Introduction to Thoracic Radiology

1. Introduction to Thoracic Radiology Dr. LeeAnn Pack Dipl. ACVR

2. Indications • Coughing • Dyspnea/ Tachypnea • Heart Murmur, Collapse • Primary or Secondary Neoplasia • Check for metastasis • Thoracic Trauma • Chest Wall Mass • Exercise Intolerance, Weight Loss

3. Technical Factors • Potential for Movement • Decrease mAs • High inherent contrast area • High kVp • Collimation • Centering – caudal scapula • Thoracic inlet to diaphragm • Pull forelimbs forward

4. Determining the Phase of Respiration • Always expose at peak inspiration • Maximizes lung contrast • Inspiratory lateral view • Caudodorsal aspect of lung caudal to T12 • Increased aeration of accessory lung lobe • Separation of heart silhouette and diaphragm • Inspiratory VD/DV view • Diaphragmatic cupola caudal to mid T8 • Lung tips caudal to T10

5. Inspiratory vs. Expiratory Lateral Note the space inside the triangle

6. Inspiratory vs. Expiratory VD Easy to see the difference in well visualized lung

7. DV vs. VD • DV • Less stressful, better for heart • Diaphragm rounded • Caudal pulmonary vessels better visualized • Better to see small amount of pleural air • VD • Better for lungs • Hear appears elongated • Flat diaphragm – Mickey Mouse ears • Better to see small amount of pleural fluid

8. DV vs. VD

9. Right vs. Left Lateral etal. • Right Lateral • Better cardiac detail • R crus forward • See Cava go into it • Left Lateral • Heart appears round • L crus forward • See Cava go past • Anesthesia • Breed Differences

10. Importance of Both Lateral Views

11. The Effects of Lateral Recumbency • Lung lesions (mass, nodule, infiltrate) may only be seen on 1 view!!! • Only the non-dependent (up) lung can be critically evaluated • Dependent lung loses aeration (atelectasis) • Increases in opacity • Silhouettes with lesions

12. Special Views • Horizontal beam • Upright VD view • Pleural fluid will fall caudally so CMM can be seen • Recumbent lateral VD • Position patient to move pleural fluid away from area of interest • Cranial mediastinal mass • Lung mass • Check for free air – side up

13. Interpretation of Thoracic Radiographs • Develop your own routine • Systematically evaluate everything on every view • Evaluate a specific structure simultaneously on both views (i.e. assess lungs on VD and lat before moving on to mediastinum)

14. Interpretation of Thoracic Radiographs • Heart • Lungs • Mediastinum • Pleural space • Chest wall • Bones, Abdomen,Neck

15. Normal Cardiac Silhouette • Subjective • Dog = 2 ½ - 3 ½ intercostal spaces • Cat = 2 – 2 ½ intercostal spaces • 65% or less on VD/DV view • Objective • Buchanan method

16. Clock Face • 11-1 Aortic Arch • 1-2 Main Pulmonary Trunk • 2-3 Left Auricle • 2-5 Left Ventricle • 5-9 Right Ventricle • 9-11 Right Atrium • Centrally – Left Atrium

17. Lateral View • Make a Plus sign • Bermuda triangle • Left atrium • Left Ventricle • Right Ventricle

18. Thoracic and Pulmonary Vessels • Aorta • Caudal Vena Cava • Cranial pulmonary vessels • Proximal third rib • Caudal pulmonary vessels • 9th rib where crosses • Veins are ventral and central

19. Trachea, Bronchial Tree • Carina – then splits to the main stem bronchi then lobar bronchi • Tracheal rings can mineralize • Decreased tracheal diameter • Tracheal narrowing (stenosis, extramural compression), Tracheal hypoplasia, Tracheal collapse

20. Lungs • Normal anatomy • Left • Cranial (cranial subsegment) • Cranial (caudal subsegment) • Caudal • Right • Cranial • Middle • Caudal • Accessory

21. Lungs • Normal lung boundaries • 4th to 5th ICS on VD • Fissure b/w L cranial lung subsegments • Fissure b/w R cranial and middle lung lobes • 6th to 7th ICS on VD • Fissure b/w L cranial and caudal lobes • Fissure b/w R middle and caudal lobes

