Although lung cancer is the most common primary pulmonary neoplasm, a variety of uncommon or rare primary pulmonary tumors may occur, including both benign and malignant entities. This chapter reviews the most frequently encountered uncommon tumors of the lung.
Benign lung tumors include hamartomas, chondromas, papillomas, and inflammatory myofibroblastic tumors, each of which is discussed below.
Pulmonary hamartoma is the most common benign pulmonary neoplasm, accounting for 6% of all solitary pulmonary nodules. Hamartomas are composed of varying amounts of at least two mesenchymal tissues, such as cartilage, fat, bone, connective tissue, and smooth muscle, in combination with entrapped respiratory epithelium.1–6 Most hamartomas occur as solitary nodules in the periphery of the lung (Fig. 117-1), and affected patients are asymptomatic. However, approximately 10% of hamartomas may involve the airways and produce symptoms and imaging signs of bronchial obstruction. Affected patients may present with cough, dyspnea, or pneumonia. Hamartomas occur more often in men than women, with a peak incidence in the sixth decade. They should be considered in the imaging diagnosis of pulmonary nodules that exhibit intrinsic fat and calcification on CT.7–10 MRI in-phase and out-of-phase imaging can also be used to demonstrate the presence of macroscopic fat.1,12
Hamartoma. Contrast-enhanced coronal CT images in lung window (A) and mediastinal window (B) demonstrate a well-circumscribed peripheral pulmonary nodule in the right lower lobe. The mediastinal window image (B) reveals macroscopic fat manifesting as low attenuation within the nodule. Most hamartomas occur as peripheral nodules in asymptomatic patients, but 10% occur as central lesions that may be endobronchial and cause obstructive symptoms and imaging findings. The CT demonstration of macroscopic fat within a pulmonary nodule is considered diagnostic of pulmonary hamartoma.
Small, slow-growing hamartomas can be managed conservatively. If the diagnosis is uncertain or if larger lesions or endobronchial lesions cause postobstructive findings, then surgical resection is often performed.13–15
Multiple hamartomas may occur in Cowden syndrome, an autosomal dominant disorder that may affect multiple organs, including the skin, thyroid gland, and gastrointestinal tract. In addition to its association with benign hamartomas, the syndrome carries an increased risk of breast and thyroid cancers.16
Pulmonary chondromas are benign cartilaginous tumors that consist entirely of cartilaginous components that may calcify.17 Chondromas may be associated with Carney triad, which is defined by the coexistence of extra-adrenal paragangliomas, gastric gastrointestinal stromal tumors (GIST), and pulmonary chondroma and is typically seen in young women.
Squamous cell papilloma is a benign papillary tumor that arises from the wall of a mainstem, secondary, or tertiary bronchus as an exophytic “cauliflower-like” growth. The tumor consists of delicate connective tissue ...