Introduction:
Bronchial mucoid pseudotumor is an abnormal mucus formation most commonly precipitated by smoking and may result in the formation of a mucoid pseudotumor. The collection of mucus, if seen on a radiograph, may mimic a polypoid mass. However, a large collection of mucoid impact may give an impression of a pseudotumor.
A mucus is a gel-like substance produced by the lungs or glands lining the respiratory tract. On exposure to toxic irritants, the lungs respond by increasing mucus production. The composition of the mucus varies according to environmental and pathophysiologic conditions. A healthy individual produces an average of a hundred milliliters of mucus, most of which is reabsorbed into the bronchial lining.
The mucus's appearance and odor are important in identifying the underlying lung condition. For example, jelly-like sputum is typically seen in cases of Klebsiella infection. In contrast, green sputum suggests pseudomonal infection, a rotten egg smell suggests anaerobic infections, and a pungent smell is suggestive.
What Is a Mucus Plug?
Mucus plug refers to the mucus collected within the lungs and reduces airflow in the larger airways. Numerous mucus plugs can lead to a collapse of the alveolar sacs. In addition, mucous plugs can lead to shortness of breath or dyspnea.
These mucus plugs can partially or completely obliterate the airways leading to serious life-threatening consequences such as atelectasis or alveolar collapse and recurrent infections. The impacted plugs can also form casts, a semisolid occlusion that fits into the bronchus and takes the shape of the airways in which it is formed.
On chest radiography, these impacted mucus plugs appear as a pseudotumor and are named bronchial mucoid pseudotumor. Chronic respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis produce thick sticky mucin, and the acute exacerbation of the disease further contributes to this effect. In addition, the excess mucin produced has a high affinity for pathogenic invasion, specifically by Pseudomonas aeruginosa and Klebsiella pneumonia.
What Are the Causes of Mucus Impaction?
The causes may be obstructive or non-obstructive.
For example, the causes of mucus impaction include the following:
Obstructive Causes:
1. Congenital Causes:
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Congenital bronchial atresia.
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Intralobar sequestration.
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Intrapulmonary bronchogenic cyst.
2. Neoplastic Causes:
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Benign Causes:
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Bronchial hamartoma.
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Bronchial lipoma.
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Tracheobronchial papillomatosis.
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Malignant Causes:
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Bronchogenic carcinoma.
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Bronchial carcinoid.
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Endobronchial metastases.
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3. Acquired Causes:
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Broncholithiasis.
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Tuberculous bronchostenosis.
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Foreign body aspiration.
Non-Obstructive Causes:
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Cystic fibrosis.
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Allergic bronchopulmonary aspergillosis.
What Are the Diseases in Which Mucus Pluggings Are Seen?
Mucus pluggings are seen in various diseases, as listed below:
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Cystic Fibrosis: It is an autosomal recessive disorder that causes sticky, thick, hyper-viscous mucus to build up in the lungs. It's a defect in the cystic fibrosis transmembrane regulator (CFTR) gene. The CFTR is an epithelial anion channel in the alveolar ducts that facilitates the transfer of chloride and bicarbonate ions.
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Allergic Bronchopulmonary Aspergillosis (ABPA): A lung disease that occurs in people allergic to a fungus known as aspergillus fumigatus. It is a type of hypersensitivity reaction with increased eosinophils. The typical clinical presentation is hemoptysis or coughing blood, weight loss, and fatigue. It can often be confused with malignancies, and diagnosis is made based on the history of asthma, expectoration of mucus plugs, and increased eosinophil levels in the peripheral blood smear.
On chest radiography, dense mucoid impactions can be seen that are denser than the paraspinal skeletal muscles. The mucus plugs are usually deposited in the upper lobes and segmental bronchi, whereas plastic bronchitis tend to deposit in the central airways and lower lobes. A characteristic finger-in-glove sign can be observed due to obstruction of the lobar bronchi, leading to lobar collapse. Under the microscope, the mucin or allergic mucin appears as an alternating layer of pale-colored mucin and dark-colored fibrin, consisting of numerous viable and necrotic eosinophils along with Charcot-Leyden crystals.
These crystals are synthesized by eosinophilic-rich inflammation; fungal hyphae may sometimes be present. The management involves long-term corticosteroid therapy along with antifungal drugs. In addition, bronchoscopy with bronchoalveolar lavage can be done to remove the thick mucus impactions.
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Asthma: Bronchial asthma is a chronic inflammatory disease characterized by hyperresponsiveness of the tracheobronchial smooth muscle to various stimuli causing narrowing of the airways and increased secretion, mucosal edema, and mucus plugging. This makes it difficult for the air to flow easily through the airways and to breathe.
Thick mucoid secretions within the lumen characterize the bronchial wall, marked eosinophilic infiltration, and hypertrophied smooth muscles.
These plugs have multilobar involvement, unlike allergic bronchopulmonary aspergillosis. Histologic examination showed fibrin mixed with mucin and numerous scattered inflammatory cells such as neutrophils, T-lymphocytes, and eosinophils. However, they lack the alternating layer pattern of mucin and fibrin and an eosinophil-rich inflammation, as seen in ABPA.
A characteristic histologic feature is the Curschmann spirals which may be well appreciated in asthma patients. It may also contain Charcot-Leyden crystals and Creola bodies. The management involves long-term corticosteroid therapy and anticholinergics to help reduce mucus hypersecretion.
Conclusion:
Thick, viscous mucus plugs within the large airways can either partially or completely obliterate the airways leading to serious life-threatening consequences such as atelectasis and recurrent respiratory infections. Proper diagnosis with bronchoscopy and bronchoalveolar lavage is highly recommended in such cases. The management requires long-term corticosteroid therapy along with anticholinergics and mucolytic agents are the drugs of choice.
