Bronchial Adenoma - Causes, Symptoms, Diagnosis, and Treatment

Introduction

A bronchial adenoma is a rare tumor of the respiratory tract. Adenoma refers to noncancerous tumors, but bronchial adenoma is potentially malignant. It is a slow-growing tumor and can spread to other parts. It often occurs as a locally invasive tumor that can metastasize. Bronchial adenomas usually occur as carcinoids or salivary gland tumors to a lesser extent.

What Is Bronchial Adenoma?

Bronchial adenoma denotes various types of tumors that arise from mucous glands and ducts of the trachea (windpipe) or bronchi (large airways that branch from the trachea). The term bronchial adenoma includes:

• Neuroendocrine tumors (carcinoids).

• Adenoid cystic carcinomas (cylindromas).

• Mucoepidermoid carcinomas.

• Mucous gland adenomas.

• Mixed seromucinous tumors arise from mucous glands and ducts of the windpipe and bronchi.

Mucous gland adenomas are noncancerous tumors, but other types have cancerous potential. They are slow-growing tumors and spread slowly.

How Does Bronchial Adenoma Occur?

Carcinoids (two types of bronchial neuroendocrine tumors), adenoid cystic carcinoma, and mucoepidermoid carcinomas constitute 95 % of bronchial adenomas.

• Adenoid Cystic Carcinoma - Adenoid cystic carcinomas spread in a submucosal plane involving the perineural lymphatics and spread beyond the endoluminal margins of the tumor. It results in an extensive submucosal spread, but most of the time, they do not metastasize.

• Mucoepidermoid Carcinoma - Mucoepidermoid carcinomas arise from the glandular tissue of the submucosa located in the trachea and bronchus. It comprises a mixture of mucus-producing, glandular, squamous epithelial, and intermediate cells. It has various growth patterns like cystic, papillary, and solid structures. Mucoepidermoid carcinomas can be high-grade or low-grade tumors. Low-grade malignant tumors have cystic components, and high-grade tumors have solid growth patterns. Typical carcinoids and atypical carcinoids are considered bronchial adenomas. They cause endobronchial occlusion. They are commonly situated in the lobes or segments of the lungs and bronchus.

• Carcinoids - Carcinoid syndrome includes respiratory, cardiovascular, gastrointestinal, and cutaneous manifestations. It is associated with endocrinopathies like Cushing syndrome (increase in corticotropin levels), hyperpigmentation (increase in melanocyte-stimulating hormone), inappropriate excretion of antidiuretic hormone, and hypoglycemia.

What Are the Causes of Bronchial Adenoma?

Bronchial carcinoids originate from neuroendocrine cells called kulchitsky cells. Amine precursor uptake and decarboxylation cells produce and store amines and peptides. Typical carcinoids arise as clusters of polyhedral cells in a fibrovascular stroma and have features similar to small-cell neuroendocrine carcinoma of the lung. Adenoid cystic carcinoma arises from the salivary gland tissue. It may arise from myoepithelial cells. Adenoid cystic carcinoma is called cylindroma, adenoid cystic basal cell carcinoma, adenomyoepithelioma, and pseudoadenomatous basal cell carcinoma. Mucoepidermoid carcinomas are squamous and intermediate elements with intercellular bridges. They arise from the trachea and proximal bronchi. The microscopic features are similar to mucoepidermoid carcinoma of the salivary glands. Mucous gland adenomas are benign submucosal tumors that arise from the mucous glands.

What Are the Signs and Symptoms Associated With Bronchial Adenoma?

Individuals with bronchial adenomas remain asymptomatic. If present, the following are the symptoms of endobronchial involvement:

• Triad of cough, hemoptysis, and recurrent infection.

• Dyspnea.

• Wheezing and stridor.

• Cough with sputum.

• Pneumonia.

The following symptoms are present due to mediastinal involvement:

• Hoarseness of voice due to the involvement of recurrent laryngeal nerves.

• Chylothorax due to involvement of the thoracic duct.

• Chest pain.

Adenoid cystic carcinoma causes the following symptoms:

• Presence of lump on the roof of the oral cavity, under the tongue, or at the bottom of the mouth.

• Difficulty in swallowing.

• Hoarseness of voice.

• Numbness in the mouth, face, or tongue.

• Presence of bump under the jaw or in front of the ear.

Mucoepidermoid carcinoma causes the following symptoms:

• Swelling in the glands near the ears, under the jaw, or in the mouth.

• Numbness or weakness in the face.

• Pain in the face.

Bronchial adenoma presents with the following systemic signs:

• Endocrinopathies.

• Unexplained weight loss.

• Low-grade temperature elevation.

What Are the Complications Associated With Bronchial Adenoma?

The following complications are associated with bronchial adenoma:

• Delayed hemorrhage.

• Bronchial anastomotic leak.

• Bleeding and coagulopathy.

• Myocardial ischemia.

• Atelectasis.

• Pneumonia.

• Respiratory failure, need for persistent mechanical ventilation.

Mucoepidermoid carcinoma results in intracranial metastases even during minimal bronchial involvement. Carcinoids result in solid organ metastases like liver involvement.

How Is Bronchial Adenoma Diagnosed?

The diagnosis is based on laboratory tests and imaging studies. The diagnostic studies include the following:

Laboratory Tests - Laboratory tests include the following:

• Complete Blood Count - It helps in the diagnosis of pneumonia and helps in quantifying the volume of hemoptysis associated with endobronchial lesions.

• Serum Electrolytes, BUN (Blood Urea Nitrogen), creatinine, and calcium - These tests are useful in evaluating paraneoplastic involvement.

• Liver Function Tests - This test helps identify hepatic metastases.

• Arterial Blood Gas Test - This test is done to detect the presence of respiratory conditions like acidosis, hypercarbia, and hypoxia.

Radiographic Imaging - Radiographic imaging studies are carried out to locate the lesion.

• Chest Radiograph - It shows the presence of a nodule, mass, infiltrate or atelectasis, mediastinal or hilar lymphadenopathy, or pleural effusion.

• CT (Computed Tomography) Scan - It helps visualize the nodules, calcifications, tumor components, extra luminal extensions, carinal involvement, and distant metastases.

• Magnetic Resonance Imaging - This scan is done when the CT scan findings are unsatisfactory.

• Radiolabeled Peptides - Octreotide and 99m technetium (Tc) depreotide are used. This test yields weakly positive results. These tests are not usually recommended due to their high costs and less sensitive results.

How Is Bronchial Adenoma Treated?

The treatment of bronchial adenoma includes the following:

• Chemotherapy - Combination therapy with platinum-based drugs is effective in treating carcinoids. Chemotherapy after radiation is used in the treatment of atypical lesions.

• Radiation Therapy - It is recommended in cases of incomplete resection of atypical lesions and mediastinal nodal involvement.

• Surgical Resection - Surgical resection is the main treatment for bronchopulmonary carcinoids. Radical resection is performed for mucoepidermoid carcinomas. Lobectomy, sleeve resection, or endoscopic removal is recommended for mucoepidermoid carcinomas of the lung.

Conclusion:

Bronchial adenoma is a rare respiratory tract neoplasm. It consists of a diverse group of tumors with malignant potential. It remains undiagnosed because of its slow growth pattern. It is important to consult the physician if any symptoms like breathing difficulty arise. Timely diagnosis and intervention are vital in preventing tumor spread and the risk of complications.