Radiology of the Trachea, Lungs and Heart

Question 1

Trachea on radiograph.

Answer 1

Should be air filled, of even diameter and have smooth internal surface.
Some normal variation in its course, influenced by head and neck.
Bifurcation should be at the 4th or 5th intercostal space.
Mineralisation of tracheal rings normal.

Question 2

Identifying a tracheal collapse on radiograph.

Answer 2

Aim to take radiograph on expiration as more likely to see collapse this way w/ the positive pressure in the thorax.
Still quite hit and miss so endoscopy is good for viewing the trachea in real time.
Or fluoroscopy (real time radiographs).
Most commonly collapses at caudal neck at thoracic inlet.

Question 3

Tracheal FB.

Answer 3

Inhaled FB.
Easy to identify on radiograph unless of soft tissue opacity.

Question 4

Lung lobe anatomy.

Answer 4

Right – cranial, middle, caudal, accessory.
Left – cranial (cranial and ‘middle’ united dorsally) and caudal.

Question 5

Lung lobes on the dorsoventral view.

Answer 5

R cranial lobe crosses midline.
L cranial lobe extends further forward.
Accessory lobe caudal to the heart, extends across midline to the left.
Caudal lung lobes overlap the middle ones dorsally to some extent.
Caudal lung lobes extend over the diaphragm.

Question 6

In what state do the lungs need to be in order to properly assess them on radiograph?

Answer 6

Inflated well.
So there is minimal pulmonary opacity and any pathology can be identified.

Question 7

Normal lung on radiograph.

Answer 7

Mostly radiolucent.
Some lung pattern - mainly vascular – pulmonary vessels.
Vasculature=soft tissue opacity.
They are thicker closer to the heart and get narrower further away.
End-on blood vessels same width as other blood vessels but will be more radiopaque than long blood vessel as beam passing down length of vessel.
Bronchi only seen where quite big e.g. around heart base. Have air in middle so walls seen as much thinner soft tissue lines. End-on bronchi look like radiolucent circles.

Question 8

3 main pathological lung ‘patterns’.

Answer 8

Bronchial.
Alveolar.
Interstitial.
- nodular.
- unstructured.

Question 9

1. Normal bronchial markings.
2. Pathological bronchial markings.
   - causes.
   - what is seen?

Answer 9

1. Bronchial walls commonly visible in hilar region.
   Markings tend to become more prominent w/ age.
2. Calcification of the walls.
   Thickening of the walls.
   Peri-bronchial infiltration.
   See ‘tramlines and doughnuts’ in longitudinal / transverse section.

Question 10

Causes of bronchial changes.

Answer 10

Chronic lower airway disease.
- bacterial.
- viral.
- parasitic.
- allergic.
Cushing’s disease - damaging effect of steroids on bronchial wall causes mineralisation.
Age - normal.
also be concerned if the bronchi do not narrow as they branch

Question 11

Alveolar pattern due to alveolar filling…
Appearance on radiograph.

Answer 11

Fluffy or hazy patches, which may coalesce.
Soft tissue margins obscured:
- blood vessels.
- heart / diaphragm.
Radiolucent airways remain visible:
- “air bronchograms”.

Question 12

Alveolar filling causes.

Answer 12

• Pulmonary oedema – cardiogenic (e.g. L sided heart failure) or non-cardiogenic (e.g. vasculitis).
• Haemorrhage.
• Pneumonia.
• Neoplasia (e.g. bronchogenic carcinoma).

Question 13

1. Ventral alveolar filling cause.
2. Alveolar filling around the heart base cause.
3. Caudodorsal alveolar filling cause.
4. Peripheral alveolar filling cause.

Answer 13

1. Aspiration pneumonia.
2. Cardiogenic oedema (dogs).
3. Inhaled FB e.g. grass seed.
4. Angiostrongylus vasorum infestation.

Question 14

1. What can interstitial lung pattern be subdivided into?

Answer 14

1. Nodular and unstructured.

Question 15

1. Nodules on radiograph.
2. Ensuring complete assessment for interstitial lung pattern on radiograph.

Answer 15

1. Not visible if <4-5mm diameter.
2. Look over heart and diaphragm.
   Take right and left lateral projections.
   Ensure the radiograph is inspiratory.

Question 16

1. Distinguishing nodules from end-on vessels.
2. Consistency of the nodules.
3. What is a nodular lung pattern most likely to represent?

Answer 16

1. • Compare size to adjacent nodules.
     - Opacity of nodule less than end-on vessel of similar size.
2. Solid or cavitary.
3. Pulmonary metastasis.
   Beware of cutaneous nodules e.g. nipples, warts, ticks.
   Also ddx abscesses, granuloma, pneumatocyst, haematoma, ‘plugged’ bronchus.

Question 17

1. Mass vs nodule.
2. What usually are lung masses?

Answer 17

1. Size difference – mass >3cm, nodule <3cm.
2. Often neoplastic e.g. carcinoma.

Question 18

1. Unstructured interstitial lung pattern on radiograph.
2. How could unstructured interstitial lung pattern be accidentally diagnosed?

Answer 18

1. Increased opacity of the lung.
   Blurring of vessel margins but they remain visible.
2. Can be seen artefactually of expiration or under-exposed film.
   Can be mimicked by incidental aging change / obesity.

Question 19

What pathologies can cause unstructured interstitial lung pattern?

Answer 19

• Infiltration of the supporting lung tissue w/ fluid, cells or fibrous tissue.
• Diseases in transition e.g. oedema, pneumonia, haemorrhage.
• Pulmonary fibrosis.
• Diffuse neoplasia – lymphoma, some metastatic disease.
• Pneumocystitis carinii pneumonia, viral pneumonia.

