Introduction to Thoracic
Radiology
Dr. LeeAnn Pack
Dipl. ACVR
Indications
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Coughing
Dyspnea/ Tachypnea
Heart Murmur, Collapse
Primary or Secondary Neoplasia
– Check for metastasis
• Thoracic Trauma
• Chest Wall Mass
• Exercise Intolerance, Weight Loss
Technical Factors
• Potential for Movement
– Decrease mAs
• High inherent contrast
area
– High kVp
• Collimation
• Centering – caudal
scapula
– Thoracic inlet to
diaphragm
– Pull forelimbs forward
Determining the Phase of
Respiration
• Always expose at peak inspiration
– Maximizes lung contrast
– Inspiratory lateral view
• Caudodorsal aspect of lung caudal to T12
• Increased aeration of accessory lung lobe
• Separation of heart silhouette and diaphragm
– Inspiratory VD/DV view
• Diaphragmatic cupola caudal to mid T8
• Lung tips caudal to T10
Inspiratory vs. Expiratory Lateral
Note the space inside the
triangle
Inspiratory vs. Expiratory VD
Easy to see the difference in well
visualized lung
DV vs. VD
• DV
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Less stressful, better for heart
Diaphragm rounded
Caudal pulmonary vessels better visualized
Better to see small amount of pleural air
• VD
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Better for lungs
Hear appears elongated
Flat diaphragm – Mickey Mouse ears
Better to see small amount of pleural fluid
DV vs. VD
Right vs. Left Lateral etal.
• Right Lateral
– Better cardiac detail
– R crus forward
– See Cava go into it
• Left Lateral
– Heart appears round
– L crus forward
– See Cava go past
• Anesthesia
• Breed Differences
Importance of Both Lateral Views
The Effects of Lateral
Recumbency
• Lung lesions (mass, nodule, infiltrate)
may only be seen on 1 view!!!
• Only the non-dependent (up) lung can
be critically evaluated
– Dependent lung loses aeration
(atelectasis)
• Increases in opacity
• Silhouettes with lesions
Special Views
• Horizontal beam
– Upright VD view
• Pleural fluid will fall
caudally so CMM can be
seen
– Recumbent lateral VD
– Position patient to move
pleural fluid away from
area of interest
• Cranial mediastinal mass
• Lung mass
– Check for free air – side
up
Interpretation of Thoracic
Radiographs
• Develop your own routine
• Systematically evaluate everything on
every view
• Evaluate a specific structure
simultaneously on both views (i.e.
assess lungs on VD and lat before
moving on to mediastinum)
Interpretation of Thoracic
Radiographs
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Heart
Lungs
Mediastinum
Pleural space
Chest wall
Bones, Abdomen,Neck
Normal Cardiac Silhouette
• Subjective
– Dog = 2 ½ - 3 ½ intercostal spaces
– Cat = 2 – 2 ½ intercostal spaces
• 65% or less on VD/DV view
• Objective
– Buchanan method
Clock Face
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11-1 Aortic Arch
1-2 Main Pulmonary Trunk
2-3 Left Auricle
2-5 Left Ventricle
5-9 Right Ventricle
9-11 Right Atrium
Centrally – Left Atrium
Lateral View
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Make a Plus sign
Bermuda triangle
Left atrium
Left Ventricle
Right Ventricle
Thoracic and Pulmonary
Vessels
• Aorta
• Caudal Vena Cava
• Cranial pulmonary
vessels
– Proximal third rib
• Caudal pulmonary
vessels
– 9th rib where crosses
• Veins are ventral and
central
Trachea, Bronchial Tree
• Carina – then splits to the main stem
bronchi then lobar bronchi
• Tracheal rings can mineralize
• Decreased tracheal diameter
– Tracheal narrowing (stenosis, extramural
compression), Tracheal hypoplasia,
Tracheal collapse
Lungs
• Normal anatomy
– Left
• Cranial (cranial
subsegment)
• Cranial (caudal
subsegment)
• Caudal
– Right
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Cranial
Middle
Caudal
Accessory
Lungs
• Normal lung boundaries
– 4th to 5th ICS on VD
• Fissure b/w L cranial lung subsegments
• Fissure b/w R cranial and middle lung lobes
– 6th to 7th ICS on VD
• Fissure b/w L cranial and caudal lobes
• Fissure b/w R middle and caudal lobes
Lungs
• Regions of a specific
lung lobe
– Perihilar (hilar)
– Midzone
– Periphery
• Distribution of
disease may lead to
etiology
– Edema
– Pneumonia
The Mediastinum
• Cranial, middle, caudal compartments
• Routinely visible structures:
– Heart, trachea, cvc, aorta, +/- thymus, +/esophagus
– Cranioventral mediastinal reflection
– Caudoventral mediastinal reflection
• Aka phrenopericardiac ligament
Mediastinal reflections
Mediastinal Abnormalities
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Shift
Masses
Fluid
Pneumomediastinum
Mediastinal Shift
• Assess on VD or DV
– Position of heart, trachea, aorta, cvc
• ***MUST BE STRAIGHT or may be
artifactual!!!
