SILHOUETTE SIGN
- This classic roentgenographic sign first described by Felson in 1950 states that “an intrathoracic lesion touching a border of the heart,
aorta,
or diaphragm will obliterate that border on the roentgenogram
- An intra-thoracic lesion not anatomically contiguous with a border or a normal structure will not obliterate that border
- Reliable sign distinguishing anterior lung lesions from posterior or lower lesions
- When two objects of the same density touch each other the edge between them disappears (figure 2)
Fig. 2: SILHOUETTE SIGN. Chest radiograph shows middle and inferior right lobe pneumonia.
AIR BRONCHOGRAM SIGN
- It occurs in infiltration or edema in tissues adjacent to patent bronchi
- Seen on chest radiographs or CT
- Associated with air-space disease
- It implies: patency of proximal airways,
evacuation of alveolar air by absortion (atelectasis),
replacement (pneumonia) or both,
consolidation,
tumor,
lymphoma (figure 3)
Fig. 3: AIR BRONCHOGRAM SIGN. Chest CT and chest radiograph demonstrate air bronchograms in patients with right upper lobe pneumonia. Schematic drawings.
SIGNET RING SIGN
- Seen on CT/HRCT scans of chest
- CT finding in patients with bronchiectasis
- Ring shadow representing dilated thick-walled bronchus associated with a nodular opacity representing pulmonary artery (figure 4)
Fig. 4: SIGNET RING SIGN. Chest CT shows small bronchiectasis.
POPCORN CALCIFICATION
- A cluster of sharply defined,
irregularly lobulated,
calcifications,
usually in a pulmonary nodule (figure 5)
- Popcorn calcifications within a well-circumscribed pulmonary nodule are highly suggestive of pulmonary chondroid hamartoma
Fig. 5: POPCORN CALCIFICATION. Chest radiograph demonstrates nodule with "popcorn calcification" in the right lower lobe representing hamartoma.
TRAM-TRACK SIGN
- Parallel line opacities (tram tracks) caused by thickened dilated bronchi (figure 6)
- Bronchiectasis- defined as localized irreversible dilatation of part of the bronchial tree
- infection
- bronchial obstruction (endobronchial tumors,
encroachment of hilar lymph nodes,
foreign body aspiration)
- cystic fibrosis
- primary ciliary dyskinesia
- immunodeficiency states
- congenital anatomic defects (pulmonary sequestration,
Mounier-Kuhn syndrome) etc
Fig. 6: TRAM-TRACK SIGN. Chest CT demonstrates tram-track sign. Schematic drawing and corresponding picture.
TREE-IN-BUD SIGN
- Commonly seen at thin-section CT
- This sign appears as small,
peripheral,
centrilobular soft tissue nodules connected to multiple contiguous,
linear branching opacities (figure 7)
- This radiologic term represents the mucous plugging,
bronchial dilatation,
and wall thickening of bronchiolitis
- The histopathological correlate demonstrates small airway plugging with mucus,
pus,
or fluid,
with dilated bronchioles,
peribronchiolar inflammation,
and wall thickening
- Initially described in endobronchial spread of tuberculosis
- Recognized in diverse entities
- infection (bacterial,
fungal,
viral)
- congenital disorders (cystic fibrosis,
Kartagener syndrome)
- idiopathic disorders (obliterative bronchiolitis)
- aspiration
- inhalation (toxic fumes and gases)
- immunologic disorders
- connective tissue disorders (rheumatoid arthritis,
Sjogren)
- neoplasms (gastric,
breast and renal cancer,
Ewing sarcoma)
Fig. 7: TREE-IN-BUD SIGN. Chest CT shows tree-in-bud images. Schematic drawings and corresponding picture.
CT ANGIOGRAM SIGN
- Finding may be seen on CT of chest after IV contrast material administration
- Consists of enhancing branching pulmonary vessels in homogeneous low-attenuating consolidation (figure 8)
- Low-attenuating component can be caused by production of mucin within air spaces
- Initially described in 1990 by Im et al as a specific sign (92%) of lobar bronchoalveolar carcinoma
- pneumonia
- pulmonary edema
- obstructive pneumonitis central tumor
- metastasis from GI carcinomas
- lymphoma
Fig. 8: CT ANGIOGRAM SIGN. Chest CT and schematic drawing.
