Sunday, November 4, 2012

Fibrosing mediastinitis with severe bilateral pulmonary artery narrowing: RV-RPA bypass with a homograft conduit

Tex Heart Inst J. 2012;39(3):412-5.  Gustafson MR, Moulton MJ. Source Division of Cardiothoracic Surgery, University of Arizona College of Medicine, Tucson, Arizona 85724, USA. 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.

Monday, September 24, 2012

I am working on a book entitled DERAILED: Living with Fibrosing Mediastintis. For more information go to the website: DERAILED.

Sunday, August 26, 2012

Map of Histo

This is a map of Navy recruits who tested positive for Histoplasmosis, showing that the fungus is regional.

Saturday, August 25, 2012

Sunday, February 12, 2012

University of Kansas on FM

General Discussion

Mediastinal fibrosis is the least common, but the most severe, late complication of histoplasmosis. Many physicians believe mediastinal fibrosis to be an abnormal immunologic response to antigens released by the soil-based fungus histoplasma capsulatum. It should be differentiated from the many other less-severe mediastinal complications of histoplasmosis, and from other causes of mediastinal fibrosis, which are termed idiopathic mediastinal fibrosis. Idiopathic fibrosing mediastinitis is even less common, but may have multiple causes, none of which are related to histoplasmosis. Accordingly, there are two types of fibrosing mediastinitis; histoplasmosis-related fibrosing mediastinitis, and idiopathic fibrosing mediastinitis which may have multiple causes unrelated to histoplasmosis.

Both types are rare disorders caused by proliferations of collagen, fibrosis tissue and associated inflammatory cells within the mediastinum (the space between the lungs).

Post histoplasmosis mediastinal fibrosis is characterized by invasive, calcified fibrosis centered on lymph nodes, which, by definition, occludes major vessels or airways.

Often symptoms of fibrosing mediastinitis do not develop until the disease has progressed to a level at which there is damage to some vessel or organ. The build up of the scar tissue can be slow growing in some cases and in others the scar tissue may grow at a rapid rate.

Histoplasmosis, the most common endemic parasitic fungus in the United States, is caused by Histoplasma capsulatum. In the endemic area, along the Mississippi and Ohio River valleys, most persons are infected in childhood. Histoplasmosis also occurs in isolated spots around the world, but is most common in North and Central America, with isolated cases reported from Southeast Asia and Africa. Pulmonary infection is asymptomatic or only mildly symptomatic in the infected person. Some infected persons may suffer flu-like symptoms. H. capsulatum appears to have precise growth requirements related to humidity, acidity, temperature and nitrogen content. It flourishes in soil fertilized by bird droppings, and is carried in bat guano, although birds themselves are not infected with H. capsulatum, bats' intestinal systems may be colonized with the organism. However, chickens are known to harbor the organism in their feathers. For example, H. capsulatum has been traced to chicken feathers in pillows. Chicken houses and bat guano under bridges and their environs are notorious sources of H. capsulatum infection.

Histoplasmosis has also been found in urban settings and is occasionally referred to as an urban disease as well. In urban settings where the soil is disturbed, the fungus spores become air borne. The University of Texas Southwest Medical Center reported between 600 and 700 cases of Histoplasma infection during a 20-year period when buildings were under construction. Although a bird sanctuary existed in the area, most cases occurred in employees who had no direct contact with the sanctuary. The spores invaded buildings through air ducts.

An outbreak of histoplasmosis occurred in 384 students in a junior high school in Ohio. On Earth Day, a courtyard was raked and swept, and the entire school building was contaminated with air containing Histoplasma spores. The epidemic was short-lived and influenza-like. In 1975, bird droppings swept from the roof of a courthouse in Arkansas were distributed through the building by window air-conditioners. Overall, human histoplasmosis is considered usually to be an asymptomatic and clinically insignificant infection. In the vast majority of the many millions of infected persons, infection and recurrent infection follow a generally benign course.

The number of persons with the more severe complication, fibrosing mediastinitis, is a small fraction, estimated to total only a few hundred in the US, of the millions of individuals infected by histoplasmosis. It is not known why some individuals are predisposed to excessive immune response to the organism, which leads to excessive scarring and obstruction of major vessels or airways that characterizes FM. [Patients with deficient immune systems who are exposed, develop disseminated histoplasmosis, which is at the opposite end of the spectrum from FM, in which patients have excessive immune response to the organism. The spores are merely contained in place, and may actually be dead, but are not really destroyed, and that may be part of the problem. They persist for years, maybe indefinitely, and can release antigen to stimulate ongoing immune response.] Calcification of the infected lymph nodes is a component of healing of a chronic granulomatous process. When calcium stones of substantial size are extruded into the airways, they may cause bronchial obstruction.

Symptoms

Typically, people with fibrosing mediastinitis have become infected with H. capsulatum as children but the symptoms begin in most patients between the ages of 21 and 40 years of age. There is no evidence that it has a preferred ethnic origin or gender and it seems to affect as many males as it does females.

Patients with histoplasmosis-related fibrosing mediastinitis present with signs of fatigue, shortness of breath (dyspnea), cough with (hemoptysis) or without blood, chronic lung (pleuritic) pain and recurrent pulmonary infection. Typically these symptoms occur because there is an occlusion of one of the main vessels in the body such as the superior vena cava (the vessel that returns blood from the head and neck, upper limbs, and thorax to the right atrium formed in the superior mediastinum by union of two brachiocephalic veins), the central airways, esophagus, or pulmonary arteries and/or veins. Superior vena cava syndrome, the swelling that develops in some patients due to obstruction of the vena cava, is a common symptom. Some patients do not have the syndrome, despite having obstruction of the SVC, if collateral alternative vessels enlarge sufficiently to return blood to the heart. Cough and shortness of breath are the most common symptoms when obstruction of the central airways is occurring. Pulmonary venous obstruction usually presents with shortness of breath and coughing blood (hemoptysis). Symptoms can be present for years before diagnosis and before there is a life-threatening event.

Patients with idiopathic fibrosing mediastinitis present symptoms of fever, chills, sweats, shortness of breath, coughing and severe chest pains.

Causes

In the majority of patients, histoplasmosis-related fibrosing mediastinitis is kicked off by the body's abnormal excessive immune reaction to exposure of Histoplasma capsulatum or histoplasmosis, the fungus found in soil in the epidemic region of the United States along the Mississippi and Ohio River valleys. Although the fungus resides in the soil, and the fungus is fertilized by bird droppings, birds are not themselves infected. Spores become airborne when the soil is disturbed, and birds and bats also transport the spores.

