Cranial Mediastinum Flashcards
What is the mediastinum? What is it contiguous with?
fenestrated/incomplete potential space between two pleural spaces, allowing for effusion or pneumothorax to be bilateral
- CRANIAL = neck fascial plane
- CAUDAL = retroperitoneum
What is seen dorsally in the cranial mediastinum? What is not able to be visualized?
trachea
- great vessels
- cranial mediastinal LNs
- esophagus
- lymphatics
- nerves
What is the cranioventral mediastinal reflection?
area of mediastinum where the right cranial lung lobe extends from right to left to the cardiac silhouette
What is able to be visualized ventrally in the cranial mediastinum? What is not able to be seen?
thymic remnant in younger patients
- internal thoracic vessels
- sternal LN
In what animals is the sternal lymph node able to be seen?
some large breed dogs
What are the 3 regions of the mediastinum? Where is it divided dorsally and ventrally?
- CRANIAL - cranial to the heart
- MIDDLE - containing the heart
- CAUDAL - caudal to the heart
at the level of the carina
What is seen in this radiograph?
cranioventral mediastinal reflection
(internal thoracic vessels are found here, not seen)
What is seen in this radiograph?
sternal lymph node
(not normally seen, can be normal in larger dogs)
Mediastinal reflections:
Where is the cranial mediastinal reflection?
cranial to the heart
What is indicative of the presence of a thymus on a radiograph?
- 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!)
What 5 things is pneumomediastinum usually associated with?
- neck wounds
- dog or cat bites
- traumatic venipuncture
- transtracheal wash
- ruptured trachea or esophagus
What are the 2 Roentgen signs associated with pneumomediastinum?
- gas dissecting around structures of the cranial mediastinum dorsally
- visualize serosal borders of the trachea, esophagus, and vasculature - tracheal stripe sign
How is the mediastinum affected in these radiographs?
- tracheal stripe sign
- blue = gas around esophagus
- green = gas dissection along aorta
In what breeds is a redundant esophagus commonly found? What is the most common cause of segmental esophageal distention?
brachycephalics and Shar-Peis
vascular ring anomalies - PRAA
In What 3 places are foreign bodies most commonly found?
- thoracic inlet
- heart base
- gastroesophageal sphincter
When is it normal to find gas within the esophagus?
left lateral projections - found at the heart base
What is seen in these radiographs?
redundant esophagus of a brachycephalic dog = ventral deviation of the esophagus at the thoracic inlet
(gas U shape)
What is occurring in this radiograph?
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
What is seen in this radiograph?
esophageal diverticulum - pouch-like dilatations of the esophageal wall
- distended in the ventrum filled with gravel sign
How should the trachea be situated in the thorax?
- dorsal to the heart base with a consistent diameter
- angles away from the vertebral column
- carina where the principal bronchi divert
What is indicative of tracheal hypoplasia on radiographs? In what animal is this most common?
smaller than normal trachea extrathoracic to intrathoracic
English Bulldog
How is chondromalacia (tracheal collapse) observed based on the respiratory cycle?
- INSPIRATION = extrathoracic
- EXPIRATION = intrathoracic
How does positioning of the patient affect tracheal anatomy?
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
How is the diameter of the trachea calculated from radiographs? What are the normal values in non-brachycephalic breeds, non-bulldog brachycephalics, and bulldogs?
tracheal diameter to thoracic inlet ratio
- NON-BRACHYCEPHALICS: 21%
- NON-BULLDOG BRACHY: 16%
- BULLDOGS: 12%
Tracheal collapse:
- yellow = dorsal and ventral tracheal walls
- green = redundant tracheal membrane
Tracheal collapse:
peak expiration = complete luminal collapse = no tracheal margins
What is likely the cause of the tracheal displacement seen in these radiographs?
cranial mediastinal lymph node enlargement causes dorsal displacement
tracheobronchial lymph node enlargement at the dorsal middle mediastinum causes ventral displacement
How is the cranial mediastinal reflection different?
uniform fat deposition makes it more than 2x larger than the thoracic vertebral bodies + fat in pleural fissure
What is seen in this radiograph of a cat?
cranial mediastinal mass, likely lymphoma
What is seen in this radiograph of a dog?
cranial mediastinal mass, likely a thymoma
What is seen in these radiographs of a cat?
cranial mediastinal mass, likely lymphoma with border effacement of the heart + pleural effusion
How is the mediastinal mass affecting other organs in the thorax?
- 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
What paraneoplastic syndrome is associated with thymomas?
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)
