Download Interactive thoracic film reading

Companion Animal
Diagnostic Imaging
Interactive thoracic film reading
CONTENTS:
Radiographic technique, normal anatomy, artefacts and normal variants
Trachea Lungs
Heart
Thoracic wall: ribcage and sternum
Diaphragm
Pleural cavity
Mediastinum
Ruth Dennis
MA, VetMB, DVR, DipECVDI,
MRCVS: RCVS and European
Specialist in Veterinary
Diagnostic Imaging
Animal Health Trust
U.K.
[email protected]
Session 1: Trachea and lungs
Session 2: Heart and thoracic wall
Session 3: Pleural cavity and mediastinum
RADIOGRAPHIC TECHNIQUE, NORMAL ANATOMY, ARTEFACTS
AND NORMAL VARIANTS
Acquisition and interpretation of diagnostic thoracic radiographs can be very
challenging! These notes consider some aspects which may be of assistance in everyday
practice, especially relating to lung pathology.
RADIOGRAPHIC TECHNIQUE: Restraint
Many patients can be radiographed conscious, with or without sedation. Each restraint
approach has advantages and disadvantages:
Fully conscious:
j Quicker (?)
jCheaper
j Safer for critical cases (may need to be held)
BUT
kStressful!
k Can’t do VD
k Poor image quality – may miss lesions
Sedated:
j Less stressful than fully conscious
j Owner compliance
j Cheaper than GA
BUT:
kCompromise
k Less well-aerated lungs than when conscious
k Suboptimal image quality – may miss lesions
Anaesthetised:
j Optimum quality
j Permits manual lung inflation
j Can perform other procedures too (but radiograph first)
BUT:
k More time consuming (?)
kExpense
k Owner resistance
RADIOGRAPHIC TECHNIQUE: manual lung inflation
The question of whether or not to perform manual lung inflation when the patient is
under general anaesthesia can be debated:
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Companion Animal
Diagnostic Imaging
Advantages:
- Better aeration improves contrast and definition
- Smaller lesions are more likely to be seen (e.g. metastases)
Disadvantages:
- Lungs not in natural state: may miss pathological atelectasis or emphysema
- May reduce heart and CdVC size
- Cannot compare accurately with radiographs obtained conscious.
Special views include horizontal beam lateral with the patient standing or crouching
and ‘decubitus lateral’ (i.e. a horizontal beam DV or VD).
A compromise could be to obtain non-inflated followed by inflated views.
General anaesthesia also carries the risk of development of positional atelectasis, which
can mimic or mask pathology. It can usually be recognised as such due to its location
adjacent to the heart and the presence of mediastinal shift.
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RADIOGRAPHIC TECHNIQUE: projections for lungs
Both right and left lateral recumbent radiographs should be obtained as smaller lesions
may only be visible when in the upper lung, in which case they are surrounded by
better-aerated tissue.
VARIANTS AND ARTEFACTS
Apart from GA-induced atelectasis there are a variety of findings which may cause
confusion and misdiagnoses: it is important to recognise these. They may be due to:
Positioning faults
GA-induced oesophageal dilation
Skin folds and nipples
Breeds with extreme conformation
Young and old age
Obesity.
NORMAL RADIOGRAPHIC APPEARANCE OF THE LUNGS
A ‘normal’ thoracic radiograph may be seen when:
1.The patient is normal!
2.There are respiratory signs arising elsewhere (e.g. URT).
3.Respiratory signs are due to metabolic or physiological rather than structural disease.
4.Radiography is performed before the onset of visible changes (e.g. Paraquat
poisoning).
5.Radiographic technique is poor (e.g. underexposure).
6.A small lesion is present but is obscured or overlooked.
DV and/or VD views are also usually helpful although patients with respiratory
compromise should not be placed on their backs for a VD view. The heart is most
consistently assessed using RLR and DV projections.
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
Most lung markings in young, healthy animals are vascular. There are seven pairs of
major vessels, one pair to each lung lobe. Arteries run dorsally and laterally to their
bronchi and veins run ventrally and medially. End-on vessels appear as very radiopaque
spots similar in size to other vessels in that area.
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Bronchial walls will be seen in all animals at their origins, where they are substantial,
and elsewhere are relatively radiolucent. They do, however become more opaque with
age and so the number which is visible is very variable.
Interstitial tissue consists of alveolar walls and the connective tissue of the lungs and
is present in all animals. Its radiopacity depends on many factors, including patient age
and size, the degree of lung inflation and other technical factors, and so the amount of
background interstitial pattern to be expected in the normal animal is also very variable.
TRACHEA
much less due to tracheal hypoplasia. Laryngeal cartilages and tracheal rings often
calcify as a normal ageing change; the lateral walls of the larynx may then be mistaken
for lesions such as foreign bodies (FBs) on VD views.
In small dogs the tracheal diameter may appear to be slightly reduced in the caudal
neck and cranial thorax by a convex band of soft tissue drooping down from its dorsal
wall. In some cases this is due to genuine tracheal collapse / redundancy of the dorsal
tracheal ligament but in others it is an artefact caused by the overlying oesophagus,
which drops down to the left side of the trachea at this level. The two effects can be
impossible to differentiate.
RADIOGRAPHIC TECHNIQUE FOR THE TRACHEA
TRACHEAL DISEASE
The trachea is easily seen throughout its length on lateral radiographs. The head and
neck should be positioned in gentle extension: flexion may cause the intrathoracic
trachea to curve dorsally, mimicking a cranial mediastinal mass, and hyperextension
may compress the trachea through the thoracic inlet giving a false impression of
tracheal collapse. DV/VD projections are much less useful, except to detect marked
lateral displacement of the trachea.
Exposures made on inspiration and expiration have been advocated for the detection
of tracheal collapse, but this is rarely successful due to the difficulty of exposing at the
correct moment in time and to the normally-shallow respiration.
An oblique DV projection (skyline) of the thoracic inlet with the head and neck
extended can be very helpful for the detection of tracheal collapse but is technically
difficult. Radiography has generally been superseded by endoscopy for diagnosis of
tracheal collapse.
NORMAL RADIOGRAPHIC APPEARANCE OF THE TRACHEA
The tracheal diameter is normally regular, and slightly less than that of the larynx. In
most breeds of dog the tracheal diameter : thoracic inlet ratio is not less than 0.2 but in
brachycephalic and chondrodystrophic breeds (notably the Pug and Bulldog) it is often
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
Tracheal displacement
Dorsal displacement:
Whole trachea:
• Shallow-chested conformation e.g. toy breeds; mimics cardiomegaly
• Cardiomegaly
• Large cranial mediastinal mass
• Large amount of mediastinal fluid
• Ruptured diaphragm and with displacement of the trachea by herniated organs
within the thorax
Cranial trachea elevated but dips down towards the carina:
• Artefact: neck flexion
• Cranial mediastinal mass (CMM)
• Enlarged cranial mediastinal lymph nodes
• Heart base tumour
• Severe right atrial dilation
• Lung lobe torsion.
