Cranial Mediastinum

Question 1

What is the mediastinum? What is it contiguous with?

Answer 1

fenestrated/incomplete potential space between two pleural spaces, allowing for effusion or pneumothorax to be bilateral

• CRANIAL = neck fascial plane
• CAUDAL = retroperitoneum

Question 2

What is seen dorsally in the cranial mediastinum? What is not able to be visualized?

Answer 2

trachea

• great vessels
• cranial mediastinal LNs
• esophagus
• lymphatics
• nerves

Question 3

What is the cranioventral mediastinal reflection?

Answer 3

area of mediastinum where the right cranial lung lobe extends from right to left to the cardiac silhouette

Question 4

What is able to be visualized ventrally in the cranial mediastinum? What is not able to be seen?

Answer 4

thymic remnant in younger patients

• internal thoracic vessels
• sternal LN

Question 5

In what animals is the sternal lymph node able to be seen?

Answer 5

some large breed dogs

Question 6

What are the 3 regions of the mediastinum? Where is it divided dorsally and ventrally?

Answer 6

1. CRANIAL - cranial to the heart
2. MIDDLE - containing the heart
3. CAUDAL - caudal to the heart

at the level of the carina

Question 7

What is seen in this radiograph?

Answer 7

cranioventral mediastinal reflection

(internal thoracic vessels are found here, not seen)

Question 8

What is seen in this radiograph?

Answer 8

sternal lymph node

(not normally seen, can be normal in larger dogs)

Question 9

Mediastinal reflections:

Answer 9

Question 10

Where is the cranial mediastinal reflection?

Answer 10

cranial to the heart

Question 11

What is indicative of the presence of a thymus on a radiograph?

Answer 11

• lucency in front of the cardiac silhouette and in the area of the R cranial lung lobe
• thymic tail sign seen in cranioventral mediastinal reflection

(young patient!)

Question 12

What 5 things is pneumomediastinum usually associated with?

Answer 12

1. neck wounds
2. dog or cat bites
3. traumatic venipuncture
4. transtracheal wash
5. ruptured trachea or esophagus

Question 13

What are the 2 Roentgen signs associated with pneumomediastinum?

Answer 13

1. gas dissecting around structures of the cranial mediastinum dorsally
2. visualize serosal borders of the trachea, esophagus, and vasculature - tracheal stripe sign

Question 14

How is the mediastinum affected in these radiographs?

Answer 14

• tracheal stripe sign
• blue = gas around esophagus
• green = gas dissection along aorta

Question 15

In what breeds is a redundant esophagus commonly found? What is the most common cause of segmental esophageal distention?

Answer 15

brachycephalics and Shar-Peis

vascular ring anomalies - PRAA

Question 16

In What 3 places are foreign bodies most commonly found?

Answer 16

1. thoracic inlet
2. heart base
3. gastroesophageal sphincter

Question 17

When is it normal to find gas within the esophagus?

Answer 17

left lateral projections - found at the heart base

Question 18

What is seen in these radiographs?

Answer 18

redundant esophagus of a brachycephalic dog = ventral deviation of the esophagus at the thoracic inlet

(gas U shape)

Question 19

What is occurring in this radiograph?

Answer 19

segmental esophageal distention due to stricture at heart base —> PRAA

• opacity in parenchyma
• caudal and right sift of the cardiac silhouette
• trachea displaces ventrally and to the right

Question 20

What is seen in this radiograph?

Answer 20

esophageal diverticulum - pouch-like dilatations of the esophageal wall

• distended in the ventrum filled with gravel sign

Question 21

How should the trachea be situated in the thorax?

Answer 21

• dorsal to the heart base with a consistent diameter
• angles away from the vertebral column
• carina where the principal bronchi divert

Question 22

What is indicative of tracheal hypoplasia on radiographs? In what animal is this most common?

Answer 22

smaller than normal trachea extrathoracic to intrathoracic

English Bulldog

Question 23

How is chondromalacia (tracheal collapse) observed based on the respiratory cycle?

Answer 23

• INSPIRATION = extrathoracic
• EXPIRATION = intrathoracic

Question 24

What parasite can be found in the trachea?

Answer 24

Filaroides osleri —> can form granulomas

Question 25

How does positioning of the patient affect tracheal anatomy?

Answer 25

flexion of the neck kinks the trachea, making it stenotic and commonly mistaken as a mediastinal mass - will resolve with the head and neck in a neutral position

Question 26

How is the diameter of the trachea calculated from radiographs? What are the normal values in non-brachycephalic breeds, non-bulldog brachycephalics, and bulldogs?

Answer 26

tracheal diameter to thoracic inlet ratio - NON-BRACHYCEPHALICS: 21% - NON-BULLDOG BRACHY: 16% - BULLDOGS: 12%

Question 27

Tracheal collapse:

Answer 27

- yellow = dorsal and ventral tracheal walls - green = redundant tracheal membrane

Question 28

Tracheal collapse:

Answer 28

peak expiration = complete luminal collapse = no tracheal margins

Question 29

What is likely the cause of the tracheal displacement seen in these radiographs?

Answer 29

cranial mediastinal lymph node enlargement causes dorsal displacement tracheobronchial lymph node enlargement at the dorsal middle mediastinum causes ventral displacement

Question 30

What is indicative of cranial mediastinal masses? Where can they be seen?

Answer 30

widening of the cranial mediastinum by a soft tissue opaque structure - DORSAL: thoracic lymphadenopathy - VENTRAL: sternal lymphadenopathy or thymoma

Question 31

What are the most common etiologies of cranial mediastinal masses in cats and dogs? What are some other differentials?

Answer 31

- CATS: lymphoma - DOGS: lymphoma or thymoma branchial cyst, ectopic thyroid neoplasia, hemorrhage, round cell neoplasia

Question 32

How is the cranial mediastinal reflection different?

Answer 32

uniform fat deposition makes it more than 2x larger than the thoracic vertebral bodies + fat in pleural fissure

Question 33

What is seen in this radiograph of a cat?

Answer 33

cranial mediastinal mass, likely lymphoma

Question 34

What is seen in this radiograph of a dog?

Answer 34

cranial mediastinal mass, likely a thymoma

Question 35

What is seen in these radiographs of a cat?

Answer 35

cranial mediastinal mass, likely lymphoma with border effacement of the heart + pleural effusion

Question 36

How is the mediastinal mass affecting other organs in the thorax?

Answer 36

- enlarged cranial mediastinal lymph nodes cause dorsal displacement of the trachea - enlarged sternal lymph nodes - enlarged tracheobronchial lymph nodes cause ventral displacement of the carina and principal bronchi

Question 37

What paraneoplastic syndrome is associated with thymomas?

Answer 37

myasthenia-like megaesophagus ---> leads to regurgitation from esophageal dysfunction and aspiration pneumonia (blue = alveolar pattern in RM lung lobe, yellow = lobar sign, green = air bronchogram + thymoma, and megaesophagus)