Guttural Pouch Tympany Lucy Russell & Emma Gordon

CASE REPORT

MEDICAL MANAGEMENT OF BILATERAL GUTTURAL POUCH TYMPANY IN A THOROUGHBRED FOAL

Lucy Russell

lucy@srvs.co.nz

Emma Gordon

E.Gordon1@massey.ac.nz

GP tympani in a TB foal

INTRODUCTION

Guttural pouch tympany most commonly affects foals but is occasionally seen in older horses. Entrapment of air in one, or less commonly both, guttural pouches occurs due to inability of trapped air to escape via the normal route into the pharynx via the pharyngeal opening. The exact cause is not known but theorised to be due to an anatomical or functional abnormality at the pharyngeal orifice causing a one-way valve effect (McKinnon et al, 2011). Evidence of a genetic component has been demonstrated in Arabian and Warmblood foals (Blazyczek et al, 2004; McKinnon et al, 2011).

CLINICAL EXAMINATION AND CASE PROGRESSION

A Thoroughbred colt foal was presented for evaluation at two days of age for acute onset, bilateral, soft swelling behind the mandibular rami, accompanied by a loud respiratory noise.

Clinical examination revealed mild-moderate enlargement in the region caudal to the ramus of the mandible, in the parotid region on the left and right sides. The swellings were soft, fluctuant and non-painful. A mild-moderate inspiratory and expiratory stertorous respiratory noise was present. The swelling and noise were observed to wax and wane, being least significant when the foal was relaxed and more significant when restrained, excited and after exercise. The foal’s clinical examination was otherwise unremarkable. Given the age, onset and clinical appearance, a presumptive diagnosis was made of bilateral guttural pouch tympany (Caston et al, 2015).

It was initially elected to monitor the foal closely in the short term, owing to the fact that the swelling was soft and appeared to fluctuate during the day, suggesting that there may be some ability for trapped air to escape the guttural pouches into the pharynx. Over the following weeks the swelling and respiratory noise was observed to be gradually reducing overall, although some daily fluctuation was still seen.

At 28 days of age, the foal was presented for examination due to an acute bilateral increase in swelling in the region of the guttural pouches and increased respiratory noise. Clinical examination revealed marked inspiratory and expiratory stertorous respiratory noise at rest and marked soft, fluctuant swelling in the region of the guttural pouches on the left and right. The foal was dull, with rectal temperature of 39.8oC.

DIAGNOSIS

A thoracic ultrasound examination revealed moderate numbers of scattered comet tails on the left and right cranioventral lung lobes coalescing to sheets ventrally. No free pleural fluid was seen. Upper respiratory tract endoscopy showed marked, bilaterally symmetrical dorsal pharyngeal collapse, causing intermittent, intermittent partial obstruction of the airway during inspiration (Figure 1).

Figure 1: Endoscopic view showing partial naso-pharyngeal collapse during inspiration in top frame, and same view during expiration in bottom frame, with left guttural pouch opening visible on right of images .

No other abnormalities were seen. A venous blood sample revealed a moderate leucocytosis, with a neutrophilia, lymphocytosis and monocytosis, and elevated fibrinogen (Table 1).

Blood parameter

WBC x109/L 16.7 10.1 6.0-11.4

Neutrophils x109/L 11.3 5.1 2.7-7.4

Lymphocytes x109/L 4.5 4.3 1.8-4.4

Monocytes x109/L 0.7 0.5 0-0.3

Fibrinogen g/L 6 5 3-5

Diagnoses of bilateral guttural pouch tympany and aspiration pneumonia were made.

Antibiotic course Ref. Day 1 Day 4 Range

TREATMENT

Blood results were consistent with infection/inflammation (Carrick and Begg, 2008; Walton, 2013). This supported the clinical suspicion of pneumonia, based upon ultrasonographic findings. The pneumonia was postulated to be due to dysphagia secondary to the pharyngeal dysfunction. Treatment was commenced with ceftiofur sodium at 5 mg/kg IM, BID for five days, and gentamycin at 6.6mg/kg IV, SID for three days. A repeat blood sample showed the leucocytosis, neutrophilia, and lymphocytosis to have resolved, and the monocytosis, and elevated fibrinogen to have markedly improved [Table 1] and repeated ultrasound examination of the thorax revealed occasional, scattered, comet tails in the cranio-ventral lung lobes on the left and right. The foal’s condition remained stable during treatment. Guttural pouch distension and respiratory noise remained unchanged.