Idiopathic fibrosing mediastinitis is not related to histoplasmosis. It has been reported in the setting of autoimmune disease, Behcet disease, rheumatic fever, and radiation therapy, severe viral infections of coxsackieB, or trauma. In addition, it can occur in association with other idiopathic fibroinflammatory disorders such as retroperitoneal fibrosis, sclerosing cholangitis, Ridel thyroiditis, and pseudotumor of the orbit.

Affected Populations

It is estimated that, of the population who contract histoplasmosis, less than 1% of that group has an excessive healing response to the fungal infection that is the basis of FM. Reliable prevalence information is not available, but the affected population of histoplasmosis-related fibrosing mediastinitis is estimated to be only a few hundred people in the United States. The number of persons with idiopathic fibrosis mediastinitis is estimated to be several dozen in the United States.

Standard Therapies

There is no standard therapy for either form of fibrosing mediastinitis. Currently there are no drugs identified that will stop the histoplasmosis-related fibrous tissue from growing. Some have reported the tissue may grow 1 mm per year.

Individual reports describe treatment of patients with idiopathic fibrosing mediastinitis with the following drugs: tamoxifen, prednisone, non-steroid anti-inflammatory medication such as indomethacin, and immunosuppressants such as azathioprine. There is not good data about the effectiveness of these treatments. If there is fluid build-up, patients are treated with a diuretic therapy, which may require supplementing potassium. Antibiotics can be used to treat complications such as pneumonia and chest infections. Corticosteroids such as prednisone can cause serious side effects. It has been demonstrated that carefully supervised cardiovascular exercise workouts at least four days a week can improve a patient's functional status and sense of well-being.

Diagnosis
Diagnosing both forms of fibrosing mediastinitis is best accomplished by chest CT, a scan that shows the abnormal tissue in the mediastinum (the space between the lungs). A ventilation/perfusion nuclear medicine scan is the best test to show the location of any abnormality in the distribution of blood flow to each lung. Sometimes surgical biopsy of the abnormal tissue in the mediastinum is needed to exclude malignancy such as a lymphoma, especially if the CT scan shows that the tissue does not have dense calcification, which is typical for the form that occurs after histoplasmosis.

If the patient has occlusion of the vena cava and there are collateral veins that have developed, the superior mediastinum may be widened. Pneumonia and/or collapse of a lung are sometimes present when the central airways are affected. Pulmonary venous obstruction will show localized pulmonary hypertension. A Magnetic Resonance Angiography (MRA) can be helpful in special circumstances.

Diagnosis in most cases is delayed, often for a period of years. Erroneous initial diagnoses include pneumonia, chronic obstruction lung disease, pulmonary embolism with infarction, and, in a few, mitral stenosis and congestive heart failure either as independent diagnoses or together, a symptom complex produced by obstruction of the pulmonary veins as they enter the left atrium.

Treatment:
Treatment options include systemic antifungal or corticosteroid treatment, local therapy for complications and possibly surgical resection. Each option has its complications and risks associated.

Itraconazole is an oral antifungal treatment which is sometimes used to treat patients who are believed to have contracted fibrosing mediastinitis from the histoplasma organism. There is limited evidence or clinical studies to indicate that any antifungal therapy will control FM, but treatment is reasonably safe and some data suggest it may help in some patients.

If there is occlusion of the superior vena cava or pulmonary veins and arteries, it may be possible to utilize balloon dilation and/or the placement of a stent(s) to open the vessels. These methods of treatment have been successful in a number of patients. It is also possible to perform a surgical bypass of the occluded vena cava by using a spiral vein graft. The most common tool to manage the occlusion of vessels involves the placement of stents in the vessel.

If the scar tissue in FM is localized, and in the form of a mass, surgical resection may improve symptoms, but is very high risk and appropriate for very few patients. This option may require extensive reconstruction of the vascular or airways structures. Procedures of this nature are only offered at a few medical locations. This is not a preferred method of treatment and should only be used in the most extreme cases due to a high level of morbidity and mortality. Very rarely, surgical reconstruction of serious airway obstruction may be life-saving, but should only be done by thoracic surgeons who are very experienced with fibrosing mediastinitis.

The mortality rates for fibrosing mediastinitis have been reported as high as 30% and are typically the result of infection, coughing blood (hemoptysis) or heart disease caused by thickening of the heart muscle. If both lungs of a patient are involved the mortality rate may be higher.

Investigational Therapies

James Loyd, M.D., Professor of Medicine, Division of Allergy, Pulmonary & Critical Care at Vanderbilt University School of Medicine in Nashville, Tennessee, is conducting a study of fibrosing mediastinitis, using persons with fibrosing mediastinitis who voluntarily submit their medical test results. For more information, please contact:

James E. Loyd, MD
Vanderbilt University Medical Center
Nashville, TN 37232-2650
615-322-3412
jim.loyd@vanderbilt.edu

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222
TTY: (866) 411-1010
Email: prpl@cc.nih.gov

For information about clinical trials sponsored by private sources, contact:
www.centerwatch.com

References

TEXTBOOKS
Carol A. Kauffman, MD. 2003. Clinical Mycology. Chapter 18: Histoplasmosis. 285- 298. Oxford University Press, Inc.

Mediastinal Fibrosis. 2001. W.B. Saunders Company.

ARTICLES
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. (2001). Fibrosing Mediastinitis. Radiographics. 2001;21:737-757.

Robert A. Goodwin, James E. Loyd, Robert M. Des Prez. Histoplasmosis in Normal Hosts. Medicine. 1981; 60: 231-266.

James P. Luby, Paul M. Southern, Jr., Charles E. Haley, Kirby L. Vahie, Robert S. Munford, and Robert W. Haley. Clinical Infectious Diseases. 2005;41:170-176.

Angela M. Davis, Richard N. Pierson, and James E. Loyd. Mediastinal Fibrosis. Seminars in Respiratory Infections. 2001. 16:119-130.

James E. Loyd, Barry F. Tillman, James B. Atkinson, Roger M. Des Prez. Mediastinal Fibrosis Complicating Histoplasmosis. Medicine. 1988. 67:295-309.

FROM THE INTERNET
James Loyd, MD, Lucille Enix, Candace McIntosh. Idiopathic Fibrosis Mediastinitis Questions and Answers. http//www. fibrosing-mediastinitis.com

Resources

Genetic and Rare Diseases (GARD) Information Center
PO Box 8126
Gaithersburg, MD 20898-8126
Tel: (301)251-4925
Fax: (301)251-4911
Tel: (888)205-2311
TDD: (888)205-3223
Email: http://rarediseases.info.nih.gov/GARD/EmailForm.aspx
Internet: http://rarediseases.info.nih.gov/GARD

Fibrosing Mediastinitis Informational Website
Email: tlewy1@yahoo.com
Internet: http://www.fibrosing-mediastinitis.com

Sunday, October 2, 2011

Latest

Hi all. It's been 2 1/2 years since my last angioplasty. I still feel pretty good. In fact, I recently completed a hike and climb to Half Dome in Yosemite. The higher altitudes are a bit of a challenge, but this was a personal thing I wanted to accomplish. It was slow-going, but I did it.

