eMedicine Specialties > Radiology > Chest

Lung Cancer, Non-Small Cell: Imaging

Author: Sat Sharma, MD, FRCPC, Professor and Head, Division of Pulmonary Medicine, Department of Internal Medicine, University of Manitoba; Site Director, Respiratory Medicine, St. Boniface General Hospital
Coauthor(s): Bruce Maycher, MD, Director of Pulmonary Radiology, St Boniface General Hospital; Associate Professor, Department of Radiology, University of Manitoba
Contributor Information and Disclosures

Updated: May 31, 2009

Radiography

Findings

On chest radiography, the findings of non–small cell lung carcinomas are varied and considered in the differential diagnosis of many disorders. The most common findings are described below.

• Bronchial stenosis
  • Bronchial stenosis and poststenotic changes are common because most non–small cell carcinomas demonstrate intraluminal growth. Narrowing of the main bronchi or a complete cutoff can be identified on chest radiographs.
  • An endobronchial lesion commonly leads to partial or complete atelectasis and is the most common sign of bronchogenic carcinoma. Complete endobronchial obstruction can sometimes produce distal mucoid impaction, which may be visible on plain radiographs as a tubular or branching opacity.
    • Atelectasis of a segment, a lobe, or an entire lung may occur.
    • Radiographic signs include patchy irregular or homogeneous opacities in a lobar or segmental distribution.
    • A loss of lung volume may be seen, as well as displacement of interlobar fissures, the mediastinum, the diaphragm, and the ribs.
    • Postobstructive pneumonia may be identified in a segmental or lobar distribution. In patients with recurrent pneumonia, bronchogenic carcinoma is suggested unless proven otherwise.
• Regional hyperlucency
  • An endobronchial lesion reduces the ventilation despite normal or increased air volume.
  • As a result, hypoxic vasoconstriction reduces perfusion, and attenuation is seen as hyperlucency on chest radiography. In partially atelectatic areas of the lung, hyperlucency rather than opacity may be evident.
• Hilar mass
  • Central bronchogenic carcinomas manifest added opacity in the hilar region.
  • In the early stage, the tumor may fill the lateral concavity of the hilar shadow, and in the advanced stage, all hilar structures are obliterated.
  • Infiltration of lymphatics with bronchogenic carcinomas may be demonstrated as linear opacities radiating from the hilar mass into the lung periphery.
• Solitary pulmonary nodule
  • A solitary pulmonary nodule may be relatively well marginated and appears as a rounded lung opacity.
  • Reportedly, a solitary pulmonary nodule is benign in as many as 60% of patients in some series. All patterns of calcification except eccentric or scattered punctate (stippled) calcification are associated with a benign lesion.
  • Procuring and identifying the lesion on previous chest radiographs is extremely important. This may help establish the doubling time interval for the nodule. A doubling time of 30-365 days commonly is associated with a malignancy.
  • Other possible signs of malignancy include the following:
    • Diameter more than 3 cm
    • Ill-defined or spiculated margin
    • Rigler notch sign (a notch on the nodule corresponding to the vascular supply)
    • Radial striated markings at the nodular margin (termed corona radiata)
    • Thick-walled cavity
    • Eccentric calcification
• Nonresolving pneumonia
  • An ill-defined homogeneous or patchy consolidation in a segmental or nonsegmental distribution may be an indication of bronchogenic carcinoma. Patients with these findings often are treated initially for pneumonia; the lack of response to antibiotic therapy suggests the diagnosis of a malignancy.
  • The opacity may contain air bronchograms and air alveolograms. This presentation is often seen with adenocarcinoma and bronchoalveolar carcinoma.
• Indirect signs of involvement of contiguous structures also may be found. Bronchogenic carcinoma may involve the surrounding thoracic structures, which often indicates that the tumor is not resectable. Findings include the following:
  • Osteolytic lesions and pathologic fractures of rib and vertebra
  • Phrenic nerve involvement causing diaphragmatic paralysis and exhibiting ipsilateral elevation of involved diaphragm
  • Pleural effusion secondary to visceral pleural involvement or lymphatic obstruction (confirm the presence of a malignant effusion using thoracentesis)
• Mediastinal lymph node enlargement: Metastases to paratracheal, tracheobronchial, peribronchial, aortopulmonary, and subcarinal lymph nodes may be identified on chest radiographs. The radiographic signs include a widened mediastinum, an increase in the right paratracheal stripe, a convex margin of the mediastinum, an absence of concavity in the aortopulmonary window, and splaying of carina.