Ventral displacement:
• Oesophageal dilation: generalised megaoesophagus or vascular ring anomaly (VRA)
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• Oesophageal FB • Craniodorsal mediastinal mass or loculated mediastinal fluid (e.g. haemorrhage)
• Severe spondylosis or other spinal deformity.
Right lateral displacement:
• Artefact: ventral or lateral neck flexion; rotation
• Chondrodystrophic conformation
• Obesity with large amount of mediastinal fat
• Cranial mediastinal mass
• Oesophageal dilation (since oesophagus is to left of trachea)
• Cranial mediastinal shift to right
• Ruptured diaphragm
• Heart base tumour.
Widening of the trachea
• Normal variant in chondrodystrophic dogs
• Manual lung inflation in dogs with tracheal collapse
• Laryngeal or proximal tracheal obstruction, on inspiration
• Tracheal collapse (neck on expiration, thorax on inspiration)
• Tracheal avulsion in cats.
Left lateral displacement:
• VRA – persistent right aortic arch
• Cranial mediastinal shift to left.
Tracheal lumen opacification
Structures within the tracheal lumen are easily seen as they contrast with surrounding
air.
• Artefact: superimposed structures e.g. lung nodules
• Aspirated FB
• Oslerus (Filaroides) osleri nodules (terminal trachea and bronchi, young dogs)
• Tracheal wall neoplasia: some may mineralise
• Tracheal wall abscess, polyp or granuloma
• Tracheal intussusception (rare)
• Aspirated contrast medium.
Variations in tracheal diameter
Variations in visibility of the tracheal wall
Narrowing of the trachea
• Artefact: hyperextension of the neck or superimposition of the longus colli muscles;
superimposition of mediastinal structures e.g. in pneumomediastinum
• Hyperextension of the neck
• Breed-related tracheal hypoplasia (Pugs, Bulldogs)
• Tracheal hypoplasia in other breeds and in cats
• Tracheal collapse
• Diffuse mucosal thickening due to tracheitis or submucosal haemorrhage
• Compression by e.g. CMM, VRA, oesophageal FB
• Tracheal stricture e.g. post trauma; tight ETT in cats
• Focal tracheal wall masses including neoplasia.
• M
ineralisation of tracheal rings: ageing change, especially in chondrodystrophic dogs
• ‘ Tracheal stripe sign’ due to gas-filled megaoesophagus, with ventral oesophageal
wall summating with the dorsal tracheal wall to produce a distinct band of soft tissue
• Pneumomediastinum – the external margins of the tracheal walls are seen due to
surrounding free air; other mediastinal structures e.g. large blood vessels are outlined
too (see lecture on mediastinum)
• Tracheal rupture due to trauma e.g. penetrating stick injury in dogs; avulsion or ETT
injuries in cats.
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
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Companion Animal
Diagnostic Imaging
LUNGS
NORMAL RADIOGRAPHIC APPEARANCE OF THE LUNGS
A ‘normal’ thoracic radiograph may be seen when:
1.The patient is normal!
2.There are respiratory signs arising elsewhere (e.g. URT).
3.Respiratory signs are due to metabolic or physiological rather than structural disease.
4.Radiography is performed before the onset of visible changes (e.g. Paraquat
poisoning).
5.Radiographic technique is poor (e.g. underexposure).
6.A small lesion is present but is obscured or overlooked.
Most lung markings in young, healthy animals are vascular. There are seven pairs of
major vessels, one pair to each lung lobe. Arteries run dorsally and laterally to their
bronchi and veins run ventrally and medially. End-on vessels appear as very radiopaque
spots similar in size to other vessels in that area.
Bronchial walls will be seen in all animals at their origins, where they are substantial,
and elsewhere are relatively radiolucent. They do, however become more opaque with
age and so the number which is visible is very variable.
Interstitial tissue consists of alveolar walls and the connective tissue of the lungs and is
present in all animals. Its radiopacity depends on many factors, including patient age
and size, the degree of lung inflation and other technical factors, and so the amount of
background interstitial pattern to be expected in the normal animal is also very variable.
PATHOLOGICAL LUNG PATTERNS
The system of pattern recognition allows the radiologist to establish which part of the
lung tissue is abnormal (alveoli, airways, blood vessels, connective tissue) and to draw
up a list of differential diagnoses. However, disease processes with different aetiologies
may produce identical patterns.
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
There are four pathological patterns;
- bronchial
- alveolar
- vascular (hyper- or hypo-)
- interstitial.
There are a number of other factors which produce radiological “red herrings”
mimicking in particular the interstitial and alveolar patterns:
- underexposure
- underdevelopment of analogue film
- ageing
- poor lung inflation due to the following:
- expiration
- prolonged lateral recumbency, especially under anaesthesia
- conformation e.g. bulldogs
- obesity - hepatomegaly - ascites
- laryngeal paralysis.
Border effacement
The concept of border effacement is used to determine whether or not two soft tissue
structures or areas of pathology in the chest (or less commonly in the abdomen) are
in contact, which aids in recognising their position and origin. Such structures may
be normal, such as the heart or a major vessel, or abnormal such as a mass or area of
consolidation. If they are not touching and there is therefore air-filled lung between
them, their margins are still visible even though they may be superimposed; this is
negative border effacement. If they are touching then the contact parts of their borders
merge and they appear to be a single mass; this is called “border effacement” (formerly
called the “silhouette sign”). Border effacement is responsible for loss of clarity of normal
intra-thoracic structures when an alveolar or severe interstitial pattern is present.
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Bronchial pattern
Causes:
- normal aging changes (especially in chondrodystrophic dogs)
- chronic bronchitis and bronchiectasis
- calcification e.g. hyperadrenocorticism (Cushing’s disease)
- pulmonary oedema (e.g. left-sided heart failure) – in loose tissue around airways
- neoplasia surrounding the airways e.g. lymphoma
- eosinophilic bronchopneumopathy (pulmonary infiltrate with eosinophils, PIE).
Changes are usually widespread but may be lobar in certain conditions (e.g. bronchial
FB).
The markings are linear (“tramlines”) and ring-like (“doughnuts”) with “signet rings”
being doughnuts with adjacent end-on vessels. The size and clarity of the marking
depends on the pathology. Take care not to confuse parallel blood vessels for tramlines.
