6 – Thoracic Radiography 2

Question 1

Mediastinum

Answer 1

• Space b/w right and left pleural sacs
• Bounded on each side by mediastinal parietal pleura
• From thoracic inlet to the diaphragm
• Contains all thoracic structure BUT the lungs

Question 2

Cranial mediastinum: what can you see?

Answer 2

• Cranial aorta
• Multiple important vasculature
• Some lymph nodes
• Soft tissue band: cranioventral mediastinal reflection (multiple pleura that surround the lung lobes)
• At front: L cranial slightly extends to right side

Question 3

Middle mediastinum: what can you see?

Answer 3

• Caudal portion of thoracic trachea
• Cardiac silhouette
• Lymph nodes (tracheal-bronchial)

Question 4

Caudal mediastinum: what can you see?

Answer 4

• Not many structures
• Descending aorta
• Caudal vena cava
• Caudal mediastinal reflection (can only see in DV/VD view)
  o Accessory lung lobe pushes It to the left side
  o Multiple pleura’s=normal structure

Question 5

What is one of the most common mediastinal disease?

Answer 5

• Mediastinal lymphoma
  o Displaces many structures (ex. trachea displaced)

Question 6

Trachea in normal conditions

Answer 6

• Lumen is radiolucent (filled with air)
• Sligh angle relative to axis of thoracic spine rather than parallel (lateral views)
• May be slightly to the right of thoracic spine on VD/DV views

Question 7

What are some normal variations that might happen with the trachea?

Answer 7

• Dorsal displacement secondary to changes in head positioning
• Redundant dorsal tracheal membrane

Question 8

Redundant dorsal tracheal membrane

Answer 8

• Broad based soft-tissue opacity protruding from the dorsal tracheal walls
• Can be incidental OR may be associated with collapsing airway
  o Present in large breed dogs

Question 9

Collapsing trachea

Answer 9

• Disease process, toy/small breeds
• Airway collapse
• ENTIRE lumen being narrowed (not just the walls)
• Honking cough and respiratory distress

Question 10

Normal esophagus

Answer 10

• NOT visible

Question 11

Generalized esophageal dilation

Answer 11

• May occur due to hypomotility secondary to sedation/GA OR disease processes
• 1. Congenital megaesophagus
• 2. Acquired megaesophagus
     o Hypothyroidism
     o Myasthenia gravis
     o Paraneoplastic (thymoma)
     o Dysautonomia
     o Polyneuropathy
     o Toxicity

Question 12

Esophagram: dogs and cats

Answer 12

• Use static barium esophagram
  o *Contraindicated for esophageal perforation!
• Dogs: linear mucosal folds
• Cats: ‘herringbone’ appearance of mucosa at caudal esophagus due to obliquely oriented smooth muscle

Question 13

What are the clinical relevant lymph nodes located in the mediastinum?

Answer 13

1. Sternal lymph nodes=usually the only one that can be visualized (R. lateral)
2. Cranial mediastinal lymph nodes
3. Tracheobronchial lymph nodes

Question 14

Sternal lymph node

Answer 14

• Only one that is visualized in right lateral view above the 2nd or 3rd sternebrae
• DRAINS the CRANIAL ABDOMEN, ribs, sternum, thymus, adjacent muscles and mammary glands

Question 15

Cranial mediastinal lymph nodes

Answer 15

• Lie just ventral to trachea
• Superimposed by the vasculatures

Question 16

Three tracheobronchial lymph nodes

Answer 16

• Right and left lie abaxial to the carina
• Middle is just caudal to tracheal bifurcation

Question 17

Diaphragm

Answer 17

• Left crus
• Right crus
• Cupula

Question 18

Pleural space in normal conditions

Answer 18

• Not visualized
• Occasionally, solitary interpleural fissure ID due to tangential X-ray beam or pleural thickening

Question 19

Pleural space: abnormal conditions

Answer 19

• Multiple and easily identifiable interpleural fissures
• Fluid or air filling the pleural space

Question 20

Thoracic walls

Answer 20

• In some dogs as cats (older), costochondral degeneration
  o Osseous proliferation may be present=incidental
  o Do NOT confuse with lung nodules or with aggressive bone lesions (infection or neoplasia)

Question 21

Thymus

Answer 21

• Young animals (<4months)
• “looks like a ‘sail’
• Cranioventral mediastinal reflection

Question 22

Cranial mediastinal fat deposition

Answer 22

• Obese dogs
• Opacity is in between the lungs and cardiac silhouette opacity=fat

Question 23

Why might you use non-standard radiographic views?

Answer 23

• Aid in diagnosis of small volume of pleural effusion or pneumothorax
• Reduce effacement of a thoracic mass by pleural effusion
• Complex diaphragmatic hernias
• Unstable patients (ex. respiratory distress): standing patient

Question 24

Left lateral recumbency horizontal view

Answer 24

• Detection of small volume of pleural effusion

Question 25

Standard orthogonal views: see a soft-tissue opacity in right ventral hemithorax

Answer 25

- Differentials o Pleural effusion o Diaphragmatic hernia - *use dorsal recumbency horizontal beam

Question 26

Dorsal recumbency horizontal beam: when see a soft-tissue opacity in right ventral hemithorax

Answer 26

- Detection of diaphragmatic hernia - If there was pleural effusion: it would accumulate in dorsal thoracic region (gravity dependent aspect) rather than ventral

Question 27

Equine thorax

Answer 27

- Patient standing: horizontal X-ray beam - Equipment o Large, stationary x-ray tube o High output o Large plate o Portable in foals

Question 28

What are the 4 quadrants for equine thoracic radiographs?

Answer 28

1. Craniodorsal a. Heart, aorta, main bronchi, caudal vena cava, diaphragm 2. Caudodorsal 3. Caudoventral a. Heart, aorta, main bronchi, caudal vena cava, diaphragm, carina 4. Cranioventral a. Trachea, hear, lungs and cranial mediastinum

Question 29

Thoracic ultrasound

Answer 29

- Abnormal ‘wet’ lung: B-lines o DDx: pulmonary edema OR pneumonia - Lung consolidation: “shred sign” - Lung nodule - Intra-thoracic mass - Pleural effusion