SAEVA Congress 2018 Proceedings | 12-15 February 2018 | ATKV Goudini Spa
Thoracocentesis performed where pleural effusion was detected ultrasonographically usually results in the successful aspiration of fluid from the thorax . This fluid is usually found in the most ventral portion of the thorax and causes compression of normal healthy lung parenchyma ( compression atelectasis ), retraction of the lung towards the pulmonary hilus , and a ventral lung tip that floats in the surrounding fluid . The larger the effusion , the greater the amount of compression atelectasis and lung retraction that occurs . The thoracocentesis should be performed several centimeters above the normal ventral-most margin of the thorax in the first interspace caudal to the heart where nonloculated pleural fluid or the largest pocket of loculated fluid is imaged ( usually the 7th ICS ). With pleural effusions , another normal structure , the pericardialdiaphragmatic ligament , a normal pleural reflection of the parietal pleura over the diaphragm and heart is imaged as a thick membrane floating in pleural fluid . This membrane is imageable in the ventral thorax of every horse with pleural effusion , regardless of etiology . This membrane runs from the thoracic side of the diaphragm over the heart and appears as a 3-6 mm thick , undulating sheet of homogeneous tissue .
Pericardiodiapragmatic ligament
Similarly , scanning in the cranial mediastinum in horses with pleural effusion usually reveals sonolucent fluid with dorsal displacement of the lung . A thick echoic band of tissue that tapers dorsally is imageable dividing the mediastinum into right and left sides .
The amount of pleural fluid in the thorax can be roughly estimated by the fluid level and the amount of pulmonary parenchymal consolidation or abscesses present . In horses with pleuropneumonia , less than 1 liter of fluid was recovered / side by thoracocentesis when the only pleural fluid imaged was around the cranioventral tip of the lung . A pleural fluid line level with the point of the shoulder corresponds to the recovery of 1-5 liters of pleural fluid / side while 4 - 10 liters were recovered by thoracocentesis in horses with a pleural fluid line extending above the point of the shoulder . With pleural effusions extending 25 cm above the point of the shoulder up to 30 liters of pleural fluid can be recovered / side .
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