(Radiographics. 2000;20:43-58.)
© RSNA, 2000
Solitary Pulmonary Nodules: Part I. Morphologic Evaluation for Differentiation of Benign and Malignant Lesions1
Jeremy J. Erasmus, MD ,
John E. Connolly, MD ,
H. Page McAdams, MD and
Victor L. Roggli, MD
1 From the Departments of Radiology (J.J.E., H.P.M.) and Pathology (V.L.R.), Duke University Medical Center, Erwin Road, Durham, NC 27710; and the Department of Radiology, Rush Presbyterian Medical Center, Chicago, Ill (J.E.C.). Presented as a scientific exhibit at the 1998 RSNA scientific assembly. Received February 19, 1999; revision requested March 29 and received June 9; accepted June 10. Address reprint requests to J.J.E.
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Abstract
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The solitary pulmonary nodule is a common radiologic abnormality that is often detected incidentally. Although most solitary pulmonary nodules have benign causes, many represent stage I lung cancers and must be distinguished from benign nodules in an expeditious and cost-effective manner. Evaluation of specific morphologic features of a solitary pulmonary nodule with conventional imaging techniques can help differentiate benign from malignant nodules and obviate further costly assessment. Small size and smooth, well-defined margins are suggestive of but not diagnostic for benignity. Lobulated contour as well as an irregular or spiculated margin with distortion of adjacent vessels are typically associated with malignancy. There is considerable overlap in the internal characteristics (eg, attenuation, cavitation, wall thickness) of benign and malignant nodules. The presence of intranodular fat is a reliable indicator of a hamartoma. The presence and pattern of calcification can also help differentiate benign from malignant nodules. Computed tomography (CT) (particularly thin-section CT) is 10–20 times more sensitive than standard radiography and allows objective, quantitative assessment of calcification. Initial evaluation often results in nonspecific findings, in which case nodules are classified as indeterminate and require further evaluation to exclude malignancy. Growth rate assessment, Bayesian analysis, contrast material–enhanced CT, positron emission tomography, and transthoracic needle aspiration biopsy can be useful in this regard.
Index Terms: Lung, calcification, 60.2811, 60.3226 • Lung, cavitation, 60.2812 • Lung, nodule, 60.11, 60.1211, 60.281, 60.332
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Introduction
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Solitary pulmonary nodules are defined as focal, round or oval areas of increased opacity in the lung that measure less than 3 cm in diameter (1,2). An estimated 150,000 solitary pulmonary nodules are detected annually in the United States and are often discovered incidentally at chest radiography or computed tomography (CT) (3). These nodules are caused by a variety of disorders including neoplasms, infection, inflammation, and vascular and congenital abnormalities (Table). Although most solitary pulmonary nodules have benign causes, 30%–40% of these nodules are malignant (4–11). In this article, we discuss and illustrate initial radiologic evaluation of solitary pulmonary nodules and assessment of morphologic features (size, margins, contour, internal characteristics) that can help differentiate benign and malignant lesions.
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Initial Evaluation
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The goal of radiologic evaluation of suspected solitary pulmonary nodules is to noninvasively differentiate benign from malignant lesions as accurately as possible. This is important because a solitary pulmonary nodule is the initial radiographic finding in 20%–30% of patients with lung cancer, and prognosis depends in part on stage at presentation (2). Standard radiologic evaluation of a suspected solitary pulmonary nodule includes careful review of findings at chest radiography and, when appropriate, comparison with findings at prior radiography, chest fluoroscopy, and CT and correlation with clinical signs and symptoms.
The initial step in evaluation is to determine whether the abnormality is in fact a solitary pulmonary nodule.
This assessment is important because up to 20% of suspected nodules prove to be entities mimicking a solitary pulmonary nodule such as rib fractures, skin lesions, or composite areas of increased opacity (Figs 1, 2). If it is probable that a radiographic abnormality is not a pulmonary nodule, the use of shallow oblique radiographic views or chest fluoroscopy can avert extensive, costly work-up (Figs 3, 4). An added benefit of low-kilovoltage fluoroscopy is improved detection of calcification within nodules. If the location or cause of the area of increased opacity remains indeterminate following fluoroscopy, CT is used to confirm the location and further characterize the nodular abnormality (Figs 5, 6). CT can also help distinguish a solitary pulmonary lesion from multiple pulmonary nodules (Fig 7).
