CV Radiology

Introduction

This lecture revisits fundamental concepts in radiology with a focus on diagnostic imaging of the cardiovascular system. The speaker emphasizes the importance of mastering imaging gradually throughout the course and clinical practice, alongside a review of key anatomical and pathological concepts relevant to radiography.

Learning Outcomes

The objectives of this lecture include:

  • Describe the normal anatomy of the cardiac silhouette on thoracic radiography.

  • Describe the changes that may occur to the cardiac silhouette with cardiac disease.

  • Recognize radiographic signs of congestive heart failure, frequently encountered in small animal practice.

Revisiting Radiography

The speaker emphasizes the importance of accuracy in recognizing normal anatomical structures against pathological changes during the journey through learning radiology. It is essential to:

  1. Play "Spot the Difference": Comparisons between normal and pathological states help build an understanding. A reference guide featuring peer-reviewed examples is essential to avoid misinterpretations based on unreliable sources (e.g., general Google searches).

  2. Considerations Affecting Normality: Changes in normality may arise due to:

    • Breed and conformation of the patient.

    • Degree of inspiration or expiration during radiographic capture.

    • Patient's recumbency and cardiac cycle phase.

    • Respiratory cycle and pulmonary distension.

The Cardiac Silhouette

The cardiac silhouette is viewed in relation to various images taken of a dog (specifically a boxer). The key features of the cardiac silhouette on right lateral and left lateral thoracic radiographs include:

  • Anatomical Markings: The trachea, carina, cardiac silhouette, aorta, and cauda vena cava.

  • Right Lateral Radiograph: Presents a typical outline for a boxer of middle age under anesthesia, with the trachea visible and the carina marked, serving as a reference point for measuring.

  • Differences between Right and Left Lateral Views: The left lateral view tends to produce a rounder cardiac silhouette. It's noted that typical measurements of cardiac size usually rely more heavily on right lateral radiographs due to inherent shape differences created during left lateral images.

Influence of Breed and Conformation

Dog breeds exhibit diverse thoracic configurations impacting how radiographs are interpreted:

  • Example - English Cocker Spaniel: This breed's thoracic shape contributes to a rounder cardiac silhouette compared to that of a boxer. The evaluation includes:

    • No clinical signs of cardiac disease presented.

    • The degree of inspiration/expiration significantly impacting radiographs.

    • Comparative clinical evaluations and the importance of correlating image changes with physical observations.

  • Dachshund vs French Bulldog: Here, the speaker compares boxy-shaped breeds vs. longer thoracic breeds, noting that the variation in thoracic shape can create challenges in interpreting cardiac silhouettes.

Dorsal Ventral Radiographs

Dorsal-ventral views are often preferred for assessing cardiovascular structures as they better depict the vessels leading to the lung lobes. The evaluation of these views includes:

  • The trachea and bronchi visibility.

  • The assessment of pulmonary vessels observed via vascular patterns and their implications, with considerations on inspiration degree affecting how the structures present in images.

Measurement of Cardiac Silhouette Size

Accurate measurements help determine the potential presence of cardiac disease. The following measurements are often referenced:

  • Size of Cardiac Silhouette for Dogs: Should be between 2.5 and 3.5 intercostal spaces. For cats, it should not exceed 2.5 intercostal spaces. Notably, breed discrepancies can result in normal variations, requiring the clinician to interpret measurements contextually.

  • Vertebral Heart Scale: The ratio of the long and short axes of the heart silhouette relative to the spine. Measurements greater than 8.5 to 10.5 vertebral bodies for dogs and 6.9 to 8.1 for cats raise suspicions of enlargement. This method accounts for breed size while providing a diagnostic tool.

Recognition of Cardiac Disease

  • Signs of Cardiac Disease: While not all cases present with radiographic abnormalities, significant findings can include:

    • Enlarged cardiac silhouettes due to hypertrophy or dilation (e.g., mitral insufficiency, dilated cardiomyopathy, pericardial effusion).

    • Visual assessment of vessel changes and other related cardiac structures.

  • Congestive Heart Failure (CHF) Indicators: Radiographic signs include venous congestion in case of left-sided heart failure and pulmonary edema affecting the lung opacity. The differences in ventricular pressure can lead clinicians to assess further treatment routes based on identification of CHF indicators.

Practical Application of Cardiac Imaging

The integration of echocardiography with radiology enhances diagnostic accuracy and helps with clinical decision-making. Regular monitoring of cardiac size, shape, and patient signs are emphasized:

  • Conduct initial radiographs to guide treatment directions while being aware of limitations.

  • Identify possible diagnoses based on simultaneously observed manifestations in conjunction with clinical history and additional diagnostic support (e.g., echocardiograms).

Resources for Further Learning

Suggested readings mentioned include:

  • BSAVA Manual

  • Throll's textbooks on radiology

  • Veterinary Information Network (VIN)

Conclusion

Awareness of the limitations and capabilities of radiography in cardiovascular evaluations is crucial. A comprehensive understanding of normal anatomy variations by breed and potential disease signals can greatly inform diagnostic imaging efforts, enabling better patient management.