FIGURE 2-1. Air bronchogram sign. CT of the chest shows bilateral subpleural areas of airspace opacity with air bronchograms (arrows) resulting from acute eosinophilic pneumonia. Air bronchograms can also be seen with other causes of airspace disease, including infectious pneumonia, hemorrhage, edema, bronchoalveolar cell carcinoma, lymphoma, lipoid pneumonia, "alveolar" sarcoidosis, and alveolar proteinosis and can also be seen in atelectasis not caused by central obstruction. The presence of the sign indicates that the process is parenchymal in location, rather than mediastinal or pleural.
FIGURE 2-2. Air crescent sign. CT of the chest shows bilateral pulmonary nodules in a predominantly subpleural distribution resulting from septic emboli. Some of the nodules are cavitary. A resulting crescent of air (arrows) is contained within and outlined by the thin cavity wall.
FIGURE 2-3. Bulging fissure sign. A: Posteroanterior (PA) chest radiograph shows dense opacification of the right upper lobe resulting from Klebsiella pneumonia. The inflammatory process is extensive and results in expansion of the lobe and bulging of the fissure inferiorly (arrows). B: Lateral view shows bulging of the superior portion of the major fissure inferiorly (larger arrows). The right upper lobe is outlined by the superior portion of the major fissure and the minor fissure (arrowheads). The middle lobe is outlined by the inferior portion of the major fissure (smaller arrows) and the minor fissure. The right lower lobe is outlined by the major fissure, which is divided into superior and inferior portions by the minor fissure.
FIGURE 2-4. Continuous diaphragm sign. In this patient with pneumomediastinum, a continuous lucency is seen between the heart and the diaphragm (solid arrows). Air in the mediastinum is also seen tracking into the neck bilaterally (dashed arrows).
FIGURE 2-5. CT angiogram sign. CT with intravenous contrast shows opacification of the left lower lobe from bronchoalveolar cell carcinoma. The pulmonary vessels (arrows) are seen prominently against a background of low-attenuation mucus within the tumor. Other processes producing low-attenuation material within the lung can also produce this sign, including lymphoma, lipoid pneumonia, and bacterial pneumonia.
FIGURE 2-6. Deep sulcus sign. Anteroposterior (AP) supine chest radiograph shows bilateral pneumothoraces (intrapleural air) as a result of barotrauma from mechanical ventilation. On the right, the visceral pleura is separated from the parietal pleura by intrapleural air along the apicolateral chest wall (larger arrows). On the left, the intrapleural air is collecting at the lung base, expanding the costophrenic sulcus (smaller arrows). The stiff lungs do not collapse completely in this patient with acute respiratory distress syndrome.
FIGURE 2-7. Deep sulcus sign. AP supine chest radiograph of a patient involved in chest trauma shows a right basilar pneumothorax (arrow), which expands the costophrenic sulcus, creating a tonguelike extension of air that continues inferiorly along the right lateral chest wall. Note bilateral lung contusion, pneumomediastinum, and bilateral subcutaneous emphysema.
FIGURE 2-8. Fallen lung sign. AP supine chest radiograph of a man involved in a motor vehicle accident. There is a large pneumothorax on the right, which persists with adequate chest tube placement, as a result of a fractured right mainstem bronchus. The lung has collapsed inferiorly and laterally (arrows), instead of toward the hilum, because it is hanging from a fractured pedicle (bronchus).
FIGURE 2-9. Flat waist sign. A: Frontal chest radiograph shows left lower lobe opacification from left lower lobe collapse. Note loss of the medial contour of the left hemidiaphragm, which is known as the silhouette sign. The left lower lobe bronchus has a more vertical course than normal (arrowheads). Leftward displacement and rotation of the heart in left lower lobe collapse results in flattening of the contours of the aortic knob and adjacent main pulmonary artery (arrows), termed the flat waist sign. B: Frontal chest radiograph obtained 1 day later shows partial re-expansion of the left lower lobe. The medial left hemidiaphragm is now visible (smaller arrows). There is a notch between the aorta and the pulmonary artery (larger arrow) and no flat waist sign.
FIGURE 2-10. Finger-in-glove sign. A: PA chest radiograph of a patient with cystic fibrosis and allergic bronchopulmonary aspergillosis. Bronchi impacted and distended with mucus, cellular debris, eosinophils, and fungal hyphae produce tubular or masslike opacities, as seen in both lower lobes (arrows). Also shown is diffuse bronchiectasis related to cystic fibrosis. B: CT scan of the same patient shows dilated and impacted central bronchi in the left lower lobe (arrow).
FIGURE 2-11. Golden S sign. A: PA chest radiograph of a man with bronchogenic carcinoma of the right upper lobe. The endobronchial tumor causes collapse of the right upper lobe, and upward displacement of the minor fissure (solid arrow). The tumor mass produces a convex margin toward the lung at the right hilum (dashed arrow). The contour of the displaced fissure and central mass creates a reverse S shape. Note the elevation of the right hemidiaphragm, another sign of right upper lobe volume loss. B: CT of the chest shows tumor encasing and occluding the right upper lobe bronchus (solid arrow) and collapse of the right upper lobe, with superior and medial displacement of the minor fissure (dashed arrow).