Degree of Confidence

Lung cancer screening with chest radiographs has improved the 5-year survival rates, but a mortality benefit has not been demonstrated.

Computed Tomography

Findings

CT scanning of the thorax plays multiple roles in evaluation of patients with bronchogenic carcinoma. These include lung cancer screening, evaluation of a solitary pulmonary nodule, and staging.

Using CT to detect lung cancer

A few trials have used low-dose helical CT to screen patients at risk for lung cancer. CT has depicted noncalcified nodules, although a small number have been found to be malignant.

• Solitary pulmonary nodule: CT plays a significant role in workup of solitary pulmonary nodules.
  • CT scans may help establish a specific diagnosis in some patients.
  • CT densitometry may help in differentiating between benign and malignant lesions.
  • CT scans may help in the diagnosis of arteriovenous fistulas, rounded atelectasis, fungus balls, mucoid impaction, and lung infarcts. CT scans may also help in identifying a fungus ball that is not well delineated on a chest radiograph.
  • A peripheral nodule with ill-defined, irregular, and spiculated border is malignant in more than 90% of patients.
  • Air bronchogram findings and pseudocavitation (focal lucency) are seen more commonly in malignant nodules.
  • Cavitation may be a feature of both malignant and benign lesions.
  • The thickness of the wall cavity may be helpful in distinguishing between benign and malignant lesions. A wall of less than 1 mm indicates a benign lesion in 95% of patients, and a wall thickness of more than 15 mm indicates a malignant lesion in more than 80% of patients.
• CT densitometry: CT densitometry is useful in detecting the presence and distribution of calcification and fat within solitary nodules.
  • CT scan is more sensitive than chest radiography for detecting the presence of calcification. Approximately one third of indeterminate nodules found on chest radiography can be demonstrated to have calcium on CT scans. CT numbers can be obtained by placing a cursor over the lesion; a value of more than 200 HU indicates calcification.
  • The presence of fat, detected either from direct visualization or from CT numbers ranging from –40 to –120 HU, is diagnostic of hamartoma.
• Contrast-enhanced CT: Enhanced scans may help in distinguishing between malignant and benign lesions.
  • Malignant lesions enhance to a greater degree than do benign lesions after the administration of a contrast material; however, active granulomas or other infectious lesions can also enhance.
  • A measurement of CT numbers during enhancement is useful. An increase of 20 HU or more indicates a sensitivity for lung cancer of 98% and a specificity of 73%.¹⁵ Contrast enhancement may be used in patients who do not have characteristic findings of either malignant or benign lesions. The nonenhancing nodules may be monitored as long as other features suggesting malignancy are not present.