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Figure 1a. Rib fracture in a 50-year-old woman with multiple myeloma. (a) Close-up posteroanterior radiograph of the right upper lung shows a poorly marginated nodular area of increased opacity overlying the anterior aspect of the right second rib (arrow). (b) CT scan shows a healed fracture of the right second rib (arrow). Note the lytic lesions in the vertebral body secondary to multiple myeloma.
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Figure 1b. Rib fracture in a 50-year-old woman with multiple myeloma. (a) Close-up posteroanterior radiograph of the right upper lung shows a poorly marginated nodular area of increased opacity overlying the anterior aspect of the right second rib (arrow). (b) CT scan shows a healed fracture of the right second rib (arrow). Note the lytic lesions in the vertebral body secondary to multiple myeloma.
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Figure 2a. Pseudonodule in a 50-year-old man. (a) Close-up posteroanterior radiograph of the right lung shows a smoothly marginated nodular area of increased opacity projecting over the lung (arrow). Note the adjacent electrocardiographic lead attachment pad (arrowhead). On a follow-up radiograph obtained after removal of the attachment pad (not shown), no nodule was observed. (b) Front and back views of the electrocardiographic lead attachment pad show an eccentrically located silver nitrate pad, which explains the contiguous nodular area of increased opacity on the chest radiograph.
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Figure 2b. Pseudonodule in a 50-year-old man. (a) Close-up posteroanterior radiograph of the right lung shows a smoothly marginated nodular area of increased opacity projecting over the lung (arrow). Note the adjacent electrocardiographic lead attachment pad (arrowhead). On a follow-up radiograph obtained after removal of the attachment pad (not shown), no nodule was observed. (b) Front and back views of the electrocardiographic lead attachment pad show an eccentrically located silver nitrate pad, which explains the contiguous nodular area of increased opacity on the chest radiograph.
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Figure 3a. Bone island in a 61-year-old man with melanoma. (a) Close-up posteroanterior radiograph of the upper chest shows a focal area of increased opacity overlying the right seventh rib posteriorly (arrow). (b) Fluoroscopic images show a well-marginated intraosseous lesion (arrow). This finding is consistent with a bone island and obviated further investigation.
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Figure 3b. Bone island in a 61-year-old man with melanoma. (a) Close-up posteroanterior radiograph of the upper chest shows a focal area of increased opacity overlying the right seventh rib posteriorly (arrow). (b) Fluoroscopic images show a well-marginated intraosseous lesion (arrow). This finding is consistent with a bone island and obviated further investigation.
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Figure 4a. Osteophyte of the left first rib in a 60-year-old woman. (a) Posteroanterior chest radiograph shows a poorly defined nodular area of increased opacity overlying the anterior aspect of the left first rib (arrow). (b) Posteroanterior chest radiograph obtained 2 years earlier shows that interval growth has occurred (cf a). This interval growth raised suspicion for malignancy. (c) Contiguous chest CT scans (image on right obtained at a lower level) reveal that the area of increased opacity is a large osteophyte of the first rib. Had fluoroscopy been performed, costly CT could have been avoided.
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Figure 4b. Osteophyte of the left first rib in a 60-year-old woman. (a) Posteroanterior chest radiograph shows a poorly defined nodular area of increased opacity overlying the anterior aspect of the left first rib (arrow). (b) Posteroanterior chest radiograph obtained 2 years earlier shows that interval growth has occurred (cf a). This interval growth raised suspicion for malignancy. (c) Contiguous chest CT scans (image on right obtained at a lower level) reveal that the area of increased opacity is a large osteophyte of the first rib. Had fluoroscopy been performed, costly CT could have been avoided.
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Figure 4c. Osteophyte of the left first rib in a 60-year-old woman. (a) Posteroanterior chest radiograph shows a poorly defined nodular area of increased opacity overlying the anterior aspect of the left first rib (arrow). (b) Posteroanterior chest radiograph obtained 2 years earlier shows that interval growth has occurred (cf a). This interval growth raised suspicion for malignancy. (c) Contiguous chest CT scans (image on right obtained at a lower level) reveal that the area of increased opacity is a large osteophyte of the first rib. Had fluoroscopy been performed, costly CT could have been avoided.
