SAEVA Congress 2018 Proceedings | 12-15 February 2018 | ATKV Goudini Spa
Examination Technique
Ideally, the hair over the portion of the thorax under examination should be surgically
clipped with a #40 blade. The size of the clipped area should initially be based upon
the auscultatory findings and enlarged as needed to include the entire abnormal lung.
In horses with very fine hair coats, the hair and skin can be thoroughly cleaned,
coupling gel applied in the direction of hair growth, and an adequate image obtained to
determine if any abnormalities exist. Soaking the hair and skin with alcohol can also
result in obtaining reasonably good images in horses with a fine hair coat.
In a normal horse lung can be imaged on both sides of the thorax from just below the
dorsal epaxial musculature to where lung crosses the diaphragm. The initial scanning
of the thorax in adult horses should be performed with a 6.0-10.0 MHz transducer and
a depth setting of 6 - 10 cm. If extensive pulmonary or pleural disease is detected in an
adult horse, or the horse is obese, a lower frequency transducer (5.0, 3.5 or 2.5 MHz)
and/or an increased displayed depth (25 - 30 cm in adult horses with severe pleural or
pulmonary disease) may be needed to penetrate and successfully image the
abnormality in its entirety. The scan should proceed slowly in a dorsal to ventral
direction so that an entire respiratory cycle is imaged before moving ventrally to a
different area. Many subtle pulmonary and pleural abnormalities are only detected
during exhalation, with respiratory movement or by the lack of movement of the lung
against the parietal pleura during deep inspiration. The right apical lung lobe and
cranial mediastinum are imaged by placing the transducer in the right 3rd ICS just
above the level of the point of the elbow and angling the transducer cranially across the
thorax towards the point of the left shoulder. This imaging window is very narrow and
the scan plane orientation must be obliqued to fit between the ribs and yet remain in
the axilla. The cranial mediastinum can also be imaged by placing a lower frequency
transducer over the triceps muscle in the 3 rd intercostal space just caudal to the
scapulohumeral joint and scanning through the musculature into the cranial thorax.
Normal Structures
There is a large difference between the acoustic impedance of air and soft tissue
resulting in air being a near perfect reflector of ultrasound. Therefore, the normal
visceral pleural edge of the lung appears as a straight hyperechoic line with
characteristic equidistant reverberation air artifacts indicating normal aeration of the
pulmonary periphery.
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