TV4101 - RI - Thorax - Mediastinum

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What is the mediastinum?

All the organs along the middle of the thorax between the lungs

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What can we see in the mediastinum?
What can’t we see in the mediastinum on normal RG?

Visible
- Cranial mediastinal width
- Trachea

Not visible
- Lymph nodes
- Oesophagus

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Cranial Mediastinum width

Extends where?

From the first ribs to the cranial aspect of the heart

<p>From the first ribs to the cranial aspect of the heart</p>
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Cranial mediastinum – normal anatomy

The structures in the cranial mediasnum are all?

Structures include?

soft tissue opacity (except the trachea) so they efface.

Trachea, oesophagus, blood vessels, lymph nodes

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Cranial mediastinal width

Which view?
How to measure?

• Measured on the VD view

• Locate the first ribs and the cranial border of the heart

• Measure the width half way between these structures

<p>• Measured on the VD view</p><p>• Locate the first ribs and the cranial border of the heart</p><p>• Measure the width half way between these structures</p>
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Cranial mediastinal width
What is normal?
Why would it be wider if not diseased?

• Normal is <2 mes the width of the vertebra

• Wider in brachiocephalic and obese dogs

<p>• Normal is &lt;2 mes the width of the vertebra</p><p>• Wider in brachiocephalic and obese dogs</p>
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<p>Which is abnormal, why?</p>

Which is abnormal, why?

Right - Too wide

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<p>What can we see here?</p>

What can we see here?

Cranial mediastinal mass

<p>Cranial mediastinal mass</p>
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Cranial mediastinal mass DDx?

• Lymphoma

• Thymoma

• Less common – other neoplasia (eg ectopic thyroid), cyst, abscess, granuloma

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Not all cranial mediastinal masses are?
What is a cause that isn’t uncommon?

Neoplasia

Mediastinal cysts are not uncommon and are benign & of no clinical signicance

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<p>What can we see here?<br>Any features?</p>

What can we see here?
Any features?

The trachea
The trachea is normally to the right of midline on the VD view

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<p>Describe each of these photos, both of these animals came in and are healthy</p>

Describe each of these photos, both of these animals came in and are healthy

Left - Normal brachiocephalic – curves more rightward (DDx heart base mass (very unlikely)
Right - normal non-brachiocephalic

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<p>Trachea - describe each of these photos</p>

Trachea - describe each of these photos

Left - Trachea with greater angle with spine → deep chested dog
Right - Trachea is parallel to the spine → barrel chested dog

<p>Left - Trachea with greater angle with spine → deep chested dog<br>Right - Trachea is parallel to the spine → barrel chested dog</p>
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<p>What can we see here?</p>

What can we see here?

Normal cat trachea
Cranial trachea is parallel
Caudal trachea at angle to spine due to natural lordosis

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<p>What can we see here?</p>

What can we see here?

Normal dog trachea - thoracic spine in dog is straight so the angle with the trachea is constant

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Trachea - abnormalities inc?

•Tracheal hypoplasia

•Tracheal collapse

•Tracheal displacement

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Tracheal Displacement at different regions and causes inc?

Cranial mediastinal trachea

  • Megaoesophagus

  • Cranial mediastonal LNs or mass

  • Head flexed during RG

  • High vol pleural effusion

  • LV enlargement

Tracheal bifurcation

  • Tracheobronchial enlargement

  • LA enlargement

Left mainstem bronchus

  • LA enlargement

<p>Cranial mediastinal trachea</p><ul><li><p>Megaoesophagus</p></li><li><p>Cranial mediastonal LNs or mass</p></li><li><p>Head flexed during RG</p></li><li><p>High vol pleural effusion</p></li><li><p>LV enlargement</p></li></ul><p></p><p>Tracheal bifurcation</p><ul><li><p>Tracheobronchial enlargement</p></li><li><p>LA enlargement</p></li></ul><p></p><p>Left mainstem bronchus</p><ul><li><p>LA enlargement</p></li></ul><p></p>
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Tracheal Hypoplasia

Physical change on RG?
Why does it occur?

How to measure?

Generalised decrease in width of the trachea

Part of brachiocephalic airway syndrome

Congenital but CX worse in pups

Measured by the ratio of the tracheal width to the

width of the thoracic inlet

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<p>What this?</p>

What this?

Tracheal hypoplasia The trachea to thoracic inlet ratio is 8%.

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Tracheal Hypoplasia

Trachea width : Thoracic inlet ratio?

• Normal = 20% +/-3%

• Bulldog = 13% +/-4%

• Other brachiocephalic = 16% +/-3%

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Tracheal collapse

Signalment?

Caused by?

CX?

In middle-aged to old small breed dogs

Due to chondromalacia (softening of the tracheal rings)

Chronic cough

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Tracheal collapse - How to Image?

• Endoscopy of the trachea is the best

• Fluoroscopy is the best imaging method

• Radiographs are not sensitive

<p>• Endoscopy of the trachea is the best</p><p>• Fluoroscopy is the best imaging method</p><p>• Radiographs are not sensitive</p>
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<p>What is this? Same dog btw</p><p>Ass with?</p>

What is this? Same dog btw

Ass with?

