Radiographic interpretation paradigm: The small animal thorax (Proceedings)


Radiographic interpretation paradigm: The small animal thorax (Proceedings)

Aug 01, 2010

Thoracic radiography is still the most common first line assessment for diseases and conditions of the thorax. With the advent of digital radiography, a new interest in diagnostic radiology has emerged. However, even though certain artifacts are not an issue (e.g., processing, exposure), problems with inadequately positioned patients still exist. If one does not quality control their radiographs, then there is no sense in even taking them as a poor set of radiographs can mislead a veterinary and result in inappropriate treatment and/or diagnosis for the pet. Thoracic radiography is a quick and easy test to perform and because of the air/soft tissue contrast, provides for an ideal radiographic subject for evaluation. However, interpretation of the thorax can be frustrating and thereby reduce the number of cases that are being imaged even in the face of clear indications for radiographs based on the clinical presentation of the pet. A systematic approach to interpretation is the key to success. This approach will include a step by step overview for the evaluation of all aspects of the thoracic radiograph. This approach will be reviewed in broad strokes during this hour, as all aspects cannot be covered.

Objectives of the Presentation
      1. Provide practitioners with a basic interpretation paradigm for the evaluation of the small animal thorax.
     2. Provide practitioners with the appropriate assessments for technical quality control of the thoracic radiographs.
     3. Provide practitioners with a step-by-step overview for assessing abnormalities of intrathoracic structures.

Key Etiologic and Pathophysiologic Points
     1. Technical factors including technique, phase of respiration and the positioning of the patient have to be taken into account when interpreting thoracic radiographs.
     2. Often, thoracic diseases are multicompartmental.
     3. Often, pulmonary patterns are mixed with disease being in transition or involving a variety of lung components.
     4. All radiographic abnormalities are described based on the standard roentgen sign approach. Ultimately, the abnormalities should be interpreted in light of the patient, physical examination and laboratory data. There will be incidental findings that may or may need to be pursued.
     5. Thoracic ultrasound is limited to peripheral masses (pleural, pulmonary or mediastinal) or generalized disease (pleural or pulmonary)
     6. Repeat thoracic radiographs should be thought of in terms of repeat blood work. You are evaluating a very small time period (1/120th of a sec or faster) of the disease process and all diseases are not static.

Key Clinical Diagnostic Points
     1. One should try to compartmentalize radiographic abnormalities into extrathoracic, pleural, pulmonary and mediastinal (including cardiac), recognizing that any disease can have multicompartmental components.
     2. Most radiographic changes are non-specific and the creation of a prioritized differential list that goes from general to as specific as possible should be written out in the medical record as a summary to the interpretation.
     3. Lesions within the down lung lobe are more difficult to see due to atelectasis of the normal lung adjacent to the abnormal lung.
     4. On a left lateral radiograph, the cardiac silhouette will rotate away from the sternum and should not be mistaken for a pneumothorax.
     5. Always practice radiation safety. Be sure that this is enforced with the techs taking the radiographs and there are penalties associated with violations of standard ALARA principles. Standard radiation safety measures are beyond the scope of this talk; however, remember several key factors: use high mA and low time stations for a given mAs; collimate, collimate, collimate, wear lead apron, thyroid shields and gloves (none of which protect from the primary beam), do not stand directly in front of the tube when making an exposure and use sedation and restraint devices as a first line prior to someone being in the room.

Key Therapeutic Points
     1. Follow-up radiographs should be obtained in rapid succession if warranted (within the same day or within 24 to 48 hours).
     2. Follow-up radiographs will often document the progression or regression of disease.
     3. In certain diseases, the radiographic resolution of abnormalities may lag behind the clinical response by the patient.
     4. Dogs and cats in congestive left sided heart failure usually clear within 24 hours if an adequate diuretic dose has been used.