Concepts in Small Animal Thoracic Radiology Thoracic Radiology

Transcription

1 Concepts in Small Animal Thoracic Radiology + Radiology of the Pleural Space VMB 960 2/21/2011 Optimizing Image Quality Inherent subject contrast Thorax has high inherent subject contrast c/f abdomen Primarily air and soft tissue Looking for subtle changes in opacity Need a long gray scale = wide latitude Patient motion Optimizing Image Quality film / screen systems Motion and contrast High detail not critical (except cats) System speed and latitude more important Use a detail system when table top Use a grid when patient thicker than 4 with a 250 speed or higher system 1

2 Optimizing Image Quality Machine Settings Maximize kvp Maximize ma setting Minimize exposure time Use variable kvp technique charts Consider film type High kvp affords latitude and reduces the total mas required for optimal film blackness Optimizing Image Quality film Machine Settings kvp / mas relationship (same film blackness) Decrease mas 50% ( 1 / 2 ) Increase kvp 20% Increase mas 100% (2) Decrease kvp 16% 2

3 Optimizing Image Quality Digital Systems Digital Systems can result in significantly increased lesion conspicuity.. due to Extended image latitude (available on well configured digital systems) Wide exposure latitude Digital Processing both processing and post processing These advantages outweigh reduced resolution of digital systems compared to film/screen systems (for the most part ) Thoracic Radiography Std exam comprises 3 views DV or VD Left and Right Lateral Aeration is critical Minimize sedation Peak inspiration Minimize prolonged recumbency 3

4 L L R 4

5 R Effect of Recumbency Impact of vertical beam Trade off Patient handling Accuracy of positioning Radiation safety issues vs Impact of recumbency on compression / aeration / atelectasis 5

6 Effect of Recumbency Impact of vertical beam Recumbency results in reduced aeration of the down lung. This reduces lesion conspicuity in the dependent hemithorax (silhouette sign) Most pronounced when patients are in lateral recumbency Also occurs when in dorsal recumbency Effect of Recumbency Impact of vertical beam Recumbent atelectasis is exacerbated by sedation, anesthesia, and patient size Solution Take radiographs at full inspiration Minimize sedation PPV when anesthetized Make both lateral radiographs and if necessary both a VD and DV projections 6

7 L R R L 7

8 L R Caudodorsal lung mass 8

9 Cranial Lobe Vessels Vessel/bronchus triad more easily seen in the left lateral projection Right cranial lobe vessels are ventral Vein is always ventral Vessel size = width of 4 th rib at most narrow point 9

10 R L L R Caudal Lobe Vessels 9 VD DV Approx same size as 9 th rib at the point at which they cross on DV view 10

11 Other Effects of Recumbency Down (recumbent) lung anatomy rises relative to up lung Can be used to help differentiate side of lesion = reason why the right cranial lobe vessels often cross the left cranial lobe vessels in the right lateral projection L R Effect of Sedation on Aeration 11

12 Aeration and Positioning Reduced lung aeration has advantages Confirm pneumothorax Better assess airway collapse Cavitated masses, bullae, blebs will be more conspicuous if the pathology is down - increased opacity surrounding pathology Other Important Technique Related Issues Snapshot in time Assess dynamic problems with static images? Hiatal hernia Dynamic airway disease Disclose a hidden dynamic lesion Vary posture/position Inspiration vs expiration 12

13 Complete intrathoracic tracheal collapse Principles of Interpretation Evaluate Radiographic Study Is there a complete set of radiographs? Thorax 3 or 4 views Technical quality Positioning / phase of respiration Collimation Contrast / film blackness Safety issues Artifacts The Systematic Approach. Consider false positive findings Right heart enlargement Dorsocaudal rotation of the apex in left lateral view Breed variations Alveolar disease Pneumothorax Esophageal dilation Pleural effusion - atelectasis - skin folds - sedation - thickening 13

14 Principles of Interpretation Silhouette sign When 2 structures of the same opacity are in contact it is impossible to distinguish a border between them Summation When parts of an object in different planes are superimposed, the resultant film opacity is a summation of x ray absorption of each structure 14

15 A structure not readily visible can become more apparent when there is a change in opacity adjacent to it Roentgen signs of Pleural Fluid widened interlobar fissures- fissures of soft tissue opacity retraction of lung from thoracic wall space between lung and chest wall soft tissue opacity increased opacity dorsal to sternum on lateral radiographs- scalloped margins blunting of costophrenic sulci in VD view decreased visualization of the heart in DV view obscured diaphragmatic outline in DV and lateral view VD is best view to detect small amounts of pleural fluid 15

16 Pleural Fluid Pleural fluid Pneumothorax Trauma, Lung rupture, Chest wall rent Extension of pneumomediastinum Rupture of cavitary lung mass Air within the pleural space results in collapse of lung and lack of the heart cushion There is a resulting mediastinal shift to the side of greatest lung collapse 16