Small, peripheral bronchial markings just make the lungs appear ‘scruffy’.
The vascular pattern may be less prominent due to border effacement.
Bronchiectasis produces wavy or wide tramlines and large doughnuts.
Causes: the usual types of fluid are oedema (many causes; most commonly left-sided
heart failure), haemorrhage (e.g. trauma, coagulopathy) and exudate (pneumonia), and
they cannot be distinguished except by their distribution and by other radiographic
signs (e.g. enlarged heart, fractured ribs). Aspirated fluid will produce a similar
appearance and neoplastic cell infiltrate (especially in cats) may occasionally give rise to
an alveolar pattern. Atelectasis can create a similar pattern, although reduction in lung
volume should be evident.
The flooded or infiltrated areas are not well-defined and so the appearance is of “fluffy”
or “mottled” soft tissue markings with ill-defined aerated areas or air alveolograms
between them. The vascular pattern, heart outline and diaphragm may be blurred.
Lobar divisions may become apparent due to the “wallpaper effect”. As the patches
of flooding coalesce and become larger the airways may be seen running through
the consolidated areas due to their contained air; a sort of natural negative contrast
technique and so logically called air bronchograms. The blood vessels are completely
obscured. N.B. it requires severe flooding for air bronchograms to be seen and so many
alveolar patterns occur without them. Air bronchograms will also be seen if the lung
is collapsed and poorly-aerated, and this will also appear as a severe alveolar pattern
although other features such as mediastinal shift may help to indicate its cause.
Alveolar pattern
Patches of alveoli become filled with fluid or neoplastic cells and so lose their air
lucency and take on a soft tissue opacity. Depending on the cause, the changes may be
widespread or localised, symmetrical or asymmetrical.
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Vascular pattern
Interstitial pattern
The normal vessel size is very variable, but arteries and veins are usually similar in size.
They are said to be 1/4 - 1 X the diameter of the proximal third (narrowest part) of the
4th rib where they cross it on the lateral view (9th rib on DV). Actually, this size range is
so large that it is not very helpful!
Most apparent interstitial patterns are incidental and due to technical factors or aging,
but there are a few specific causes which usually cause a dramatic and unequivocal
interstitial pattern. Interstitial markings are also often a ‘background’ to other patterns,
especially bronchial. Digital radiographs always show a prominent interstitial pattern
and take some getting used to!
a) Hypervascular pattern:
Causes: left heart failure, left-to-right shunts (ventricular septal defect VSD, patent
ductus arteriosus PDA), iatrogenic fluid overload, Dirofilaria infestation (arteries only).
The blood vessels are increased in size (arteries or veins or both) +/- differ in diameter.
Veins distend more readily than arteries. Engorged vessels may become tortuous,
and in the case of Dirofilariasis, truncated due to end-artery fibrosis. The heart is often
enlarged too.
Causes: chronic respiratory disease (often with a bronchial pattern), acute viral
pneumonia, acute pulmonary oedema, diffuse neoplasia such as lymphoma or
scirrhous mammary tumour metastases, Paraquat poisoning. In rare cases chronic
Cushing’s disease may progress from bronchial calcification to alveolar calcification.
A diffuse, hazy, honeycomb or meshwork pattern is seen in all of the lung fields with
some similarity to the alveolar pattern, but it is finer, more uniform and less fluffy.
Border effacement, the ‘wallpaper effect’ and air bronchograms may occur in severe
cases. If the lungs become ‘stiff’, cor pulmonale may ensue.
b) Hypovascular pattern:
Causes: lung over-inflation (iatrogenic or emphysema), hypovolaemia, shock,
hypoadrenocorticism (Addison’s disease), right-sided heart failure (forward failure),
right-to-left shunts (e.g. Tetralogy of Fallot), severe pulmonic stenosis, pulmonary
embolism (lobar).
The blood vessels are reduced in size and are very thready, often mimicking a bronchial
pattern. The lungs may appear hyperlucent. The heart and CdVC may also be small if the
cause is hypovolaemia but may be enlarged if the cause is a congenital heart defect.
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Mixed pattern
PULMONARY VOLUME CHANGES
Commonly, more than one pattern is present. Both may be pathological (e.g. alveolar
and bronchial in bronchopneumonia/aspiration pneumonia; bronchial and interstitial in
chronic bronchitis; hypervascular, bronchial, alveolar and interstitial in Dirofilariasis) or
one may be an incidental finding (e.g. aging bronchial markings).
The seriousness of the condition is alveolar > interstitial > bronchial, and the worst
pattern present should be considered to be representative of the severity of disease.
PULMONARY MASSES
Circumscribed soft tissue masses in the lungs are referred to as “nodules” if they are less
than 4cm diameter and “masses” if larger than this. Pulmonary nodules are classified
as interstitial pathology, but produce a granular rather than a reticular appearance.
Small nodules are not usually visible individually when they are less than about 5mm
diameter, but if a number are superimposed they are seen due to superimposition
(the “Bunch of Grapes Effect”). Beware interpreting other composite thoracic shadows,
end-on vessels or calcified plaques as metastases.
Most pulmonary nodules and masses are neoplastic although abscesses, granulomata,
cysts and haematomata occasionally occur. Remember that a “solid” soft tissue opacity
may contain a fluid centre seen with ultrasound; this may be due either to abscessation
or to necrosis of a tumour so does not rule out neoplasia. If the mass ruptures, liquefied
material will enter adjacent lung creating an alveolar pattern, and/or be coughed up.
The mass will then be seen to have an air-filled centre, i.e. be ‘cavitary’.
Solitary large masses, often taking on the shape of a whole lobe due to distal
consolidation, are most likely to be primary lung tumours. Multiple nodules and masses
are likely to be metastatic neoplasia in cooler parts of Europe; in other parts of the world
tuberculosis and fungal diseases must be considered as differential diagnoses.
Assessment of lung volume is important in interpretation of disease. Changes are
evident when other structures such as the heart, mediastinum or diaphragm are in an
abnormal location, and are usually best assessed on DV radiographs (mediastinal shift
can be artefactual in VD images). In particular, mediastinal shift is an important sign
and its presence and direction helps to differentiate between increased lung volume
(e.g. mass or emphysema), normal volume (consolidation) and reduced volume (e.g.
atelectasis or compression).
ABNORMAL PULMONARY LUCENCY
Focal pulmonary lucencies
Causes:
-Congenital or acquired lung bullae and blebs - spherical, thin-walled
-Cavitated masses - often other shapes, thick and irregular walls. Mainly neoplastic;
also ruptured abscesses and granulomata
- Air-trapping due to localised or lobar emphysema
- Pulmonary thromboembolism (rarely a radiographic diagnosis).
