Lecture 8 Introduction to Thoracic Radiology

haddockhellskitchenUrban and Civil

Nov 15, 2013 (3 years and 9 months ago)

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INTRODUCTION TO THORACIC RADIOLOGY


The thoracic radiographic study is probably the most common study performed in
veterinary medicine.

Indications

for performing thoracic radiographs:



Coughing



Dyspnea/ Tachypnea



Heart Murmur, Collapse



Primary or Seconda
ry Neoplasia



Check for metastasis



Thoracic Trauma



Chest Wall Mass



Exercise Intolerance, Weight Loss


Technical Factors



Potential for Movement



Decrease mAs


with a shorter time, this will minimize the possibility of
motion



High inherent contrast area



High
kVp


we are not worried about the loss of contrast by using a high
kVp technique since the thorax has so many different radio opacities
present.



Collimation


the beam should be collimated to include from the thoracic inlet
to the diaphragm. The tighter
the beam is collimated the less scatter will be
present.



Centering


caudal aspect of the scapula


this is usually easy to palpate



Thoracic inlet to diaphragm



Pull forelimbs forward


it is imperative that the forelimbs are pulled
cranially so the triceps

musculature does not overlie the cranial mediastinal
area.


Determining the Phase of Respiration



Always expose at peak inspiration



Maximizes lung contrast


allow better visualization of pulmonary
parenchyma. The diaphragm will be displaced caudally so
the lung
parenchyma is not compressed.



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



Lun
g tips caudal to T10



DV vs. VD



DV



Less stressful for patients who are dyspenic, very large or difficult to
handle. Many believe the DV is better for evaluation of the heart.



Diaphragm rounded


like one large dome



Caudal pulmonary vessels better visuali
zed


this is especially important
when evaluating for heartworm disease.



Better to see small amount of pleural air


the air will rise to the tips of the
thorax caudally



VD



Better for lungs


most people routinely do the VD view



Hear appears elongated



Flat diaphragm


Mickey Mouse ears


3 lumps



Better to see small amount of pleural fluid




Right Lateral



most people routinely do the Right lateral



Better cardiac detail



R crus forward



See Cava go into the right crus



Left Lateral



done if pathology is su
spected in the right lung lobes or if a
metastasis check is being performed



Heart appears round



L crus forward



See Cava go past the first crus (left) and enters the caudal one (right)




Anesthesia

Rads made while under general anesthesia or while heavily s
edated

-

This should be avoided if possible.

-

Will cause the pulmonary parenchyma particularly on the dependent side
to become congested or show evidence of partially atelectasis

o

Due to decreased expansion of the down lung

o

Due to change in blood flow to the l
ung

-

If the radiographs must be made while the patient is under anesthesia, the
position of the patient should be changed to allow for expansion of the
lungs with a re
-
breathing bag.

A breath hold technique can be performed to inflate the lungs before the
e
xposure



Breed Differences

-

The appearance of the thoracic cavity including the heart and pulmonary
parenchyma can appear slightly different depending on the breed of dog

Deep chested

Dobe, giant breeds ect.



Cardiac silhouette usually 2 ½ intercostals space
s on the
lateral



Cardiac shape is more upright with less contact of the
diaphragm



The cardiac shape is round on the VD view

Barrel chested


round body short leg dogs


bull dog, Bassett
hound, dachshund and many toy breeds



Cardiac silhouette usually 3 ½ i
ntercostals spaces on the
lateral



Cardiac shape is more rounded on the lateral and there is
increased contact with the diaphragm

Average


in between


The Effects of Lateral Recumbency

Which “side” of the hemithorax is best seen on laterals?

-

The dependent
lung will become compressed because the lung can not
fully expand with the weight of the patient on that lung thus causing an
increase in radiopacity

-

The non dependent lung will be better aerated thus highlighting a soft
tissue pulmonary change in that lun
g

-

In practice this is used in many ways:

o

Pneumonia


commonly occurs in the right middle lung lobe


take
a left lateral

o

Solitary pulmonary mass


if is located in left cranial lung


the
right lateral would allow better visualization of the mass

Criticall
y thinking about which lateral will show the pulmonary change you are
expecting is imperative.



