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.