Diffuse pulmonary lucency
Causes:
-Incorrect technique - artefactual radiolucency due to overexposure,
overdevelopment or fogging of the film
- Iatrogenic overinflation
- Air-trapping due to generalised emphysema
- Reduced pulmonary soft tissue due to hypoperfusion.
Masses which are in contact with the chest wall can be examined using ultrasound, with
guided aspiration or biopsy.
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
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HEART
Radiography and ultrasonography (echocardiography) are complementary techniques
for the investigation of heart disease.
Radiography is usually the first-line technique in general practice and has much
to recommend it. It gives an overview of heart size and shape although of course
it cannot differentiate between chamber dilation and heart muscle hypertrophy
(cardiac hypertrophy may not cause visible changes on radiography) nor demonstrate
accurately which chamber(s) may be enlarged. In addition, radiography shows size and
shape changes in the major blood vessels (aorta and caudal vena cava), pulmonary
over- or under-circulation, and pulmonary oedema. Assessment of pulmonary vessel
size is especially important in the attempted radiographic diagnosis of congenital heart
disease in young animals with murmurs (see the lecture on lung patterns). Pleural
effusion, hepatomegaly and ascites are also radiographic signs associated with heart
disease. As well as demonstrating heart changes and signs of failure at the time of
diagnosis, radiography is useful for monitoring heart disease, especially response of
pulmonary oedema to diuresis.
Two important points must be remembered:
1. There is great variation in the appearance of the normal heart between dog breeds,
although the appearance in cats is much more consistent.
2. A normal radiograph does not rule out heart disease, as there may be internal
changes not visible radiographically (e.g. hypertrophic disease, endocarditis,
myocarditis) or arrhythmias that do not produce a change in the heart size or shape.
Echocardiography is a more accurate tool than radiography for the investigation of
less severe heart disease but requires skill and experience. It is generally the province of
cardiologists although pericardial effusions, pericardial masses, fractional shortening,
chamber dilation and hypertrophy are easier changes to detect. As well as showing
structural detail it provides functional information about myocardial contractility and
blood flow through valves.
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
RADIOGRAPHIC TECHNIQUE
1.Lateral view: the right lateral recumbent projection is preferred as the heart is more
consistent in outline; it usually appears more rounded on the LLR view.
2.Dorsoventral/ventrodorsal view: on the DV view the heart “hangs” in a more normal
position and is to be preferred; on the VD it often tilts over, appearing triangular or
bumpy in outline.
Follow-up radiographs must always be obtained using the same technique as the
originals.
NORMAL APPEARANCE
Heart size and shape varies between dog breeds and on the lateral radiograph reflects
the thoracic conformation, e.g. upright and narrow in deep-chested dogs and rounded
and relatively large in toy and chondrodystrophic breeds. Although measurements
may be made, they are rather crude. Assessment of heart size is largely subjective
and is most easily made on the lateral radiograph, although it is easy to overdiagnose
cardiomegaly and a genuinely enlarged heart should also look abnormal on the DV
projection. The heart is usually about 2/3 the height of the chest in dogs and cats; 2.5
- 3.5 rib spaces across in dogs and 2 - 2.5 rib spaces in cats. The vertebral heart score
(VHS) can also be used (95% of the population should lie between 8.7-10.7 in dogs)
but still gives too wide a range to be helpful in diagnosis although it can be used for
monitoring an individual heart over a period of time. It may be slightly larger during
expiration. The VHS can be artificially reduced in dogs by the use of manual lung
inflation or by severe dehydration, potentially masking cardiomegaly. In cats the VHS is
much more useful: most are 7.2-7.8 and 95% are 6.9-8.1 with 8.1 being the cut-off above
which the heart should be considered to be enlarged.
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Chamber locations can be estimated by dividing the heart into quarters using the
long and short axes. In the normal heart, the right heart chambers are cranial, forming
the cranial heart margin and the left chambers are caudal. The atria are dorsal and the
ventricles are ventral.
On the DV radiograph the clock-face analogy is used to describe the locations of
chambers and major vessels:
11-1 o’clock
1-2 o’clock
2-3 o’clock
3-5 o’clock
5-9 o’clock
9-11 o’clock
aorta
pulmonary artery
left auricular appendage
left ventricle
right ventricle
right atrium.
From: Thoracic Radiography of the Dog and Cat:
Suter and Lord
VHS
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
In older cats, the heart often lies at a much more horizontal angle on the lateral
radiograph, with increased sternal contact. The aortic arch may bulge cranially and
appeared slightly tortuous on both the lateral and DV projections: so-called ‘redundant
aorta’.
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CARDIAC DISEASE
-separation or “splitting” of the mainstem bronchi by the enlarged left atrium; the left
mainstem bronchus may be compressed
Normal cardiac silhouette but heart disease is present
The absence of radiographic changes does not rule out the possibility of heart disease,
for example with the following conditions:
Conduction disturbances and arrhythmias
Over-diuresis for heart disease
Concentric ventricular hypertrophy
- (sub)aortic stenosis: LV hypertrophy
- pulmonic stenosis: RV hypertrophy
- hypertrophic cardiomyopathy (idiopathic; hyperthyroidism in cats)
-hypertension
Small shunts (PDA, VSD)
Endocarditis or myocarditis
Constrictive or acute pericardial effusion or haemopericardium
Acute ruptured chordae tendineae
Myocardial neoplasia.
Left-sided cardiomegaly
Radiographic signs - DV view:
- increased length +/- width of heart
- rounding of left heart margin; apex may be displaced to the right
- 2-3 o’clock bulge due to dilated left auricular appendage
-circular area of increased radio-opacity over the caudal heart shadow due to
superimposed dilated left atrium; may mimic hilar lymphadenopathy or a lung mass
- increased divergence of the mainstem bronchi; the ‘cowboy sign’
Radiographic signs - left-sided failure:
- engorgement of pulmonary vessels (thin-walled veins may dilate more)
- pulmonary oedema - alveolar (sometimes interstitial) lung pattern
- bronchial pattern due to engorgement of peribronchial lymphatics.