I am hoping to make it another year and a half before I have to have another angioplasty to open my stents.


A Brief Film of My Angioplasty

Wednesday, June 15, 2011

Dr. Abraham Rothman Ahead of Current Research

I found this study published in March 2001. Dr. Rothman did this exact procedure on me in May 2000 at UCSD.

Treatment of Pulmonary Artery Compression Due to Fibrous Mediastinitis With Endovascular Stent Placement*
Alejandro Guerrero, BA, Eric K. Hoffer, MD, Leonard Hudson, MD, FCCP, Paul Schuler, MD, FCCP and Riyad Karmy-Jones, MD

We present the case of a 32-year-old woman with high-grade right pulmonary artery stenosis secondary to fibrous mediastinitis. The patient was managed with balloon angioplasty and stent placement. Only 15 cases of this nature have been reported in the literature, and this is one of the first to be managed with endovascular stent placement.

Fibrous mediastinitis is a rare condition first described in 1855 by Nathan Oulmont.1 It is typically associated with mycobacterial and mycotic infections.2 Patients typically present with superior vena cava (SVC) syndrome.34 Most cases have a benign clinical course until the lesion constricts a major mediastinal structure.2 Fifteen other cases of fibrous mediastinitis with pulmonary artery compression have been described in the literature.56789101112 In the past 10 years, endovascular approaches have provided an effective treatment option for those individuals suffering from SVC syndrome.1314 Recent advances in endovascular techniques have allowed the dilation and stenting of the pulmonary artery. To our knowledge, only one other case of fibrous mediastinitis has been managed with pulmonary artery endovascular stenting.

A 32-year-old woman from the Mississippi Valley presented with severe shortness of breath and chronic cough. Physical examination demonstrated distended neck veins and symptoms consistent with SVC syndrome. Chest radiograph revealed an area of calcification in the right parasternal region at the level of the third rib (Fig 1 ). A pulmonary perfusion scan was performed that indicated essentially no perfusion to the right lung. A CT scan was performed that revealed a lesion adjacent to the right main pulmonary artery. The patient underwent two mediastinoscopies. Frozen section evaluation and cultures demonstrated a fibrous histology with no evidence of mycobacterial or fungal infection. The patient was prescribed an anti-inflammatory steroid regimen, with some resolution of the SVC syndrome. A CT scan demonstrated a mass approximately 3.0 cm by 2.5 cm by 2.0 cm and SVC stenosis with significant collateral veins. Peripheral administration of contrast was unable to visualize the right pulmonary circulation, so a catheter was employed to administer the contrast proximal to the right pulmonary artery (Fig 2 ). This showed an abrupt stenosis of the right main pulmonary artery. An angiographic study revealed 95% stenosis of the right pulmonary artery at its junction with the right lower pulmonary artery, and total occlusion of the right upper pulmonary artery (Fig 3 ). The stenosis was dilated and stented with a Palmaz 424 medium catheter (Cordis/Johnson and Johnson; Miami, FL) over a 5.8F 10-mm balloon catheter. A poststent angiogram confirmed the appropriate placement of the stent and patency of the right lower and middle pulmonary arteries (Fig 4 ). The patient was prescribed aspirin, 5 grains tid, and discharged.

Shortly after the stent placement, the patient had complete resolution of symptoms. At 3-month follow-up, she had continued absence of symptoms, and a pulmonary perfusion scan indicated appropriate ventilation and perfusion to the right lower and middle lobes.

Fibrous mediastinitis is a rare condition that was recognized as a cause of SVC obstruction by Osler in 1903.3 Cases may be idiopathic or associated with tuberculosis, histoplasmosis, sarcoidosis, silicosis, or other fungal infections.2 Mediastinoscopy is warranted to distinguish this inflammatory process from a malignancy. Patients with fibrous mediastinitis generally have a benign clinical course until a mediastinal structure is compressed.15 The first and most common structure affected is the SVC, but involvement of the pulmonary artery, phrenic nerve, recurrent laryngeal nerve, and pulmonary veins have also been documented.2

SVC stent placement is an effective approach to managing SVC syndrome associated with fibrous mediastinitis.1213 In addition, steroid therapy may be an appropriate option in patients with mild obstruction, or as an adjunct to other treatment approaches, although this has not been established.16

Endovascular pulmonary artery angioplasty has been used extensively in pediatric patients with tetrad of Fallot.17 The use of this approach in treating pulmonary stenosis with fibrous mediastinitis has been employed only recently.11 We believe it is an appropriate option that should be considered when presented with such a condition.