17 Roentgen signs of pneumothorax Retraction of lung from chest wall Space between lung and chest wall is radiolucent Lung markings do not extend to thoracic wall Lung atelectasis with increased opacity Apparent dorsal displacement of the heart on lateral views 17

18 Tension Pneumothorax 18

19 Conditions mimicking pneumothorax Deep chested dog Skin fold Pleural Space 19

20 Pleural Fibrosis Inflammatory pleural fluids can result in fibrosis of the visceral and rounding of lung margins 20

21 Introduction to Thoracic Radiology and Pleural Space Case Discussions 2/22/2011 Why do we use a vertical beam in veterinary radiography? What effect does this have on the appearance of the thorax? What factors exacerbate the disadvantages of a vertical beam configuration On what side is the dog most likely lying? Why? 1

22 Case 1 3 year old Labrador Hit by car 6 weeks ago Now suddenly distressed 2

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24 Case 1 Findings Dorsal displacement of the heart from the sternum on the lateral view. Gas opacity between heart and sternum Retraction of caudodorsal lung lobes Space between chest wall and lung gas opacity Increased lung opacity, likely secondary to atelectasis Chest wall trauma right T12 Sternal lymphomegaly 4

25 Case 2 10 year old Pekingese Male castrate Sudden onset of seizures 5

26 Case 2 Findings Pleural fissure lines are present on the right and left, with lung lobe retraction, consistent with pleural fluid. The cardiac silhouette and pulmonary vasculature appear normal. There is a slightly increased interstitial pulmonary pattern, probably secondary to atelectasis due to pleural fluid. No rib masses or thoracic wall masses are seen, so differential diagnoses for the pleural fluid include hypoproteinemia, hemorrhage, chylous effusion, inflammatory or non inflammatory effusions/transudates. Labrador Retriever 6 months Male Case 3 Breathing hard for 10 days 6

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28 Case 3 There is retraction of the lung lobes on the right, with interposed soft tissue opacity, consistent with pleural fluid accumulation. This fluid appears unilateral, suggestive of viscous effusion. There are rounded gas opacities within the fluid in the pleural space, most likely representing iatrogenic pneumothorax. There is a smooth, bulbous periosteal reaction on the right 5th rib, consistent with a healing rib fracture. Case 3 continued There is a mild alveolar pattern in the ventral aspects of the right cranial and right caudal lung lobes, likely due to fluid atelectasis. The right middle bronchus is not definitively identified. There is a metallic transponder chip in the dorsal soft tissues. The cardiovascular structures appear within normal limits, although silhouetting with pleural and pulmonary disease complicates interpretation. 8

29 Case 3 Assessment Right sided pleural fluid; consider pyothorax Mild right pneumothorax; possibly iatrogenic Healing fracture, right 5th rib Suspect fluid atelectasis, right cranial and caudal lung lobes Case 4 9 year old Rottweiler Male castrate Respiratory distress and collapse 9

30 Case 4 Pleural fissure lines and lung lobe retraction indicate the presence of pleural fluid, which is more severe on the left. Poorly defined, expansile rib lesion (left 7th) characterized by marked osteolysis and irregular osteoproliferation. A rounded soft tissue opacity is superimposed over a 4th rib on the left lateral projection and likely represents a cutaneous nodule present in the right axillary region on the DV projection. An ovoid soft tissue opacity is seen on the right lateral projection at the 6th intercostal space; this opacity may be due to a pulmonary nodule. A focal region of increased soft tissue opacity is seen in the right cranial lung lobe, possibly representing fluid related atelectasis; however, a pulmonary nodule cannot be ruled out. Causes of Pleural Fluid Heart Disease Effusions Septic -pyothorax Non septic lung torsion Malignant Chylothorax Coagulopathies Hypoproteinemia Diaphragmatic hernia Vasculitis 10

31 Case 5 5 year old Labrador Male castrate Fell off an ATV and hit a tree Paraplegic suspect broken back Horizontal beam view done because of neurological status 11

32 Case 5 There is probable subluxation at T12-T13. T13. Retraction of the right caudal lung margins is present, consistent with mild pneumothorax. A left sided alveolar pattern and leftward mediastinal shift are consistent with recumbent atelectasis. 12

33 Case 6 13 year old Golden Retriever Nasal carcinoma Here for thoracic metastasis check 13

34 Case 6 Normal thorax The heart and pulmonary vessels are smaller than normal suggesting hypovolemia. 14

35 Case 7 6 year old Bassett Hound Lethargy and pitting edema 15

36 Case 7 Essentially Normal Thorax The increased opacity along the thoracic wall is common in chondrodystrophoid breeds The cardiac silhouette is mildly enlarged. Extra 2 year old DSH Acc Female Sp Had routine dental prophylaxis 10 days ago puffy and breathing hard 16

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38 Extra A left tension pneumothorax is present. The diaphragm is flattened, the left cranial and caudal lung lobes markedly collapsed and the mediastinum is shifted to the right. Pneumomediastinum is present. Extensive subcutaneous gas is present throughout the neck, thorax, abdomen and forelimbs. 18