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Developments in guttural pouch disease
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Summary
Surgical access is sometimes required to treat complicated cases of guttural pouch (GP) empyema, tympany, mycosis, and for stylohyoid ostectomy. Using a hyovertebrotomy, a Viborg's triangle or a Whitehouse approach offers good direct access to the GP’s medial compartment. A modified Garm’s technique under endoscopic guidance can be used to drain GP’s lateral compartment. Guttural pouch mycosis can induce fatal epistaxis and dysphagia and affects horses of all ages, ponies and donkeys. Most common signs of the disease are nasal discharge, neurological disorders and epistaxis. If the Trans Arterial Coil Embolization (TACE) procedure is efficient to treat and prevent epistaxis, it does not necessarily help in reducing neurological deficiencies. Therefore, a multimodal approach including Topical Oxygen Therapy (TOT) can potentially reduce convalescence time and neurological symptom but this last clinical aspect has yet to be proven.
Guttural pouch lateral compartment approach
Under endoscopic approach a direct access to the GP’s lateral compartment, is possible using a modified Garm’s technique [1] and can be used to drain and remove material. After local anesthesia and with the head and neck in extension, a 6 cm caudo-rostral skin incision is made 2 cm caudal to the vascular incisura within the submandibular space on the medial aspect of the ramus of the mandible. Using digital and blunt dissection, the mylohyoid and digastric muscles are separated and the dissection continued in a 45o dorsocaudal direction towards the base of the ear (Figure 1). A 50 cm long, 0.7 mm diameter metallic tapered end trocar retracted within a 45 cm long, 0.9 mm diameter plastic blunt end rigid sheath is used to penetrate into the lateral compartment under endoscopic guidance.
Figure 1: Left – Lateral radiographic view of the throat and the guttural pouch in which chondroids can be observed; Center - modified Garm’s technique approach on a standing horse, with the head and neck in extension. The finger shows the site of incision and the direction of dissection; Right – endoscopic visualization of the drainage-lavage catheter placement into the lateral compartment.
Epistaxis
Surgical vascular occlusion is the recommended procedure to prevent or treat epistaxis, with the TACE procedure being presently the best option [2]. Coils are mechanical permanent blocking agents and their size should be carefully selected to occlude a specific vessel (Figure 2). Major complications are mainly related to the absence of adequate material and lack of technique. Standing TACE procedure [3] is a minimally invasive and effective method that should be reserved for surgeons experienced with the technique performed under general anesthesia. A more minimally invasive approach, with ultrasound guidance, to percutaneously access, via a skin stab incision, the common carotid artery for coil placement in the ICA has also been described in anesthetized and standing horses (Maninchedda et al. 2015). At the end of the procedure the angiographic catheter and the introducer sheath are removed together and manual pressure is applied to the insertion site. This technique avoids suture of the common carotid arteriotomy site and any surgical incision closure but it can induce secondary hematoma.
Figure 2 – Left: validation (with contrast product) of coil positioning and internal carotid artery (ICA) occlusion, external carotid artery (ECA); Right: standing horse during a Topical Oxygen Therapy session.
Topical Oxygen Therapy
Spontaneous mycosis regression is well described [5] and after a variable period of time, secondary regression of fungal lesions is also observed in all equids treated with a TACE procedure [2]. But in case of neurologic disorders, only 50% of individuals will fully recover from their deficit. Oxygen therapy is a potent antifungal [6] that improves polymorphonuclear function and bacterial clearance; it is toxic to anaerobic bacteria and it can stop the production of alpha toxin. In horses, a decrease in macroscopic mycotic inflammatory reactions is observed after four TOT session at 9L/min for 30 minutes (Figure 2). Presently we offer a multimodal approach to individuals affected with GPM consisting in a first oxygenotherapy session [7] at 15L/min during the TACE procedure under general anaesthesia, followed by a certain number of sessions at a same debit for 45 minutes in the standing animal.
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1. Munoz Moran, J.A., et al. (2008) A surgical approach to the lateral compartment of the equine guttural
pouch in the standing horse: Modification of the forgotten "Garm technique”. Vet J 177, 260-265.
2. Lepage, O.M. (2015) Challenges associated with the diagnosis and management of guttural pouch
epistaxis in equids. Equine Vet Educ 28, 372-378.
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