• Ipsilateral shift
– Unilateral decrease in lung volume (atelectasis)
• Contralateral shift
– Increase in lung volume
– Intrathoracic mass
Mediastinal Shift
Cranial Mediastinal Masses
• Lie on or adjacent to midline
• Lateral or dorsal displacement of mediastinal
structures
– Elevation of trachea
• ***Diff dx= large volume pleural effusion
• Widening of mediastinum on VD
– Should be < 2x width of vertebrae on VD
– Fat may artifactually widened, esp. Bulldogs
• Increased opacity in mediastinum
Cranial Mediastinal Mass
Examples of CMM’s
Mediastinal Fluid
• Increased soft tissue in mediastinum
• May appear as a soft tissue mass
• Common causes
– Feline infectious peritonitis
– Hemorrhage
• Trauma
• Coagulopathy
– Esophageal perforation
Pneumomediastinum
• Free air in mediastinum
– Enhanced visualization of mediastinal structures
– Not dyspneic
• Can progress to pneumothorax
– Pneumothorax does NOT progress to
pneumomediastinum
• ***Mediastinum communicates with neck and
retroperitoneal space
– Subcutaneous emphysema
– Pneumoretroperitoneum
Pneumomediastinum
Causes of
Pneumomediastinum
• Air escaping into lung interstitium from
ruptured alveoli
– Trauma, hyperinflation during anesthesia
• Extension of gas from neck fascia
• Tracheal perforation
– Trauma, venipuncture, TTW, cuff overinflation
• Esophageal perforation
• Extension of retroperitoneal gas
• Gas producing organism in mediastinum
The Pleural Space
• Two layers
– Parietal
• Lines
thoracic wall
and
diaphragm
– Visceral
• Lines outer
lung surface
The Pleural Space
• Normal pleura not usually
visible
• May be visible with
pleural thickening or if
beam strikes normal
pleura tangentially
– Between right middle and
right caudal lobes on Left
Lateral
• Visible with pleural
effusion or pneumothorax
LCr-cr
RC
LCr-cd
RM
LCa
RC
Acc
Pleural Effusion
• Radiographic signs
– Interlobar fissure lines
• VD more sensitive with small volumes
– Retraction of lungs
– Increased soft tissue in thorax outlining
lungs
• Esp. dorsal to sternum on lateral
– Silhouetting of heart/ diaphragm
Pleural Effusion
Pneumothorax
• Air in pleural space
– External, lung, or mediastinum
• Radiographic signs
– Retraction of lungs
– Lucent space between lung and chest wall
• ***Vessels do not extend to chest wall
• Use a hotlight
– Dorsal “displacement” of heart on lateral
• Actually sliding into dependent thorax
Pneumothorax
Causes of Pneumothorax
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Trauma
Lung rupture
Chest wall rent
Extension of pneumomediastinum
Rupture of cavitary lung mass
Tension Pneumothorax
• Pleural space pressure exceeds
atmospheric pressure during both
phases of respiration
• Severe lung collapse
– Lungs lose normal shape
• If unilateral, may cause contralateral
medistinal shift
• Caudal displacement of the diaphragm
Tension Pneumothorax
Extrathoracic Structures
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Sternum
Vertebrae
Ribs
Adjacent soft
tissues
• Diaphragm
Extrathoracic Structures
• Extrathoracic
changes may
indicate cause of
intrathoracic findings
– Examples
• Pneumothorax
– Rib fractures may
suggest secondary to
trauma
• Pleural effusion
secondary to rib or
chest wall mass
The Diaphragm
• Cupola
– Cranioventral convex
portion
• Right and left crura
– Attach to cranioventral
border of L3 and body of
L4
– May cause irregularity on
these surfaces
• Appearance depends on
centering of X-ray beam
The Diaphragm