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Figure 5a. Cutaneous nodules in a 51-year-old man with neurofibromatosis and prostatic adenocarcinoma. (a) Posteroanterior radiograph shows numerous well-marginated nodular areas of increased opacity projecting over the lower aspect of the thorax and a poorly marginated nodule overlying the upper aspect of the left hemithorax (arrow). Because the location of the upper nodule was uncertain, CT was performed. (b) CT scan helps confirm the intraparenchymal location of the nodule in the left upper lobe. (c) CT scan demonstrates multiple cutaneous nodules.
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Figure 5b. Cutaneous nodules in a 51-year-old man with neurofibromatosis and prostatic adenocarcinoma. (a) Posteroanterior radiograph shows numerous well-marginated nodular areas of increased opacity projecting over the lower aspect of the thorax and a poorly marginated nodule overlying the upper aspect of the left hemithorax (arrow). Because the location of the upper nodule was uncertain, CT was performed. (b) CT scan helps confirm the intraparenchymal location of the nodule in the left upper lobe. (c) CT scan demonstrates multiple cutaneous nodules.
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Figure 5c. Cutaneous nodules in a 51-year-old man with neurofibromatosis and prostatic adenocarcinoma. (a) Posteroanterior radiograph shows numerous well-marginated nodular areas of increased opacity projecting over the lower aspect of the thorax and a poorly marginated nodule overlying the upper aspect of the left hemithorax (arrow). Because the location of the upper nodule was uncertain, CT was performed. (b) CT scan helps confirm the intraparenchymal location of the nodule in the left upper lobe. (c) CT scan demonstrates multiple cutaneous nodules.
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Figure 6a. Segmental bronchial atresia in a 17-year-old girl. (a) Close-up posteroanterior radiograph of the right lower lung shows a nodular area of increased opacity in the lower lobe (arrow). (b) Chest CT scans (image on left obtained at a lower level) show a branching tubular area of increased attenuation in the right lower lobe as well as pulmonary parenchyma with lower than expected attenuation. These findings are characteristic of segmental bronchial atresia and obviated further work-up.
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Figure 6b. Segmental bronchial atresia in a 17-year-old girl. (a) Close-up posteroanterior radiograph of the right lower lung shows a nodular area of increased opacity in the lower lobe (arrow). (b) Chest CT scans (image on left obtained at a lower level) show a branching tubular area of increased attenuation in the right lower lobe as well as pulmonary parenchyma with lower than expected attenuation. These findings are characteristic of segmental bronchial atresia and obviated further work-up.
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Figure 7a. Multiple arteriovenous malformations in a 23-year-old woman with hereditary hemorrhagic telangiectasia. Contiguous chest CT scans reveal multiple small nodular areas of increased attenuation bilaterally with enlarged feeding and draining vessels, findings that are diagnostic for arteriovenous malformations. A chest radiograph obtained earlier (not shown) demonstrated a possible small solitary pulmonary nodule in the right lower lobe.
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Figure 7b. Multiple arteriovenous malformations in a 23-year-old woman with hereditary hemorrhagic telangiectasia. Contiguous chest CT scans reveal multiple small nodular areas of increased attenuation bilaterally with enlarged feeding and draining vessels, findings that are diagnostic for arteriovenous malformations. A chest radiograph obtained earlier (not shown) demonstrated a possible small solitary pulmonary nodule in the right lower lobe.
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Morphologic Evaluation
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Size, Margins, and Contour
Generally, the smaller the nodule, the more likely it is to be benign: 80% of benign nodules are less than 2 cm in diameter (6,9,12). However, small size alone does not exclude lung cancer because 15% of malignant nodules are less than 1 cm in diameter and approximately 42% are less than 2 cm in diameter (2,13,14).
Nodule margins and contours can be classified as smooth, lobulated, irregular, or spiculated. Although most nodules with smooth, well-defined margins are benign, these features are not diagnostic for a benign cause: 21% of malignant nodules have well-defined margins (Figs 8, 9) (15).
