Mediastinum Flashcards
1
Q
Mediastinal anatomy
A
- Consists of 2 layers of mediastinal pleura and the space between them
- Fenestrated; unilateral disease is uncommon
- Communicates with the neck cranially and retroperitoneal space caudally
- 3 mediastinal reflections
- Cranioventral
- Caudoventral
- Plica vena cava
2
Q
Radiographic anatomy
A
- Of the many structures present in the mediastinum of the normal thorax, only a few structures are seen normally
- Heart
- Caudal vena cava
- Aorta
- Trachea
- Thymus (young animals)
- Occasionally esophagus (left lateral)
3
Q
Structures that normally aren’t visible?
Why?
A
- Cranial vena cava
- Azygos vein
- Lymph nodes
- Nerves
- Why are other structures not seen?
- Silhouetting
- Insufficient thickness or size to absorb the x-rays
- Scant amount of fat to provide contrast
4
Q
Radiographic anatomy: DV or VD view
A
- Width of mediastinum depends on fat accumulation (or disease)
- In the dog, should be less than 2x the width of the thoracic body vertebral bodies
- In the cat, should be less than 1x the width of the thoracic body vertebral bodies
- Often in obese patients width of mediastinum exceeds these cut-offs
5
Q
Caudoventral mediastinal reflection
A
- Between accessory and left caudal lobes
- On the left, since accessory lobe extends to the left
- Only seen on DV/VD views
6
Q
Thymus: radiographic anatomy
A
- Normally seen in young animals
- Resides in the cranial MR
- Best seen as “sail” sign in a VD or DV view
- Usually not seen in the lateral view
- If detected, it may silhouette with the cranioventral margin of the heart
7
Q
Mediastinal disease: 4 general classifications
A
- Mediastinal masses
- Mediastinal fluid
- Pneumomediastinum
- Mediastinal shift
- Lung- or pleural space-related disease
8
Q
Mediastinal masses
A
- Common disease entity
- Radiographic appearance of mediastinal masses have a similar appearance
- DDx:
- Neoplasia, abscessation, cysts, lymphadenopathy, granulomas (parasit. or fungal), hernias, hematomas, congenital
- Clinical signs may vary due to size, location, and complicating/confounding factors (e.g. pleural fluid)
- Pyrexia, muffled heart sounds, cough, palpable mass, malaise, regurg, exc. int.
- DV or VD best views for addressing mass location
9
Q
Mediastinal masses: displacement
A
- Cranial masses
- May result in displacement of heart and lungs caudally
- May deviate trachea dorsally (note: pleural fluid)
- May compress trachea
10
Q
Mediastinal masses: location
A
- DDx will depend on lesion location
- Important to know location of lymph nodes, as well as afferent and efferent lymph vessels
- Sternal
- Cranial mediastinal
- Tracheobronchial
11
Q
Examples of cranioventral diseases:
A
- Sternal lymphadenopathy
- Mediastinal lymphadenopathy
- Vascular ring anomaly –> megaesophagus
- Abscessation/esophageal perforation secondary to foreign body
- Thymoma
- Hemorrhage
12
Q
Examples of dorsal diseases:
A
- Neurogenic and paraspinal tumors
- Tracheobronchial (perihilar) lymphadenopathy
- Vascular ring anomaly –> megaesophagus
13
Q
Tracheobronchial lymph nodes
A
- “Bow-legged cowboy sign” on DV view
- Enlargement of the lymph nodes results in the displacement of the principle bronchi laterally and/or a curved appearance
- On lateral view may obscure the ventral margin of aorta
- DDx: left atrial enlargement
14
Q
Diseases not typically assoc. w/ mediastinal lymphadenopathy
A
- Mammary adenocarcinomas
- Metastatic lung tumors
- Bacterial pneumonia
- Pyothorax
- Thoracic wall tumors
15
Q
Pitfalls for mediastinal masses? Additional diagnostics?
A
- Pleural effusion can ‘hide’ them
- Additional diagnostics
- US first
- Then consider draining and re-radiographing only