Following resolution of pneumonia, the foal was anaesthetised, and Foley catheters were placed bilaterally into the guttural pouches. An intravenous catheter was placed into the left jugular vein. The foal was sedated with xylazine (1.1mg/kg) and anaesthesia was induced with ketamine (2.5mg/kg) and diazepam (0.05mg/kg). The foal was placed on a padded mat in left lateral recumbency and a video endoscope introduced into the right nostril to allow visualisation of the left guttural pouch opening. The tip of a 24 Fr Foley catheter (Greet, 2015) was threaded onto a bent mare uterine catheter which acted as a guide (Figure 2), allowing the catheter to be introduced via the left nostril into the nasopharynx where it was manipulated through the guttural pouch opening into the pouch (Figure 3) when 10mL of saline was used to inflate the balloon on the Foley catheter before the guide was gently twisted and removed and the Foley catheter placed under slight tension to ensure it remained lodged in place (Figure 3). The procedure was repeated on the right side. The catheter ends protruding from the nostril were secured through a tape butterfly placed around the Foley on the internal side and a second tape to disperse pressure on the external, through the lateral edge of the false nostril using non-absorbable, monofilament suture (Supramid, USP 2) (Figure 4). The procedure used for Foley catheter placement was that described by Caston et al, 2015, and Greet 2015. Recovery from anaesthesia was uneventful. Maintenance included daily cleaning of the protruding catheter ends, suture sites and nostrils, and the catheters were flushed daily with 5mL of air to ensure patency.

The foal pulled each catheter once during the first week of treatment and these were replaced following the above protocol under GA, using a hand-held fibre-optic endoscope. Securing of the Foley catheters was thus modified. The free ends were initially secured by taping with human strapping tape to the sides of the face (Figure 4). A button was added on the external side of the nostril to disperse pressure due to pressure necrosis at the original suture site (Figure 4). This resulted in no further damage to the nostrils, and the catheters were not pulled out after the tape was added.

CASE PROGRESSION

Once the Foley catheters were placed, the guttural pouch distension reduced substantially within minutes, one side at a time, and only recurred when the foal pulled the catheters out during the first two weeks of treatment. Gradual resolution of the remaining distension occurred over the next week. Catheters were retained in place for a period of five weeks (Greet, 2015) after which no recurrence of tympany was observed. Upper airway endoscopic examination four months after removal was normal, with normal appearance of the guttural pouch ostia (plica salpingopharyngia).

DISCUSSION

This case shows that management of cases of guttural pouch tympany on farm is feasible. Use of the hand-held endoscope yielded a successful outcome and was not markedly more difficult than performing catheter placement with a video endoscope. The treatment process was easily managed on farm, reducing the stress of travel on a dyspnoeic foal, and obviating hospitalisation costs. A high level of patient care and monitoring was certainly necessary, and the on-farm presence of a qualified equine vet nurse, and 24-hour foal-watch meant the foal could be adequately managed on the farm.

Figure 2: Modified mare intra-uterine pipette inserted into end of Foley catheter to act as stylet for catheter placement. A Chambers catheter is usually used but this was not available. An A.I. pipette was thus modified by immersion in boiling water to soften the pipette end sufficiently to allow a small bend at the tip to be made using gentle pressure, that was then inserted into the lateral orifice of the catheter.

Figure 3: Foley catheter with attached pipette inserted into the left guttural pouch opening [top] and the Foley catheter in place following pipette withdrawal [bottom].

Gradual reduction in guttural pouch distension seen over two weeks after the initial reduction was possibly due to tissue stretching and the time taken for this to reduce, accompanied by growth of the foal.