FINGER-IN-GLOVE SIGN
- Visible on chest radiographs or CT
- Indicates mucoid impaction within an obstructed bronchus
- Characterized by branching tubular or fingerlike opacities (figure 9)
- Originate from the hilum and are directed peripherally
- Also seen in cases of dilated bronchi with secretions
- Visualization of the gloved fingers is made possible by collateral air drift through the interalveolar pores of Kohn and canals of Lambert aerating lung distal to the point of mucoid impaction (distal lung remains aerated)
- There are two broad etiologic categories: non-obstructive and obstructive
Non-bstructive:
- allergic bronchopulmonary aspergillosis (ABPA)
- asthma
- cystic fibrosis (secondary to mucociliary dysfunction and thick mucous secretions)
Obstructive:
- neoplasms (bronchial hamartomas,
lipomas,
bronchogenic carcinoma,carcinoid).
- congenital (bronchial atresia,
intralobar sequestration,
bronchogenic cysts)
Fig. 9: FINGER-IN-GLOVE SIGN. Chest CT, schematic drawing and illustrative picture.
HALO SIGN
- Ground glass attenuation surrounding a pulmonary nodule/mass on CT images (figure 10)
- Described by Kuhlman in 1985 in patients with invasive aspergillosis
- In febrile neutropenic patients,
the sign suggests angioinvasive fungal infection,
(which is associated with a high mortality rate in the immunocompromised host) the zone of attenuation represents alveolar hemorrhage whereas the nodules represent areas of infarction and necrosis caused by thrombosis of small to medium sized vessels
- Associated with hemorrhagic nodules and may be caused by neoplasms or inflammatory conditions
- Familiarity with adequate clinical setting helps to narrow differentials:
- multiple nodules in immunocompromised patients could be infections,
Kaposi or lymphoma
- leukemia and fever may represent invasive aspergillosis
- immunocompetent patients with a solitary nodule may indicate bronchioloalveolar carcinoma
Fig. 10: HALO SIGN. Chest CT shows halo sign in a patient with schistosomiasis. Schematic drawings.
REVERSE HALO SIGN
- Central ground-glass opacity surrounded by denser consolidation of crescentic or ring shape,
at least 2 mm thick (figure 11)
- First described by Voloudaki in 1996
- Kim in 2003 used the term reverse halo
- Found to be relatively specific for cryptogenic organizing pneumonia (COP)
- Seen in other conditions:
- Wegener’s and lymphomatoid granulomatosis
- paracoccidiodomycosis
- neoplastic (metastasis)
- invasive aspergillosis
- lipoid pneumonia
- schistosomiasis
Fig. 11: REVERSE HALO SIGN. Chest CT demonstrates reverse halo images in a patient with schistosomiasis. Schematic drawings.
COIN LESION
- The term coin lesion was defined by Thornton et al in 1944 as a solitary lesion,
1 to 5 cm in size,
round or oval with well defined margins
- Solitary,
round,
circumscribed shadows found in the lungs in x-ray or CT examinations (figure 12)
- Smaller than 3 centimeters in diameter
- tuberculosis
- coccidioidomycosis
- histoplasmosis
- neoplasms (primary bronchogenic carcinoma,
metastatic tumors,
bronchial adenomas etc)
- cysts
- vascular anomalies
Fig. 12: COIN LESION. Chest CT shows a nodule in the left lower lobe. Metastasis. Schematic drawing and illustrative picture.
MILIARY SHADOWING
- The term miliary derives from the radiograqphic picture of diffuse,
discrete nodular shadows about the size of a millet seed
- Innumerable,
small (1-4mm) pulmonary nodules are seen scattered throughout the lungs (figure 13)
- tuberculosis
- histoplasmosis
- sarcoidosis
- rheumatoid arthritis
- pneumoconiosis
- COPD
- pulmonary siderosis
- bronchoalveolar carcinoma
- metastasis (thyroid,
kidney,
trophoblast and some sarcomas)
Fig. 13: MILIARY SHADOWING. Chest CT. Tuberculosis.