Left - Redundant dorsal tracheal membrane

Right - Normal trachea (same dog on the other lat view)

Can be associated with tracheal collapse if they have a chronic cough, but can also be seen in normal dogs

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Redundant dorsal tracheal membrane - large breed versus small breed dog

If this is seen in a large breed dog it is likely normal superimposiotin of the oesophagus as tracheal collapse is very rare in large breed dogs.

<p>If this is seen in a large breed dog it is likely normal superimposiotin of the oesophagus as tracheal collapse is very rare in large breed dogs.</p>
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3 Lymph Nodes we need to think about?

Sternal LNs

Cranial mediastinal LNs

Tracheobronchial LNs

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3 Lymph Nodes - Sternal LNs

Features?

At the level of S2 in dogs, and S3 in cats.

They drain the abdomen and mammary glands.

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3 Lymph Nodes - Cranial mediastinal LNs

Features?

They efface with the soft tissue in the cranial mediastinum so they are not seen until they cause a cranial mediastinal mass.

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3 Lymph Nodes - Tracheobronchial LNs

Lymph nodes at the carina

They displace the caudal aspect of the trachea ventrally.

They can be difficult to tell apart from le atrial enlargement, but patient presentation is helpful.

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<p>What can we see?</p>

What can we see?

Very large sternal LNs

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<p>What can we see?</p>

What can we see?

Large tracheobronchial and cranial mediastinal LNs

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Large LNs Ddx?

• Mulcentric neoplasia - lymphoma, hisocyc sarcoma

• Disseminated fungal infection

Metastasis from the draining area eg mammary neoplasia to the sternal LNs

Reactive hyperplasia from the draining area - this only applies to the sternal LNs (peritonitis, haemoabdomen due to benign or malignant causes). Mild enlargement due to reactive hyperplasia of the other LNs (cranial mediastinal & tracheobronchial LNs) is not seen.

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<p>Oesophagus</p><p>Normal oesophagus - location</p><p>VD view?</p><p>Lateral view?</p>

Oesophagus

Normal oesophagus - location

VD view?

Lateral view?

VD view it is superimposed on the midline/mediastinum and often not seen even if it is abnormally large

Better assessed on the lateral view.

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<p>What is this?</p><p>How can we tell?</p>

What is this?

How can we tell?

Oesophageal foreign body

Not a lung mass as it is not seen on the VD (and therefore must be superimposed on the spine on the VD (ie midline)).

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<p>What is this?</p><p>Types and features?</p>

What is this?

Types and features?

Megaoesophagus

•Generalised

  • Transient due to GA or sedation

  • Pathology – such as idiopathic, oesophagitis, myasthenia gravis, myopathy, hypoadrenocorticism, hypothyroidism, toxin (lead, OP)

Focal

  • Vascular ring anomaly (VRA)

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<p>What is this?</p>

What is this?

Megaesophagus - generalised

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<p>What is this?</p>

What is this?

Megaesophagus - focal

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Pneumomediastinum

What view to assess?

The key to idenfying pneumomediasnum is seeing?

Lateral view only

Separation of the blood vessels on lateral view

<p>Lateral view only</p><p>Separation of the blood vessels on lateral view</p>
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<p>Which is abnormal?</p><p>What is it?</p>

Which is abnormal?

What is it?

Left - Pneumomediastinum

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<p>What is this?</p>

What is this?

Pneumomediastinum

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Other mediastinal things to think abt?

Pneumomediastinum

Mediastonal Shift

Normal thymus - seen in young puppies and sometimes kittens

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Mediastinum Anatomy

Communications?

Cranially - Neck via thoracic inlet

  • SC gas in neck → enters mediastinum

  • Gas from mediastinum → cranially into neck (Rare)

Caudally - Retroperitoneum via aortic hiatus in diaphragm

  • Gas from mediastinum (pneumomediastinum) → retroperitoneum (rare)

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Pneumomediastinum

Causes?

Significance?

TX?

• Gas in the mediasnum

• Caused by blunt trauma (HBC) or rupture of the trachea or oesophagus

Clinically insignicant, but can cause pneumothorax which is clinically signicant (Pneumothorax can’t make pneumomediastinum)

  • Can also cause pneumoretroperitoneum, subcutaneous emphysema

Pneumomediasnum is not specically treated

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Mediastinal Shift

Causes inc?

Appearance on RG? What view to use?

• One side has increased volume à heart shis away eg tension pneumothorax

• One side has decreased volume à heart shi towards that side eg lung atelectasis, occasionally with regular pneumothorax

•Heart ‘shifts’ to the left or right

•Assess on the VD only

•The VD has to be PERFECTLY straight

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<p>What is this?</p>

What is this?

Mediastinal shift

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<p>What is this? Sam animal btw</p>

What is this? Sam animal btw

Left - Mediastinal shift as an artefact from positioning (Rotated VD view)

Right - Normal positioning as not rotated

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<p>What is this?</p>

What is this?

Normal thymus in a puppy

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