe. The right hilum is enlarged. (b) CT scan (lung window) shows marked thickening of interlobular septa (arrows) in the right lung. (c) Contrast-enhanced CT scan (mediastinal window) shows a right hilar and subcarinal soft-tissue mass obstructing the right pulmonary artery (R) and superior pulmonary vein (arrowhead). More caudal images (not shown) demonstrated obstruction of the inferior pulmonary vein. Note punctate subcarinal calcification (arrow). A = aorta, S = superior vena cava. (d) Frontal pulmonary arteriogram shows mild, smooth narrowing of the right pulmonary artery (P) and marked narrowing of the truncus anterior (arrows) and right interlobar pulmonary artery (arrowhead).
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Figure 13d. Fibrosing mediastinitis due to histoplasmosis in a 36-year-old woman with dyspnea. (a) Posteroanterior chest radiograph shows volume loss in the right hemithorax and findings of localized edema in the right lower lobe. The right hilum is enlarged. (b) CT scan (lung window) shows marked thickening of interlobular septa (arrows) in the right lung. (c) Contrast-enhanced CT scan (mediastinal window) shows a right hilar and subcarinal soft-tissue mass obstructing the right pulmonary artery (R) and superior pulmonary vein (arrowhead). More caudal images (not shown) demonstrated obstruction of the inferior pulmonary vein. Note punctate subcarinal calcification (arrow). A = aorta, S = superior vena cava. (d) Frontal pulmonary arteriogram shows mild, smooth narrowing of the right pulmonary artery (P) and marked narrowing of the truncus anterior (arrows) and right interlobar pulmonary artery (arrowhead).
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Computed Tomography
Fibrosing mediastinitis typically manifests on CT scans as an infiltrative mass of soft-tissue attenuation that obliterates normal mediastinal fat planes and encases or invades adjacent structures (47–49) (Figs 8, 9, 13). Fibrosing mediastinitis most commonly affects the middle mediastinal compartment, including both the right and left paratracheal and subcarinal regions as well as the hila. The anterior and posterior mediastinum are much less frequently involved (30,50) (Figs 14, 15).
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Figure 14. Idiopathic fibrosing mediastinitis in a 30-year-old woman with chest pain. CT scan (mediastinal window) shows a soft-tissue attenuation mass in the anterior mediastinum. Biopsy specimen revealed fibrosing mediastinitis. A = aorta, S = superior vena cava.
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Figure 15. Idiopathic fibrosing mediastinitis in a 43-year-old woman with chronic cough and dyspnea. CT scan (mediastinal window) shows a soft-tissue attenuation mass diffusely infiltrating the middle and posterior mediastinum, encasing the descending aorta (a), and extending into both pleural spaces. Note extensive calcification within the pleura.
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As previously noted, Sherrick et al (28) identified two patterns of involvement on CT scans: a focal pattern and a diffuse pattern. The focal pattern, seen in 82% of cases, manifests as a mass of soft-tissue attenuation that is frequently calcified (63% of cases) and is usually located in the right paratracheal or subcarinal regions or in the hila(Fig 16). This type of fibrosing mediastinitis is, in all probability, caused by histoplasmosis in patients from the United States. The diffuse pattern, seen in 18% of cases, manifests as a diffusely infiltrating, noncalcified mass that affects multiple mediastinal compartments (Fig 17). The diffuse pattern is probably not related to histoplasmosis but often occurs in the setting of other idiopathic fibrosing disorders such as retroperitoneal fibrosis.
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Figure 16a. Fibrosing mediastinitis due to histoplasmosis in a 45-year-old woman with recurrent pneumonia. (a) CT scan (mediastinal window) demonstrates a calcified right hilar and mediastinal mass obstructing the right upper lobe bronchus. Note the right pleural thickening (arrows), patent bronchus intermedius (arrowhead), and enlarged azygous vein (a). R = right pulmonary artery, S = superior vena cava. (b) Axial T1-weighted (680/20) MR image shows an infiltrative hilar mass of intermediate signal intensity narrowing the right upper lobe bronchus (arrow). Note the narrowed but patent superior vena cava (arrowhead). Calcification seen on the CT scan (a) is not apparent. A = aorta, P = main pulmonary artery. (Reprinted, with permission, from reference 66.)
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Figure 16b. Fibrosing mediastinitis due to histoplasmosis in a 45-year-old woman with recurrent pneumonia. (a) CT scan (mediastinal window) demonstrates a calcified right hilar and mediastinal mass obstructing the right upper lobe bronchus. Note the right pleural thickening (arrows), patent bronchus intermedius (arrowhead), and enlarged azygous vein (a). R = right pulmonary artery, S = superior vena cava. (b) Axial T1-weighted (680/20) MR image shows an infiltrative hilar mass of intermediate signal intensity narrowing the right upper lobe bronchus (arrow). Note the narrowed but patent superior vena cava (arrowhead). Calcification seen on the CT scan (a) is not apparent. A = aorta, P = main pulmonary artery. (Reprinted, with permission, from reference 66.)
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Figure 17a. Idiopathic fibrosing mediastinitis in a 25-year-old man with sickle cell anemia. (a) Contrast-enhanced CT scan (mediastinal window) shows a soft-tissue attenuation mass diffusely infiltrating the mediastinum. Note encasement and narrowing of the left main bronchus (*), ascending (A) and descending (D) aorta, proximal right (R) and left (L) pulmonary arteries, and esophagus (arrowhead). (b) Contrast-enhanced CT scan (mediastinal window) obtained at a more caudal level shows the subcarinal mass (M), encasement of the left main coronary artery (arrow), and narrowing of the left superior pulmonary vein (S). Note the small left pleural effusion. A = ascending aorta, D = descending aorta, P = main pulmonary artery. (c) Contrast-enhanced CT scan (mediastinal window) obtained at a more caudal level shows encasement of the descending aorta (D) and marked narrowing of the left inferior pulmonary vein (arrowhead). Note the small left pleural effusion. The periaortic mass continued into the upper abdomen (not shown). A = ascending aorta, LA = left atrium.
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Abstract
LEARNING OBJECTIVES FOR TEST...