Question 20

Vascular marking on thoracic radiograph.

Answer 20

• Main pulmonary artery/vein for each lung lobe, run beside bronchus.
• Lateral projections: see cranial lobar vessels.
• DV/VD projections: see caudal lobar vessels.
• Veins lie ventral and central (medial) to their respective artery/bronchus.
• Caudal vessels should not exceed the width of the 9th rib.
• Cranial vessels compared to proximal 1/3 of 4th rib. – typically 0.25-1.2 x width of rib (large normal range).
  – artery and vein should be equal in size.

Question 21

What would be seen on radiograph in the case of…
1. L sided congestive heart failure.
2. Heartworm.
3. Left-to-right shunts.
4. Hypovolaemia, Addison’s disease.

Answer 21

1. Enlarged pulmonary veins.
2. Enlarged, tortuous pulmonary arteries.
3. Both arteries and veins large (over-circulation.
4. Vessels small.

Question 22

1. Width of heart in the cat (on lateral).
2. Width of heart in the dog (on lateral).
3. Height of the heart (apex to base) (on lateral).
4. Width of heart (DV projection).

Answer 22

1. 2-2.5 intercostal spaces.
2. 2.5-3.5 intercostal spaces.
3. 2/3-3/4 of the height of the thoracic cavity.
4. 2/3 width of thoracic cavity (relies on inspiratory).

Question 23

Vertebral heart scoring.

Answer 23

• Measure long axis from apex to base of the carina.
• Measure width, perpendicular to long axis measurement, through central 1/3 of the heart.
• Take each measurement in turn and count from the cranial border of T4 as to how many vertebral length it was.
• Add the vertebral lengths of the 2 measurements together.

Question 24

1. Normal range of vertebral heart scores in dogs.
2. Normal range of vertebral heart scores in cats.
3. Usefulness of vertebral heart scoring.

Answer 24

1. 8.5-10.6.
2. 7-8.
3. Normal variation limits usefulness.
   - Some breeds have a normal score of 11+.
   - Scores vary with:
   – Positioning: rotation, L vs R lateral.
   – Inspiration / expiration.
   – Systole / diastole.

Question 25

1. What indicator is more useful than VHS?
2. On lateral radiograph, which side of the heart sits more cranially and which sits more caudally?
3. Which side of the heart takes up a higher proportion of the cardiac silhouette? – why?

Answer 25

1. Shape.
2. Right more cranially, left more caudally.
3. Left takes up a higher proportion than the right – thicker walls.

Question 26

1. Position of aorta on DV projection.
2. Position of main pulmonary artery on DV projection.
3. Position of the left auricular appendage on DV projection?
4. Presentation of patent ductus arteriosus (PDA) on DV projection?

Answer 26

1. 12-1 o’clock.
2. 1-2 o’clock.
3. 2-3 o’clock.
4. 3 bulges (of aorta, main pulmonary artery and left auricular appendage).

Question 27

1. Left cardiac enlargement on lateral radiograph.
2. Left cardiac enlargement on DV projection.

Answer 27

1. • Tall heart.
     - Elevation/compression of caudal lobar bronchus.
     - Straight caudal border.
     - ‘Tenting’ L atrium.
2. • Increased heart length.
     - Rounding of left ventricular border.
     - Apex may be displaced to right.
     - Enlarge L auricular appendage at 2-3 o’clock.
     - L atrium may be seen superimposed on cardiac silhouette as distinct structure or as an increase in opacity of the heart base.

Question 28

1. Acquired causes of left cardiac enlargement.
2. Congenital causes of left cardiac enlargement.

Answer 28

1. • Dilated cardiomyopathy (DCM).
     - Mitral valve insufficiency (endocardiosis).
2. • Patent ductus arteriosus (PDA).
     - Ventricular septal defect (VSD).
     - Mitral dysplasia.
     - Aortic stenosis.

Question 29

Appearance of left cardiac failure on radiograph.

Answer 29

• Pulmonary oedema.
• Leads to alveolar filling.
• Dogs – perihilar in distribution.
• Cats – less predictable distribution and pattern, pleural effusion.

Question 30

1. Appearance of right cardiac enlargement on lateral radiograph.
2. Appearance of right cardiac enlargement of DV projection.

Answer 30

1. • Wide heart.
     - Apex may lift from sternum.
2. Rounding on the right side.
   Reverse ‘D’.

Question 31

1. Acquired causes of right cardiac enlargement.
2. Congenital causes of right cardiac enlargement.

Answer 31

1. • Tricuspid insufficiency.
     - Cor pulmonale – pulmonary hypertension.
     - Dirofilarias (Travel history?)
2. • Pulmonic stenosis.
     - Tricuspid dysplasia.
     - Tetralogy of Fallot.
     - Ventricular Septal Defect (VSD).

Question 32

Right cardiac failure on radiograph.

Answer 32

• Distension of caudal vena cava.
• Hepatic venous congestion (larger liver).
• Ascites.
• Pleural fluid.
• Pericardial fluid.

Question 33

Generalised cardiomegaly on radiograph.

Answer 33

Both L and R sided enlargement.
Wide and tall heart.

Question 34

Pericardial disease on radiograph.

Answer 34

• Rounded and globular heart.
• Sharp margin (cardiac movement less evident?)
• Uniform opacity (except PPDH).
• DDx:
  – idiopathic.
  – neoplasia –> haemangiosarcoma, chemodectoma.
  – Others –> coagulopathies, FIP, hypoproteinaemia.

Question 35

PPDH.

Answer 35

Peritoneo-pericardial diaphragmatic hernia.
Herniation contained w/in pericardium so more centrally.
Congenital communication between peritoneal and pericardial cavities (failure for these cavities to separate).
Often an incidental finding.