References

↵ Oulmont, N (1855) Des Oblitérations de la veine cave supérieure. J.B. Ballière. Paris, France:
↵ Fauci, AS, Braunwald, E, Fuselbacher, KJ, et al Harrison’s principles of internal medicine 14th ed. 1998,1476 McGraw-Hill. San Francisco, CA:
↵ Osler, W On obliteration of the superior vena cava. Johns Hopkins Hosp Bull 1903;14,169
↵ Schowengerdt, CG, Suyemoto, R, Main, FB Granulomatous and fibrous mediastinitis: a review and analysis of 180 cases. J Thorac Cardiovasc Surg 1969;57,365-379 MedlineWeb of Science
↵ Sherrick, AD, Brown, LR, Harms, GF, et al The radiographic findings of fibrosing mediastinitis. Chest 1994;106,484-489 Abstract/FREE Full Text
↵ Berry, DF, Buccigrossi, D, Peabody, J, et al Pulmonary vascular occlusion and fibrosing mediastinitis. Chest 1986;89,296-301 Abstract/FREE Full Text
↵ Shure, D, Gregoratos, G, Moser, KM Fiberoptic angioscopy: role in the diagnosis of chronic pulmonary arterial obstruction. Ann Intern Med 1985;103(Pt 1),844-850
↵ Farmer, DW, Moore, E, Amparo, E, et al Calcific fibrosing mediastinitis: demonstration of pulmonary vascular obstruction by magnetic resonance imaging. AJR Am J Roentgenol 1984;143,1189-1191 FREE Full Text
↵ Hicks, GL, Jr Fibrosing mediastinitis: causing pulmonary artery and vein obstruction with hemoptysis. NY State J Med 1983;83,242-244 Medline
↵ Zorn, SK, Schachter, EN, Smith, GJ, et al Pulmonary artery obstruction with fibrosing mediastinitis. Lung 1978;155,91-100 MedlineWeb of Science
↵ Deblanco, TL, Medina, JR, Sadler, TR, et al Bilateral pulmonary artery obstruction due to fibrosing mediastinitis: case report. Mil Med 1976;May; 141,335-339 MedlineWeb of Science
↵ Kandzari, DE, Warner, JJ, O’Laughlin, MP, et al Percutaneous stenting of right pulmonary artery stenosis in fibrosing mediastinitis. Catheter Cardiovasc Interv 2000;49,321-324 CrossRefMedlineWeb of Science
↵ Chazova, I, Robbins, I, Loyd, J, et al Venous and arterial changes in pulmonary veno-occlusive disease, mitral stenosis and fibrosing mediastinitis. Eur Respir J 2000;15,116-122 Abstract
↵ Dodds, GA, III, Harrison, JK, O’Laughlin, MP, et al Relief of superior vena cava syndrome due to fibrosing mediastinitis using the Palmaz stent. Chest 1994;106,315-318 Abstract/FREE Full Text
↵ Mahajan, V, Strimlan, V, Ordstrand, HS, et al Benign superior vena cava syndrome. Chest 1975;68,32-35 Abstract/FREE Full Text
↵ Horikoshi, M, Ebina, A, Imai, T, et al Retroperitoneal fibrosis with involvement up to the mediastinal space. Nihon Kyobu Shikkan Gakkai Zasshi 1996;34,331-335 Medline
↵ Pihkala, J, Nykanen, D, Freedom, RM, et al Interventional cardiac catheterization. Pediatr Clin North Am 1999;46,441-464

Wednesday, December 8, 2010

Fibrosing Mediastinitis: Causes, Diagnosis, and Treatment

By Meredith E. Pugh, MD; and James E. Loyd, MD

Dr. Pugh is Clinical Fellow in Pulmonary and Critical Care, and Dr. Loyd is Professor, Vanderbilt University Medical Center, Nashville, TN.

Drs. Pugh and Loyd have disclosed no significant relationships with the companies/organizations whose products or services may be discussed within this chapter.

Objectives

1.Define the two major syndromes of fibrosing mediastinitis.
2.Describe the incidence and prevalence of fibrosing mediastinitis.
3.Understand the clinical and radiographic features of post-histoplasmosis fibrosing mediastinitis.
4.Understand the role of intravascular stenting in post-histoplasmosis fibrosing mediastinitis.
5.Describe the clinical and radiographic features of idiopathic proliferative fibrosing mediastinitis.
Key words: fibrosing mediastinitis; idiopathic proliferative fibrosing mediastinitis; late complications of histoplasmosis; mediastinal granuloma

Abbreviations: FM = fibrosing mediastinitis; IPFM = idiopathic proliferative fibrosing mediastinitis; MG = mediastinal granuloma; MIF = multifocal inflammatory fibrosclerosis; SVC = superior vena cava

At least two different syndromes of fibrosing mediastinitis (FM) can be distinguished from other mediastinal disorders. The vast majority of FM in the United States (>90%) occurs as a late consequence of Histoplasma capsulatum infection (post-histoplasmosis FM, or post-histo FM) and is characterized by obstruction of central vessels and airways by proliferative tissue, usually containing ectopic calcification. Another syndrome, idiopathic proliferative fibrosing mediastinitis (IPFM), is a rare disorder that is characterized by extensive mediastinal proliferation without calcification and may affect additional extrathoracic sites concomitantly. Many synonyms for FM have been used, including mediastinal fibrosis or sclerosing mediastinitis, but fibrosing mediastinitis is now the preferred term.

Definition of Fibrosing Mediastinitis
Simply identifying fibrosis in the mediastinum is not in itself sufficient to constitute a diagnosis of FM. In addition to demonstrating the proliferative process in the mediastinum, the definition of post-histo FM should include significant obstruction of major vessels or airways1 in the absence of malignancy, emboli, or other relevant diseases that might otherwise explain this finding. Confidence in a clinical diagnosis of post-histo FM is strengthened by the presence of heavy calcification within the proliferative material, which is located at sites of mediastinal lymph nodes. An original classification used to define FM was based on a thickness of the encompassing fibrotic capsule being >10 mm,2 but that pivotal information is usually not available except postmortem. Other late complications of histoplasmosis, including mediastinal granuloma (MG), may similarly manifest a component of mediastinal inflammation and scarring, but it is important to distinguish these complications from FM because they are not as invasive and thus their outcomes are more favorable.3,4 IPFM is characterized by a proliferative process within the mediastinum that can lead to obstruction of major vessels or airways, but unlike post-histo FM, this form is not associated with heavy calcification.

Incidence and Prevalence of Fibrosing Mediastinitis
Anecdotal data are the only source for information about the prevalence of FM. The condition appears to be rare, although currently it is recognized more commonly than had been described in the past; this is probably related to broader application of improved imaging methods. We reviewed FM two decades ago and identified 71 patients in the English literature.1 In the last 2 decades, our center has consulted in the cases of another 200 FM patients. Referral bias clearly contributes to this experience, as access to the Internet facilitates patient self-referral to centers with interest and expertise. In the geographic regions near the Mississippi River, endemic Histoplasma infects the vast majority of the population3 and crude estimates are that roughly one in 20,000 among those infected go on to develop FM,5 usually several years after the initial disease. Certain individuals appear to have an underlying predisposition to post-histo FM.6 The prevalence of the other form of FM, IPFM, is similarly not known, but appears to be far less common, as the largest valid series included only six patients.7 Our center has consulted on 20 cases of IPFM in the past decade.

Post-Histoplasmosis FM
Characteristics
Histoplasmosis can manifest in a wide variety of clinical syndromes,3,5 but FM is the most severe late complication1 and is characterized by invasive fibrosis that encases the previously infected mediastinal or hilar lymph nodes. Post-histo FM usually presents in the third and fourth decades and is manifested by symptoms that result from occlusion of central vessels and airways.1,2,8 Patients often report symptoms for several years prior to diagnosis, and imaging reveals that the proliferative tissue usually contains heavy calcification (Fig 1). Distinction from other syndromes is usually possible clinically, but a few patients have syndromes that overlap. For instance, MG is a different late complication of histoplasmosis that is characterized by a mass comprising mostly semiliquid material within a thin fibrotic capsule (<5 mm), which occasionally may compress compliant structures such as the superior vena cava (SVC) or esophagus, but generally MG is not invasive.3,4 MGs may develop fistulae and drain their semiliquid contents, often into the esophagus, sometimes leading to the communicating cavity of the MG becoming superinfected by enteric bacteria.4,9 MG may demonstrate heterogeneity in the density of the mass, a finding that may also be seen in necrotic lymphoma, but not FM. Imaging cannot distinguish the capsule thickness of post-histo FM to definitively separate it from MG, so it is either the severe vascular and airway occlusion in post-histo FM or the heterogeneous density in MG that helps to distinguish between the two syndromes. In rare cases, however, features overlap between both syndromes.

