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Radiographic Anatomy The Thorax

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1 Radiographic Anatomy The Thorax
Lesley A. Zwicker, BScPharm, DVM Resident, Diagnostic Imaging Radiographic Anatomy The Thorax

2 Structures to identify
Heart Lungs Mediastinum Pleural space Chest wall …Everything else! Bones, soft-tissues

3 Indications for thoracic radiographs
Coughing Dyspnea/tachypnea Neoplasia Primary/metastases Trauma ( i.e. hit-by-car) Chest wall mass Exercise intolerance Weight loss

4 Technical considerations
High potential for movement Respiration High inherent contrast region Bone Soft tissue Fat Air

5 Technical considerations
High kVp Due to high inherent contrast → can use a high kVp Decreased mAs Minimize motion due to decreased time Collimation Thoracic inlet → diaphragm Decrease scatter Minimize distracting content

6 Technical considerations
Pull legs forward Decrease superimposition of musculature

7 Phase of respiration Exposure at peak inspiration Lateral views
Better aeration of lungs → better contrast → better visualization of lesions/disease Lateral views Caudodorsal aspect of lung → caudal to T12 Increased aeration of accessory lung lobe Separation of cardiac silhouette and diaphragm

8 Phase of respiration VD/DV views Diaphragmatic cupola caudal to mid T8
Lung tips caudal to T10

9 DV vs. VD projection Less stressful i.e. dyspneic
Dorsoventral Ventrodorsal Less stressful i.e. dyspneic Potentially better evaluation of the heart Better evaluation of the caudal pulmonary vessels Better visualization of small volume pneumothorax (tips of thorax caudally) Diaphragm is rounded Better evaluation of lungs (routine view) Flat diaphragm – Mickey Mouse ears Better to see small volume of pleural fluid Heart appears elongated

10 DV vs. VD projection Dorsoventral Ventrodorsal

11 Right vs. left lateral projections
Right crus is cranial See vena cava entering right crus cranially Routine projection Heart is more elongated Crura are more parallel* Left crus is cranial See vena cava crossing left crus and entering right crus caudally Performed for metastasis check or if suspect pathology in right lung lobe Heart appears more round Crura diverge* * Does not always hold true but often the case!

12 Right or left lateral? Right

13 Right or left lateral? Right

14 Right or left lateral? Left

15 Effects of lateral recumbency
Which side of the hemithorax is seen best with each lateral projection?? The dependent (“down”) lung → compressed → increased radiopacity Harder to see lesions due to decreased contrast Compressed lung silhouettes with lesions The non-dependent (“up”) lung → aerated lung → decreased radiopacity Easier to see lesions due to increased contrast

16 Effects of lateral recumbency
Only non-dependent lung can be critically evaluated Clinical applications in practice Neoplasia Solitary lesion or metastasis check Pneumonia Contusions

17 The cardiac silhouette
Lateral projection Dog: 2 ½ to 3 ½ intercostal spaces Cat: 2 to 2 ½ intercostal spaces As cats age → heart lies more parallel to sternum

18 The cardiac silhouette
VD/DV projection Heart should be 65% or less (width) of the thorax Objective method Buchanan method

19 The cardiac silhouette
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

20 The cardiac silhouette
The “Plus Sign” Left atrium Left ventricle Right ventricle “Bermuda Triangle” Right atrium Aorta Main Pulmonary Trunk Bermuda triangle Left atrium Right ventricle Left ventricle

21 Vessels Aorta Caudal vena cava Cranial pulmonary vessels
Best evaluated on lateral view Should be smaller than proximal portion of 3rd rib Caudal pulmonary vessels Best evaluated on DV Vessel should make a “□” with the 9th rib

22 Vessels

23 Story time…

24 The lungs Normal Anatomy Left Right Cranial (cranial subsegment)
Cranial (caudal subsegment) Caudal Right Cranial Middle Accessory

25 The mediastinum Compartments → cranial, middle, caudal
What can you routinely see?? Heart, caudal vena cava, aorta Trachea +/- thymus +/- esophagus Cranioventral mediastinal reflection Caudoventral mediastinal reflection

26 Mediastinal reflections

27 Extrathoracic structures
Sternum Vertebrae Ribs Adjacent soft tissues Diaphragm

28 Mediastinal abnormalities
Masses Neoplasia Cysts Granulomas Abscesses Lymphadenopathy Fluid Hemomediastinum

29 The diaphragm Appearance depends on centering of X-ray beam 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

30 aorta trachea artery vein bronchus caudal vena cava

31 Any questions???

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