22. Lungs • Regions of a specific lung lobe • Perihilar (hilar) • Midzone • Periphery • Distribution of disease may lead to etiology • Edema • Pneumonia

23. The Mediastinum • Cranial, middle, caudal compartments • Routinely visible structures: • Heart, trachea, cvc, aorta, +/- thymus, +/- esophagus • Cranioventral mediastinal reflection • Caudoventral mediastinal reflection • Aka phrenopericardiac ligament

24. Mediastinal reflections

25. Mediastinal Abnormalities • Shift • Masses • Fluid • Pneumomediastinum

26. Mediastinal Shift • Assess on VD or DV • Position of heart, trachea, aorta, cvc • ***MUST BE STRAIGHT or may be artifactual!!! • Ipsilateral shift • Unilateral decrease in lung volume (atelectasis) • Contralateral shift • Increase in lung volume • Intrathoracic mass

27. Mediastinal Shift

28. Cranial Mediastinal Masses • Lie on or adjacent to midline • Lateral or dorsal displacement of mediastinal structures • Elevation of trachea • ***Diff dx= large volume pleural effusion • Widening of mediastinum on VD • Should be < 2x width of vertebrae on VD • Fat may artifactually widened, esp. Bulldogs • Increased opacity in mediastinum

29. Cranial Mediastinal Mass

30. Examples of CMM’s

31. Mediastinal Fluid • Increased soft tissue in mediastinum • May appear as a soft tissue mass • Common causes • Feline infectious peritonitis • Hemorrhage • Trauma • Coagulopathy • Esophageal perforation

32. Pneumomediastinum • Free air in mediastinum • Enhanced visualization of mediastinal structures • Not dyspneic • Can progress to pneumothorax • Pneumothorax does NOT progress to pneumomediastinum • ***Mediastinum communicates with neck and retroperitoneal space • Subcutaneous emphysema • Pneumoretroperitoneum

33. Pneumomediastinum

34. Causes of Pneumomediastinum • Air escaping into lung interstitium from ruptured alveoli • Trauma, hyperinflation during anesthesia • Extension of gas from neck fascia • Tracheal perforation • Trauma, venipuncture, TTW, cuff overinflation • Esophageal perforation • Extension of retroperitoneal gas • Gas producing organism in mediastinum

35. The Pleural Space • Two layers • Parietal • Lines thoracic wall and diaphragm • Visceral • Lines outer lung surface

36. The Pleural Space • Normal pleura not usually visible • May be visible with pleural thickening or if beam strikes normal pleura tangentially • Between right middle and right caudal lobes on Left Lateral • Visible with pleural effusion or pneumothorax LCr-cr RC LCr-cd RM LCa RC Acc

37. Pleural Effusion • Radiographic signs • Interlobar fissure lines • VD more sensitive with small volumes • Retraction of lungs • Increased soft tissue in thorax outlining lungs • Esp. dorsal to sternum on lateral • Silhouetting of heart/ diaphragm

38. Pleural Effusion

39. Pneumothorax • Air in pleural space • External, lung, or mediastinum • Radiographic signs • Retraction of lungs • Lucent space between lung and chest wall • ***Vessels do not extend to chest wall • Use a hotlight • Dorsal “displacement” of heart on lateral • Actually sliding into dependent thorax

40. Pneumothorax

41. Causes of Pneumothorax • Trauma • Lung rupture • Chest wall rent • Extension of pneumomediastinum • Rupture of cavitary lung mass

42. Tension Pneumothorax • Pleural space pressure exceeds atmospheric pressure during both phases of respiration • Severe lung collapse • Lungs lose normal shape • If unilateral, may cause contralateral medistinal shift • Caudal displacement of the diaphragm

43. Tension Pneumothorax

44. Extrathoracic Structures • Sternum • Vertebrae • Ribs • Adjacent soft tissues • Diaphragm

45. Extrathoracic Structures • Extrathoracic changes may indicate cause of intrathoracic findings • Examples • Pneumothorax • Rib fractures may suggest secondary to trauma • Pleural effusion secondary to rib or chest wall mass

46. The Diaphragm • Cupola • Cranioventral convex portion • Right and left crura • Attach to cranioventral border of L3 and body of L4 • May cause irregularity on these surfaces • Appearance depends on centering of X-ray beam

47. The Diaphragm