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Figure 1. Chest radiograph, nuclear medicine perfusion scan, and CT scan of a 39-year-old man with post-histo FM. Upper left, posteroanterior chest radiograph demonstrates small right pleural effusion and increased opacity in right lower medial lung zone. Lower left, nuclear medicine perfusion lung scan demonstrating severe reduction of perfusion of right lung. Upper right, coronal view of chest CT scan demonstrating subcarinal mass lesion containing a 2.5-cm densely calcified portion. Lower right, transverse CT view showing right pleural effusion and calcified mass causing narrowing of right main bronchus and right pulmonary artery.

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Diagnosis
The diagnosis of post-histo FM is a clinical one: Heavy ectopic calcification in a proliferative mediastinal lesion causing major vascular or airway occlusion, in the absence of other conditions such as known malignancy or emboli, is sufficiently characteristic such that a biopsy is not needed for diagnosis in most cases.4,5 In the United States, the cause of this presentation is nearly always former histoplasmosis, which itself may have been unrecognized because it was initially asymptomatic or transient.

Biopsy rarely adds important unanticipated findings, and hemorrhage during surgery is a substantial risk because of large venous collaterals in the chest wall and mediastinum as a result of SVC obstruction, and/or systemic arterial collaterals (bronchial or chest wall) that develop in the setting of pulmonary vascular obstruction. Inspection for calcification is best done by CT scan in the absence of radiographic contrast agents. Plain chest radiography often minimizes the extent of mediastinal proliferation (see Figure 1) and may not demonstrate the calcification, even when it is substantial. The duration required for calcification to develop may be several years, although post-histo FM cases without calcification have occasionally been described.10 Although a few organisms may be found in the small center of the FM lesion, they are not usually accessed by surgical biopsy. Antigen testing for Histoplasma is usually negative in FM, but serologic studies for antibodies to Histoplasma may be positive.5 Nuclear medicine perfusion lung scanning provides information about the regional distribution of blood flow and can help in determination of the critical prognostic feature of whether or not both lungs are affected. Similarly, the absence of pulmonary hypertension or right ventricular changes by echocardiography provides reassurance that only one lung is affected, at least at the time of such evaluation.

Catheterization with comprehensive pulmonary arterial and venous hemodynamic evaluation is the most definitive method to clarify the extent and location of pulmonary vascular obstruction. Because noninvasive imaging is usually compelling, careful planning makes it feasible to consider mechanical intervention during the initial catheterization, thus minimizing the number of separate interventional procedures. Catheter-based methods for both the diagnostic component and intervention require specialized expertise, in particular for pulmonary venous obstruction. In addition to the skills of stent selection, placement, and deployment, the basics of obtaining access to the left atrium across its septum and correct interpretation and analysis of pressure gradients are critical skills. As the pulmonary venous system is rarely the site of primary disease in adults, in many medical centers the most relevant experience is possessed by pediatric interventional cardiologists.

The presence of ectopic calcification identified on CT scan is a pivotal diagnostic finding. The mechanisms of ectopic calcification are poorly understood and it may occur in a variety of other conditions, including sarcoidosis, Castleman disease, and certain malignancies (eg, osteosarcoma). However, heavy calcification of highly invasive central vascular and airway proliferation is nearly always attributed to prior histoplasmosis. Of interest, calcium binding protein is integral to the pathogenesis of histoplasmosis.11 The lung parenchymal calcifications caused by histoplasmosis are more prominent than those from tuberculosis12 and the presence of splenic punctate calcifications is highly indicative of prior histoplasmosis. Integration of all the clinical data and radiographic findings, and most importantly a recognition that mediastinal calcification in this circumstance is a signature of prior histoplasmosis, is essential to establish a correct diagnosis of post-histo FM. For example, in one report of the pathologic features of 30 patients with “idiopathic fibroinflammatory...lesions of the mediastinum,” the authors did not analyze the radiographic data, but did show a CT with a very large subcarinal calcification, confirming that post-histo FM cases were included therein, but were not attributed as such.13 Sufficient data were not included to permit assessment of how many other cases were erroneously labeled as idiopathic.

Clinical Manifestations and Course
SVC obstruction is a common manifestation and central airways, pulmonary arteries or veins, or the pericardium may be involved in any combination in post-histo FM.1,2,4 Paratracheal or right hilar node involvement often causes SVC or right pulmonary artery obstruction, while subcarinal nodes often obstruct central airways or vessels. The specific group of nodes affected relates to the site draining the parenchymal lung infection; often a large calcified parencyhmal histoplasmoma marks the site of previous primary disease.

Fortunately, the vast majority of FM patients (~80%) manifest loss of function of only one lung, usually the right, and progression of FM to affect the contralateral lung after the original diagnosis is uncommon in our experience. Unilateral loss of lung function may have surprisingly few symptoms in many patients. Although significant morbidity with chronic intermittent chest pain or hemoptysis does occur, our recent experience suggests that long-term survival is generally favorable for this cohort. Therefore, the value of intervention when only one lung is affected is uncertain. When multiple central vessels or the airway of the same lung are affected, the likelihood of restoring function becomes progressively lower, especially when the airway is involved. Hemoptysis is common, usually from systemic arterial ingrowth into the affected lung, from either bronchial arteries or systemic arteries of the chest wall. When hemoptysis is substantial, therapeutic systemic arterial embolization may be helpful, at least transiently. Anticoagulation/antiplatelet therapy or systemic hypertension may exacerbate hemoptysis when the systemic arterial vasculature to a lung is enlarged and hyperemic. Chronic pleuritic chest pain is usually periodic and typically is localized in the hemithorax with pulmonary vascular occlusion. Pain severity varies greatly among different patients; it can usually be controlled with nonsteroidal antiinflammatory drugs, but in a few patients, pain is sufficiently severe to require chronic narcotics.