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 me
diastinal 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



Heart



Lungs



Mediastinum



Pleural space



Chest wall



Bones, Abdomen, Neck


Normal Cardiac Silhouette



Subjective on the lateral view



Dog = 2 ½
-

3 ½ intercostal spaces



Cat = 2


2 ½
intercostal spaces


as cats age the heart may lie more
parallel to the sternum



65% or less on VD/DV view



Objective



Buchanan method



Clock Face



11
-
1 Aortic Arch



1
-
2 Main Pulmonary Trunk



2
-
3 Left Auricle



2
-
5 Left Ventricle



5
-
9 Right Ventricle



9
-
11 Right At
rium



Centrally


Left Atrium



Lateral View



Make a Plus sign



Bermuda triangle = right atrium, aorta and main pulmonary trunk



Left atrium



Left Ventricle



Right Ventricle


Thoracic and Pulmonary Vessels



Aorta



Caudal Vena Cava



Cranial pulmonary vessels


best
seen on lateral view



The size should be smaller than the proximal portion of the third rib



Caudal pulmonary vessels


best seen on DV view



The vessel should form a square with the 9
th

rib where it crosses it (as
opposed to a rectangle.



Veins are ventral an
d central


Trachea, Bronchial Tree



Carina


then splits to the main stem bronchi then lobar bronchi



Tracheal rings can mineralize


this is particularly seen in brachycephalic
breeds



Decreased tracheal diameter



Tracheal narrowing (stenosis, extramural comp
ression), Tracheal
hypoplasia, Tracheal collapse


Lungs



Normal anatomy



Left



Cranial (cranial subsegment)



Cranial (caudal subsegment)



Caudal



Right



Cranial



Middle



Caudal



Accessory



Normal lung boundaries



4
th

to 5
th

ICS on VD



Fissure b/w L cranial lung sub
-
seg
ments



Fissure b/w R cranial and middle lung lobes



6
th

to 7
th

ICS on VD



Fissure b/w L cranial and caudal lobes



Fissure b/w R middle and caudal lobes



Regions of a specific lung lobe



Perihilar (hilar)



Midzone



Periphery



Distribution of disease may lead to etio
logy



Edema



Pneumonia


The Mediastinum



Cranial, middle, caudal compartments



Routinely visible structures:



Heart, trachea, cvc, aorta, +/
-

thymus, +/
-

esophagus



Cranioventral mediastinal reflection



Caudoventral mediastinal reflection


seen on left side of t
horax

Mediastinal Abnormalities



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


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 m
ediastinum on VD



Should be < 2x width of vertebrae on VD



Fat may artifactually widened, esp. Bulldogs



Increased opacity in mediastinum


Mediastinal Fluid



Increased soft tissue opacity in mediastinum



May appear as a soft tissue mass



Common causes



Feline inf
ectious 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 pneumomediasti
num



***Mediastinum communicates with neck and retroperitoneal space



Subcutaneous emphysema



Pneumoretroperitoneum


Causes of Pneumomediastinum



Air escaping into lung interstitium from ruptured alveoli



Trauma, hyperinflation during anesthesia



Extension of ga
s from neck fascia



Tracheal perforation



Trauma, venipuncture, TTW, cuff over inflation



Esophageal perforation



Extension of retroperitoneal gas



Gas producing organism in mediastinum


The Pleural Space



Two layers



Parietal



Lines thoracic wall and diaphragm



Vi
sceral



Lines outer lung surface



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


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


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 tho
rax


Causes of Pneumothorax



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



Lu
ngs lose normal shape



If unilateral, may cause contralateral mediastinal shift



Caudal displacement of the diaphragm


Extrathoracic Structures



Sternum



Vertebrae



Ribs



Adjacent soft tissues



Diaphragm



Extrathoracic changes may indicate cause of intrathoracic f
indings



Examples



Pneumothorax



Rib fractures may suggest secondary to trauma



Pleural effusion secondary to rib or chest wall mass


The Diaphragm



Cupula



Cranioventral convex portion



Right and left crura



Attach to cranioventral border of L3 and body of L4



M
ay cause irregularity on these surfaces



Appearance depends on centering of X
-
ray beam