Affections of Guttural Pouch and Its Surgical Management

Presented by:Amir Sadaula

Roll No: 01BVSc & AH, 8th Semester

Rampur CampusIAAS, Rampur

January, 2010

Figure 1: Anatomical location of Guttural pouches

The guttural pouches are diverticula of the auditory (or eustachian) tubes found in equids and a limited number of other species. The function of the guttural pouch is unclear, although it may have a role in regulation of cerebral blood pressure, swallowing, and hearing. It is unlikely to have a role in brain cooling. Each guttural pouch of an adult horse has a volume of approximately 300 mL and is divided by the stylohyoid bone into lateral and medial compartments. Guttural pouches are paired extensions of the Eustachian tubes that connect the pharynx to the middle ear.Anatomical Consideration:The medial compartment of the guttural pouch contains a number of important structures including the internal carotid artery and glossopharyngeal hypoglossal, and spinal accessory nerves in addition to branches of the vagus nerve and the cervical sympathetic trunk. Retropharyngeal lymph nodes lie beneath the mucosa of the ventral aspect of the medial compartment, an important factor in the development of guttural pouch empyema.In the lateral compartment the external carotid artery passes along the ventral aspect as do the glossopharyngeal and hypoglossal nerves. Involvement of any of the above-mentioned structures is important in the pathogenesis and clinical signs of guttural pouch disease and may result in abnormalities, such as Homer's syndrome, that are not readily recognized as being caused by guttural pouch disease.The pouches are separated from each other on the midline by the rectus capitis ventralis and the longus capitis muscles and the median septum. Each is in close contact rostrally with the basisphenoid bone, ventrally with the retropharyngeal lymph nodes, pharynx, and the esophagus, caudally with the atlantooccipital joint, laterally with the digastricus muscle and the parotid and mandibular salivary glands, and dorsally with the petrous part of the temporal bone, tympanic bulla, and auditory meatus. Each guttural pouch is divided ventrally into a medial and a lateral compartment by the stylohyoid bone, and it communicates with the pharynx through the pharyngeal orifice of the eustachian tube.

Functions of Guttural PouchPossible functions of the guttural pouches include

pressure equilibration across the tympanic membrane contribution to air warming a resonating chamber for vocalization a flotation device.

A role more recently proposed, on the basis of measurement of lower arterial temperatures in the cerebral side of the internal carotid artery compared with the cardiac side, is brain-cooling. Based on cadaver studies, opening of the pharyngeal orifice of the guttural pouch involves the levator and tensor veli palatini muscles and the pterygopharyngeus and palatopharyngeus muscles. Passive opening of the auditory tube involves a reduced tone in the stylopharyngeus and pterygopharyngeus muscles, accompanied by increased inspiratory pressure. Although guttural pouch filling was previously reported to occur on expiration, the latter study demonstrated that filling occurs on inspiration.

Relations:2

Dorsally: Base of the cranium and atlasVentrally: Pharynx, Origin of OesophagusLaterally: Relations are numerous and complex. Pterygoideus, Stylohoideus muscles,

external carotid artery, maxillary artery, Vagus nerve, parotid and mandbular glands, ventral articular muscles etc.

Medially: In apposition in part and rectus capitis ventralis musclesRostral end: Is a small cul-de-sac, which lies ventral to the presphenoid bone, between

auditory tube and the median recess of the pharynx.Caudal end: Ventral to the atlantal attachment of the longus coli muscles

Each pouch communicates with the pharynx through the pharyngeal orifice of the auditory tube and is in direct continuity with the mucous membrane of the latter. It is lined with ciliated epithelium and has mucous glands. Numerous lymph nodules are present in the young subjects.

