Characteristics

Hamartomas (Box 11-1) are acquired lesions composed of tissues normally found within the organ, but they demonstrate disorganized growth. Hamartomas, the most common benign tumors of the lung, account for 5% to 8% of solitary pulmonary nodules.

Clinical Features

The peak incidence occurs in the sixth decade of life, with an age range of 30 to 70 years. The lesions are slightly more predominant in women. Most patients are asymptomatic, and the hamartoma is discovered on a routine chest radiograph as a solitary pulmonary nodule. Occasionally, hamartomas can occur endobronchially and may produce obstructive symptoms (see Chapter 13).

Pathologic Features

These tumors contain nests of cartilage surrounded by fibrous tissue and mature fat cells. Other mesenchymal components, such as bone, vessels, and smooth muscle, may be present.

Radiographic Features

Characteristically, hamartomas appear as well-defined, solitary, spherical nodules or masses. They are usually less than 4 cm in diameter, and they have well-defined margins. Calcification is seen in 10% to 15% of cases on standard radiographs, although it is more frequently identified on CT. The calcification has a characteristic morphology that produces a popcorn appearance (Fig. 11-1). Hamartomas typically grow slowly, and in rare cases, they can be multiple.

Figure 11-1 Hamartoma. A well-defined, 3-cm, spherical nodule in the left perihilar area in lung parenchyma has a classic popcorn pattern of calcification.

Thin-collimation CT can be valuable in diagnosing pulmonary hamartomas. The presence of focal deposits of fat (−50 to −150 HU) is most helpful in making this diagnosis (Fig. 11-2). In approximately 25% of cases, calcification can be identified.

Figure 11-2 Hamartoma. A, CT shows a well-defined, 3-cm, spherical nodule in the right lower lobe that contains fat (arrow). B, A small, focal calcification is seen inferiorly in the nodule (arrow).

Characteristics

Amyloid, a waxy pink material that stains with Congo red, has a typical birefringence with polarization microscopy (Box 11-2). It occurs in two major forms: primary and secondary. Lung involvement in primary amyloidosis is estimated to occur in 30% to 90% of cases. Secondary amyloidosis is usually associated with rheumatoid arthritis, suppurative disease such as osteomyelitis, and malignant neoplasms. Amyloidosis may also be associated with multiple myeloma. In the thorax, amyloid occurs in two locations. The first is the tracheobronchial tree. Airway amyloidosis is discussed in Chapter 12. Amyloidosis may also involve the lung parenchyma in a nodular form or as a diffuse, infiltrative process.

Clinical Features

Nodular disease usually occurs late in life (i.e., seventh decade), and it has an equal sex prevalence. Patients are usually asymptomatic, and the prognosis is excellent. The diffuse, infiltrative form is less common and usually occurs in the sixth decade. Patients with the diffuse form are symptomatic. Diffuse infiltration of amyloid material associated with giant cells and plasma cells involves the vascular walls and interstitial compartments of the lung. The disease is accompanied by symptoms of progressive dyspnea, which leads to eventual death from respiratory insufficiency.

Radiographic Features

The radiologic appearance of the nodular form consists of solitary or multiple nodules and masses (Fig. 11-3). Calcification is common, occurring in 30% to 50% of patients, but cavitation is rare. The lower lobes are more frequently involved, often in a subpleural distribution. These nodules may exhibit slow growth.

Figure 11-3 Amyloidosis, nodular form. A, Frontal radiograph shows multiple pulmonary nodules. B and C, CT using mediastinal and lung windows shows several calcified and noncalcified nodules. Notice the cysts in the lungs.

In the diffuse, infiltrative form, bilateral and fine linear, nodular, or reticulonodular patterns may be present (Fig. 11-4). There is no specific distribution in the lung parenchyma. Associated nodal calcification may be identified.

Figure 11-4 Amyloidosis, diffuse infiltrative form. A, Frontal radiograph shows a diffuse reticulonodular pattern. B, High-resolution CT shows linear and nodular opacities with septal thickening (arrows). Note also presence of calcification.

Characteristics

Pulmonary pseudotumors include a number of histologic entities, such as plasma cell granuloma, inflammatory pseudotumor, histiocytoma, xanthoma, and mast cell granuloma (Box 11-3). The cause of pulmonary pseudotumors is unknown, although they were thought to represent a localized form of organizing pneumonia in patients with subclinical infection. Plasma cell granuloma is discussed more extensively in Chapter 9. Pulmonary pseudotumors occur slightly more frequently in males than in females over a wide age range. Patients are often asymptomatic, and antecedent infection can be documented in less than one fifth of cases.

