Ch 33 Mediastinum Flashcards
Where does the connection between the (mediastinal) parietal pleura and visceral pleura occur?
At the hilus of each lung
The mediastinum is a closed space - T or F
False;
Cranially, it communicates with the fascial planes of the neck by way of the mediastinal structures passing through the thoracic inlet, such as the esophagus and trachea and some major vessels.
Caudally, it communicates with the retroperitoneal space through the aortic hiatus.
Why might mediastinal pleura be non-fenestrated?
Either congenital (rare), or acquired - inflammation > plugging.
Fluid may also not pass if it is too thick.
The cranial mediastinum ventral to the trachea is homogenous on radiographs, but contains which structures?
L subclavian
brachiocephalic trunk
cranial vena cava
mediastinal lnn
In lateral radiographs, the mediastinum just ventral to the trachea is more radiopaque than the mediastinum just dorsal to the sternum because of
the greater thickness just ventral to the trachea.
What are the 3 reflections (where mediastinum deviates from midline)?
cranioventral
caudoventral
vena caval (AKA plica vena cava)
Where is the plica ven cava seen on radiographs?
it isn’t normally seen
where is the cranioventral mediastinal reflection?
which cranial lung lobe crosses the midline?
right;
The cranioventral mediastinal reflection is caused by extension of the right cranial lobe across the midline, pushing the mediastinum to the left.
The thickness of the cranioventral mediastinal reflection is affected by ____.
the amount of fat it contains
What structure lies in the cranioventral mediastinal reflection in young animals?
thymus
Where is the thymus located?
in the cranioventral mediastinal reflection
In which projection is the thymus seen?
DV or VD, like the cranioventral reflection in general
In which projection is the caudoventral mediastinal reflection seen?
DV or VD (same as cranioventral)
The caudoventral mediastinal reflection is created by _________.
extension of the accessory lobe (R lung) across the midline; consists of 4 layers (mediastial pleura x 2, 1 x R visceral pleura, 1 x L visceral pleura)
Where is the caudoventral mediastinal reflection seen?
In DV/VD: straight radiopaque line in the caudal left hemithorax, extending from the region of the cardiac apex in a caudolateral direction toward the gastric fundus
In a normal dog, why would there be an increased opacity of the cranial mediastinum?
Fat
Is the sternopericardiac ligament visible radiographically?
No; was previously incorrectly assumed to be the caudoventral mediastinal reflection.
Where is the plica vena cava?
____________ is the most reliable sign of a mediastinal shift.
Displacement of the heart (to L/R)
an obese dog. The caudoventral mediastinal reflection is thick as a result of fat deposition (white arrows). Compare its thickness with that in Fig. 33.8 (attached).
What is the most common cause of mediastinal shift?
Atelectasis (reduced ventilation or prolonged lateral recumbency)
To which side will mediastinal shift be in atelectasis?
ipsilateral
How many sternal lymph nodes in the dog and in the cat?
Dog: 2 (left + right), sometimes just 1
Cat: 1
Mediastinal masses are _______, as a lung mass would be.
rarely completely outlined by gas
- they are in contact with other soft tissue structures of the mediastinum
What size canine sternal lymph node is normal? Which view/projection is best?
Up to 3cm in length
Right lateral
Where do the afferent lymphatics for the sternal lymphocenter arise, and which tributaries do they receive?
Abdominal wall
+ peritoneal cavity
+ serous membranes
+ mammary glands
+ ribs, sternum, muscles
+ thymus
Mediastinal cysts are more common in cats/dogs.
cats
Mediastinal cysts are typically more cranial/caudal than sternal lymph nodes.
caudal
Do the cranial mediastinal lymph nodes enlarge / react to abdominal disease?
No
By which age should the thymus involute in dogs?
1 year of age
In which projection can the caudal mediastinum be assessed more thoroughly - DV or VD?
VD; in DV the diaphragm protrudes more cranially.
Enlargement of the tracheobronchial lymph nodes results in a soft tissue mass .. where?
and it displaces the trachea how?
- dorsocaudal to the tracheal bifurcation on the lateral view
*** they can be ventral in some dogs, and cause dorsal displacement of the trachea - cranioventral displacement of the tracheal bifurcation
Splaying of the principal bronchi is caused by:
L atrial enlargement or tracheobronchial lnn enlargement
How many tracheobronchial lnn are there?
3 - left, right, middle
where are the tracheobronchial lnn located?
lateral to the bronchi, but also in contact with the trachea
R - ventral to the azygous vein
L - ventral to the aorta
middle - in the bifurcation
Which of the tracheobronchial lnn is the largest?
the middle
What drains into the tracheobronchial lnn?
lungs and bronchi primarily, but also the thoracic parts of the aorta, esophagus, trachea, heart, mediastinum, and diaphragm
Heart base masses typically displace the trachea how and where?
Rightward displacement, just cranial to the bifurcation
a heart base mass may represent: (3 anatomical structures)
- heart base tumor
- R atrial tumor
- enlarged MPA
mediastinal cyst
mediastinal cyst
mediastinal cyst
thymoma
thymoma
thymoma
In VD or DV views, caudoventral mediastinal masses are often located :
to the left of midline because of the normal left-sided
location of the caudoventral mediastinal reflection.
Which diseases most commonly cause mediastinal lymphadenomegaly?
Mycoses and primary lymphoid neoplasia
Which infections have a high prevalence of mediastinal lymphadenomegaly?
Pulmonary mycoses, especially blastomycosis and coccidioidomycosis,
Canine lymphoma causes which pattern of lymphadenomegaly?
In the dog, lymphoma results in enlargement of the sternal lymph nodes in slightly more than half of affected patients, but enlargement of cranial mediastinal or tracheobronchial lymph nodes is uncommon
Which neoplastic conditions cause mediastinal lymphadenomegaly?
Lymphoma
Pulmonary lymphomatoid granulomatosis
Disseminated histiocytic sarcoma
In feline lymphoma, which mediastinal lymph nodes are commonly enlarged?
In the cat, lymphoma is a common cause of enlargement of the CRANIAL mediastinal lymph nodes. The THYMUS may also be affected.
In canine lymphoma, which mediastinal lymph nodes are commonly enlarged?
In the dog, lymphoma results in enlargement of the STERNAL lymph nodes in slightly more than half of affected patients, but enlargement of cranial mediastinal or tracheo- bronchial lymph nodes is uncommon
