INTRODUCTION

Solitary pulmonary nodules are found at a rate of 1-2 per 1000 chest radiographs. About 30% of these nodules prove to be malignant. Of the rest of the nodules, benign tumors of the lung make up about 2-5% of primary lung tumors. Benign lung tumors are a heterogenous group of neoplastic lesions originating from pulmonary structures. These tumors include bronchial adenomas, hamartomas, and a group of uncommon neoplasms (eg, chondromas, fibromas, lipomas, leiomyomas, hemangiomas, teratomas, pseudolymphomas, endometriosis).

Problem: Although benign lung tumors do not pose a significant health problem, complications can result from an obstructive lesion that could predispose the patient to pneumonia, atelectasis, and hemoptysis. These tumors are considered benign, and, therefore, their malignant/cancerous potential is minimal.

Frequency: Benign tumors make up 2-5% of all primary lung tumors. The exact incidence is not known because these tumors are often asymptomatic and are only detected during autopsy. Reported series suggest that benign lung tumors affect men more frequently than women (adenoma and hamartoma). The age range of patients affected is 17-77 years, with a mean age of 56.2 years for all types.

Etiology: The cause of benign lung tumors is not known.

Pathophysiology: The cause and pathogenesis of benign lung tumors are poorly understood. The nomenclature of benign lung tumors is based on histological findings. Some of these tumors have benign features, while others are hamartomas.

Neoplastic lesions are characterized by the autonomous proliferation of cells without a response to the normal control mechanisms governing their growth. An additional characteristic of benign tumors is extension without local tissue invasion or spread to other sites.

Hamartomas, on the other hand, consist of haphazardly organized mature cells and tissues. Hamartomas are composed mostly of masses of hyaline cartilage with a myxoid connective tissue, adipose cells, smooth cells, and clefts lined by respiratory epithelium.

Benign lung tumors can be classified pathologically, but a clinically useful classification would combine location (ie, endobronchial or parenchymal) and information about whether the lesions are single or multiple. Adenomas and hamartomas constitute the largest group of benign lung tumors and, thus, deserve detailed descriptions.

Hamartomas

Hamartomas (chondroadenomas) are the most common type of benign lung tumor. They mainly occur in adults but, on occasion, occur in children. Hamartomas are peripherally located. Grossly, they have a firm marblelike consistency. Histologically, hamartomas generally consist of epithelial tissue and other tissues such as fat and cartilage. Hamartomas can be easily enucleated, but wedge resection is also appropriate.

Bronchial adenomas

Bronchial adenomas make up 50% of all benign pulmonary tumors. The term bronchial adenoma, when used loosely, includes carcinoid tumors, adenocystic carcinomas, and mucoepidermoid carcinomas, which in fact are low-grade malignant tumors. The use of the term bronchial adenoma should be discouraged because it encompasses several benign and malignant tumors.

Mucous gland adenomas

Mucous gland adenomas are true benign bronchial adenomas. Mucous gland adenomas are also called bronchial cystadenomas, and they arise in the main or local bronchi. Histologically, they consist of columnar cell–lined cystic spaces with a papillary appearance.

Other rare tumor types

Tracheobronchial tumors

Multiple laryngeal papillomatosis is a viral disease of the upper airway that affects children. Multiple laryngeal papillomatosis has malignant potential and may spread to the tracheobronchial tree later.

Solitary papillomas usually are less than 1.5 cm in diameter. They usually are lobar or segmental in location and are histologically similar to viral papillomatosis.

Inflammatory papilloma is a solitary polypoid mass of granulation tissue that is associated with an underlying pulmonary inflammatory condition.

Granular cell myoblastomas are of neural cell origin. A granular cell myoblastoma contains polygonal or spindle cells with granular cytoplasm. Granular cell myoblastomas tend to be multiple in 10% of cases and are more common in men aged 30-50 years.

Other parenchymal tumors occasionally occurring in the endobronchial tree (eg, leiomyoma, lipoma) almost exclusively are found at an endobronchial location.

Solitary parenchymal tumors

Sclerosing hemangioma is an uncommon tumor derived from the epithelial cells of pneumocytes (terminal bronchiolar cells). This tumor consists of several elements, including solid cellular areas, papillary structures, sclerotic regions, and blood-filled spaces. This tumor is most commonly found in middle-aged women. Chest radiograph shows a well-defined nodule that is less than 4 cm.

Other mesenchymal tumors include lipoma, leiomyoma, neural tumors, fibroma, benign clear-cell tumor, teratoma, plasma cell granuloma, fibrous histiocytoma, xanthoma, pulmonary hyaline granuloma, pulmonary endometrioma, and pseudolymphoma.

Multiple parenchymal tumors

Many of these benign lung tumors may occasionally have multiple origins. Among these are hamartomas, hyalinizing granulomas, leiomyomas, and sclerosing hemangiomas.

The Carney triad is a syndrome of gastric epithelioid leiomyosarcoma, pulmonary chondromas, and extra-adrenal paragangliomas. The Carney triad mainly affects women.

Pulmonary tumorlets are minute collections of neuroendocrine cells scattered throughout the lung. Pulmonary tumorlets predominantly affect older women.

Clinically significant intrapulmonary chemodectomas apparently are paragangliomas. They behave in a benign fashion. Multiple minute pulmonary tumors, on the other hand, are of no clinical significance.

Clinical: When recording a patient’s history, include questions related to the usual differential diagnoses and lung cancer. For example, smoking history, age, exposure to carcinogens, previous malignant tumor or lung disease, domicile, and travel history are important.

The diagnostic approach is basically the same for these tumors. Clinical presentations depend upon the location of the tumor (eg, trachea, other airways, parenchyma). Hemoptysis, lung mass on chest radiograph, and unresolved infiltrates may be present. Symptoms may include pseudoasthmatic wheezing; persistent coughing; shortness of breath; hemoptysis; fever, especially when associated pneumonia is present; diminished breath sounds; dullness to percussion; and rales.

If a patient is asymptomatic, the tumor may be found serendipitously and, sometimes, classified as a solitary pulmonary nodule.

INDICATIONS

The purpose of surgical intervention for benign lung tumors is to avoid missing potentially malignant lesions. Otherwise, remove benign lung tumors when they are symptomatic, which indicates the presence of complications such as pneumonia, atelectasis, and/or hemoptysis.

RELEVANT ANATOMY AND CONTRAINDICATIONS

Relevant Anatomy: Determination of whether a lung mass is benign or malignant based solely on its anatomical location is an incorrect practice. Anatomical location has no predictability on the malignant potential of a tumor.

Contraindications: Perform a biopsy on lung masses in order to determine the mass malignant potential. Contraindications to a biopsy procedure are bleeding diathesis and cardiopulmonary conditions, which may place the patient's life at risk as a result of the procedure.