Pathologic Features

These tumors usually consist of a mixture of spindle cells, plasma cells, lymphocytes, and histiocytes. Plasma cells predominate in the plasma cell granuloma form.

Radiographic Features

Pulmonary pseudotumors manifest as solitary, peripheral pulmonary nodules that are well marginated (Fig. 11-5). Calcification occurs in about one fifth of cases, and airway involvement is uncommon. Rarely, particularly in children, these tumors may invade adjacent structures. Airway involvement is unusual.

Figure 11-5 Inflammatory pseudotumor. Coronal CT shows a spiculated nodule in the right upper lobe and adjacent to the major fissure that mimics malignancy.

Adenocarcinoma

Radiographic Features

These neoplasms are typically peripheral in location. They manifest as a solitary nodule or mass, often with lobulated, spiculated, and ill-defined borders (Fig. 11-7).

Figure 11-7 Adenocarcinoma. A, Frontal radiograph shows a small, irregular, spiculated lesion in the left upper lobe. B, Thin collimation CT of the lesion better illustrates the irregular margins. The tail (arrow) extends to the pleural surface and may represent a fibrous strand or local tumor extension.

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.

Figure 11-8 Bronchioloalveolar carcinoma. A, CT shows an irregular, focal, ground-glass lesion with a central, solid component in the right upper lobe (arrow). B, CT after 8 months shows an increase in size.

Figure 11-9 Bronchioloalveolar carcinoma, pneumonic form. The bilateral, multifocal consolidation results from a tumor that contains air bubbles and air bronchograms.

Figure 11-10 Bronchioloalveolar carcinoma, diffuse nodular form. In both lungs, multiple nodules of various sizes have fuzzy, irregular borders.

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

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.

Figure 11-11 Squamous cell carcinoma A, Frontal radiograph shows a large, left hilar mass with atelectasis of the left upper lobe B, CT shows an endobronchial tumor occluding the left upper lobe bronchus (arrow).

Figure 11-12 Squamous cell carcinoma. A, A tumor surrounds and narrows the right lower lobe bronchus (arrow). Notice the enlarged subcarinal lymph node. B, Sagittal reformatted image shows atelectasis of the right lower lobe (arrows).

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.

Figure 11-13 Cavitary squamous cell carcinoma. A, The frontal radiograph shows a thick-walled cavity in the right upper lobe. B, CT shows a cavity with a thick, irregular, and nodular wall. Notice the bronchi in the cavity (black arrow) and the tree-in-bud opacities in the right lower lobe due to postobstructive pneumonia (white arrow).

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

Radiographic Features

The radiographic features usually consist of a hilar or perihilar mass associated with massive, bilateral mediastinal adenopathy (Fig. 11-14). There may be associated lobar collapse. The primary tumor may not be readily evident because it is obscured by the extensive adenopathy. However, CT may show the primary tumor to better advantage. Occasionally, an SCLC manifests as a peripheral nodule that can be resected, and in these relatively uncommon cases, the prognosis is better (Fig 11-15).

Figure 11-14 Extensive small cell carcinoma. A, The frontal radiograph shows a left hilar mass, widening of the mediastinum and a left pleural effusion. B, On CT, the large left hilar and mediastinal mass encases the left main pulmonary artery. Notice the left pleural effusion and a pleural nodule (arrow). C, FDG-PET demonstrates diffuse metastases in the bones, liver, and right kidney. Notice the increased FDG uptake in the chest mass.

Figure 11-15 Limited small cell carcinoma. A and B, The frontal and lateral radiographs show a nodule in the right lower lobe. C and D, CT shows lobulated right lower lobe nodule and an enlarged right hilar node.

Undifferentiated Large Cell Carcinoma

Radiographic Features

The lesions are usually peripheral and quite large. More than 70% of the tumors are larger than 4 cm at presentation (Fig. 11-16).

Figure 11-16 Large cell (giant cell) carcinoma. A, A lateral view shows a mass in the right lower lobe and overlying the spine (arrow). B, CT shows a peripherally enhancing mass. C, There is increased uptake on the FDG-PET scan.

Multidifferentiated Tumors

Adenosquamous carcinoma consists of malignant squamous and glandular components. It is typically peripherally located, and it is associated with early metastases and a poor prognosis.

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