Causes:
- mitral insufficiency (congenital dysplasia; acquired endocardiosis or endocarditis)
- dilated cardiomyopathy
-PDA
- severe aortic stenosis
Radiographic signs - lateral view:
- increased height of heart, elevating trachea and CdVC
- straight, upright caudal heart border
-dilation of the left atrium, which may be very large and may mimic hilar
lymphadenopathy or a lung mass
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
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Right-sided cardiomegaly
Causes:
- tricuspid insufficiency
- pulmonic stenosis (alone, or as part of Tetralogy of Fallot)
- cor pulmonale
- heartworm (Dirofilariasis)
Radiographic signs - lateral view:
- increased craniocaudal heart diameter
- rounding of the cranial heart margin
- increased sternal contact (beware left lateral radiographs!)
-elevation of the distal trachea cranial to the carina; elevation of cranial lobe blood
vessels
Radiographic signs - DV view:
- increased heart width
-further rounding of the right heart border, producing an inverted “D” shape to the
heart
- heart apex may be displaced further to the left
Radiographic signs - right-sided failure:
- engorgement of the caudal vena cava
-hepato(spleno)megaly
-ascites
- pleural effusion (especially in cats).
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
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Companion Animal
Diagnostic Imaging
Generalised cardiomegaly
Pericardial effusion
Note that dilation and hypertrophy cannot be differentiated radiographically, although
dilation is likely to be more dramatic. Since right- and left-sided chambers may not be
distinguishable on plain radiographs, marked enlargement confined to one or the other
system may nevertheless manifest as generalised cardiomegaly. The list below only
includes causes of genuine enlargement of both right and left chambers.
Pericardial disease may be difficult to differentiate from generalised cardiomegaly
radiographically, especially when it is not severe. The main suggestive feature is lack of
a dilated left atrium and right- rather than left-sided failure. Characteristic auscultation
and ECG changes may also be present.
Causes:
-artefact – toy and chondrodystrophic breeds, golden retrievers, some Labradors and
spaniels; intrapericardial or mediastinal fat; expiratory radiograph
- normal in athletic breeds e.g. greyhound and in very young animals
- fluid overload
- bradycardia – increased diastolic filling e.g. medetomidine sedation
-concurrent left- and right-sided disease or right-sided disease secondary to left-sided
failure (congestive heart failure)
-shunts (e.g. PDA, VSD, with pressure overload on right side and volume overload on
left)
- dilated cardiomyopathy; severe hypertrophic cardiomyopathy
-myocarditis
- chronic anaemia
- hyperviscosity syndrome e.g. multiple myeloma
- acromegaly (cats); muscular dystrophy (golden retrievers, cats)
- (pericardial effusion)
Radiographic signs:
-heart enlarged in all dimensions with a combination of left- and right-sided signs as
described above.
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
Causes:
- artefact – obesity, with pericardial fat
- idiopathic, especially St. Bernard and golden retriever; usually larger, male dogs
-neoplasia, e.g. right atrial haemangiosarcoma, heart base tumour and mesothelioma:
H/S is often associated with abdominal neoplasia too
-haemopericardium: atrial tears, bleeding tumours, trauma, ruptured left atrium due
to severe jet lesion
- septic pericarditis
-hypoalbuminaemia
-FIP
Radiographic signs:
-“cardiac” silhouette enlarged and rounded in chronic cases - globular or pumpkinshaped
-in acute cases the cardiac silhouette is normal and the heart is severely compressed
instead
- cardiac silhouette margins may be very distinct due to lack of movement blur
-right-sided failure due to cardiac tamponade (engorged CdVC, hepatosplenomegaly,
ascites)
- occasional pleural and mediastinal fluid
- absence of pulmonary overcirculation or oedema
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Differential diagnoses:
-generalised cardiomegaly, pericardioperitoneal diaphragmatic hernia; pericardial
cyst.
Reduced heart size - microcardia
Causes:
- Artefactual: deep-chested dogs, deep inspiration, manual over-inflation
- hypovolaemia (dehydration, blood loss, shock)
- hypoadrenocorticism (Addison’s disease) - due to dehydration and electrolyte
changes: may also see megaoesophagus
-emphysema
- constrictive pericarditis
Radiographic signs:
- heart reduced in size and becomes triangular with a pointed apex
- heart apex may be elevated from the sternum
- pulmonary vessels small and thread-like
- caudal vena cava +/- aorta reduced in diameter
- hyperlucent lungs due to reduction in soft tissue content.
Heart base tumours
Heart base tumours (aortic body tumours or chemodectomas) may be present without
causing pericardial effusion. The characteristic radiographic sign is elevation of the
intrathoracic trachea which then curves downwards quite sharply to the heart base and
carina.
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
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THORACIC WALL : RIBCAGE AND STERNUM
Anatomy
The thoracic wall consists of skin, subcutaneous fat, bone, muscle, connective tissue
and parietal pleura. There are normally thirteen pairs of ribs and costal cartilages. The
last three pairs of ribs are ‘floating’ and do not attach to the sternum. There are normally
eight sternebrae, with a caudal xiphoid cartilage.
Cats:
-The young cat has very fine, uniform costal cartilages.
-Older cats show mineralisation in short segments giving the appearance of multiple
fractures.
- The feline costochondral cartilage is a regular “T” shape.
-Anatomical sternal variants are seen as in the dog and it is not unusual to see signs
suggestive of previous trauma, such as (sub)luxation between sternebrae.
Congenital ribcage and sternal variants
For assessment of the ribs, both lateral and DV/VD views are needed as each show
different parts of the ribs best: mid and distal rib on lateral views and proximal rib on
DV/VD views. It may be helpful to view the radiographs upside down or rotated through
90o to make the ribs appear more obvious, when looking for lesions. Lesion-orientated
oblique (LOO) views, usually slightly tilted-over DVs, are most helpful for chest wall
deformities such as swellings as they profile the greatest area of abnormality.
Normal radiographic appearance
Dogs:
-In the young dog the costal cartilages have a uniform granular or stippled pattern.
-As the dog ages, the costochondral junctions and costal cartilages undergo
calcification, forming ‘rosettes’ around the costochondral junctions and sometimes
giving the appearance of costal cartilage fractures. Some of these benign ageing
changes may appear quite aggressive.
-Sternal ‘spondylosis’ is a common finding in older, large dogs.
-The heads of the first two ribs on DV/VD views may have an expansile, lytic
appearance suggestive of neoplasia.
- The costal cartilage on rib 1 is often poorly mineralised.
-Anatomical sternal variants are common and include partial or complete fusion of
adjacent sternebrae.
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
A number of anatomical variants are seen but are rarely clinically significant.
-Transitional vertebrae at the cervicothoracic and thoracolumbar junctions, e.g.
unilateral or bilateral vestigial ribs or elongated transverse processes on C7 or L1 and
unilateral or bilateral absence of T13 ribs: TLJ anomalies are important when ribs are
used as palpable surgical landmarks.
