BENIGN TUMORS OF THE LUNG
Pulmonary granulomas are the most common cause of a benign pulmonary nodule and are a sequela of infection. The next most common benign tumor is hamartoma. It is composed of varying proportions of mesenchymal tissues, including smooth muscle, fat, and connective tissue and cartilage. The incidence in the population is 0.25% with two to four times male predominance. Most hamartomas occur in the periphery of the lung and present as an asymptomatic solitary pulmonary nodule. The edges of the tumor are typically smooth. Approximately 10% may occur endobronchially and may present with symptoms of cough, wheeze, dyspnea, or obstructive pneumonia. The presence of “popcorn” calciﬁcation on chest radiography or computed tomography (CT) scan is a classic pattern but is present in only a small percentage of cases. The presence of fat on thin-section CT chest images or fat alternating with areas of calciﬁcation is diagnostic of this lesion, but many hamartomas do not have either of these ﬁndings. Because of the peripheral location, bronchoscopy is typically nondiagnostic. The positron emission tomography (PET) scan is negative for increased metabolic activity. Because of the indeterminate diagnostic results, many of these tumors are treated with surgical resection, although removal is not necessary for the peripherally located and asymptomatic tumor if it has the diagnostic radiographic appearances discussed above.
Solitary ﬁbrous tumors occur in numerous sites, including the pleura, and may present as a mass in the chest. Previously called benign localized mesothelioma (this term is now discouraged), it has no association with asbestos exposure, and 80% to 90% of these lesions are benign and do not spread. It is an uncommon tumor of spindle cell mesenchymal growth thought to be of ﬁbroblastic origin and arises from the visceral pleura most commonly but may also arise in the lung parenchyma or mediastinum. The tumor is usually detected as an asymptomatic nodule or mass on chest radiography. Some patients may present with cough, dyspnea, or chest pain. Rarely, patients may present with hypertrophic pulmonary osteoarthropathy or symptomatic hypoglycemia caused by production of insulin-like growth factor. These latter symptoms are more likely when the tumor is quite large. There are no diagnostic radiographic features, and the PET scan results are usually negative or have a low level of uptake. Bronchoscopy is nondiagnostic because of the pleural origin of these lesions, and transthoracic needle biopsies are unreliable for a deﬁnitive diagnosis. The treatment of choice is surgical resection. Local recurrence may occur in 10% to 15% of cases.
Chondromas are a rare tumor of cartilage. They usually occur in female patients with the Carney triad of gastrointestinal stromal tumor, pulmonary chondroma, and paraganglionoma. Pulmonary chondromas are usually asymptomatic unless they are numerous or of large size. Occasionally, they may cause obstructive pneumonia. Radiographically, they are well-circumscribed tumors, usually multiple, and calciﬁed or may have “popcorn” calciﬁcation. If the pulmonary tumors are asymptomatic, then there is no reason for treatment. Symptomatic tumors may require surgical resection.
Inﬂammatory myoﬁbroblastic tumor, previously called inﬂammatory pseudotumor or plasma cell granuloma, is composed of a mixture of collagen, inﬂammatory cells, and the cytologically bland spindle cells showing myoﬁbroblastic differentiation. It occurs in all ages, with an equal gender distribution. It is the most common pulmonary tumor of childhood and may have a signiﬁcant endobronchial component. Symptoms may include cough, dyspnea, fever, and weight loss. Some patients are asymptomatic. The majority of these tumors are solitary in lung parenchyma but occasionally may involve the chest wall or mediastinum. The mass is usually well circumscribed, lobulated, or smooth, but irregular borders occur in 20%. Calciﬁcation may be present, and rarely cavitation has been reported. Complete surgical resection is the treatment of choice with excellent long-term survival of 90% at 5 years in one reported series. Local recurrence may occur with incomplete resections.