Although only a small portion of patients (~20%) have FM obstructing structures of both lungs, this syndrome is usually life threatening. Our center has evaluated 20 patients with bilateral posthisto FM in the past two decades, with fatal outcomes in 14 of these to date.14 Any combination of obstruction of vasculature or airways may occur, but the combination of right pulmonary artery followed later by left mainstem bronchial obstruction is a common one. When obstruction predominantly affects the pulmonary veins, progressive right heart failure and a syndrome that physiologically resembles mitral stenosis may occur.15,16 Pulmonary venous obstruction causing interstitial edema has often been mistaken for pneumonia or interstitial lung disease, and some FM patients have received surgical lung biopsy only to have infarction diagnosed.

The course of FM is not well described. For many patients, the most disease progression appears to occur before diagnosis, but our experience suggests that post-histo FM does occasionally progress during follow-up. When vascular or airway obstruction does develop later, it usually occurs at sites where surrounding mediastinal proliferation encompassed them formerly. Posthisto FM rarely, if ever, extends to new sites where there was not mediastinal proliferation at the time of the initial diagnosis. Most patients with bilateral disease manifested involvement of both lungs at the time of presentation. Very rarely, we have seen patients who had a syndrome clinically consistent with post-histo FM, but who experienced surprising later improvement in vascular or airway obstruction. This was associated with resolution of a mediastinal lesion that had evidence for heterogeneous density, suggesting this was spontaneous drainage of a mediastinal granuloma, rather than true FM.

Treatment
No pharmacologic treatment has been shown to affect the outcome of this form of FM.1,2,5 Indeed, we do not recommend pharmacologic therapy for post-histo FM because we have never seen a response. Because the condition is desperate, however, and because oral antifungal therapy is relatively safe, this therapy is recommended by many clinicians. A few case reports describe anecdotal responses to antifungal therapy, but these cases were likely other syndromes, such as MG, which can show decrease in size of a mediastinal mass, spontaneously or during antifungal therapy.

Surgery should be approached with great caution in patients with fibrosing mediastinitis. A common surgical complication is severe hemorrhage relating to distended venous collaterals from SVC obstruction, or to systemic arterial collaterals when pulmonary vascular obstruction exists. The proliferative material of post-histo FM is extremely dense and is often described by surgeons as “concrete” that invades and incorporates the vascular and airway wall, making blunt dissection nearly impossible. If surgery is to be undertaken, surgeons experienced in fibrosing mediastinitis should participate and should have a specific and achievable operative goal. Surgical reconstruction has rarely been described9 and even lung transplantation has surprisingly been possible (M. Chakinala, MD; personal communication; May 2, 2008), but FM presents an enormous challenge to even the most experienced surgeons.

Intravascular stenting of the pulmonary artery, vein, or SVC during cardiac catheterization has been helpful in some patients.17 Stenting should be considered for patients who are at highest risk, as when FM affects critical structures of both lungs. Noninvasive studies, including CT scans, echocardiography, and nuclear medicine perfusion scans, can reliably identify which patients have bilateral involvement and make it feasible to plan interventional as well as diagnostic catheterization as one procedure. Catheterization is the only approach to confirm whether pulmonary vascular lesions are anatomically and technically amenable to stenting. We find that many radiologists may not describe pulmonary venous obstruction, whereas pulmonary arterial or airway involvement is usually correctly recognized. Comprehensive attention to inflow, outflow, and airflow is essential to successful restoration of lung function. Assessment and stenting of pulmonary veins requires gaining access to the left atrium across the atrial septum, which requires special techniques and expertise. Catheterization to intervene for bilateral disease is performed under general anesthesia with continuous transesophageal echocardiography and endotracheal intubation, which facilitates endobronchial inspection if concern remains about airway involvement. We no longer routinely perform bronchoscopy in all patients because bronchial arterial friability has been associated with provocation of severe hemoptysis after bronchoscopy in some patients. Target areas for revascularization should obviously be chosen at sites where airways are not significantly obstructed, which generally are readily identifiable by noninvasive imaging. Superior vena caval stenting should not be performed simply for an obstructed SVC without the clinical syndrome. Such occlusion is fully compensated in many patients by development of venous collaterals in chest wall, mediastinum, and esophagus (“downhill varices”). Infusion of radiographic contrast simultaneously in both upper extremities can be helpful during CT to evaluate the SVC and collaterals and to distinguish thrombus from the flow void of venous return from a noncontrasted extremity.

Autoamputation of one lung is rarely life threatening, so we do not encourage pulmonary vascular stenting for this subgroup, as the long-term risk is not known. Rarely, however, we have stented unilateral vascular occlusion to relieve severe symptoms, such as exertional dyspnea probably arising from wasted ventilation, or refractory pain and pleural effusion related to infarct-in-progress.

Stenting is not always feasible and has many possible complications, some of which are serious. In our experience with more than 50 stents for FM during the past decade, roughly two thirds of patients whose lesions can be stented experience significant hemodynamic benefit, including substantial clinical improvement in half of these. We have found that approximately 25% of patients taken to the catheterization suite for anticipated intervention have lesions that either are not amenable to stent implantation or would not benefit from stent implantation. Furthermore, some patients in whom a stent is appropriately placed do not have full restoration of blood flow owing to an inability to expand the stent to full native vessel diameter. Stent placement can have serious complications; multiple reports have described laceration of the aorta after placement of SVC stents.18,19 We have seen a variety of complications of pulmonary vascular stenting, including pulmonary artery dissection, reperfusion pulmonary edema, pulmonary hemorrhage, hypoxia requiring supplemental oxygen for several weeks, cerebral vascular accident, and in-stent thrombosis. Fatal complications of stenting are possible, such as nearly occurred in a 30-year-old woman whose disease resulted in her entire cardiac output passing through a stenotic right lower pulmonary artery. During routine angiography in the patient’s right pulmonary artery, a large pulmonary artery dissection developed with immediate hypotension, but fortunately the catastrophe was successfully managed by emergent extracorporeal membrane oxygenation and stenting of both the stenosis and the dissection, so that she remains alive and even clinically improved 2 years later. Late complications of stents include recurrent stenosis inside or adjacent to the stent. These have been seen in roughly 20% of SVC or pulmonary vein stents. The need for anticoagulation to maintain stent patency adds an additional risk for hemorrhagic complications.

Airway occlusion presents similarly difficult management challenges. Placement of expandable mesh airway stents has been associated with rapid growth of intraluminal granulation tissue leading to recurrent obstruction. Airway management is especially challenging in patients with post-histo FM; experienced interventional airway experts are usually needed, and even then, success at restoring sufficient ventilation is not universal.

