Page 232 - Adams and Stashak's Lameness in Horses, 7th Edition

198 Chapter 3

diametrically opposed sites, and 40% reduction of the PRINCIPLES OF RADIOGRAPHIC
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entire dural diameter. 58 INTERPRETATION
VetBooks.ir interpreted with caution due to the risk of false‐positive tation: (1) evaluating the quality of the examination,
The results obtained from these methods should be
There are three basic steps to radiographic interpre­
results. It has been suggested that a reduction of 70% of
the dorsal contrast column is needed to avoid false‐posi­ (2) listing radiographic findings, and (3) synthesizing a
tive diagnosis. A study by van Biervliet et al. in 2004 radiographic impression, diagnosis, and/or prognosis.
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showed a high sensitivity and specificity of the reduction Checking film exposure, labeling, collimation, and
of 20% of the entire dural diameter at C6–C7 in neutral positioning are performed to evaluate image quality.
or flexed myelographic projections for diagnosing cervi­ This is an important step because poor‐quality radio­
cal stenotic myelopathy. Using this parameter at any graphs result in missed or improperly diagnosed condi­
other site, the test had only low sensitivity and high tions. A properly exposed radiograph should allow
specificity. One should be aware that besides obtaining observation of bone and soft tissue outlines, and the
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false‐positive results, misinterpretation of myelograms film detail should be sufficient to demonstrate bone
can occur with suboptimal technique or when the lesion trabeculae.
is lateralized, and only lateral radiographic views are Positioning should be evaluated by inspecting joint
made. Increasing use and availability of CT myelogra­ space and bone alignment. Poorly positioned studies
phy of the cervical spine has also revealed lateralized may result from the horse not standing squarely and/
compressive lesions from enlarged articular process or improper alignment of the X‐ray tube and
joints that may be occult on standard radiographic detector.
myelograms. 30 Complete radiographic studies with orthogonal and
oblique images are required for thorough evaluation of
the region of interest. Limiting studies for the sake of
Arthrography saving time or money risks lesions going undetected. In
For diagnosis of articular cartilage and subchondral addition to standard studies, special projections are
bone injury, arthrography in most cases has been sometimes needed to better define and demonstrate sus­
replaced by more advanced imaging modalities and pected lesions.
arthroscopy. However, positive and double contrast When reading the radiograph, a systematic thor­
examinations may provide diagnostic information when ough inspection of the entire image should be done so
evaluating cartilage and subchondral bone damage in that nothing is missed. Identifying radiographic
joints that are not accessible for advanced imaging such abnormalities requires knowledge of both normal
as the shoulder. Arthrography continues to prove use­ radiographic anatomy and radiographic signs of dis­
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ful in assessment of traumatic joint injuries for joint ease. Without knowledge of either, a correct radio­
capsular disruption or synovial defects (fistulae or her­ graphic interpretation is usually not made and risks
nias). In cases of trauma, care must be exercised to not both false‐negative and false‐positive diagnoses. One
enter the joint through damaged or contaminated tis­ of the most common errors in assessment is termed
sues to minimize the risk of joint infection or inflamma­ “satisfaction of search” and refers to the tendency to
tory reaction. incompletely examine the study for other abnormali­
ties once one lesion is identified. This is particularly
common when other abnormalities are on the periph­
Tendonography ery of the image.

Although the use of ultrasound has rendered con­ The third step is formulating a radiographic impres­
trast studies of tendon sheaths almost obsolete, there sion, diagnosis, or differential diagnosis. Knowledge
remain cases in which contrast studies can be useful of disease pathophysiology and its relationship to
and can be more readily interpreted than an ultrasound radiographic signs is necessary for this step. The
evaluation. In particular, the use of contrast studies radiographic diagnosis cannot be made in a vacuum,
when trying determining the presence of synovial her­ and the radiographic findings and their significance
niation or intrasynovial communication is generally must be correlated with other diagnostic information,
rewarding. For example, distension of an extensor such as history, signalment, physical examinations,
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tendon sheath on the dorsal aspect of the carpus is eas­ and perineural anesthesia results, to arrive at a final
ily evaluated with a contrast study and can determine if diagnosis.
communication with the carpal joint exists. In addi­
tion, the use of intrathecal contrast radiography along­
side intrathecal analgesia for detection of digital flexor Radiology of Soft Tissue Structures
tendon sheath pathology has been shown to provide Soft tissue changes may be primary pathologic
high sensitivity (96%) and specificity (80%) for detec­ changes, secondary to more serious bone changes, or
tion of manica flexoria tears. Reported detection of incidental findings of no clinical significance. Fascial
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these tears on ultrasonographic evaluation alone is as planes, tendons, ligaments, and some portion of joint
low as 52%. 53 capsules may be seen because of adipose tissue (fat)
Other modalities such as computed tomography and within and around these structures. Fat is less opaque
magnetic resonance imaging have proved to add sub­ and appears slightly darker than muscle, skin, tendons,
stantial diagnostic information in the diagnosis of soft or ligaments on a radiograph (Figure 3.9). Soft tissue
tissue and bone injuries and will be discussed further in structures should be evaluated for thickening, minerali­
this chapter. zation, and free gas (radiolucencies).