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Figure 8a. Lung nodule caused by Dirofilaria (canine heartworm) in an asymptomatic 70-year-old man. (a) Close-up CT scan of the right lung shows a peripheral, smoothly marginated, noncalcified lung nodule. (b) Photograph of a specimen obtained with wedge resection shows a well-circumscribed, 2-cm nodule with yellow areas of geographic necrosis. (c) High-power photomicrograph (original magnification, x175; hematoxylin-eosin stain) shows intravascular Dirofilaria. Most infections manifest as lung nodules from embolic infarction caused by intravascular worms.
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Figure 8b. Lung nodule caused by Dirofilaria (canine heartworm) in an asymptomatic 70-year-old man. (a) Close-up CT scan of the right lung shows a peripheral, smoothly marginated, noncalcified lung nodule. (b) Photograph of a specimen obtained with wedge resection shows a well-circumscribed, 2-cm nodule with yellow areas of geographic necrosis. (c) High-power photomicrograph (original magnification, x175; hematoxylin-eosin stain) shows intravascular Dirofilaria. Most infections manifest as lung nodules from embolic infarction caused by intravascular worms.
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Figure 8c. Lung nodule caused by Dirofilaria (canine heartworm) in an asymptomatic 70-year-old man. (a) Close-up CT scan of the right lung shows a peripheral, smoothly marginated, noncalcified lung nodule. (b) Photograph of a specimen obtained with wedge resection shows a well-circumscribed, 2-cm nodule with yellow areas of geographic necrosis. (c) High-power photomicrograph (original magnification, x175; hematoxylin-eosin stain) shows intravascular Dirofilaria. Most infections manifest as lung nodules from embolic infarction caused by intravascular worms.
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Figure 9. Solitary metastasis from bladder cancer in a 45-year-old woman. Chest CT scan shows a smoothly marginated, 1-cm peripheral nodule. Metastatic disease was confirmed at resection. Solitary metastases account for 3%-5% of all resected solitary pulmonary nodules.
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A lobulated contour implies uneven growth, which is associated with malignancy (Fig 10) (9). However, lobulation also occurs in up to 25% of benign nodules (Figs 11, 12) (12). A nodule with an irregular or spiculated margin with distortion of adjacent vessels (often described as having a sunburst or corona radiata appearance) is likely to be malignant (Figs 13, 14) (9,12,13,17,18).
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Figure 11a. Arteriovenous malformation in a 34-year-old man with hereditary hemorrhagic telangiectasia. (a) Close-up posteroanterior radiograph of the right lung shows a lobulated, well-marginated nodule in the lower lobe (arrows). (b) Chest CT scan demonstrates a feeding artery (arrow) and an enlarged draining vein (arrowhead). (c) CT scan shows the nidus of the malformation. (Figure 11b and 11c reprinted, with permission, from reference 16.) (d) Pulmonary angiogram helps confirm arteriovenous malformation. Note the early draining vein (arrows).
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Figure 11b. Arteriovenous malformation in a 34-year-old man with hereditary hemorrhagic telangiectasia. (a) Close-up posteroanterior radiograph of the right lung shows a lobulated, well-marginated nodule in the lower lobe (arrows). (b) Chest CT scan demonstrates a feeding artery (arrow) and an enlarged draining vein (arrowhead). (c) CT scan shows the nidus of the malformation. (Figure 11b and 11c reprinted, with permission, from reference 16.) (d) Pulmonary angiogram helps confirm arteriovenous malformation. Note the early draining vein (arrows).
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Figure 11c. Arteriovenous malformation in a 34-year-old man with hereditary hemorrhagic telangiectasia. (a) Close-up posteroanterior radiograph of the right lung shows a lobulated, well-marginated nodule in the lower lobe (arrows). (b) Chest CT scan demonstrates a feeding artery (arrow) and an enlarged draining vein (arrowhead). (c) CT scan shows the nidus of the malformation. (Figure 11b and 11c reprinted, with permission, from reference 16.) (d) Pulmonary angiogram helps confirm arteriovenous malformation. Note the early draining vein (arrows).