Idiopathic Proliferative Fibrosing Mediastinitis
Characteristics
In contrast to post-histo FM, the fibrous proliferation seen in IPFM characteristically lacks calcifications on CT imaging. IPFM may be localized to the thorax, but rarely is part of a multisite process as in multifocal inflammatory fibrosclerosis (MIF), which can involve the mediastinum as well as the retroperitoneum, anterior neck (sclerosing cervicitis), thyroid (Reidel thyroiditis), retro-orbital pseudotumor, and other sites.20,21 IPFM is often extensive and diffuse in contrast with post-histo FM, which is lymph node centered and limited to intrathoracic locations. For example, in one IPFM patient here, the fibrosis diffusely surrounded and encapsulated the entire trachea above the carina, extending cranially into the anterior neck as a palpable dense mass around the extrathoracic trachea. The clinical syndrome was sufficiently convincing for malignancy that she underwent three separate surgical procedures, including a neck biopsy, a parasternal anterior mediastinotomy (Chamberlain procedure), and finally a median sternotomy to rule out this possibility. IPFM is more rare than post-histo FM, but similarly affects patients in the third and fourth decades, although patient age in reported cases ranges from 13 to 64 years.7

Diagnosis
In patients with excessive tissue in the mediastinum but without significant calcification by CT scan, there are many possible causes, so diagnosis is not possible without biopsy.22 CT inspection for calcification of the lesion is most sensitive and specific in scans without radiographic contrast agents, which confound identification of calcification. Concomitant proliferation at an extrathoracic site contributes strong support for an IPFM diagnosis, but extrathoracic involvement is seen in only about half of patients with IPFM. It is rare that the diagnosis of IPFM is completely secure, because pathologic examination of all the abnormal tissue is rarely feasible. False-negative biopsies occur because the tissue sampled was simply superficial reactive tissue overlying a lymphoma or malignancy. In a patient with a provisional diagnosis of IPFM, if a later increase in the mediastinal tissue should occur, another deeper biopsy should be considered, as lymphoma has presented in this fashion in several patients.23 Excessive mediastinal tissue also has been described as the first sign of Wegener granulomatosis, so appropriate serologic testing should be performed.24

Clinical Course and Outcome
The cause of IPFM is unknown and its prognosis is unpredictable, but mortality from the disease seems rare. In most patients the excess tissue in the mediastinum is bulky and persists indefinitely, but is generally less invasive and obstructive than in post-histo FM. The course of IPFM is unknown, and our anecdotal experience suggests that the majority of patients have stable proliferation over the long term, but a few of our patients have experienced regression, either spontaneously or during therapy. An increase of proliferative material has led to a subsequent follow-up biopsy that yielded a diagnosis of lymphoma for many patients who were originally believed to have IPFM. Thus, the diagnosis of IPFM is not really secure unless another site typical for MIF is found. The proliferative material in IPFM appears to be less dense (hard rubber) than for post-histo FM (concrete). In our patient with IPFM encapsulating the entire trachea, surgical removal was performed via sternotomy, but the proliferative material recurred within 6 weeks. IPFM rarely appears to be life threatening, but a recent report describes fatality related to pulmonary venous obstruction in a 16-year-old boy in Greece after a 3-month illness.25 We have not seen fatality from IPFM in our referral base, in contrast to the high mortality seen in bilateral post-histo FM, as noted above.

Treatment
Individual case reports suggest that IPFM can sometimes respond to pharmacologic approaches, but the preferred agent(s) is not known. Treatment literature for retroperitoneal fibrosis or MIF may also have relevance because coexistence in many patients suggests they have similar pathogenesis. One IPFM radiology report describes three patients in whom the fibrosis decreased slightly during treatment with prednisone7; another report describes improvement in one patient after tamoxifen.26 In our experience, these treatments had minimal benefit for five IPFM patients. A recent report describes response to cyclosporine for MIF.20 Newer antiproliferative agents may be reasonable to consider, but may also carry inherent risk of obscuring diagnosis of an occult lymphoma.

Summary
Two distinctive syndromes of FM have different pathogenesis and treatment and should be distinguished from other mediastinal disorders, especially lymphoma. Most FM cases in the United States occur in a small subset of young adults who have an exuberant response to prior histoplasmosis. Post-histo FM is characterized by obstruction of central vessels and airways by calcified proliferative tissue and has high mortality in the subset of cases in which both lungs are affected. Pharmacologic responses do not occur in post-histo FM, but some patients appear to have benefited from vascular stents. The other form, IPFM, is a very rare disorder that probably occurs worldwide; it is characterized by diffuse, bulky mediastinal proliferation that sometimes is associated with concomitant extrathoracic sites of proliferation, such as retroperitoneal fibrosis, as in the systemic syndrome MIF. Pharmacologic responses are described anecdotally in IPFM and MIF. It is hoped that a better understanding of the pathogenesis and treatment of these disorders will be developed in the future.