MONOD’S SIGN
- Air surrounding fungus ball or mycetoma (figure 14) in preexisting air cavity (old tuberculosis,
histoplasmosis,
sarcoidosis,
neoplasm)
- It should not be confused with the air crescent sign which is seen in recovering angioinvasive aspergillosis and heralds improvement in the condition
- The air around the mycetoma is often crescent shaped and hence,
the term air crescent sign is often used interchangeably by many to refer to both pathological processes
Fig. 14: MONOD’S SIGN. Chest CT. Mycetoma. Schematic drawing.
FALLEN LUNG SIGN
- This sign refers to the appearance of the collapsed lung occurring with a fractured bronchus (figure 15)
- It refers to the collapsed lung in a dependent position,
hanging on the hilum only by its vascular attachments and was first described by Oh et al in 1969 and by Kumpe et al in 1970
- The bronchial fracture results in the lung to fall away from the hilum,
either inferiorly and laterally in an upright patient or posteriorly,
as seen on CT in a supine patient
Fig. 15: FALLEN LUNG SIGN. Chest radiograph and schematic drawing.
BULGING FISSURE SIGN
- The bulging fissure sign refers to lobar consolidation causing lobar expansion and bulging of the adjacent fissure inferiorly (figure 16)
- Historically Klebsiella pneumoniae involving the RUP- Friedlander pneumonia
- Although previously reported in up to 30% of patients with Klebsiella pneumonia,
the finding is identified less commonly today,
most likely due to rapid prophylactic implementation of antibiotics.
- The most common infective causative agents are:
- Klebsiella pneumoniae
- Streptococcus pneumoniae
- Pseudomonas aeruginosa
- Staphylococcus aureus
- It may also be seen with bronchoalveolar carcinoma and tuberculosis
Fig. 16: BULGING FISSURE SIGN. Chest radiograph. Right upper lobe pneumonia. Schematic drawing.
FLAT WAIST SIGN
- Indicates left lower lobe collapse
- Visualized on frontal views
- Hilar structures shift downward and rotation of heart produces flattening of cardiac waist (figure 17)
Fig. 17: FLAT WAIST SIGN. Chest radiograph and schematic drawing.
GOLDEN S SIGN
- Described by Ross Golden in 1925
- Resembles a reverse S shape
- It can be seen on PA/lateral views and CT
- This sign is typically seen with right upper lobe collapse
- The medial portion of minor fissure is convex inferiorly due to a central mass and the lateral portion of the fissure is concave inferiorly (figure 18)
- It can be observed in cases of bronchial carcinoma,
primary mediastinal tumor,
metastasis and enlarged lymph nodes
Fig. 18: GOLDEN S SIGN. Chest radiograph and CT images demonstrate this sign. Bronchial carcinoma.
BAT WING APPEARANCE
- Bat's wing or butterfly pulmonary opacities refer to a pattern of bilateral perihilar shadowing (figure 19)
- It is classically described on a frontal chest radiograph but can also refer to appearances on chest CT
- pulmonary edema (especially cardiogenic)
- pneumonia (aspiration pneumonia,
PCP,
viral,
lipoid)
- inhalation injury (noxious gas,
liquid)
- pulmonary alveolar proteinosis
- pulmonary hemorrhage (e.g.
Goodpasture syndrome)
- lymphoma
- leukaemia
- bronchoalveolar carcinoma
Fig. 19: BAT WING APPEARANCE. Chest radiograph, schematic drawing and corresponding picture.
GROUND GLASS PATTERN
- Ground glass opacity is a hazy,
increased attenuation of lung with preservation of bronchial and vascular margins (figure 20)
- It is a nonspecific radiologic finding
- It is caused by partial filling of air spaces,
interstitial thickening,
partial collapse of alveoli,
normal expiration,
or increased capillary blood volume
- It can be seen with alveolar wall inflammation or thickening,
with partial air-space filling,
or with some combination of the two
- pulmonary edema
- adult respiratory distress syndrome (ARDS)
- viral,
mycoplasmal,
and pneumocystis pneumonias
hypersensitivity pneumonia
- pulmonary hemorrhage
- other diffuse interstitial lung diseases
Fig. 20: GROUND GLASS PATTERN. Chest CT images and illustrative picture.
