Common misconceptions and mistakes
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Believing that reading a chest x-ray (CXR) requires advanced training, experience, and/or a “special eye”
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Declaring a “blunted costophrenic angle” when the entire diaphragm is silhouetted out
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Using a myriad of adjectives to describe an opacity (eg, fuzzy, hazy)
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Missing segmental collapse
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Deciding endobronchial obstruction is the etiology of whole lung atelectasis based on a sharply demarcated cut in the mainstem air column
Approach to the chest radiograph
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How we see discrete structures in the chest (eg, heart borders, hemidiaphragms):
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Borders and outlines are seen on CXR when adjacent structures are of different densities (eg, air and soft tissue)
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Two adjacent soft tissue densities (eg, the left and right ventricles) will not be visible separately because they lack an air interface
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How we detect pathology (eg, pneumonia, tumor)—the silhouette sign :
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When a new process occurs in the chest (eg, pneumonia or tumor) it will often opacify or “silhouette out” an expected structure by removing an expected air–soft tissue interface, leading to the loss of an expected line (eg, right middle lobe [RML] pneumonia opacifying the right heart boarder)
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This area of decreased clarity ( or missing line ) is described as an “opacity”
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Loss of clarity of a structure (eg, diaphragm, heart border) implies a supervening abnormality
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Even when the abnormality itself is vague, often just a missing or interrupted line
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The missing or interrupted line is the finding ( Fig. 4.1 )
Fig. 4.1
Silhouette sign. (A) Frontal view of the chest shows that the line generated by the right heart boarder is interrupted by a vague, focal, veil-like opacity. The interrupted line is the objective abnormal finding. The lateral film shows a well-circumscribed, wedge-shaped, dense opacity extending from the hilum to the chest wall. Diagnosis: right middle lobe atelectasis. (B) Markup of the same film.
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Do not (let your mind and eye) repair interrupted lines (natural tendency)
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Screening for opacities:
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Screening for opacities on the frontal film = looking for an interruption or absence of an anticipated line
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The anticipated lines are:
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Right and left : hemidiaphragm, heart border, main pulmonary artery (PA), and the paratracheal stripe
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Left only (the anteroposterior [AP] window) : ascending and descending aorta, with the top of the left PA
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Normal hemidiaphragms and heart boarders are always sharp
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Right and left PAs are less distinct (vessels branching in all planes)
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Should get a sense of left and right main PA and right descending PA ( Fig. 4.2 )
Fig. 4.2
Anticipated lines. The frontal chest radiograph shows the anticipated lines are right and left: paratracheal stripe, main pulmonary artery (PA), heart border, and hemidiaphragm. The anticipated lines of the anteroposterior window are the ascending and descending aorta, with the top of the left PA (forming the floor of the triangle/window). Note: normal hemidiaphragms and heart boarders are always sharp, where normal pulmonary arteries are less distinct (should get a sense of left and right main PA and right descending PA).
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After anticipated lines are identified, screen the remaining lung fields for abnormally increased or decreased attenuation and/or abnormal lines (coarse or fine)
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Screening for opacities on the lateral film = looking for an opacified “clear” space
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The anticipated clear spaces are:
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Anterior clear space
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Subcarinal space
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Base of the spine
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The hemidiaphragms should also be visualized
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Note the anterior portion of the left hemidiaphragm is silhouetted out by the apex of the heart ( Fig. 4.3 )
Fig. 4.3
Screening for opacities on the lateral film involves looking for an opacified “clear” space. The anticipated clear spaces are the anterior, and subcarinal spaces and base of the spine. The hemidiaphragms should also be visualized. Note: the anterior portion of the left hemidiaphragm is silhouetted out by the apex of the heart.
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Characterizing the opacity:
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Dense Consolidation (soft tissue density / white), implies complete alveolar filling or atelectasis
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Cannot see normal underlying structures (causes complete opacification)
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DDx: Atelectasis vs. Pneumonia vs. Mass
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Vague bordered dense consolidation ≈ Pneumonia
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Well circumscribed dense consolidation:
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With air bronchograms ≈ Atelectasis
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Without air bronchograms:
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With volume loss ≈ Atelectasis with airway obstruction
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Without volume loss ≈ Mass / Tumor
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Ground glass (increased attenuation / gray), implies partial alveolar filling or atelectasis
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Can still see some normal underlying structures (causes incomplete opacification)
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DDx: Any alveolar filling process (e.g. edema, inflammation, atypical infection, hemorrhage)
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Fine reticular lines (lots of fine lines), implies Interstitial edema
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Normal underlying structures clearly visible, but close inspection shows that anticipated lines are not sharp, and are instead ‘blurry’ or ‘hazy’
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Corse reticular lines (lots of larger lines in lattice like pattern) implies fibrosis
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Veil – like (homogenous increased attenuation / gray) implies effusion (no meniscus anticipated when the patient is supine, or semi supine)
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Cannot see normal underlying structures (causes complete opacification)
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Note: Basilar subsegmental atelectasis may appear veil like (indistugusiable from a small effusion)
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Visually isolating areas of the CXR can help (ie, mentally or by zooming in and focusing on just the opacified right hemidiaphragm) ( Fig. 4.4 )
Fig. 4.4
Five basic types of opacities are shown “silhouetting out” the right hemidiaphragm.
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Different types of opacities often occur together ( Fig. 4.5 )
Fig. 4.5
The right hemidiaphragm is nearly completely opacified (white line denotes only remaining visualized portion). It is opacified by both a poorly circumscribed dense consolidation, medially, (with air bronchograms) and a lateral veil. Note: this constellation of findings represents either effusion with compressive atelectasis or pneumonia with parapneumonic effusion (clinical correlation required).
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After an opacity is identified and characterized, decide if it is focal or diffuse :
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If focal , decide if it is well-circumscribed (clearly defined borders) versus vague (poorly defined borders)
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Well-circumscribed ≈ segmental atelectasis, lobar PNA, or tumor (note: subsegmental atelectasis may also be well-circumscribed/linear (eg, plate-like atelectasis) ( Fig. 4.6 )
Fig. 4.6
(A) Frontal view of the chest shows a right middle lobe spherical opacity ≈ tumor. Note: subsegmental atelectasis (seen at the superior/lateral aspect of the opacity) may also be linear and well-circumscribed (eg, plate-like atelectasis). (B) Frontal view of the chest shows a well-circumscribed, triangular, right lower lobe opacity (a.k.a. sail sign ) of the right lower lobe segmental collapse/atelectasis (note right sided volume loss).
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