Guttural Pouch Tympany
Basic Information 
Epidemiology
Species, Age, Sex
The most commonly affected age is 1 year or younger, with fillies being more commonly affected.
Clinical Presentation
Etiology and Pathophysiology
• Tympany of the guttural pouch is the direct result of the entrapment of air within one or both guttural pouches.
• In normal horses, the guttural pouch openings open when the horse swallows, allowing passage of air in and out of the pouch.
• In horses affected with guttural pouch tympany, air is allowed into the guttural pouch via the plica salpingopharyngea but is not allowed to exit the guttural pouch.
• The cause of guttural pouch tympany is most likely secondary to redundancy or abnormal function of the plica salpingopharyngea. The plica salpingopharyngea is a soft tissue structure that lies just beneath the cartilaginous opening of the guttural pouch.
• A redundant plica salpingopharyngea can be congenital or secondary to chronic guttural pouch inflammation.
Diagnosis 
Initial Database
• Complete blood count: Typically normal unless the horse has aspiration pneumonia or severe guttural pouch empyema
• The diagnosis is readily made based on clinical signs alone. The characteristic nonpainful, pliable swelling in the parotid region is difficult to confuse with any other condition.
• The most challenging diagnostic dilemma is determining whether the condition is unilateral or bilateral, since a unilateral disorder will often result in a mild external swelling on the contralateral side.
• Methods of determining whether the condition is bilateral include passage of an endoscope into one or both guttural pouches, aspiration of air from the pouch with the most distension, and obtaining a dorsoventral radiographic view of the skull.
• In unilateral guttural pouch tympany, passage of the endoscope into the affected guttural pouch results in complete decompression of the guttural pouch. If the side with endoscope decompresses but the contralateral side does not, then the condition is bilateral. If there is no change in the external appearance of either guttural pouch, then the condition is most likely unilateral on the contralateral side.
• The second method of determination is to pass a Chambers catheter into the most distended guttural pouch under endoscopic guidance. The findings as described above hold true for this technique.
• Some authors have mentioned external needle decompression of the guttural pouch, but we do not recommend it because of the chance for iatrogenic damage to the neurovascular structures within the guttural pouch.
• The final method of determination of unilateral or bilateral disease is a dorsoventral radiographic view of the skull. Whereas unilateral guttural pouch tympany causes displacement of the affected medial septum of the guttural pouch toward the contralateral side, bilateral guttural pouch tympany results in bilateral air distension of each guttural pouch.
• Endoscopic findings compatible with guttural pouch tympanites include collapse of the dorsal pharyngeal wall, and if concurrent guttural pouch empyema is present, purulent exudate can be visualized exiting the guttural pouch opening.
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