90: Overview of Benign Lung Disease: Anatomy and Pathophysiology

Introduction

Benign tumor, bronchogenic cyst, pulmonary hamartoma, pulmonary sequestration, bronchiectasis, and arteriovenous malformation (AVM) are the principal benign and acquired conditions of the lung encountered in thoracic surgery. This chapter reviews the etiology, clinical presentation, diagnosis, and therapeutic modalities for each of these benign and acquired conditions. Established surgical techniques are described in the ensuing chapters of this section.

Bronchogenic Cysts

Definition

Bronchogenic cysts are the most common cystic masses in the mediastinum. They are thought to be congenital lesions arising from the primitive foregut. Usually, they are found within the mediastinum or lungs. The mediastinal lesions may be found in close proximity to the carina, mainstem bronchi, trachea, esophagus, or pericardium. Bronchogenic cysts of the skin and subcutaneous tissue also have been reported.

Etiology

The precise embryonic pathway leading to the development of bronchogenic cysts remains unknown. The respiratory tree develops by an outpouching of the primitive foregut during the first 16 weeks of development. Some have theorized that this process fails when a cyst develops in place of the mature structure. These congenital cystic lesions comprise not only the bronchogenic cyst, but also a heterogeneous group of bronchopulmonary malformations, including congenital cystic adenomatoid malformations, sequestrations, congenital lobar emphysema, bronchial atresia, and congenital parenchymal cysts.¹ As with other structures of the bronchus, bronchogenic cysts are lined by ciliated columnar or squamous epithelial cells (respiratory and gastrointestinal). Mucus-secreting bronchial glands found in the epithelium cause the cysts to fill. As the cysts grow, they exert pressure on surrounding structures, particularly the membranous trachea or bronchi, which may lead to severe respiratory obstruction. Cartilage and smooth muscle cells also are found in the cyst wall.

Clinical Features

These cystic malformations may present in the early neonatal period or they may remain entirely asymptomatic until later in life.¹ Symptoms may be evident in both children and adults depending on many factors such as the presence of a communication between the lumen of the cyst and the airways, infection of the fluid within the cyst, and bleeding. If the cyst grows large enough to cause mediastinal shift¹ and obstruction in adjacent structures, the main symptoms will be cough, dyspnea, dysphagia, and chest pain of varying degrees as a result of irritation of the airways and esophagus or inflammation of the mediastinal or parietal pleura. Infectious complications may cause symptoms of fever, elevated leukocyte count, and cough with purulent sputum. Pneumonia localized to the pericystic parenchyma may accompany chronically recurring cysts. Hemoptysis is a sign of an ulcerative process in the cyst wall. Rare complications include cardiac arrhythmias, superior vena cava syndrome, and cancer.

Diagnosis

Plain chest radiographs are diagnostic only when the cavity of the cyst contains an air–fluid level. This finding, especially when the cyst is located in the mediastinum, ...