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Figure 11d. Arteriovenous malformation in a 34-year-old man with hereditary hemorrhagic telangiectasia. (a) Close-up posteroanterior radiograph of the right lung shows a lobulated, well-marginated nodule in the lower lobe (arrows). (b) Chest CT scan demonstrates a feeding artery (arrow) and an enlarged draining vein (arrowhead). (c) CT scan shows the nidus of the malformation. (Figure 11b and 11c reprinted, with permission, from reference 16.) (d) Pulmonary angiogram helps confirm arteriovenous malformation. Note the early draining vein (arrows).
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Figure 12. Intralobar sequestration in a 14-year-old boy. Chest CT scan shows a lobulated, well-marginated nodule with homogeneous attenuation in the right lower lobe. Intrapulmonary sequestration was confirmed at resection.
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Figure 13. Bronchioloalveolar cell carcinoma in a 65-year-old man. Chest CT scan shows an irregular nodule abutting the major fissure. Note the indentation of the adjacent portion of the major fissure owing to desmoplastic reaction around the tumor.
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Internal Characteristics
There is considerable overlap in the internal characteristics of benign and malignant nodules. Homogeneous attenuation is seen at thin-section CT in both benign (55%) and malignant (20%) nodules (12). Pseudocavitation (small, focal, low-attenuation regions within or surrounding the periphery of a nodule) and air bronchograms within a nodule are suggestive of bronchioloalveolar cell carcinoma (Fig 15) and lymphoma, respectively (12,19,20).
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Figure 15. Bronchioloalveolar cell carcinoma in a 68-year-old woman. Close-up chest CT scan of the right lung shows a poorly marginated nodule in the midlung. Small focal areas of low attenuation in the nodule (pseudocavitation) are suggestive of bronchioloalveolar cell carcinoma.
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Cavitation also occurs in both benign and malignant nodules. Benign cavitary nodules generally have smooth, thin walls (Fig 16), whereas malignant nodules typically have thick, irregular walls (Fig 17) (12,18). Most nodules with a wall thickness greater than 16 mm are malignant, whereas those with a wall thickness less than 4 mm are usually benign (21,22). However, there is significant overlap, and wall thickness alone cannot be used to confidently differentiate benign from malignant cavitary nodules (Fig 18).
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Figure 17. Squamous cell lung cancer in a 60-year-old woman. Close-up posteroanterior radiograph of the right lung shows a smoothly marginated nodule in the lower lobe. Note the eccentric cavitation and thick walls.
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Figure 18. Bullet track from a gunshot wound in a 20-year-old man. Close-up posteroanterior radiograph of the right lung shows a smoothly marginated, thick-walled nodule with eccentric lucency in the midlung. Note the bullet fragments overlying the right lung. These findings are consistent with parenchymal hematoma and a bullet track.
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The presence of intranodular fat (attenuation, -40 to -120 HU) is a reliable indicator of a hamartoma (Fig 19). Fat is seen at CT in up to 50% of hamartomas and is best visualized at thin-section CT (Fig 20) (23).
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Figure 19a. Hamartoma in an asymptomatic man. (a) Chest CT scan shows a heterogeneous, sharply marginated lesion with small focal areas of calcification and fat. These findings are typical features of hamartoma. (b) Photograph of a resected specimen demonstrates a yellowish, glistening, lobular cut surface, a finding that is consistent with fat. (c) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) helps confirm the presence of adipose tissue (arrow) and shows epithelial tissue containing an island of basophilic cartilage (arrowhead). This mixture of epithelial and mesenchymal tissue is diagnostic for hamartoma. (Fig 19 courtesy of M. Rosado de Christenson, Col, USAF, MC, Armed Forces Institute of Pathology, Washington, DC.)
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Figure 19b. Hamartoma in an asymptomatic man. (a) Chest CT scan shows a heterogeneous, sharply marginated lesion with small focal areas of calcification and fat. These findings are typical features of hamartoma. (b) Photograph of a resected specimen demonstrates a yellowish, glistening, lobular cut surface, a finding that is consistent with fat. (c) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) helps confirm the presence of adipose tissue (arrow) and shows epithelial tissue containing an island of basophilic cartilage (arrowhead). This mixture of epithelial and mesenchymal tissue is diagnostic for hamartoma. (Fig 19 courtesy of M. Rosado de Christenson, Col, USAF, MC, Armed Forces Institute of Pathology, Washington, DC.)
