Middle & Caudal Mediastinum

Question 1

What is able to be visualized in the dorsal middle mediastinum? What is not able to be seen?

Answer 1

• trachea, carina, principal bronchi
• descending thoracic aorta

tracheobronchial LNs, esophagus, lymphatics, nerves

Question 2

What is seen in the ventral middle mediastinum?

Answer 2

cardiac silhouette

Question 3

What is being highlighted in the middle mediastinum?

Answer 3

• red = trachea to carina
• yellow = R cranial lung lobe bronchus
• purple = descending thoracic aorta

(no esophagus seen!)

Question 4

What is being highlighted in the middle mediastinum in this radiograph?

Answer 4

opening into the L cranial lung lobe bronchus in the cranial and caudal subsegment

Question 5

Normal anatomy:

Answer 5

Question 6

What parasite is most commonly associated with the esophagus?

Answer 6

Spirocerca lupi

Question 7

What are 3 causes of tracheal compression?

Answer 7

1. left atrial enlargement
2. tracheobronchial LNs
3. pulmonary masses

Question 8

What are the 2 most common locations for tracheal foreign bodies?

Answer 8

1. caudal thoracic trachea at carina
2. caudal bronchi

Question 9

What are 3 causes of tracheobronchial lymph node enlargement?

Answer 9

1. metastatic neoplasia - pulmonary neoplasia
2. round cell neoplasia - lymphoma, histiocytic sarcoma
3. fungal disease - Blastomycosis, Coccidiomycosis

Question 10

What is seen in this radiograph?

Answer 10

• tracheobronchial lymph node enlargement (metastatic adenocarcinoma) + ventral displacement
• cranial mediastinal and sternal lymphadenopathy
• pulmonary metastasis

Question 11

What is seen in this radiograph?

Answer 11

• tracheobronchial lymph node enlargement with ventral displacement and stenosis
• cranial mediastinal lymphadenopathy with some dorsal displacement of the trachea
• sternal lymphadenopathy

Question 12

What is seen in these radiographs?

Answer 12

• tracheobronchial lymphadenopathy cause ventral displacement of principal bronchi
• bowlegged cowboy sign: lateral displacement of principal bronchi caused by the enlarged LNs

Question 13

What is visible in the caudal mediastinum? What is not visible?

Answer 13

descending thoracic aorta and caudal vena cava (+ plica vena cava of the accessory lung lobe)

• caudal thoracic esophagus/esophageal hiatus (visible if it contains fluid or gas)
• thoracic duct
• azygous vein to the right of the vena cava

Question 14

What is highlighted in the caudal mediastinum?

Answer 14

• red = caudal vena cava in accessory lobe
• yellow = caudoventral mediastinal reflection

Question 15

When is the esophagus visible?

Answer 15

left lateral projection —> faint soft tissue opacity

Question 16

What is seen on this radiograph?

Answer 16

megaesophagus with fluid opacity, possibly FB

Question 17

What is likely happening in this radiograph?

Answer 17

hiatal hernia of the stomach through the gastroesophageal sphincter

Question 18

What is indicative of gastroesophageal intussusception?

Answer 18

• absence of stomach within the abdomen due to intussusception into the esophagus
• ventral deviation of trachea and cardiac silhouette due to stomach presence in the thorax
• megaesophagus cranial to intussusception

Question 19

What can pneumomediastinum lead to?

Answer 19

• pneumoretroperitoneum and cervical emphysema due to migration of gas along fascial planes and descending aorta
• pneumothorax

Question 20

What are 2 causes of absent caudal vena cava?

Answer 20

1. congenital abscence with abdominal venous return through azygous vein
2. border effacement due to accessory lung lobe mass

Question 21

Pneumomediastinum:

Answer 21

mediastinal gas outlining cranial vessels and walls of the trachea

+ pneumopericardium

Question 22

How do accessory lung lobe masses affect thoracic radiographs?

Answer 22

wraps around the caudal vena cava —> border efface margins