Pulmonary Neoplasms

Chapter 11 Pulmonary Neoplasms



The most important neoplasm involving the lung is lung cancer (i.e., bronchogenic carcinoma), the leading cause of cancer mortality in the United States. It accounts for more than 150,000 deaths each year. In addition to lung cancer, there are other primary malignant neoplasms, benign neoplasms, and other tumoral processes that originate in the lung. The lungs are a common site of metastases from extrathoracic malignancies.



BENIGN NEOPLASMS AND OTHER NONNEOPLASTIC TUMORS


A wide variety of benign tumoral lesions can occur in the lung. Some are true neoplasms, and others are of uncertain nature or origin. Benign neoplasms may arise in the tracheobronchial glands, soft tissue, bone, and cartilage, or they may be from mixed mesenchymal origin. Nonneoplastic tumors include hamartomas and inflammatory pseudotumors.



Hamartoma







Amyloid









Pulmonary Pseudotumor






LUNG CANCER


Bronchogenic carcinoma is the leading cause of cancer mortality in the United States, with more than 160,000 individuals diagnosed each year and more than 140,000 succumbing to the disease. It is the most common cancer in men worldwide, and it has surpassed breast cancer as the leading cause of cancer death in women. Lung cancer is one of the most common lung diseases that radiologists in practice encounter. Computed tomography (CT), positron emission tomography (PET), magnetic resonance imaging (MRI), and standard radiography play important roles in the diagnosis and staging of patients with lung cancer.



Clinical Features


Between 85% and 90% of lung cancer deaths are directly attributable to cigarette smoking. The risk is related to the number of cigarettes smoked, the duration of smoking years, the age at which smoking began, and the depth of inhalation. The risk decreases with cessation of smoking but never completely disappears. Other etiologic factors may play a role in the development of bronchogenic carcinoma, including genetic profiles, occupational exposures, and concomitant disease in the lungs.


Certain occupational agents may increase the risk of lung cancer, and they are listed in Box 11-4. The most important of these is asbestos. A combination of asbestos exposure and cigarette smoking is multiplicative and results in a marked increased risk of lung cancer, particularly if asbestosis is present in the parenchyma of the lungs. Most of the concomitant lung diseases associated with bronchogenic carcinoma reflect the presence of fibrosis in the lungs (Box 11-5), including any cause of end-stage lung disease, such as idiopathic pulmonary fibrosis, and localized fibrosing disease, such as tuberculosis.




Only 10% of patients with lung carcinoma are asymptomatic (Box 11-6). Most often, symptoms are caused by central tumors that result in obstruction of a major bronchus. This leads to cough, wheezing, hemoptysis, and postobstructive pneumonia. Local intrathoracic spread may result in related symptoms, such as pleuritic or chest wall pain, Pancoast syndrome, and symptoms related to obstruction of the superior vena cava. Occasionally, patients may have symptoms that result from distant metastases (i.e., a seizure related to metastases to the brain).



Several paraneoplastic syndromes are associated with lung carcinoma, including clubbing and hypertrophic pulmonary osteoarthropathy, which consists of periosteal new bone formation that usually involves the bones of the lower arms and legs (Fig. 11-6). These lesions are usually associated with pain. Other paraneoplastic syndromes include migratory thrombophlebitis and ectopic hormone production, including Cushing’s syndrome from adrenocorticotropic hormone (ACTH) production, hyponatremia associated with inappropriate secretion of antidiuretic hormone (ADH), and hypercalcemia due to excessive parahormone production. There are also a variety of neurologic paraneoplastic syndromes.




Radiologic-Pathologic Correlation


Lung cancer is broadly divided in to small cell lung cancer (SCLC) and non–small cell lung cancer (NSCLC) based on histologic features and differences in treatment approach. SCLC is considered to be a systemic disease and is treated with a combination of chemotherapy and radiotherapy. NSCLC in the early stages can be treated with surgery. NSCLC is broadly further subclassified as adenocarcinoma, squamous cell carcinoma, and large cell carcinoma (Box 11-7).




Adenocarcinoma






Bronchioloalveolar Carcinoma


Bronchioloalveolar carcinoma is a subtype of adenocarcinoma. It may manifest with one of three distinct radiologic patterns (Box 11-9). The most common is a solitary nodule. The nodules share the same appearance as adenocarcinoma, although they are often rather hazy and ill defined (Fig. 11-8). They are located peripherally and exhibit lipidic growth, and the growth along the alveolar walls probably accounts for the relatively low density on standard radiographs. On CT, they may exhibit ground-glass opacification, particularly around the periphery of the nodule (see Fig. 11-8). The solitary nodule is associated with an excellent prognosis when it is resected at this stage. An air bronchogram may be identified on standard x-ray films and on CT. The second appearance is that of a pneumonia-like consolidation, which occurs in approximately 20% of cases (Fig. 11-9). This consolidation may be associated with nodules in the same lobe or in other lobes of either lung. This appearance reflects the presumed mode of dissemination of this tumor through the tracheobronchial tree. The third appearance is that of multiple nodules scattered throughout both lungs (Fig. 11-10). These nodules are typically 5 to 6 mm in diameter and tend to have very irregular borders. Very few patients present with this pattern of disease.






One of the classic clinical features of bronchioloalveolar carcinoma is the presence of bronchorrhea, which may be extreme and may lead to the expectoration of a large amount of mucus with severe morbidity.