FIGURE 2-12. Halo sign. CT shows nodular consolidation associated with a halo of ground-glass opacity (GGO) in both apices (arrows) resulting from invasive pulmonary aspergillosis. This halo represents hemorrhage and, when seen in leukemic patients, is highly suggestive of the diagnosis of invasive pulmonary aspergillosis.
FIGURE 2-13. Hampton hump sign. A: CT with lung windowing shows a focal subpleural area of consolidation in the left lower lobe (arrows). This hump-shaped area of opacification represents pulmonary infarction secondary to pulmonary embolism. There are also small bilateral pleural effusions, which are commonly seen with acute pulmonary emboli. B: CT with mediastinal windowing shows low-attenuation filling defect, which represents a saddle embolus (arrows) bridging the lingular and left lower lobe pulmonary arteries.
FIGURE 2-14. Juxtaphrenic peak sign. PA chest radiograph of a man treated with mediastinal radiation shows paramediastinal radiation fibrosis (dashed arrows) and upward retraction of both hila. There is tenting of the left hemidiaphragm (solid arrow), indicating a loss of left upper lobe volume, seen as the juxtaphrenic peak sign.
FIGURE 2-15. Luftsichel sign. A: PA chest radiograph shows a crescentic lucency adjacent to the aortic arch (arrows), representing hyperaeration of the superior segment of the left lower lobe, which is positioned between the aortic arch medially and the collapsed left upper lobe laterally. There is hazy opacification of the left lung (sparing the apex and costophrenic angle), elevation of the left hemidiaphragm, and partial obscuration of the left heart border (the silhouette sign), indicating a loss of left upper lobe volume. B: Lateral view shows anterior displacement of the major fissure (arrows). The superior extent of the displaced fissure indicates extension of the superior segment of the lower lobe to the lung apex. The luftsichel sign is just one sign of upper lobe collapse. The associated signs of volume loss make the diagnosis obvious. In an adult, left upper lobe collapse is highly suggestive of an obstructing bronchogenic carcinoma.
FIGURE 2-16. Melting ice cube sign. A: PA chest radiograph of a 69-year-old man with a 6-week history of cough, pleuritic chest pain, and hemoptysis shows bilateral, subpleural airspace opacities at the costophrenic angles (arrows), representing parenchymal infarcts. B: CT scan obtained 2 weeks later shows bilateral peripheral opacities (arrows), an appearance typical of resolving pulmonary infarcts. Note that the opacities are not wedge shaped or rounded, as expected with acute infarcts. Infarcts resolve from the periphery inward, like a melting ice cube.
FIGURE 2-17. Ring around the artery sign. A: PA chest radiograph of a patient with acute respiratory distress syndrome shows a ring of lucency around the right pulmonary artery (arrows), signifying pneumomediastinum. B: CT confirms air surrounding both pulmonary arteries (arrows).
FIGURE 2-18. Silhouette sign. A: PA chest radiograph of a patient with pneumococcal pneumonia shows opacification of the right lower lung, which partially obscures the right heart border (the silhouette sign), indicating a process involving the right middle lobe. B: Lateral view shows a triangular opacity over the heart (arrows), confirming a right middle lobe process.
FIGURE 2-19. Silhouette sign. A: PA chest radiograph of a patient with pneumonia shows opacification of the left lower lung partially obscuring the left heart border (silhouette sign), indicating a lingular process. Note that the left hemidiaphragm is not obscured, as would be seen with a process involving any of the basilar segments of the lower lobe. B: Lateral view shows an opacity over the heart (arrows), confirming the lingular location of the pneumonia.
FIGURE 2-20. Split pleura sign. CT with intravenous contrast shows empyema in an intrapleural location with associated thickening, contrast enhancement, and separation of the visceral and parietal pleura (arrows).
FIGURE 2-21. Westermark sign. A: PA chest radiograph shows oligemia of the right lung, the so-called Westermark sign. Note how the vessels on the right are diminutive compared with those on the left. As a result, the right hemithorax appears hyperlucent. B: CT with lung windowing better shows the diminution of vessels on the right compared with the left. There is also a right pleural effusion. C: CT with mediastinal windowing shows thrombus expanding and filling the main and right pulmonary arteries (arrows).
FIGURE 2-22. Spine sign. A: PA chest radiograph of a patient with left lower lobe pneumonia shows abnormal opacity in the left lower lung. B: Lateral view shows this opacity projected over the lower spine (arrows). Normally, the spine becomes progressively more lucent from the top to the bottom on the lateral view. The presence of increased opacity over the lower spine is an indication of a lower lobe process, typically pneumonia, and is called the spine sign.
FIGURE 2-23. Honeycomb pattern. CT shows layers of subpleural cysts (solid arrows) representing the honeycomb pattern of pulmonary fibrosis. Also shown is traction bronchiectasis (dashed arrow), another sign of pulmonary fibrosis.
