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Describe the anatomy of the pleural space. (4)
- potential space b/w thoracic wall and lungs
- not visible radiographically
- contains small amount of fluid for lubrication
- chest wall conformation of chondrodysplastic dogs can mimic pleural effusion
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Describe the pleural space of chondrodysplastic dogs.
- doxies and bassets
- inward curve of wall at costochondral junction--> causes summation of soft tissues
- looks like pleural effusion along thoracic body walls
- look at lateral projections- are there widening of pleural fissures, increase soft tissue in ventral pleural space?--> if not, probably normal breed variation
- can go to US to look for fluid if unsure
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How does pleural effusion appear radiographically? (5)
- presence of fluid within the pleural space (decreased vascular detail)- exudate, transudate, modified transudate (need cytology for definitive diagnosis)
- linear or triangular soft tissue opacity within interlobar fissures (best on VD)- pleural fissure lines
- blunted costophrenic angles
- separation of lung margins from thoracic walls (atelectasis)
- increased soft tissue opacity dorsal to sternum (scalloped ventral lung margins)
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____________ accompanies pleural effusion and appears as...
- Atelectasis
- increased unstructured interstitial pattern in the lungs
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What are causes of pleural effusion? (10)
- idiopathic
- congestive heart failure
- pleuritis
- malignancy
- pneumonia
- trauma
- coag defect
- hypoproteinemia
- chylothorax
- diaphragmatic hernia
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Describe the use of VD versus DV projections to look for pleural effusion.
- on the DV, fluid obscures the heart [fluid collects in ventral thorax- fluid silhouettes with cardiac silhouette]
- on the VD, lungs float on the fluid and elevate the heart [lungs float and cradle heart- can better see the cardiac margins]
- goal of VD is to move the fluid to different parts of the thorax to see pathology of the heart and lungs more clearly
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What are causes of pleural effusion? (4)
- thickened mediastinum
- trapped fluid (fibrinous fluid plugs up mediastinal pores)
- fibrinous fluid (thick, proteinaceous)
- pleural/ mediastinal mass
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What is your crucial next step if you identify pleural effusion?
- tap the chest and remove fluid- for therapeutic and diagnostic reasons
- re-radiograph after fluid removal to evaluate heart and lungs
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What is sometimes utilized in positional radiography with pleural effusion?
- Switch rad machine to shoot horizontal beams and x ray patient in various recumbencies
- free fluid moves to most gravity dependent site; loculated fluid will not change positions
- visualize masses of lung disease if present
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What are radiographic signs of pneumothorax? (3)
- separation of lung margins from the thoracic wall (no lung markings in periphery of thorax)
- heart lifted off sternum (be careful- fat in mediastinum ventral to cardiac silhouette can mimic pneumothorax)
- lung lobe collapse (atelectasis)- often uniform throughout all lobes
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How can you alter your radiographic technique to better visualize atalectasis?
- purposefully underexpose the rads
- lungs absorb more x-rays- can more dramatically see gas-lung interface
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Causes of pnuemothorax. (5)
- trauma- lung rupture, chest wall puncture
- iatrogenic (after tapping the chest)
- extension of pneumomediastinum
- bulla rupture (gas-filled area within a lung lobe)
- complication of pneumonia
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For better evaluation of the cardiac silhouette in a cat with a pleural effusion, what projection should you make?
VD (DV first if resp distress; tap chest then do VD)
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What is tension pneumothorax?
- pleural pressure exceeds atmospheric pressure
- one-way valve allows gas into, but not out of, the pleural space
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How does tension pneumothorax appear radiographically? (2)
- mediastinal shift away from tension pneumothorax
- caudal diaphragmatic displacement (flattening of diaphragm)
- [requires immediate thoracocentesis]
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What structures are in the cranial mediastinum? (5)
- trachea
- esophagus
- lymph nodes (cranial medistinum, sternal)
- great vessels
- lymphatics
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What structures are in the middle mediastinum? (4)
- trachea
- esophagus
- lymph nodes (tracheobronchial)
- heart
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What structures are in the caudal mediastinum? (2)
- esophagus
- caudal vena cava
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How wide should the cranial mediastinum normally be?
usually less than 2X the width of the thoracic vertebra (fat animal may have wider mediastinum without pathology)
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What are causes of pneumomediastinum? (5)
- air escape from lung intersititum
- extension from subQ emphysema
- hole in trachea or esophagus
- extension from retroperitoneal space
- gas producing organism (rare)
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What are causes of mediastinal shift? (4)
- decreased lung volume (shift toward this side)
- increased lung volume (shift away from this side)
- intrathoracic mass (shift away)
- ***always rule out improper positioning first
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What are common cranial mediastinal masses? (9)
- lymphsarcoma (enlargement of lymph nodes or thymus)
- inflammation/ granuloma
- metastatic neoplasia
- abscesses
- trapped fluid
- megaesophagus
- thymoma
- heart base tumors
- hematoma
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How does mediastinal fluid appear as opposed to a mediastinal mass?
mediastinal fluid will not displace or compress the trachea (will deviate around it)
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What are differentials for mediastinal fluid? (3)
blood, exudate, edema (rare)
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Describe cranial mediastinal lymphadenopathy. (3)
- ventral to thoracic trachea
- increased soft tissue opacity with rounded margins
- possible dorsal displacement of trachea
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Describe sternal lymphadenopathy. (2)
- dorsal to sternebrae 1-4
- increased soft tissue opacity that is ovoid
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What are differentials for sternal lymphadenopathy? (3)
- lymphosarcoma
- carcinomatosis
- pancreatitis (sternal lymph nodes drain peritoneal cavity)
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Describe tracheobronchial (hilar) lymphadenopathy.
- located at the tracheal bifurcation
- increased rounded soft tissue opacity
- ventral deviation of the main stem bronchi (another differential for an opacity at this location is left atrial enlargement- differentiate b/c large atria would elevated (not depress) the mainstem bronchi)
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