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Figure 19c. Hamartoma in an asymptomatic man. (a) Chest CT scan shows a heterogeneous, sharply marginated lesion with small focal areas of calcification and fat. These findings are typical features of hamartoma. (b) Photograph of a resected specimen demonstrates a yellowish, glistening, lobular cut surface, a finding that is consistent with fat. (c) Photomicrograph (original magnification, x100; hematoxylin-eosin stain) helps confirm the presence of adipose tissue (arrow) and shows epithelial tissue containing an island of basophilic cartilage (arrowhead). This mixture of epithelial and mesenchymal tissue is diagnostic for hamartoma. (Fig 19 courtesy of M. Rosado de Christenson, Col, USAF, MC, Armed Forces Institute of Pathology, Washington, DC.)
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Figure 20a. Pulmonary hamartoma in a 74-year-old woman. (a) Chest CT scan obtained with 10-mm collimation demonstrates a nodule (arrow), but its internal morphologic features are poorly visualized. (b) Thin-section CT scan obtained with 1-mm collimation better demonstrates a punctate area of fat within the nodule (arrow), a finding that is diagnostic for hamartoma.
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Figure 20b. Pulmonary hamartoma in a 74-year-old woman. (a) Chest CT scan obtained with 10-mm collimation demonstrates a nodule (arrow), but its internal morphologic features are poorly visualized. (b) Thin-section CT scan obtained with 1-mm collimation better demonstrates a punctate area of fat within the nodule (arrow), a finding that is diagnostic for hamartoma.
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The presence and pattern of calcification in a solitary pulmonary nodule can also help differentiate benign from malignant nodules. There are four benign patterns of calcification: central, diffuse solid, laminated, and "popcornlike." The first three patterns are typically seen with prior infections, particularly histoplasmosis or tuberculosis (Figs 21, 22). Popcornlike calcification is characteristic of chondroid calcification in a hamartoma (Fig 23). When present, these patterns of calcification are reliable indicators of a benign cause. Unfortunately, 38%–63% of benign nodules are not calcified, and the reported prevalence of calcification in hamartomas at CT varies from 5% to 50% (23,25,26).
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Figure 21. Granuloma in an asymptomatic 64-year-old man. Close-up chest CT scan of the left lung shows a soft-tissue nodule with central calcification in the upper lobe. Note the eccentric cavitation within the nodule.
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Figure 22a. Histoplasmoma in an asymptomatic 50-year-old man. (a) Close-up tomogram of the left lung demonstrates a smooth, well-marginated nodule. (b) Photograph of a resected specimen helps confirm central calcification and laminated fibrous tissue. (Fig 22 courtesy of M. Rosado de Christenson, Col, USAF, MC, Armed Forces Institute of Pathology, Washington, DC.)
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Figure 22b. Histoplasmoma in an asymptomatic 50-year-old man. (a) Close-up tomogram of the left lung demonstrates a smooth, well-marginated nodule. (b) Photograph of a resected specimen helps confirm central calcification and laminated fibrous tissue. (Fig 22 courtesy of M. Rosado de Christenson, Col, USAF, MC, Armed Forces Institute of Pathology, Washington, DC.)
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Lung cancers as well as typical and atypical primary pulmonary carcinoid tumors may calcify; calcification is detected at CT in up to one-third of carcinoid tumors. Thus, care must be taken to differentiate benign from malignant patterns of calcification (Fig 24). Calcification in lung cancer is rarely observed at chest radiography but is seen at CT in up to 6% of cases; such calcification is typically diffuse and amorphous (Fig 25) (27). Punctate calcification may also occur in lung cancer due to engulfment of a preexisting calcified granulomatous lesion (Fig 26) and metastases (Fig 27). Misdiagnosis can be avoided if densely calcified solitary pulmonary nodules in patients with a history of a primary bone-forming malignancy are not automatically interpreted as benign lesions.
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Figure 25a. Non-small cell lung cancer in a 45-year-old woman. (a) Close-up chest radiograph of the right lung shows a lobulated, sharply marginated nodule in the upper lobe. Note the presence of emphysema and upper lobe bullae. (b) Close-up chest CT scan of the right lung reveals amorphous calcification in the nodule, a pattern that is typical of malignancy. Adenocarcinoma was confirmed at resection.
