Introduction

Fibrosing Mediastinitis (FM) is a rare condition that happens when there is too much production and buildup of scar tissue in the middle part of your chest, an area known as mediastinum.¹ This excessive formation of scar tissue leads to narrowing and eventually blocking important structures in your heart and lungs. The condition can cause severe health problems and even be life-threatening if not treated since these structures are vital for breathing and blood circulation.¹ However, fibrosing mediastinitis isn't always easy to diagnose because its symptoms aren't always clear and can mix up with other conditions.¹ Accurate diagnosis and differentiation of FM from other diseases are crucial for its effective management and treatment. This article discusses the diagnosis of fibrosing mediastinitis and how it can be distinguished from other medical conditions with similar symptoms.

Understanding fibrosing mediastinitis

Mediastinum in our body plays a crucial by housing and protecting vital structures such as the pulmonary arteries and veins (carry blood to and from the lungs), the superior vena cava (returns blood to the heart), the bronchi (move air to the lungs), and the esophagus (transports food and liquids from the mouth to the stomach).¹ Fibrosis, sometimes referred to as scar tissue, is a thick, inflexible tissue that forms as part of the body’s healing process.² In the case of FM, too much of this scar tissue builds up, making a thick, hard layer that leads to the narrowing and blocking of these important structures.¹

What are the symptoms of fibrosing mediastinitis?

The symptoms of FM might differ from person to person based on the location and extent of the fibrous tissue growth. However, common symptoms include:

• Dyspnea or shortness of breath, typically due to blockage of central airways or pulmonary vessels
• A general feeling of tiredness or reduced energy
• Coughing with blood in it or without blood 
• Chronic chest pain, often related to breathing or localised discomfort.
• Dysphagia or difficulty swallowing due to compression or blockage of the esophagus
• Swelling of arms and face
• Fever, chills, and sweats
• Puffiness of the face
• Headache and giddiness ^1,3

What causes fibrosing mediastinitis?

There are several conditions that can cause FM. These commonly include:

Histoplasmosis

This is a fungal infection that begins in the lungs and can cause inflammation when it spreads to the mediastinum. This inflammation can gradually turn into fibrous tissue, leading to fibrosing mediastinitis. More than 80% of cases of fibrosing mediastinitis are caused by it.^4,5

Aspergillosis

Fibrosing mediastinitis may eventually arise from lesions in the mediastinum and lungs caused by a rare fungal infection known as aspergillosis. Studies have shown that, despite being less common, it does contribute to the development of FM.⁶

Tuberculosis 

Tuberculosis can lead to mediastinal fibrosis, especially in the context of chronic infection.⁷

IgG4-related disease

IgG4-related disease is an autoimmune condition marked by elevated blood levels of IgG4 protein. This condition can cause inflammation and fibrosis in the chest region, thereby contributing to the formation of fibrosing mediastinitis.⁸

Some other less common conditions include:

• Fungal infections like blastomycosis and cryptococcosis
• Behçet’s disease
• Hodgkin’s disease
• Sarcoidosis
• Rheumatic fever
• Granulomatosis with polyangitis
• Severe viral infections of Coxsackie B
• If you have undergone radiation therapy to treat cancer it could also cause scarring in the mediastinal area^1,9,10

Idiopathic fibrosing mediastinitis

Sometimes, doctors may be unable to identify the exact cause of fibrosing mediastinitis. When this happens, it’s called idiopathic fibrosing mediastinitis. This means the condition manifests with no apparent cause. It can also appear with other similar conditions,  such as problems with the area around the kidneys (retroperitoneal fibrosis), bile ducts (sclerosing cholangitis), thyroid gland (riedel thyroiditis), or around the eyes (pseudotumor of the orbit).¹

Conditions with similar symptoms

Misdiagnosis of FM can occur due to its overlap with other conditions. Some of the conditions  with comparable symptoms are the following:

• Superior Vena Cava Syndrome
• Mediastinal Granuloma
• Sarcoidosis
• Acute or Subacute Adenitis
• Asthma 
• Pneumonia 
• Chronic Obstructive Lung Disease
• Pulmonary embolism with lung infarction¹.

Diagnostic approach to fibrosing mediastinitis

As we discussed earlier, because the symptoms of fibrosing mediastinitis sometimes mimic those of several other conditions, diagnosing it can be difficult. This makes differential diagnosis essential. In order to narrow down the possible causes for your symptoms, your doctor may have to make some careful comparisons with those of other possible conditions.¹ This makes it more likely that you will receive the best diagnosis and treatment for FM.