The prognosis for unilateral or bilateral guttural pouch tympany is good using this technique. In a retrospective case series of eight foals treated via trans-nasal guttural pouch catheterisation, five foals had complete resolution of signs and went on to perform at the intended level (Caston et al, 2015). One foal was euthanased soon after admission due to severe aspiration pneumonia. Two foals died of unknown causes following catheter dislodgement, one suspected to be the result of inadvertent intracarotid administration of a sedative. Treatment in the case series (Caston et al, 2015) was completed using standing sedation, reducing the accepted risks associated with general anaesthesia, and reducing the added risks in this subset of foals associated with the presence of dyspnoea and/or inhalation pneumonia.

Presence of secondary inhalation pneumonia, likely due to dysphagia, has been implicated as an increased risk factor for poor outcome (Caston et al, 2015) in foals treated for guttural pouch tympany. For this reason, prompt and early intervention is advocated. Pneumonia was observed in this case that delayed catheterisation due to the requirement for treatment of pneumonia to first stabilise the foal’s condition. Recurrence is documented (Greet, 2015) following use of this technique. Other treatment options can be considered such as surgical / laser fenestration of the median septum between the guttural pouches, or at the guttural pouch ostium to include any abnormal membrane present, or creation of a salpingopharyngeal fistula (Caston et al, 2015; Freeman, 2006; Greet, 2015). Risks of these approaches include possible requirement for general anaesthesia and inadvertent damage to the large network of neurovascular structures associated with the guttural pouches, that can result in dysphagia, aspiration pneumonia, haemorrhage, death, possible recurrence, and potential disturbance of upper airway dynamics (Freeman, 2008).

Figure 4: Bilateral Foley catheters taped in place [top] and modification of nasal stay sutures using buttons [bottom].

The benefits of trans-nasal guttural pouch catheterisation over other treatment options include simplicity, low cost, no need for hospitalisation or for additional specialist equipment and training, reduced necessity for general anaesthesia and lowered risk of complications associated with surgical approaches. In this case, anaesthesia was necessitated due to the foal being very reactive and resented handling of the head, even when sedated.

This case appeared to involve bilateral tympany, although it is reported that unilateral tympany is more common, and difficult to distinguish from bilateral involvement. Unilateral tympany can cause swelling in the parotid region on both sides, but generally the affected side can be expected to be more distended than the other (McKinnon et al, 2011). This foal had bilaterally symmetrical swelling, and when each of the left or right catheters were pulled out during treatment, ipsilateral swelling recurred, supporting the diagnosis of bilateral tympany. The guttural pouches were not entered prior to treatment, which would have confirmed if the affliction was in-fact bilateral. And in fact, guttural pouch endoscopy is recommended in such cases to assess for presence of secondary conditions such as empyema (Caston et al, 2015).

References

Blazyczek, I., Hamann, H., Ohnesorge, B., Deegen, E., Distl, O. (2004). Inheritance of Guttural Pouch Tympany in the Arabian Horse, J Hered, 95(3), 195-199. Carrick, J., Begg, A. (2008). Peripheral blood leukocytes, Vet Clin Nth Amer Eq Pract, 24, 239-259. Caston, S., Kersh, K., Reinertson, E., Cammack, S. (2015). Treatment of guttural pouch tympany in foals with transnasal Foley catheter placement, Eq Vet Edu, 2015(27), 28-30. Freeman, D. (2006). Guttural pouch tympany – a rare and difficult disease. Eq Vet Edu, 18(5), 234-237. Freeman, D. (2008). Complications of Surgery for Diseases on the Guttural Pouch. Vet Clin Nth Amer Eq Pract, 24(3), 485-497.

Greet, T. (2015). Managing foals with guttural pouch tympany. Eq Vet Edu, 27(1), 31-33. McKinnon, A., Squires, E., Vaala, W., Varner, D. (2011). Equine Reproduction, Wiley-Blackwell, Oxford, pp. 612-613; 664. Taylor, P., Clarke, K. (2007). Handbook of Equine Anaesthesia, Elsevier Saunders, New York, 123-175. Walton, R. (2013). Equine Clinical Pathology, Hoboken, Wiley. 130.

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