Major Affections of the Guttural PouchIt includes the following affections. They are

a) Empyemab) Tympanyc) Mycosisd) Rupture of the longus capitis musclee) Neoplasm

EmpyemaEmpyema is accumulation of exudates within the guttural pouch and is usually sequel of Upper Respiratory tract infection. In recent survey, Streptococcus equi was isolated from 32% of case evaluated as empyema.1 Initially, the purulent material is liquid, although it is usually viscid, but over time becomes inspissated and is kneaded into ovoid masses called chondroids. Chondroids occur in approximately 20% of horses with guttural pouch empyema.2 the condition is most commonly associated with S equi var. equi infection and is a recognized sequel to strangles. Therefore, any horse with guttural pouch empyema should be isolated and treated as if it were infected with S. equi var, equi until proven otherwise. The empyema may be associated with other conditions of the guttural pouches, especially if there is impaired drainage of the pouch through the pharyngeal opening of the eustachian tube.PATHOGENESIS3

The pathogenesis of guttural pouch empyema is unclear although when secondary to strangles it is usually due to the rupture of abscessed retropharyngeal lymph nodes into the medial compartment. Continued drainage of the abscesses presumably overwhelms the normal drainage and protective mechanisms of the guttural pouch, allowing bacterial colonization, influx of neutrophils and accumulation of purulent material. Swelling of the mucosa, especially around the opening to the pharynx, impairs drainage and facilitates fluid accumulation in the pouch. The accumulation of material in the pouch causes distension and mechanical interference with swallowing and breathing. Inflammation of the guttural pouch mucosa may involve the nerves that lie beneath it and result in neuritis with subsequent pharyngeal and laryngeal dysfunction and dysphagia.Clinical FindingThe symptoms comprise:

1. An intermittent discharge, which only appears during feeding or when the head is lowered to eat from the ground or to take the bit or during exercise. It usually liquid containing yellowish white flocculi of variable size.

2. Swelling of the submaxillary lymphatic glands

3. Swelling of parotid region only noticed when the pouch is much distended. Pressure on it causes escape of discharge through the nose.

4. Interference with swallowing and respiration observed when the guttural pouch becomes greatly distended owing to stenosis or partial obstruction of Eustachian tube. The patients have difficulty in swallowing and make respiration noisy and show dyspnea.

5. Rupture of pouch due to excessive distension to repeated efforts of swallowing and to snouting. It is rare occurrence.

6. Holding of head towards the sound side when the horse is being ridden.7. A rattling noise in pouch during exercise due to agitation of the

contents.TreatmentThe principles of treatment are removal of the purulent material, eradication of infection, reduction of inflammation, relief of respiratory distress and provision of nutritional support in severely affected horses. Removal of purulent material may be difficult but can be achieved by repeated flushing of the affected guttural pouch. The guttural pouch can be flushed through a catheter (10-20 French, 3.3-7 mm male dog urinary catheter)or Gunther Catheter inserted as needed via the nares, or a catheter (polyethylene 240 tubing) with a coiled end inserted via the nares and retained in the pouch for several days. The choice of fluid with which to flush the guttural pouch is arbitrary but frequently used fluids include normal (isotonic) saline, lactated Ringer's solution or 1% (v/v) povidone-iodine solution. In severely dyspneic horses caused by guttural pouch distention, a tracheotomy should be performed. If the response to medical treatment is poor or if the purulent material becomes inspissated or forms chondroids, surgical drainage of the guttural pouch should be considered Fig : Gunther Catheter

Tympany Tympany, as the name implies, is the distention of the guttural pouches with air under pressure, sometimes accompanied with some fluid accumulation. This condition is usually unilateral but can be bilateral and is more common in fillies than in colts. In 51 foals with guttural pouch tympany seen at a German clinic between 1994 and 2001, there were approximately three times as many fillies as colts, regardless of breed1. Possible causes include a mucosal flap that acts as a oneway valve and traps air and fluid in the pouch, inflammation from an upper airway infection, persistent coughing, and muscle dysfunction.1