-Expansion and/or partial fusion of ribs 1 and 2.
-Altered number of sternebrae or abnormally short caudal sternebra.
-‘Pectus excavatum’ – more common in cats; dorsal deviation of the caudal sternum
with dorsoventral flattening of the chest and excessive curvature of ribs and costal
cartilages; if severe may it displace the heart and compress the lungs giving rise to
clinical signs. This may be congenital or acquired.
-Ventral displacement of the caudal sternum may be seen in young animals with
severe cardiomegaly due to congenital heart defects.
Trauma to the ribcage and sternum
Rib fractures are quite common but are often overlooked at the time of injury. They tend
to be multiple, involving several adjacent ribs. Crowding of the ribs and scoliosis due to
muscle spasm may be seen on the DV radiograph. ‘Flail chest’ occurs when a section of
the chest wall becomes unstable due to the presence of multiple fractures, and moves
paradoxically with respiration (i.e. inwards on inspiration). Recent rib fractures are often
associated with pneumothorax and pulmonary contusion if traumatic in origin. If there
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is no history of trauma, check for an underlying cause e.g. osteopenia or lytic neoplasia.
Spontaneous rib fractures may occur in asthmatic cats due to bouts of dyspnoea: this
may also cause acquired pectus excavatum.
Rib fractures only heal slowly due to continuous respiratory movement and may form
a hypertrophic non- or delayed union. A smoothly-expanded section of rib may persist
long after healing has taken place. Proximal rib fractures are often only visible on DV/VD
views.
Sternal fractures and (sub)luxations are commonly seen, especially in older cats and
often without any known history of trauma. Acquired pectus excavatum may be a
consequence of severe dyspnoea in cats.
Neoplasia of the ribcage and sternum
Rib tumours are much more common in dogs than in cats and are usually
osteosarcomas or chondrosarcomas arising at the costochondral junctions. Other
tumours such as multiple myeloma and skeletal metastases are more likely to occur
higher in the ribs. (The use of chemotherapy for primary tumours increases the risk
of metastases in unusual locations). Soft tissue chest wall tumours may also occur.
Mesothelioma may provoke periosteal new bone along the ribs and sternebrae but
usually the main sign is of pleural effusion.
Clinically there is often, although not always, a chest wall swelling but many rib tumours
behave like icebergs and extend mainly inwards resulting in respiratory signs or
regurgitation. Large tumours of the cranial ribs may create cranial mediastinal masses.
The DV or DV LOO view is usually the most helpful.
Radiographic signs:
-External chest wall swelling and loss of fascial planes.
-Internal soft tissue mass producing an ‘extra-pleural sign’, displacing lung inwards.
-‘Expansile’ mixed bone lesions (i.e. displacing cortices outwards).
-Osteolysis of the rib with varying amounts of new bone formation.
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
-Displacement of adjacent ribs away from the affected one; best seen on the DV/VD
view.
-With large masses, displacement of the heart, trachea, oesophagus, diaphragm or
stomach may occur.
-+/- pleural effusion.
-+/- associated hypertrophic pulmonary osteopathy in the limbs (Marie’s disease).
-Ultrasonography, CT and MRI are helpful to give a better idea of the extent of a rib
tumour if surgery is proposed.
Osteomyelitis of the ribcage and sternum
Inflammatory disease of the ribs and sternum is not common, but penetrating sternal
injuries or tracking FBs may produce changes in the sternum similar to discospondylitis
in the spine.
DIAPHRAGM
Anatomy
A musculotendinous sheet; muscle surrounds a central tendinous area. There are two
arms or crura and central, ventral dome or cupola. The crura arise via tendons from the
ventral margins of L3 and L4, which often appear ill-defined on lateral radiographs,
especially in larger dogs, and should not be mistaken for spondylitis. There are three
openings in the diaphragm: the aortic hiatus, the oesophageal hiatus and the caval
foramen for the CdVC. The shape of the diaphragm varies with a number of factors
including phase of respiration, position of the patient, volume of abdominal contents
and centring point of the X-ray beam.
Normal radiographic appearance
In medium and large dogs in lateral recumbency the dependent crus lies more cranial
than the uppermost crus, due to the weight of the viscera behind it. In right lateral
recumbency the diaphragm is seen as two parallel lines with the CdVC emerging
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though the cranial line; in left lateral recumbency it forms a ‘Y’ shape with the CdVC
emerging from the caudal crus and crossing the cranial one and the fundus of the
stomach lies behind the dorsal part of the cranial crus, mimicking a hiatal hernia or
cavitated lung mass. On inspiration the diaphragm is pulled caudally and flattened; on
expiration it moves cranially and may overlie the heart. Being able to identify RLR versus
LLR positioning is often invaluable in interpretation of thoracic and cranial abdominal
radiographs when R / L markers have not been used.
The DV view produces a smooth dome shape to the diaphragm, usually with the apex
to the right of the midline. On the VD view the diaphragm has a three-humped shape
due to viscera falling into the crura and cupola (unless centring over the abdomen,
when it may appear smooth).
Diaphragmatic rupture
Diaphragmatic rupture is usually suspected from a history of recent trauma together
with relevant clinical signs, but sometimes dyspnoea arises weeks or months after
a traumatic incident which was relatively mild and which may have been forgotten.
This can be due to incarceration of liver in a diaphragmatic tear with resultant pleural
effusion, and may be very hard to diagnose since the effusion masks slight changes in
the contour of the diaphragm and the gastric axis may not be displaced cranially.
Animals with suspected diaphragmatic rupture require careful handling for radiography
and it may be wise to take a DV or horizontal beam lateral view first so that the patient
can remain upright. On recumbent lateral radiographs if the diagnosis is uncertain the
opposite lateral may be helpful in altering the positioning of enteric gas. Such patients
may require manual restraint, which can be justified because of the importance of
obtaining a diagnosis. The use of barium is rarely necessary as most diaphragmatic
ruptures can be diagnosed on plain films, and administration of barium may distress
the patient. However, it can be helpful in demonstrating cranial displacement of the
stomach in cases of liver incarceration. Positive contrast peritoneography has been
described as an aid to diagnosis of ruptured diaphragm.
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
Radiographic signs:
-Loss of clarity of all or part of the diaphragm line.
-Increase in intra-thoracic opacity with displacement of lung lobes and the heart, and
the presence of irregular soft tissue structures and gas bubbles; sometimes discrete
organs such as the spleen can be identified within the chest.
-Displacement of the heart laterally and/or dorsally.
-Intra-thoracic gastric dilation may occur and can be life-threatening.
-Cranial displacement of abdominal viscera; in extreme cases an ‘empty’ abdomen
with only kidneys, bladder and descending colon remaining in situ.