CRAZY PAVING SIGN
- Scattered or diffuse ground glass attenuation with superimposed intralobular and interlobular septa thickening (figure 21)
- Commonly seen at thin-section CT
- Initially described in pulmonary alveolar proteinosis
- Recognized in diverse entities
- infection (Pneumocystis jiroveci pneumonia, organizing pneumonia,
usual interstitial pneumonia,
non-specific interstitial pneumonia,
and exogenous lipoid pneumonia)
- neoplasm (bronchioloalveolar carcinoma)
- pulmonary alveolar proteinosis
- sarcoidosis
- respiratory bronchiolitis with interstitial lung disease
sanguineous (pulmonary hemorrhage syndromes,
ARDS)
Fig. 21: CRAZY PAVING SIGN. Chest CT with schematic drawing and illustrative picture.
MOSAIC PATTERN
- Patchy ground glass opacicities,
resulting in a mosaic pattern of lung attenuation (figure 22)
- Such a pattern can be seen in infiltrative lung disease,
airway abnormalities (e.g.,
asthma,
bronchiolitis obliterans),
and chronic pulmonary vascular disease (e.g.,
chronic thromboembolic disease)
- The distinction between these three entities can be made by observing the size of the pulmonary vessels in the area of increased lung attenuation (increased in both airway disease and vascular disease,
but not in infiltrative disease),
and by examining air trapping on expiratory scans (indicating airway disease)
Fig. 22: MOSAIC PATTERN. Chest CT with schematic drawing and illustrative picture.
SANDSTORM APPEARANCE
- Seen on CT or chest X-ray
- The appearance is given by the presence of diffuse,
scattered,
bilateral areas of micronodular calcifications (sandstorm appearance)
- Pulmonary alveolar microlithiasis (PAM) should be considered (figure 23)
- PAM is an uncommon chronic disease characterized by calcifications within the alveoli which occurs in the absence of any known disorder of calcium metabolism
- On CT scans diffuse ground-glass opacities throughout both lungs can be seen in association with calcified nodules
Fig. 23: SANDSTORM APPEARANCE. Chest radiograph in a patient with alveolar microlithiasis and illustrative picture.
HONEYCOMB LUNG
- The term “honeycomb lung” first appeared in the English literature in 1949 (Oswald and Parkinson)
- Radiologically,
in the latest version from the Fleischner Society,
it is defined as “clustered cystic air spaces,
typically of comparable diameters on the order of 3–10 mm but occasionally as large as 2.5 cm...
usually subpleural and characterized by well-defined walls” (figure 24)
- Recent understanding indicates that “honeycombing is often considered specific for pulmonary fibrosis and is an important criterion in the diagnosis of usual interstitial pneumonia (UIP)”
- idiopathic interstitial pneumonia
- diffuse alveolar damage
- asbestosis
- interstitial granulomatous diseases
- eosinophilic granuloma
Fig. 24: HONEYCOMB LUNG. Chest CT with schematic drawing and illustrative picture.
WESTERMARK SIGN
- Described by Neil Westermark in 1938
- Chest radiograph and CT show increased lucency or hypoattenuation (figure 25)
- Typically signifies either occlusion of a larger lobar/segmental artery or widespread small vessel occlusion
- Represents oligemia distal to PE; seen only in 2% of patients
- Sign results from combination of dilatation pulmonary arteries proximal embolus and collapse of distal vasculature
- Low sensitivity 11%,
high specificity 92%
Fig. 25: WESTERMARK SIGN. Chest radiograph and schematic drawing.
WAVE SIGN
- Sign produced by lateral indentation of thymus by adjacent anterior ribs resembling a wave (figure 26)
- This sign in seen in the pediatric population and represents a normal thymus
Fig. 26: WAVE SIGN. Chest radiograph with schematic drawing and illustrative picture.
DEEP SULCUS SIGN
- The presence of radiolucency in a deep costophrenic sulcus on a supine thoracic radiograph is characteristic of a pneumothorax in a supine patient (figure 27)
- Seen on X-rays in supine position
- Intrapleural air rises to the highest portion of the hemithorax leading to the presence of a lucency in the anteromedial,
subpulmonic,
and lateral basilar space adjacent to the diaphragm
- 30% pneumothoraces are undetected
- It is useful in confirming suspected pneumothorax on AP supine radiography in compromised patients,
such as those in the intensive care setting
Fig. 27: DEEP SULCUS SIGN. Chest radiograph with schematic drawing and illustrative picture.