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Figure 25b. Non-small cell lung cancer in a 45-year-old woman. (a) Close-up chest radiograph of the right lung shows a lobulated, sharply marginated nodule in the upper lobe. Note the presence of emphysema and upper lobe bullae. (b) Close-up chest CT scan of the right lung reveals amorphous calcification in the nodule, a pattern that is typical of malignancy. Adenocarcinoma was confirmed at resection.
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Figure 26. Lung cancer in a 72-year-old man. Close-up chest CT scan of the right lung shows a lobular lesion with peripheral punctate calcification in the upper lobe, a finding that is consistent with "engulfed" granuloma. Unlike that in calcified granulomas, calcification in engulfed granuloma is typically peripheral and constitutes only a small part of the nodule.
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Figure 27a. Metastatic osteosarcoma in a 21-year-old man. (a) Close-up chest CT scan of the left lung shows a small, high-attenuation nodule in the lower lobe (arrow). This finding was suggestive of a benign cause. (b) Chest CT scan obtained 8 months later reveals interval growth of the nodule, which has high attenuation and a lobulated contour. Resection revealed metastatic osteosarcoma.
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Figure 27b. Metastatic osteosarcoma in a 21-year-old man. (a) Close-up chest CT scan of the left lung shows a small, high-attenuation nodule in the lower lobe (arrow). This finding was suggestive of a benign cause. (b) Chest CT scan obtained 8 months later reveals interval growth of the nodule, which has high attenuation and a lobulated contour. Resection revealed metastatic osteosarcoma.
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Calcification within nodules is often not optimally visualized at high-kilovoltage-peak chest radiography. Low-kilovoltage radiography or chest fluoroscopy is more sensitive in the detection of intranodular calcification. CT (particularly thin-section CT) is 10–20 times more sensitive than standard radiography and allows objective, quantitative assessment of calcification (1,13–15). Optimally, 3–5 sections should be obtained through the nodule; thus, for a 1-cm nodule, 2–3-mm sections should be obtained (Fig 28). Visual inspection of the resulting images usually suffices for distinguishing calcified from noncalcified nodules. However, if calcification is not apparent at visual inspection, its presence can sometimes be inferred from CT attenuation values determined with CT densitometry (13–15). Although the literature varies on this point, an attenuation value of 200 HU is advocated by many as a good discriminator between calcified and noncalcified nodules. CT densitometry has two major drawbacks: It has no utility in the evaluation of spiculated nodules, which must always be regarded with a high degree of suspicion, and its sensitivity (66%) and specificity (98%) for benign disease are not optimal.
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Figure 28a. Granulomatous disease in a 48-year-old woman. (a) Chest CT scan (10-mm collimation) shows a nodule with peripheral calcification and a calcified right hilar node. (b) Thin-section CT scan (3-mm collimation) better demonstrates the diffuse solid calcification in the nodule, a finding that is typical of a benign cause.
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Figure 28b. Granulomatous disease in a 48-year-old woman. (a) Chest CT scan (10-mm collimation) shows a nodule with peripheral calcification and a calcified right hilar node. (b) Thin-section CT scan (3-mm collimation) better demonstrates the diffuse solid calcification in the nodule, a finding that is typical of a benign cause.
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Conclusions
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Evaluation of specific morphologic features (size, margins, contour, internal characteristics) of a solitary pulmonary nodule with conventional imaging techniques can help differentiate benign from malignant nodules and obviate further costly assessment. Nevertheless, initial evaluation frequently results in nonspecific findings, in which case nodules are classified as indeterminate and require further evaluation to exclude malignancy. Growth rate assessment, Bayesian analysis, contrast material–enhanced CT, positron emission tomography, and transthoracic needle aspiration biopsy can also be useful in the evaluation of these indeterminate solitary pulmonary nodules. In Part II, "Evaluation of the Indeterminate Solitary Pulmonary Nodule," we discuss in more detail how further evaluation can help distinguish benign from malignant nodules.
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Footnotes
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See also the article by Erasmus et al (pp 59–66
) in this issue.
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Top
Abstract
Introduction
