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THRALL - Thom > 33. Mediastinum > Flashcards

33. Mediastinum Flashcards

1
Q

Name the different parts of the pleura

A

Visceral

Parietal (diaphragmatic, costal and mediastinal)

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2
Q

What structures divide the mediastinum into regions?

A

Cranial to caudal: Cranial = in front of heart, mid = heart, caudal = caudal to heart

Dorsal - ventral: Tracheal bifurcation

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3
Q

What does the mediastinum communicate with?

A

Fascial planes cranially (due to trachea / oesophagus etc passing through mediastinum)

Retroperitoneum caudally (via aortic hiatus)

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4
Q

What number of dogs experimentally developed bilateral pneumothorax following unilateral injection?

A

22/24

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5
Q

What 3 reasons are provided for unilateral pleural fluid accumulation?

A

Lack of fenestrations

Inflammation of pleura

Viscus fluid

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6
Q

List 3 places where the mediastinum deviates from midline

A

Cranioventral mediastinal reflection

Caudoventral mediastinal reflection

Vena caval mediastinal reflection (= plica vena cavae)

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7
Q

What creates the appearance of the cranial mediastinal reflection?

A

The right cranial lung lobe extending towards the left

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8
Q

List 3 structures within the cranial mediastinal reflection

A

Thymus

Internal thoracic arteries

Internal thoracic veins

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9
Q

What creates the caudoventral mediastinal reflection (remember layers…)?

A

Accessory lobe extending over to left from right

4 LAYERS: Visceral pleura of accessory lobe

  • > mediastinal parietal pleura of R pleural sac
  • > mediastinal pleura of L pleural sac
  • > Visceral pleura of L caudal lobe
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10
Q

MEDIASTINAL ORGANS TABLE

A
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11
Q

What is the caudoventral mediastinal reflection mistakenly known as?

A

Sternopericardial ligament -> continuation of fibrous pericardium NOT RADIOGRAPHICALLY VISIBLE

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12
Q

What are the 3 broad classifcations of mediastinal pathology?

A

Mass

Shift

Pneumo

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13
Q

What is the most common cause of mediastinal shift? What are the 2 different types of mediastinal shift?

A

ATELECTASIS

2 types:

Ipsilateral (eg atelectasis),

contralateral -> mass, inc lung volume, inc pleural pressure

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14
Q

Where is the sternal lymph centre located?

A

Dorsal to 2nd/3rd sternebrae

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15
Q

Anatomical consideration of sternal nodes in dog and cat. Where do they drain? Can they be seen normally in radiogaphs?

A

Dogs: Typically paired, occasionally single median

Cats: Single

Drainage: Ribs, sternum, serous membranes, thymus, adjacent muscles, peritoneal cavity, mammary glands

In dogs: may be normally seen as FUSIFORM opacity, up to 3cm long in R LATERAL

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16
Q

What radiographic features are characteristic of a mediastinal cyst?

A

Small rounded mass, more caudal location than sternal nodes, more ventral than cranial mediastinal nodes

17
Q

What are the afferent and efferent components of the cranial mediastinal nodes? What important difference exists between these and sternal nodes?

A

DONT DRAIN ABDOMEN!

Afferent:

Neck, thorax and abdo mm

scapula

last 6 cervical and all thoracic vertebrae

trachea

Oesoophagus

Thyroid

Thymus

Mediastinum

Costal pleura

Heart

Aorta

Efferent:

Intercostal, sternal, middle and caudal deep cervical, TB, and pulmonary LNs

18
Q

By what age should the thymus have involuted?

A

Approximately 1yr

19
Q

CAUSES OF MEDIASTINAL MASSES - BOX

A
20
Q

To evaluate the caudal medastinum, which radiographic projection should be used (NOT A LATERAL)?

A

VD -> avoid cranial movement of diaphragm in DV

21
Q

What is the most common cause of a dorsal mediastinal mass?

A

OESOPHAGEAL ENLARGEMENT

22
Q

What are the broad classification groups for mediastinal mass location?

A

Cranioventral

Dorsal

Hilar

Caudoventral

23
Q

What are the 2 primary considerations for a perihilar mediastinal mass?

A

TB LN+

Heart base mass

24
Q

What structures do the left and right TB LNs lie ventral to?

A

Left: Ventral to aorta

Right: Ventral to azygous vein

25
Q

Afferent and efferent lymph drainage, TB LNs?

A

Afferent:

Primarily lungs / bronchi

Thoracic aorta

Oesophagus

Trachea

Heart

Mediastinum

Diaphragm

Efferent:

-> Thoracic duct, left tracheal trunk, or both

26
Q

Classically, TB LN+ appears as what?

A

ST mass dorsocaudal to bifurcation -> cranioventral displacement of the trachea

UNCOMMON: if ventrally positioned node, see dorsal displacement of trachea. Can be confused with LA dilation. Both cause bronchial splaying

27
Q

DDx for caudoventral mediastinal mass?

A

Diaphragmatic mass

Diaphragmatic eventration = elevation of hemidiaphragm due to loss of nerve / muscle function, while retaining attachments

Diaphragmatic hernia

NOTE LARGE ACCESSORY LOBAR MASSES CAN LOOK IDENTICAL

28
Q

In dogs, which mediastinal lymph nodes are enlarged in >50% of lymphoma cases?

A

STERNAL

-> rare for cranial mediastinal and TB Lns

29
Q

List 2 tumours where TB LN+ is typical (usually accompanied by pulmonary parenchymal disease)?

A

Histiocytic

Lymphatoid granulomatosis

30
Q

Mycotic disease commonly results in mediastinal LN+. Which 2 disease particularly?

A

Blastomycosis

Coccidioidomycosis

31
Q

List 5 diseases not typically associated with rx detectable mediastinal LN+

A

Primary lung tumour

Metastatic lung tumour

Bacterial pneumonia

Pyothorax

Rib tumours

32
Q

What are the described features of pneumomediastinum?

A

Small: Adventitial surface of trachea visible, heterogeneous / mottled cranioventral lucency

Large: Increased visibility of mediastinal organs / structures

33
Q

Describe the potential movement of mediastinal gas

A

Movement out: Fascial planes, pleural space, retroperitoneum

Movement in: Fascial planes and retroperitoneum

34
Q

Describe the Macklin effect, and list 2 common causes

A

Intrapulmonary alveolar rupture (not involving pleural surface) -> Tracking of gas along bronchi in retrograde manner into mediastinum

Causes:

Blunt trauma

Overinflation

NB: Will not typically see pleural gas unless pleural rupture

35
Q

List 3 common and 3 uncommon causes of pneumomediastinum

A

Common:

Macklin effect

Tracking from cervical fascial planes

Extrathoracic tracheal puncture (e.g. cuff overinflation, venipuncture, transtracheal wash)

=> intrathoracic rupture leads to direct mediastinal leakage

Uncommon:

Oesophageal rupture

Tracking from retroperitoneum

Gas producing bacteria

THRALL - Thom (40 decks)

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