References: internet
TAPERED MARGINS SIGN
- Lesions in the chest wall,
pleura or mediastinum have smooth tapered borders and obtuse angles (figure 28)
- While parenchymal lesions usually form acute angles
Fig. 28: TAPERED MARGINS SIGN. Chest radiographs with schematic drawings. Mesothelioma and thymic lymphosarcoma.
CERVICOTHORACIC SIGN
- Used to determine location of mediastinal lesion in the upper chest
- Based on principle that an intrathoracic lesion in direct contact with soft tissues of the neck will not be outlined by air (figure 29)
- Uppermost border of the anterior mediastinum ends at level of clavicles,
so when the cephalic border of a mass is obscured at or below the level of the clavicles,
it is deemed to be a “cervicothoracic lesion” involving the anterior mediastinum
- Middle and posterior mediastinum extends above the clavicles (figure 29)
- Mediastinal mass projected superior the level of clavicles must be located either within middle or posterior mediastinum
- More cephalad the mass extends the most posterior the location
Fig. 29: CERVICOTHORACIC SIGN. Chest radiographs with schematic drawings. Lymphoma.
1-2-3 SIGN
- Characterized by bilateral hilar and right paratracheal lymphadenopathy so-called Garland triad or 1-2-3 sign (figure 30)
- Suggestive of sarcoidosis
- Separation between nodes and heart which is not seen in lymphoma
Fig. 30: 1-2-3 SIGN. Chest radiographs with schematic drawings. Sarcoidosis.
HILUM OVERLAY SIGN
- Described by Benjamin Felson
- If hilar vessels are sharply delineated it can be assumed that the overlying mass is anterior or posterior (figure 31)
- If mass is inseparable from pulmonary arteries,
structures are adjacent to one another
Fig. 31: HILUM OVERLAY SIGN. Chest radiograph with schematic drawing.
HILUM CONVERGENCE SIGN
- Used to distinguish between a prominent hilum and an enlarged pulmonary artery
- If branches of PA converge toward central mass,
is an enlarged PA (figure 32)
- If branches of PA converge toward heart rather than mass,
is a mediastinal tumor
Fig. 32: HILUM CONVERGENCE SIGN. Chest radiograph with schematic drawing.
THORACOABDOMINAL SIGN
- Posterior costophrenic sulcus extends more caudally than anterior basilar lung
- Lesion extending below the dome of diaphragm must be in posterior chest whereas lesion terminating at dome must be anterior (figure 33)
- Thoracoabdominal signs were described by Felson
Fig. 33: THORACOABDOMINAL SIGN. Chest radiograph with schematic drawing. Hamartoma.
WATER BOTTLE CONFIGURATION
- Seen in pericardial effusion
- inflammatory
- infectious
- malignant
- autoimmune processes within the pericardium
- Chest radiography shows an enlarged cardiac silhouette (figure 34)
Fig. 34: WATER BOTTLE CONFIGURATION. Chest radiograph with schematic drawing and illustrative picture.
DOUBLE DENSITY SIGN
- On frontal chest radiographs,
this sign presents as a curvilinear density projecting over the right retrocardiac region,
indicating left atrial enlargement
- The curvilinear line represents the inferolateral margin of the left atrium (figure 35)
- The double density sign may be observed in patients without cardiac disease; however,
there is a semiquantitative measurement to estimate the left atrial diameter and better estimate whether it is a real finding
Fig. 35: DOUBLE DENSITY SIGN. Chest radiograph with schematic drawings.
SPLIT PLEURA SIGN
- Seen on contrast enhanced CT of chest
- Separation and enhancement of the visceral and parietal pleural layers on CT is considered strong evidence of empyema
- Normally,
individual pleural layers are not discernable as discrete structures
- Empyemic fluid fills the pleural space,
resulting in thickening and enhancement of the pleura with a denotable separation (figure 36)
- It can also be seen with exudative effusion
- bacterial pneumonia
- cancer
- viral infection
- PE
Fig. 36: SPLIT PLEURA SIGN. Chest radiograph with schematic drawing.