Thoracic Imaging Review PDF

Thoracic imaging Shona McIntyre BVMS MRCVS Learning Outcomes Describe the positioning of common species encountered in small animal practice in relation to generating interpretable radiographic views of the chest Describe the number and types of views required to achieve diagnostic quality...

Thoracic imaging Shona McIntyre BVMS MRCVS Learning Outcomes Describe the positioning of common species encountered in small animal practice in relation to generating interpretable radiographic views of the chest Describe the number and types of views required to achieve diagnostic quality films for a range of conditions and apply those to common examples Identify and recognise aspects of those views that may confound or prevent interpretation of films in relation to the chest 2 Thoracic Radiography - Indications Indication Example Coughing Pulmonary disease, L side CHF, Parasitic disease, Neoplasia, Inhaled FB Dyspnoea Airway obstruction, Pulmonary disorders, Pleural disorders Cardiovascular disease Murmurs, Congestive heart failure, Arrhythmia Thoracic Trauma Pneumothorax, Haemothorax, Rib fracture, Diaphragmatic rupture Neoplasia Primary or metastatic disease Regurgitation Megaoesophagus, Foreign body, Congenital disorders Thoracic wall lesions Neoplasia, Thoracic deformity 3 General Considerations »Exposure High kV and Low mAs Minimise effect of movement blur »Inspiratory view Exceptions include: detection bullae, detection air trapping (feline asthma), detection small pneumothorax 4 Patient Preparation Sedation and Anaesthesia Advantages Disadvantages Better positioning Atelectasis / Dependent lung collapse (GA) Less risk movement blur Manual inflation can reduce visibility small nodules and resolve pathological atelectasis Less stressful for patient Can time radiograph for end inspiration Can perform manual inflation (GA) Consideration to protective clothing if manually inflating 5 Standard Radiographic Views Patient Positioning Dorsoventral Ventrodorsal Right Lateral Left Lateral Lesion orientated oblique Decubitus view / Horizontal beam DV/VD Standing horizontal beam 6 Patient Positioning Minimum views Cardiac conditions – Right lateral and DV view Lung pathology – Right lateral and VD view Pulmonary metastases – Right lateral, Left lateral, VD view 7 Thoracic imaging - review of a thoracic radiograph Shona McIntyre BVMS MRCVS Review of a thoracic radiograph Surrounding soft tissues Cranial abdomen and diaphragm Neck Bones including ribs Pleural space Mediastinum Trachea and carina Bronchi Cardiac silhouette Great vessels and pulmonary vasculature Lungs Images courtesy of BCF technology Review of a thoracic radiograph Mediastinum The space between left and right pleural cavities Extends from thoracic inlet to diaphragm Size on VD/DV radiograph Cranial Middle Caudal Dogs: < twice width of vertebral column Trachea Heart Aorta Oesophagus Oesophagus Caudal Vena Cava Cats: no wider than width superimposed thoracic spine Cranial Vena Cava Great vessels Oesophagus Present but not visible: Cranial mediastinal Main stem bronchi Azygos vein, main pulmonary artery, and sternal lymph vagus nerve nodes Review of a thoracic radiograph Mediastinal Shift Movement of the mediastinum or structures within away from the mid line (indicates a change in volume of one hemithorax) DV or VD projection » Causes Unilateral lung collapse Pleural disease Unilateral pleural effusion or pneumothorax Large single or multiple pulmonary masses Unilateral diaphragmatic rupture Review of a thoracic radiograph - Lymph nodes Normal lymph nodes are not normally visible Those which are present are: ▪ Cranial mediastinal (blue) ▪ Sternal (green) ▪ Tracheo-bronchial (red) Enlargement ▪ Rounded soft tissue masses ▪ Can cause increased size of mediastinum Enlarged Causes sternal LN ▪ Reactive, Lymphoma, Metastatic disease #universityofsurrey 12 Review of a thoracic radiograph Heart Factors affecting cardiac size and appearance Conformation / breed Age Respiratory phase Systemic disease 13 Review of a thoracic radiograph - Heart Heart size ▪ 2–2.5 intercostal spaces (cat) / 2.5-3.5 intercostal spaces (dog) ▪ No more than 2/3 width thorax on Inspiratory view Use the following to determine which chamber is enlarged Ao Ao LA 12 12 Pulm 9 3 RA 3 9 RV 6 RV LV LV 6 Images courtesy of BCF Review of a thoracic radiograph - Heart The Vertebral heart score (VHS) Long axis + Short axis Normal dog: 8.7-10.7 Normal cat: 7.5+/- 0.3 Always refer to breed standards as they do vary. Can be used to compare same patient over time. Image courtesy of Boehringer Ingelheim 15 Vertebral Left Atrial Size Draw a line from the centre most ventral aspect of the carina to the caudal aspect of the left atria, where it intersects the dorsal 2 border of the caudal vena cava (1) Draw a second line equal in length beginning at the cranial edge of T4 and extending caudally (2) 1 Length expressed as a number of vertebral bodies to nearest 0.1 2.3 or above indicative of LA enlargement 16 Vertebral Left Atrial Size Example of enlarged LA 17  Review of a thoracic radiograph - Trachea Lateral view most useful for assessment Head must be in a neutral position so as not to cause artefact Position Forms an angle with the thoracic spine Roughly parallel to spine in lateral Superimposed on spine in DV Size Should not change during respiratory cycle Narrowing can occur in tracheal collapse but can be hard to diagnose on radiography Images courtesy of BCF technology Review of a thoracic radiograph Oesophagus Located in dorsal mediastinum Can be air-filled in normal animal if anesthetised or deeply sedated ‘Tracheal Stripe Sign’ can indicate luminal air Commonly seen in megaoesophagus (see picture where oesophagus outlined by yellow arrows. Red arrow is stripe sign) Images courtesy of A.Denning 18 Review of a thoracic radiograph - Lungs Left lung Right lung Ideally always position a DV/VD first. Placing a patient in lateral will cause atelectasis of the dependent lobe Images courtesy of A.Denning 19 Review of a thoracic radiograph Lung Opacity » Artificial increase in opacity Obesity Under-exposure Expiration Atelectasis Pleural disease » Genuine increase in opacity Reduction in air volume Increase in soft tissue/fluid within lung Combination of both 21 Review of a thoracic radiograph – Lung patterns 1. Alveolar (alveoli fill with something other than air) Oedema Exudate Blood Neoplastic cells » Features Increase in lung opacity: patchy or homogenous, focal, multifocal, diffuse Border effacement adjacent to alveolar filling Air Bronchograms – branching radiolucent lines seen over consolidated lung Increased visibility of borders of individual lung lobes – Lobar Sign Image courtesy of Clinicians brief 22 Review of a thoracic radiograph – Lung patterns 1. Alveolar » Localisation Ventral – aspiration pneumonia Perihilar- cardiogenic oedema Lobar – lung lobe torsion Caudodorsal – non cardiogenic oedema Peripheral – Angiostrongylus infection Air bronchogram Image courtesy of Clinicians brief 23 Alveolar pattern #universityofsurrey 24 Review of a thoracic radiograph – Lung patterns 2. Interstitial Nodular Cannonball Usually neoplastic. Soft tissue density with radiolucent centre Miliary pattern Small multiple coalescing nodules. Commonly neoplastic Soft tissue opacities Cannot see until 3-5mm in diameter Unstructured/reticular pattern (see picture) Diffuse swelling of the interstitial space Commonly seen in WHWH with interstitial pulmonary fibrosis Image courtesy of Martinez,Y, Martin,M 25 Review of a thoracic radiograph – Lung patterns 3. Bronchial Tram lines Donuts Thickening of bronchial walls Peribronchial changes from cellular infiltrate in interstitium Can be seen in inflammatory conditions such as those from parasites, allergy or infectious agents Image courtesy of Martinez,Y, Martin,M 26  Circles indicate donuts Bronchial pattern Parallel lines indicate tram lines The thickened bronchial walls appear more radiopaque and are therefore visible 27  Review of a thoracic radiograph Lungs - Pulmonary Vessels “ Veins are ventral and central” Arteries stay close to a bronchus, veins drift away from the bronchial wall toward the lung periphery At the same level, arteries and veins should be the same size Lateral (cranial lung lobes)