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References
1.Loyd JE, Tillman BF, Atkinson JB, et al. Mediastinal fibrosis complicating histoplasmosis. Medicine 1988; 67:295-310
2.Goodwin RA, Nickell JA, DesPrez RM. Mediastinal fibrosis complicating healed primary histoplasmosis and tuberculosis. Medicine 1972; 51:227-246
3.Goodwin RA, Loyd JE, DesPrez RM. Histoplasmosis in normal hosts. Medicine 1981; 60:231-266
4.Parish JM, Rosenow EC III. Mediastinal granuloma and mediastinal fibrosis. Semin Respir Crit Care Med 2002; 23:135-143
5.Hage CA, Wheat LJ, Loyd JE, et al. Pulmonary histoplasmosis. Semin Respir Crit Care Med 2008; 29:151-165
6.Peebles RS, Carpenter CT, Dupont WD, et al. Mediastinal fibrosis is associated with HLAA2. Chest 2000; 117:482-485
7.Sherrick AD, Brown LR, Harms GF, et al. The radiographic findings of fibrosing mediastinitis. Chest 1994; 106:484-489
8.Davis AM, Pierson RN, Loyd JE. Mediastinal fibrosis. Semin Respir Infect 2001; 16:119-130
9.Case records of the Massachusetts General Hospital: Weekly clinicopathological exercises. Case 15-1991. A 48-year-old man with dysphagia, chest pain, fever, and a subcarinal mass. New Eng J Med 1991; 324:1049-1056
10.Shapiro BP, Sprung J, Scott K, et al. Cardiovascular collapse induced by positiondependent pulmonary vein occlusion in a patient with fibrosing mediastinitis. Anesthesiology 2005; 103:661-663
11.Sebghati TS, Engle JT, Goldman WE. Intracellular parasitism by Histoplasma capsulatum: fungal virulence and calcium dependence. Science 2000; 290:1368-1372
12.Straub M, Schwarz J. The healed primary complex in histoplasmosis. Am J Clin Pathol 1955; 25:727-741
13.Flieder DB, Suster S, Moran CA. Idiopathic fibroinflammatory (fibrosing/sclerosing) lesions of the mediastinum: a study of 30 cases with emphasis on morphologic heterogeneity. Mod Pathol 1999; 12:257-264
14.Martin JB, Prudhomme JB, Scott TA, et al. Features associated with mortality in fibrosing mediastinitis [abstract]. Am J Respir Crit Care Med 2005; 2:A204
15.Davis FW, Andrus EC. Mitral stenosis in facsimile. New Engl J Med 1954; 251:297-302
16.Trinkle JK. Fibrous mediastinitis presenting as mitral stenosis. J Thorac Cardiovasc Surg 1971; 62:161-162
17.Doyle TP, Loyd JE, Robbins IM. Percutaneous pulmonary artery and vein stenting: a novel treatment for mediastinal fibrosis. Am J Respir Crit Care Med 2001; 164:657-660
18.Recto MR, Bousamra M, Yeh T Jr. Late superior vena cava performation and aortic laceration after stenting to treat superior vena cava syndrome secondary to fibrosing mediastinitis. J Invasive Cardiol 2002; 14:624-629
19.Kappert U, Schulz CG, Waldow T, et al. Perforation of the ascending aorta: a late complication of superior vena cava stenting. Thorac Cardiovasc Surg 2006; 54:63-65
20.Al-Harthy F, Esdaile J, Berean KW, et al. Multifocal idiopathic fibrosclerosis: treatment of 2 cases with cyclosporine. J Rheumatol 2006; 33:358-361
21.Comings DE, Skubi KB, Van Eyes J, et al. Familial multifocal fibrosclerosis: findings suggesting that retroperitoneal fibrosis, mediastinal fibrosis, sclerosing cholangitis, Riedel’s thyroiditiss and pseudotumor of the orbit may be different manifestations of a single disease. Ann Intern Med 1967; 66:884-892
22.Worrell JA, Donnelly EF, Martin JB, et al. Computed tomography and the idiopathic form of proliferative fibrosing mediastinitis. J Thorac Imaging 2007; 22:235-240
23.Flannery MT, M Espino, Altus P, et al. Hodgkin’s disease masquerading as sclerosing mediastinitis. South Med J 1994; 87:921-923
24.Fernandez Guerra J, Cano Gomez S, Soto Campos JG, et al. Retroperitoneal and mediastinal fibrosis with serum p-ANCA increase: a new evidence of immunological etiology[In Spanish]? An Med Interna 1995; 12:622-623
25.Malagari K, Papiris S. Fibrosing mediastinitis causing rapidly progressive dyspnea, pulmonary edema and death in a 16 yr old male. Monaldi Arch Chest Dis 2004; 61:124-127
26.Savelli BA, Parshley M, Morganroth ML. Successful treatment of sclerosing cervicitis and fibrosing mediastinitis with tamoxifen. Chest 1997; 111:1137-1140
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Fibrosing Mediastinitis Up-to-Date

Fibrosing mediastinitis, also known as sclerosing mediastinitis or mediastinal fibrosis, is a disorder characterized by an excessive fibrotic reaction in the mediastinum which can result in compromise of airways, great vessels, and other mediastinal structures [1]. The condition usually is a sequel of histoplasmosis, and its morbidity is directly related to the location and extent of fibrosis within the mediastinum. The IDSA practice guidelines for the management of patients with histoplasmosis, as well as other IDSA guidelines, can be accessed through the Infectious Diseases Society of America's website [2].

The clinical issues related to fibrosing mediastinitis will be reviewed here. General issues regarding the presentation and treatment of pulmonary histoplasmosis are discussed separately. (See "Pathogenesis and clinical features of pulmonary histoplasmosis" and "Diagnosis and treatment of pulmonary histoplasmosis".)

ETIOLOGY

Fibrosing mediastinitis results from an excessive host response to a prior infectious process which has involved the mediastinal lymph nodes. The most common precipitating factor is infection with Histoplasma capsulatum, a dimorphic fungus that is found commonly in the southeastern, mid-Atlantic, and central United States.

Infection with H. capsulatum is subclinical in the vast majority of patients. It begins as a pulmonary process and typically disseminates to mediastinal lymph nodes and other reticuloendothelial organs before specific cell-mediated immunity develops and contains the fungus. Depending upon the inoculum and the extent of host response, the involved mediastinal lymph nodes can enlarge and coalesce into an inflamed caseous mass referred to as a mediastinal granuloma, or less commonly can lead to a sclerosing process called fibrosing mediastinitis. (See "Pathogenesis and clinical features of pulmonary histoplasmosis".)

It is unclear why a minority of patients infected with H. capsulatum proceed to develop fibrosing mediastinitis, but genetic influences on the immune response may play a role. As an example, one case-control study involving 19 consecutive patients with fibrosing mediastinitis and 21,086 cadaveric kidney donors serving as controls found that the relative risk of fibrosing mediastinitis was 3.3 among persons with the HLA-A2 antigen [3]. (See "Human leukocyte antigens (HLA): A roadmap".)

Pulmonary scintigraphy in fibrosing mediastinitis due to histoplasmosis.

Park HM, Jay SJ, Brandt MJ, Holden RW.

Abstract
The pulmonary scintigraphic findings from four patients with fibrosing mediastinitis due to histoplasmosis are reported. The ventilation/perfusion (V/Q) mismatch mimicked pulmonary emboli. However, in these cases the chest radiographs and/or gallium-67 scintigraphy were abnormal, suggesting mediastinal or hilar disease. Awareness of the nonembolic conditions that can result in V/Q mismatches is important in the interpretation of lung scans.

Pulmonary artery occlusion due to histoplasmosis.

Wieder S, White TJ 3rd, Salazar J, Gold RE, Moinuddin M, Tonkin I.

Abstract
Histoplasma mediastinitis with complete or partial pulmonary artery obstruction due to compression and/or intraluminal granuloma was diagnosed in five patients and surgically verified in two. The patients, ages 12-27 years, had cough, dyspnea (four cases), and hemoptysis (two cases). Radionuclide imaging showed unilateral absence of pulmonary perfusion and minimal diminution of ventilation. Differentiation of this inflammatory process from other causes of ventilation-perfusion mismatch, for example, congenital hypoplasia and certain acquired causes of arterial obstruction, especially thromboembolism, may be possible by correlating radiographs, laminograms, and clinical history. Angiography can delineate the extent of perfusion impairment and may suggest its cause.

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