Using CT to stage lung cancer

• Primary tumors: CT scans may be useful in evaluating primary tumors. Although the size of the tumor, whether the lesion is T1 or T2, may not change the surgical approach, the site of the tumor is important to identify.
• CT scans may be helpful in determining tumor extension across the major fissure.
• CT scans are useful in assessing local invasion of the chest wall, mediastinum, mainstem bronchus, central veins, and arteries.
  • Signs of chest wall invasion include bone destruction, tumor extension into the chest wall, pleural thickening, and loss of extrapleural fat plane.
  • Identification of mediastinal invasion with CT usually is unreliable. In addition, minimal mediastinal fat invasion may be resectable in many cases.
  • Tumor invasion of the central arteries and veins may be identified by using CT, which indicates that a pneumonectomy is required.
  • Tumor invasion of the mainstem bronchus can also be visualized on CT scans. This is a useful finding for planning the surgical procedure.
• Hilar and mediastinal lymph node metastases: CT is a useful radiologic modality for noninvasive anatomic evaluation of the hila and mediastinum.
  • The indication of metastasis primarily is based on size criteria. A lymph node with a short-axis diameter of more than 1 cm is defined as enlarged.
  • Although the probability of metastasis increases with increasing lymph node size, CT scanning is not helpful in differentiating a metastasis from a benign lesion.
• Microscopic metastasis: CT may be useful in assessing metastases.
  • Normal-sized lymph nodes have been reported in 7-33% of patients undergoing CT staging. In addition, controversy exists over whether the short-axis or the long-axis diameters should be used in imaging. Another limitation may be interobserver variability in the interpretation of imaging studies.
  • Despite the limitations, CT provides useful staging information to the surgeon. Noting enlargement in a specific location may help surgeons in planning procedures, including mediastinoscopy, mediastinotomy, or percutaneous needle aspiration biopsy.
  • CT is useful in demonstrating extrathoracic metastases. Distant metastases demonstrated with CT include metastases to the adrenal glands, brain, bones, liver, and soft tissues.
  • Chest CT should include the upper abdomen to assess the liver, upper abdominal lymph nodes, and adrenal glands. However, on needle biopsy, most adrenal masses are shown to be adenomas rather than metastases.

Degree of Confidence

On contrast-enhanced CT scans, increased attenuation of 20 HU or more is 98% sensitive and 73% specific for lung cancer.¹⁵

Magnetic Resonance Imaging

Findings

MRI is an imaging modality with several advantages, including a lack of ionizing radiation, the ability to image vascular structures without contrast media, the ability to image in any plane, and superior contrast resolution. MRI is not useful as an initial imaging tool, but it may be superior to CT in the evaluation of local invasion and detection of hilar lymphadenopathy.

In particular, MRI is useful in the evaluation of superior sulcus tumors. Invasion of the brachial plexus, subclavian vessels, and adjacent vertebral bodies can be demonstrated with MRI. Compared with other techniques, MRI may be slightly more accurate in detecting extranodal tumor extension into the mediastinum.

The multiplanar capability of MRI enables a more accurate evaluation of hilar lymph nodes, aortopulmonary window lymph nodes, and subcarinal region lymph nodes, compared with that of CT.

Degree of Confidence

MRI depends on size criteria for the detection of mediastinal metastases. MRI is limited in detecting small lymph nodes containing microscopic deposits. MRI can be used as an imaging modality for apical or superior sulcus lung tumors. MRI is superior in detecting invasion of the chest wall, vertebral body, subclavian vessels, and brachial plexus. For the detection of chest wall invasion, a sensitivity of approximately 90% and a specificity of 96-100% has been reported.

Nuclear Imaging

Findings

Bone scanning

In patients who have biochemical or physical evidence of bone metastasis, a bone scan is required as part of the preoperative workup. A routine bone scan is usually not recommended in asymptomatic patients.

Positron emission tomography

PET can be used to determine the metabolic activity rather than the morphologic features of the lesions. Bronchogenic carcinoma is associated with an increased rate of glucose metabolism. PET uses deoxyglucose linked to fluorine 18 (a positron emitter). The agent, 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG), competes with glucose for transport into the cells and after phosphorylation accumulates in tumor cells. Lung tumor cells have increased glucose metabolism; however, this is not specific for tumors and may occur in infectious or inflammatory processes.

FDG-PET scan has been used to differentiate benign from malignant pulmonary nodules. PET scans also may be useful in detecting distant metastases when whole-body imaging is performed. Because of the false-positive rate, invasive staging procedures may still be required before potentially curative surgical management is denied.¹⁶

Degree of Confidence

PET imaging has higher sensitivity, specificity, and accuracy than CT in staging mediastinal disease. Published studies have demonstrated a sensitivity of 80%, an overall specificity of 92%, and an accuracy of 92%, with a positive predictive value of 90% and a negative predictive value of 93%.

False Positives/Negatives

False-negative studies can occur in patients with carcinoid syndrome, bronchoalveolar carcinomas, and bronchogenic carcinoma measuring less than 10 mm. False-positive findings are known to occur in infectious or inflammatory disorders such as tuberculosis, histoplasmosis, and rheumatoid nodules.

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