-Fractured ribs may be evident.
-Pleural effusion and effacement of falciform fat if chronic liver incarceration has
occurred.
-Ultrasonography can be used to diagnose a ruptured diaphragm, and is especially
helpful if pleural effusion is present. However, care should be taken not to mistake the
‘mirror image’ artefact for liver herniation.
Pericardioperitoneal diaphragmatic hernia (PPDH)
A congenital malformation resulting in communication between the peritoneal cavity
and pericardial sac, allowing viscera to be displaced into the thorax although still
confined within the pericardium. Often diagnosed surprisingly late in life. Clinical signs
may be respiratory, cardiovascular or gastrointestinal. Gut sounds may be auscultated
through the chest wall. May be associated with umbilical hernia (Weimaraner).
Radiographic signs:
-Enlarged, rounded ‘cardiac’ silhouette; DDx pericardial effusion.
-Irregular opacity within ‘cardiac’ silhouette, with some gas lucencies.
-Lack of abdominal content.
-In cats, the dorsal peritoneopericardial mesothelial remnant is often seen on the
lateral radiograph ventral to or superimposed on the CdVC, and is a helpful diagnostic
feature.
-May be confirmed by barium study; animal usually in less clinical distress than with
ruptured diaphragm.
- Ultrasonography is again helpful.
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PLEURAL CAVITY
Anatomy
A potential space containing a small amount of lubricant fluid between the parietal
and visceral pleura, which join at the hilus. Parietal pleura (costal, diaphragmatic and
mediastinal) forms two distinct sacs, right and left.
Types of effusion cannot usually be differentiated radiographically, but there may be
other radiographic clues as to the cause. Chronic inflammatory effusions (pyothorax,
chylothorax) may lead to loculation of fluid and pleural thickening, which in turn results
in rounding of the lung margins. Detection of even a small effusion is important for two
reasons: (a) even very small amounts are significant because they denote an underlying
disease process, even though they may not be giving rise to clinical signs; (b) aspiration
and analysis of the fluid helps in diagnosis. Radiography should be repeated after
thoracocentesis as previously-obscured lesions may become evident and the lungs
re-expand and can be assessed.
Radiographic signs:
Signs depend on the volume and distribution of the fluid and the position of the
patient relative to the X-ray beam. Normally at least 100ml of fluid must be present in a
dog before being visible radiographically, but radiography underestimates the amount
of fluid present. Horizontal beam projections with the animal standing or recumbent
are better at detecting small effusions. Asymmetrical distribution of fluid suggests an
intrathoracic cause (e.g. fluid collecting around a collapsed lung lobe, inflammatory
pleural disease) whereas bilateral, symmetrical distribution may be due either to an
intrathoracic or a systemic disease.
Pleural effusion
Causes:
- Exudate – pyothorax, pleuritis, pneumonia, extension from mediastinitis, FIP.
- Transudate – hypoproteinaemia.
-
Modified transudate – CHF, idiopathic, neoplasia, pneumonia, extensions from
mediastinitis, diaphragmatic rupture with incarcerated liver.
- Chylothorax – idiopathic, trauma, neoplastic erosion of the thoracic duct.
- Haemothorax – trauma, coagulopathy.
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
-Interlobar fissure lines – RLR shows right-sided fissures, LLR shows left-sided fissures,
DV shows ventral fissures (two on each side) and VD shows dorsal fissures (one on
each side); DDx normal pleural space struck exactly tangentially; pleural fibrosis;
costal cartilages on DV/VD view (concave cranially c.f. fissures are concave caudally).
-Retraction and rounding or “scalloping” of the lung margins, especially ventrally on
the lateral radiograph (pleural and mediastinal fat should not be mistaken for fluid).
In the cat, the dorsocaudal margin of lung normally curves away from the thoracic
spine on the lateral view.
-Surrounding soft tissue/fluid opacity with loss of clarity of the heart and diaphragm
due to border effacement, especially on lateral and DV views; DDx “cottage loaf” chest
conformation on the DV view. In some animals, although the heart outline is effaced
it outline can still be discerned by the ‘pericardial fat sign’.
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-Unilateral effusion may occur in animals without normal mediastinal fenestrations
but usually indicates loculation of fluid due to inflammatory disease e.g. pyothorax,
which seals the mediastinum. In some cases unilateral effusion causes marked
mediastinal shift to the contralateral side as trapped fluid builds up.
-Collection of fluid around a single lobe suggests lobar pathology and loss of
compliance resulting in lobe collapse.
-Overall increase in intrathoracic opacity especially on the lateral and DV views; repeat
radiography with increased kV may be necessary; on the VD view the fluid depth is
shallower as it is spread over a larger area.
-After drainage of fluid, failure of the lungs to re-expand, often with a rounded shape
and surrounding pleural thickening, indicates chronic pleurisy secondary to an
inflammatory effusion such as pyothorax or chylothorax.
It is important to understand the difference in free fluid distribution between the DV
and VD view. On the DV, fluid collects in the ventral thorax, which in most breeds is
relatively narrow, and therefore it reaches a greater depth and surrounds the heart.
This results in increased radiographic opacity and loss of cardiac visualisation (border
effacement). On the VD view the fluid lies in the dorsal thorax and the heart and
diaphragmatic cupola are “uncovered” and are seen better. Positional radiography can
be used in this way to give more information, although caution should be exercised in
placing animals with marked intrathoracic disease on their backs.
Ultrasonography for pleural effusions
When pleural fluid obscures intrathoracic detail, ultrasonography is very helpful in
giving extra information; it should be performed before drainage as the fluid acts
as a helpful acoustic window. It is used especially for the detection of underlying
mediastinal or pleural masses, pleural thickening, collapsed lung lobes and
diaphragmatic rupture, for differentiating masses from loculated fluid and for detection
of underlying heart disease. Ultrasound-guided thoracocentesis may be performed if
the effusion is small, and when biopsying masses colour-flow Doppler ultrasound is
useful in the avoidance of large blood vessels.
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
Pneumothorax
Causes:
-Rupture of a superficial air-filled lung lesion such as a bulla (the site of air leakage is
not usually identified).
-Rupture of the origin of a bronchus.
-Tear in lung parenchyma.
-Trauma through the chest wall e.g. RTA and fractured ribs, iatrogenic from
thoracocentesis needle.
-Extension from a pneumomediastinum.