Your doctor's initial assessment for fibrosing mediastinitis often consists of a thorough medical history and a physical examination that is focused on symptoms. Upon examination, they conduct imaging tests to examine the mediastinum in detail in order to identify FM.^1,3

Imaging studies

The most commonly used imaging studies to identify FM are as below:

Chest x-ray

Your doctor may suggest an initial imaging test, such as a chest X-ray, to gather preliminary clues and help diagnose FM. Typical findings from an x-ray that is indicative of FM include:

• Abnormal widening of the mediastinum: The X-ray might show that your mediastinum is unusually wide. Often, this is the initial indication of an issue
• Distortion of normal structures: The usual clear lines and shapes of the chest structures might be distorted or not visible
• Calcification: Tiny calcium deposits are sometimes seen in the area of the lungs or mediastinum. This happens in around 85% of instances⁹

CT scan 

Detailed images obtained from a chest CT scan can be used to diagnose FM and distinguish it from other medical conditions.

Here’s what the scan might show:

• Mediastinal or hilar mass: An abnormal growth of dense tissue mass closer to mediastinitis or near the lungs. This mass could help detect FM and determine its extent
• Soft-tissue mass: A dense, soft lump in the chest that hides normal fat and may press on or invade nearby organs
• Deposits of calcium in the central mass or lymph nodes, especially if there has been a past infection like histoplasmosis
• Tracheobronchial narrowing: narrowing of the airways, including the trachea (windpipe) and bronchi (tubes that lead to the lungs)
• Areas of the lungs that seem cloudy or unclear, which suggest lung tissue issues
• Endobronchial calcification or calcium buildup inside the bronchi 
• Pleural thickening and calcification: The lining around the lungs might be thicker than normal and may also show calcification
• Pulmonary granulomas: These are small, healed areas in the lungs from past infections, such as tuberculosis or histoplasmosis.
• Engorged bronchial arteries: Enlarged blood vessels in the lungs due to compromised blood flow
• Unusual patterns in the lung tissue, such as increased patterns or “crazy paving” patterns, indicate changes in the lung⁹

If the CT scan results are not conclusive, other imaging tests may be used. These include:

• An MRI scan to take detailed pictures of the heart and pulmonary vein to help doctors see FM more clearly. When compared to normal tissue, FM may appear as a lump on this scan, with some areas being brighter and others darker⁹
• A nuclear medicine scan to measures how well blood flows through the lungs¹
• PET scan  to assess the metabolic activity of the mediastinal mass¹¹

Biopsy

A biopsy is a technique in which a small sample of body tissue is taken out and examined. This test assists doctors in determining whether the tissue exhibits the fibrous features typical of FM and guarantees that the symptoms are not the result of diseases that mimic FM, such as lymphomas (a kind of cancer). The main difference is that biopsies from lymphomas will show cancer cells, while scarring or fibrosis without cancer is seen in fibrosing mediastinitis.¹² Some of these techniques include:

• Bronchoscopy 
• Lymph node biopsy
• Mediastinoscopy
• Surgical Biopsy
• Endobronchial Ultrasound ¹

Laboratory tests

When imaging techniques are inconclusive in revealing the distinct features of FM, laboratory tests are used to obtain additional information.

Blood tests for infections

When imaging techniques do not clearly show the characteristic features of FM, blood tests can help. These tests use antibodies or antigens specific to pathogens to help identify infections that may cause or contribute to FM.¹ These tests consist of:

• Histoplasmosis antigen or antibody tests are used for diagnosing histoplasmosis, which is a major cause of FM. It’s positive in most cases but not all¹
• Aspergillus antigen tests which are for detecting Aspergillus species if suspected
• Tuberculosis tests  to rule out TB
• Blood tests can also help rule out other conditions linked to idiopathic FM, like autoimmune diseases¹

Autoimmune markers

These tests search the blood for specific markers to identify autoimmune diseases that may be linked to FM.¹³ It usually includes:

• Antinuclear Antibody (ANA) Test: Look for signs of autoimmune diseases like scleroderma¹⁴
• Anti-IgG4 Antibodies detecting test: Detects IgG4-related disease, which can cause FM⁸
• ANCA Test: Checks for autoimmune conditions like granulomatosis with polyangiitis, that contribute to FM⁸

Summary

• Fibrosing mediastinitis is a rare condition marked by the formation of a high amount of scar tissue in the mediastinum, which blocks important heart and lung structures
• Breathlessness, chest pain, and difficulty swallowing are some of the common symptoms of this condition
• Histoplasmosis, aspergillosis, tuberculosis, and autoimmune disorders such as IgG4-related illness are a few common causes
• Accurate differentiation of fibrosing mediastinitis from conditions with similar features is crucial for effective treatment
• Diagnosing fibrosing mediastinitis involves imaging studies like X-rays and CT scans, biopsies, and blood tests for infections and autoimmune markers