TABLE 2-1 DIFFERENTIAL DIAGNOSIS OF PATTERNS OF DISEASE ON CT OF THE LUNGS
FIGURE 2-24. Smooth septal thickening. CT shows smooth thickening of the interlobular septae (arrows) in this patient with pulmonary edema. There are also small pleural effusions and scattered areas of GGO, which support the diagnosis.
FIGURE 2-25. Nodular septal thickening. CT shows nodular thickening of the septae (arrows), other scattered small nodules, and areas of GGO, involving only the right lung. These findings are highly suggestive of this patient's diagnosis: lymphangitic carcinomatosis associated with primary bronchogenic carcinoma involving the right lung. Lymphangitic carcinomatosis from an extrathoracic malignancy usually involves both lungs.
FIGURE 2-26. Cystic pattern. A: CT of this patient with Langerhan cell histiocytosis shows irregular, variably sized cysts with definable walls (solid arrow) and scattered small nodules (dashed arrow) involving both upper lungs. B: CT at a level inferior to A shows normal lower lungs. The sparing of the lower lungs and the combination of cysts and nodules is highly suggestive of Langerhan cell histiocytosis.
FIGURE 2-27. Cystic pattern. CT scan of a woman with lymphangioleiomyomatosis shows fairly homogeneous thin-walled cysts with normal intervening lung parenchyma. The cysts involve the upper and lower lungs equally (not shown).
FIGURE 2-28. Cystic pattern look-alike. CT scan shows lucent areas throughout both lungs, which can occasionally be confused with true lung cysts. However, the lucent areas do not have circumferential walls and in some areas, the centrilobular artery is visible within the area of lucency (arrows). These findings, along with a distribution that is predominantly in the upper lungs, are typical of centrilobular emphysema.
FIGURE 2-29. Perilymphatic nodular pattern. CT scan of a young man with sarcoidosis shows numerous small nodules distributed along the bronchovascular bundles (solid arrow) and subpleural lung (dashed arrows). This is a perilymphatic distribution, which is typical of sarcoidosis.
FIGURE 2-30. Centrilobular nodular pattern. CT scan of a man with acute hypersensitivity pneumonitis (also called extrinsic allergic alveolitis) shows numerous ill-defined ground-glass nodules in a centrilobular distribution. This appearance is highly suggestive of the diagnosis but can also be seen in respiratory bronchiolitis. A history of exposure and the presence or absence of cigarette smoking help to make the correct diagnosis.
FIGURE 2-31. Random nodular pattern. CT scan of a patient with miliary tuberculosis shows a pattern of diffuse, randomly distributed, well-defined small pulmonary nodules. Some of the nodules appear centrilobular and some are subpleural in location. The same pattern can be seen with fungal infection or pulmonary metastases.
FIGURE 2-32. Bronchovascular nodular pattern. CT scan of a patient with benign posttransplant lymphoproliferative disorder shows multiple ill-defined nodules distributed along the bronchovascular bundles (arrows). This appearance can also be seen with malignant lymphoma, leukemia, and Kaposi sarcoma.
FIGURE 2-33. Ground-glass pattern. CT scan of a patient with diffuse pneumonia shows extensive bilateral GGO. Note that the pulmonary vessels and bronchi are still visible. This is a nonspecific pattern that is also commonly seen with pulmonary hemorrhage and pulmonary edema.
FIGURE 2-34. "Crazy paving" pattern. CT scan of a patient with pulmonary alveolar proteinosis shows patchy areas of GGO associated with septal thickening, so-called “crazy paving.” This is a characteristic but not pathognomonic finding of pulmonary alveolar proteinosis.
FIGURE 2-35. Mosaic perfusion pattern. CT scan of a patient with sickle cell disease shows a mosaic pattern of lung attenuation. The abnormal lucent areas represent decreased perfusion secondary to microvascular occlusion.
FIGURE 2-36. Mosaic attenuation pattern. A: Inspiratory CT scan of a patient with asthma shows a homogeneous pattern of lung attenuation. B: Expiratory CT scan shows a mosaic pattern of lung attenuation. The abnormal lucent areas represent air trapping related to the patient's asthma. Note the anterior bowing of the posterior membranous trachea (arrow), indicating expiration.
FIGURE 2-37. Tree-in-bud pattern. Maximum-intensity projection axial CT image of a patient with bacterial bronchiolitis shows a pattern of small nodular and linear branching opacities, predominantly in the periphery of the lung (arrows). This is a bronchiolar distribution. The most common etiologies for this pattern are infection and aspiration.
FIGURE 2-38. Tree-in-bud pattern. CT scan of a patient with cystic fibrosis shows bilateral bronchiectasis and bronchiolectasis, along with "tree-in-bud" opacities in the periphery of the right lung (arrow). The opacities represent mucoid impaction of the bronchioles.
FIGURE 2-39. Tree-in-bud pattern. CT scan of a patient who aspirated shows extensive tree-in-bud pattern (arrow) bilaterally.
FIGURE 2-40. Tree-in-bud pattern. CT scan of a patient with diffuse panbronchiolitis shows tree-in-bud pattern (solid arrow) and dilated, nonimpacted bronchioles (dashed arrows).