P. 569

S. Hecht1
1University of Tennessee, Small Animal Clinical Sciences, Knoxville, USA
Silke Hecht, Dr. med. vet., Diplomate ACVR, Diplomate ECVDI
Professor in Radiology
C247 Veterinary Medical Center, University of Tennessee College of Veterinary Medicine, Knoxville, TN 37996, USA
Adequate radiographic technique and patient preparation, and familiarity with normal anatomy, variants and pitfalls in interpretation are crucial when interpreting radiographs. This lecture will cover common mistakes
in interpretation of small animal radiographs, anatomic variations and technique faults.
Radiology of the Thorax
Technique, Positioning and Respiration (“TPR”): An optimal thoracic radiograph should be obtained with a high kVp and a short exposure time. A grid should be used if the patient is thicker than 10 cm. Additionally, in digital radiography, application of a thorax algorithm is necessary for optimized evaluation. Straight positioning is a must as even slight obliquity interferes with evaluation of cardiac morphology and affects the appearance of other thoracic tissues. With the exception of dynamic studies, all thoracic radiographs should be obtained
at maximum inspiration. Expiratory radiographs will arti cially increase pulmonary parenchymal opacity
which may mimic diffuse lung disease. Relative cardiac size will also be exaggerated on expiratory radiographs. While radiographs under sedation are advisable, general anaesthesia may result in extensive pulmonary atelectasis and possibly render the study nondiagnostic. Finally, a radiographic study should in most instances include at least 2 orthogonal views, and opposite lateral views are indicated for full assessment of lung parenchyma.
Anatomic Variations and Physiologic Status: There
is marked variability in thoracic structures (thoracic
wall, cardiac size and shape) between dogs of different breeds. Lack of familiarity e.g. with thoracic radiographs in chondrodystrophic or very deep chested dogs may result in misinterpretation. Age related changes such
as costal cartilage mineralization, a mild unstructured interstitial and bronchial pulmonary pattern, and physiologic cardiovascular changes in old cats (parallel orientation of heart with the sternum and redundancy of aortic arch and descending aorta) can also be mistaken for pathology.
Thoracic Wall: Like in radiography of the musculoskeletal system (see below), an optical illusion can occur along the boundaries of adjacent (linear) structures of different opacities (“Mach line”) which
can lead to the erroneous diagnosis of a rib fracture. Subcutaneous fat planes or subcutaneous emphysema superimposed over osseous structures can also result in the misdiagnosis of rib lesions.
Diaphragm: Pitfalls in the evaluation of the diaphragm are rather rare. However, a true (congenital) diaphragmatic hernia can be mistaken for a mass, and intrathoracic masses bordering the diaphragm (e.g., accessory lung lobe tumour) may mimic a diaphragmatic rupture. Pleural Space: Chondrodystrophic chest wall conformation and abundant intrathoracic fat deposits may be confused with pleural effusion. Deep chested patient conformation, skinfolds, microcardia and overexposure of the radiograph may give the impression of pneumothorax. These pleural space “abnormalities” can usually be remedied by thorough evaluation of orthogonal radiographs and correction of exposure factors.
Mediastinum: Appearance of the cardiac silhouette is greatly in uenced by positioning. Additionally, pulmonary atelectasis and resultant mediastinal shift can affect the appearance of the heart. Abundant intrathoracic fat can mimic a (cranial) mediastinal mass, especially in barrel chested dogs and on VD views. However, unlike with
a mediastinal mass, the cranial margin of the cardiac silhouette remains visible on the lateral view, and the trachea is in a normal position. Finally, tracheal position is to some degree in uenced by  exion of the neck which has to be taken into consideration when evaluating the mediastinum.
Lung: The normal lung is air- lled and of low opacity. Underexposure, expiratory status and pulmonary atelectasis will result in increased pulmonary opacity which may mimic unstructured interstitial or alveolar pulmonary in ltrates. Pulmonary nodules can be mimicked by a variety of normal structures and variants. End-on-vessels are circular, are superimposed over vessels of equal or larger size, and are
An Urban Experience

   567   568   569   570   571