Squamous Cell Carcinoma



Clinical Features


Squamous cell carcinoma represents about one third of all lung cancers. It is associated with relatively better prognosis (Box 11-10). Although it grows rapidly, distant metastases occur at a later phase than in adenocarcinoma. There is a strong association with cigarette smoking. Squamous cell carcinoma is the most common cause of Pancoast syndrome, and the cell type is most commonly associated with hypercalcemia due to ectopic parathormone production.



Superior sulcus tumors (i.e., Pancoast tumors) occur at the very apex of the lung in the superior sulcus (Box 11-11). They are typically characterized by pain, Horner’s syndrome, destruction of bone, and atrophy of hand muscles. These tumors typically invade the chest wall and extend into the neck. Local extension may result in involvement of the brachial plexus, spread to the spinal canal and vertebral bodies, involvement of the sympathetic ganglion, and anterior extension with invasion of the subclavian artery. If the local tumor is not extensive, it can be treated successfully with a combination of preoperative irradiation and chemotherapy, followed by lobectomy and chest wall resection.





Radiographic Features


The radiologic presentation depends on the location of the carcinoma. The most common finding is that of a central endobronchial obstructing lesion, which produces a hilar or perihilar mass (Fig. 11-11). Involvement of the central bronchus may range from focal thickening to complete occlusion. When the lesion is small, the tumor may not be evident on the standard radiograph, but the bronchial wall abnormalities are well depicted on CT (Fig. 11-12). Atelectasis or obstructive pneumonitis is usually identified distal to the obstructed bronchus. Any patient presenting with atelectasis and signs of infection should be followed radiographically to complete resolution and reexpansion of the involved lobe. Failure of resolution strongly suggests a central lung carcinoma.




Approximately one third of squamous cell carcinomas occur in the lung periphery. The most characteristic appearance is a thick-walled, cavitary mass that usually does not have an air-fluid level. The diameter ranges from 2 to 10 cm (Fig. 11-13). The cavity may be indistinguishable radiographically from a primary lung abscess. A solitary nodule or mass without cavitation can occur in the periphery of the lung parenchyma.



On standard radiographs, a superior sulcus tumor usually appears as an apical mass or an asymmetric pleural thickening with irregularity that occasionally is associated with rib destruction. Apical thickening alone may be a normal finding; usually, its prevalence is related to age. Much more commonly seen in older individuals, it is usually bilateral, but it may be asymmetric. Any irregular apical thickening that is 5 mm or greater than that on the opposite side should be considered with suspicion. However, most patients with superior sulcus tumors do have clinical symptoms of chest pain. MRI is the preferred modality for evaluating superior sulcus tumors because of its ability to visualize structures at the apex of the thorax in multiple planes. Features of superior sulcus tumors on MRI are discussed later in the section on staging (see “Staging of Lung Cancer”).



Small Cell Lung Carcinoma



Clinical Features


SCLC, the most aggressive form of lung cancer, is characterized by rapid growth and early metastases, which are present in two thirds of patients at the time of presentation (Box 11-12). It is associated with the poorest survival, and it has the strongest and most irrefutable association with cigarette smoking. It accounts for approximately 15% to 20% of all lung cancers. SCLC does not respond to surgical treatment, but it is often managed successfully with chemotherapy. However, long-term survival is extremely poor, and when treated, the median survival is 9 to 18 months. SCLC is staged into two groups: limited-stage disease and extensive disease. Limited-stage disease is limited to one hemithorax with regional nodes, including hilar, ipsilateral, and contralateral mediastinal and supraclavicular nodes. Patients with ipsilateral pleural effusion, irrespective of positive cytology for malignancy, are included under limited-stage disease. Extensive disease typically has extrathoracic disease or thoracic disease that cannot be encompassed in same radiation portal as the primary tumor. Tumor-node-metastasis (TNM) staging is not used, because this system historically relied on surgical confirmation for accuracy, and patients with SCLC are seldom candidates for surgery. However, the SCLC subcommittee of the International Association for the Study of Lung Cancer (IASLC) recommends that TNM staging be applied in SCLC and that stratification by TNM stage be incorporated into clinical trials. Patients with limited-stage disease (i.e., confined to the thorax) have a 2-year survival rate of approximately 25%.



SCLC is the most common cause of superior vena cava syndrome. It is also associated with Cushing’s syndrome and inappropriate secretion of ADH.







Staging of Lung Cancer



TNM Classification


Staging of any tumor consists of the determination of the extent of the disease. The rationale for staging is to select patients who will benefit from surgical resection and to identify patients who benefit from adjuvant chemotherapy and radiotherapy. Staging also determines prognosis.


The TNM system is widely used to classify lung tumors. In the TNM classification, T indicates the features of the primary tumor, N indicates metastasis to regional lymph nodes, and M refers to the presence or absence of distant metastasis. In 1997, the staging system was revised based on epidemiologic evidence of improved survival after surgical resection in patients who had previously been classified as having unresectable disease. However, these conclusions were derived from analysis of a relatively small database accumulated since 1975. Since then, there have many innovative changes in clinical staging with the routine use of CT and with PET imaging. The IASLC established a lung cancer staging project to analyze a much larger worldwide database of lung cancer. Following this extensive analysis, the Working Committee proposed changes to existing TNM staging system, which will be incorporated in the seventh TNM classification of malignant tumors (Tables 11-1 and 11-2).


Table 11-1 Proposed Definitions for T, N, and M Descriptors






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Feb 28, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on Pulmonary Neoplasms
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