Radiographic signs:
As with pleural effusions, the signs depend on the amount of free air and the position
of the patient relative to the X-ray beam. Small amounts of free air are best seen using
a horizontal beam (standing lateral or recumbent “decubitus” VD view) although they
are not as clinically significant as a small effusion. The vertical beam DV view is more
sensitive than the VD. Radiography should be repeated after thoracocentesis and
re-expansion of the lungs.
-Retraction of lung lobes from the thoracic wall.
-Surrounding gas lucency – lung markings do not extend to the periphery; DDx “false
pneumothorax” in deep-chested dogs on the DV view. Interlobar fissures are not a
feature as air is forced out of the fissures by lung collapse.
-Increase in lung opacity due to loss of aeration – may be better seen on expiratory
films or using a lower kV. The increase in opacity may mask underlying lung
pathology.
-Heart “elevated” from the sternum on recumbent lateral views, as the dependent
lobes collapse and the heart slides dorsally along the dependent ribcage; DDx
pneumomediastinum, severe emphysema.
-Asymmetric distribution of free air suggests underlying lobar pathology leading to
collapse.
-Tension pneumothorax – valve mechanism at the site of air leakage results in pleural
pressure exceeding atmospheric pressure. The lungs are small and compressed
against the midline if the pneumothorax is bilateral (‘angel of death sign’); there
is mediastinal shift away from the affected side if the tension pneumothorax is
unilateral. The diaphragm is flattened and displaced caudally, and the ribs stick out at
right-angles to the spine on the DV view. Urgent intervention is required.
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MEDIASTINUM
Anatomy
The mediastinum consists of two layers of mediastinal parietal pleura and the
space between them. The right-sided pleura is also reflected around the CdVC. The
mediastinum divides the thorax into two halves and is continuous cranially with the
cervical fascial planes and caudally with the retroperitoneal space via the aortic hiatus.
It is divided into cranial (craniodorsal, cranioventral), middle and caudal (caudodorsal,
caudoventral) areas. It contains the heart and great vessels, trachea, origins of bronchi
and pulmonary blood vessels, thymus, oesophagus, thoracic duct, lymph nodes
and various nerves. The oesophagus, thoracic duct, lymph nodes and nerves are not
normally visible and the thymus is seen only in young animals less than about one year
old. The lymph nodes are divided into three groups: cranial mediastinal LNN ventral to
the trachea, tracheobronchial or hilar LNN between the two mainstem bronchi, and
sternal LNN. They are variable in number and size, and are only seen when markedly
enlarged. The ventral mediastinum is usually fenestrated, allowing communication
between the two pleural sacs, but unilateral pleural disease may occur if the
mediastinum is anatomically complete or inflamed.
The mediastinum lies vertically in cats but obliquely in dogs, running from right dorsal
to left ventral. It is best seen on DV/VD radiographs, and its width is variable depending
on conformation and body condition. The cranial mediastinum is normally twice the
width of the spine on the DV view, but is often wider in fat or chondrodystrophic dogs.
In the young animal the thymus is seen on DV/VD views as a triangular structure cranial
to the heart and extending to the left of the midline (the “thymic sail”) and on lateral
views as an ill-defined radiopacity against the cranial heart margin. The caudoventral
mediastinum in dogs forms a fine opaque line on the DV/VD view running from the
cardiac apex to the left side of the diaphragm, lying between the accessory and left
caudal lung lobes.
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
Mediastinal shift
A term used to describe lateral movement of the mediastinum and its enclosed
structures, seen on the DV/VD view. It is due either to expansion of a hemithorax (e.g.
emphysema, unilateral pleural effusion – shift AWAY from that side) or reduction in size
(most commonly due to GA-induced atelectasis – shift TOWARDS that side). It can be
mimicked by poor radiographic positioning i.e. lateral tilting.
Mediastinal masses
Causes:
Usually in the cranioventral mediastinum, mainly due to thymic lymphoma or
thymoma; also other neoplasia, lymphadenopathy, mediastinal abscesses.
Radiographic signs:
-Widening of the cranial mediastinum by a soft tissue opacity on DV/VD views; DDx
excessive mediastinal fat; localised fluid accumulation.
-Cranial lung lobes displaced laterally and caudally giving a diamond shape to the
cranial mediastinum on DV/VD views.
-Trachea elevated +/- displaced further to the right; DDx neck flexion during
radiography.
-Heart displaced caudally (look for the carina if the heart is unclear) and cranial heart
margin obscured, merging with the mass.
-Often associated pleural and/or mediastinal fluid, so re-X-ray after drainage.
Positional radiography may also be helpful to move free fluid away from the area of a
suspected mass, if safe to do so.
-Small mediastinal masses may be largely outlined by lung and therefore can mimic
pulmonary masses.
-Cranial mediastinal lymphadenopathy is hard to detect but may cause mild tracheal
elevation; hilar lymphadenopathy may mimic left atrial enlargement; sternal
lymphadenopathy is seen above St 2 in the cranioventral mediastinal fold. The
commonest cause of mediastinal lymphadenopathy is lymphoma.
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Mediastinal effusions
Causes:
Mediastinal masses, CHF, coagulopathy, oesophageal perforation, trauma, FIP. Often
associated with pleural fluid and so may be hard to see.
Radiographic signs:
- Widening of the mediastinum on the DV/VD view by soft tissue opacity.
- “Reverse fissures” and a square shape to the heart on the DV view due to fluid
extending laterally between lung lobes.
- Loss of clarity of the heart outline on the lateral and DV views; heart clearer on the VD
view as fluid moves into the dorsal thorax.
- +/- “elevation” of the heart on the lateral view.
- Mediastinal haemorrhage may be confined to the craniodorsal mediastinum,
depressing the trachea.
Radiographic signs:
-Lateral view best.
-Increased clarity of mediastinal structures which are not normally seen: tracheal walls,
oesophagus, azygos vein, cranial mediastinal vessels.
-Scalloped gas lucency around the heart, which may be ‘elevated’ from the sternum on
a recumbent lateral view.
- Gas may also be seen in the cervical fascial planes and the retroperitoneal space.
- Paraquat poisoning – classically with an interstitial lung pattern too.
Pneumomediastinum
Causes:
-Perforated trachea or main bronchus (may be spontaneous in racing greyhounds,
dyspnoea due to Paraquat poisoning, iatrogenic due to over-ventilation)
-Blunt trauma to the lungs causing parenchymal damage without overlying pleural
tear – gas dissects along the bronchial structures
-Perforated oesophagus
-Extension from cervical emphysema
-Extension from pneumoretroperitoneum via the aortic hiatus.
Pneumomediastinum may proceed to pneumothorax but the reverse does not occur. It
is not usually a clinical problem.
Abstracts | European Veterinary Conference Voorjaarsdagen 2016
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