Why do we need to know? To direct care while awaiting an “official read” Low level radiation for the patient Easily available and noninvasive Relatively inexpensive
Objectives Basics of technique Type of film and the “tions” Identification of structures on a “normal” CXR Alveolar vs interstitial, lobar anatomy, silhouette sign, air bronchograms, and patterns of lung disease The mediastinum, pleura, and heart Systematic approach to interpretation Cases
Technique PA and lateral AP Which is preferred and why? Lateral film – left side of chest against x-ray cassette Decubitus films
The Silhouette Sign There are 4 basic radiographic densities Gas, fat, soft tissue (water), and metal (bone) Anatomic structures are recognized on x-ray by their density differences Two substances of the same density in direct contact can’t be differentiated Loss of the normal radiologic silhouette (contour) is called the “silhouette sign”
Localizing Lesions Where is the silhouette sign?
Obscured L heart border = lingula Aortic knob obliterated = left upper lobe Right lung base w heart border seen = right lower lobe Right lung base w heart obscured = right middle lobe Descending aorta obscured = left lower lobe EXCEPTIONS: Pseudosilhouette of diaphragm in underpenetrated film Right heart border my overlap spine Heart obscures anterior left diaphragm on lateral
The Air Bronchogram When lung is consolidated and bronchi contain air, the dense lung delineates the air-filled bronchi Visualization of air in the intrapulmonary bronchi is called the “air bronchogram sign” Abnormal finding Can be seen in: PNA, edema, infarction Chronic lung lesions
NO Air Bronchograms… In pneumonia if bronchi are filled with secretions If cancer obstructs a bronchus Interstitial fibrosis Asthma/emphysema (hyperinflation)
I: Anterior Mediastinum Heart Retrosternal clear space 5 T’s II: Middle Mediastinum Esophagus Arch and descending aorta Trachea III: Posterior Mediastinum Paravertebral area Lymph nodes in all 3!
The Pleura The posterior costophrenic angle is the deepest and only seen on the lateral film The lateral film is more sensitive for detection of small pleural effusions How much fluid can be seen on a radiograph? Erect PA: 175 mL Erect lateral: 75 mL Decubitus: >5 mL Supine: Several hundred mL
The Heart The horizontal width of the heart should be less than ½ the widest internal diameter of the thorax
Left and Right Ventricular Enlargement Left ventricular enlargement Frontal: LHB moves laterally and cardiac apex inferolaterally Lateral: LHB moves inferoposteriorly Right ventricular enlargement Frontal: RHB further right Lateral: Contacts lower half of sternum (instead of lower 3 rd )
Cephalization Enlargement of the upper lobe vessels “Vascular redistribution” “Kerley B” lines: interstitial edema thickening the interlobular septa causing short lines perpendicular to the pleural surface
Systematic approach ABCDE Airway Bones and breasts Cardiac and costophrenic Diaphragm Edges and extrathoracic Fields (lung fields and failure) ATMLL (“Are There Many Lung Lesions?”) Abdomen Thorax – bones and soft tissues Mediastinum Lungs – unilateral and bilateral