In most cases, there is no gross anatomic abnormality at the guttural pouch opening.Clinical Finding:Include marked swelling of the parotid region of the affected side with lesser swelling of the contralateral side. The swelling of the affected side is not painful on palpation and is elastic and compressible. There are stertorous breath sounds in most affected foals due to impingement of the distended pouch on the nasopharynx. Respiratory distress may develop. Severely affected foals may be dysphagic and develop aspiration pneumonia.2

TreatmentTemporary alleviation can be achieved by needle decompression or by placing an indwelling catheter in the pharyngeal orifice; however, surgery is required for definitive treatment. The affected guttural pouch is usually entered through Viborg’s triangle or through a modified Whitehouse approach. The prognosis for long term resolution of the problem after surgery is approximately 60 %.2

Mycosis:Guttural pouch mycosis affects the roof of one guttural pouch, rarely both. There is no apparent age, sex, breed, or geographic predisposition to this disease. The cause of guttural pouch mycosis is unknown, although Aspergillus can be identified in the lesion. The typical lesion of guttural pouch mycosis is a diphtheritic membrane of variable size, composed of necrotic tissue, cell debris, a variety of bacteria, and fungal mycelia. Aneurysm formation does not appear to precede or follow arterial invasion consistently and, therefore, is not essential to the pathogenesis of arterial rupture.Clinical Signs1

The most common clinical sign is moderate-to-severe epistaxis, which is caused by fungal erosion of the internal carotid artery in most cases and of the external carotid and maxillary arteries in approximately one third of cases. However, any branch of the external carotid artery, such as the caudal auricular artery, can be affected. Several bouts of hemorrhage usually precede a fatal episode. Mucus and dark blood continue to drain from the nostril on the affected side for days after acute hemorrhage ceases. The second most common clinical sign is dysphagia caused by damage to the pharyngeal branches of the vagus and glossopharyngeal nerves. Aspiration pneumonia may develop in severe or protracted cases. Abnormal respiratory noise can arise from pharyngeal paresis or laryngeal hemiplegia, the latter as a result of recurrent laryngeal nerve damage. Horner’s syndrome may develop from damage to the cranial cervical ganglion and postganglionic sympathetic fibers. The classic signs associated with this denervation are ptosis, miosis, and enophthalmos; patchy sweating; and congestion of the nasal mucosa. The reason for equine sweat glands to increase their activity when denervated is unclear. Less common signs of guttural pouch mycosis are parotid pain, nasal discharge, abnormal head posture, head shyness, sweating and shivering, corneal ulcers, colic, blindness, locomotion disturbances, facial nerve paralysis, paralysis of the tongue, and septic arthritis of the atlantooccipital joint.TreatmentNONSURGICAL TREATMENTThe response to topical treatment is generally slow and inconsistent. Daily direct lavage through the endoscope can macerate the diphtheritic membrane, and the biopsy forceps or cytology brush of the endoscope can be used to detach it, provided any eroded artery was occluded beforehand. Topical povidone-iodine or thiabendazole, with or without dimethyl sulfoxide, has been used with mixed results. Nystatin, natamycin, and miconazole have little activity against Aspergillus, but amphotericin B is effective against this organism, although its use in the horse is limited by its toxicity. Successful treatment of dysphagia from guttural pouch mycosis has been reported with a combination of traconazole (5 mg/kg body weight PO) and topical enilconazole (60 mL of 33.3 mg/mL solution per daily flush) in one horse and with topical enilconazole alone in another. Itraconazole at 3 mg/kg twice a day in the feed can be effective against Aspergillus and other fungi in the nasal passage of horses, but treatment may be required for up to 4 or 5 months.SURGICAL TREATMENTThe diphtheritic membrane can be detached by gentle swabbing and lavage through a modified Whitehouse approach. This treatment does not eliminate the risk of hemorrhage completely, and it does not retard or reverse progression of neurologic signs, but it does carry the risk of iatrogenic nerve damage and hemorrhage. In horses with epistaxis, the affected artery should be identified by endoscopy and surgically occluded

Rupture of the longus capitis muscleAvulsion of its insertion on the basisphenoid bone .causes epistaxis and is usually associated with trauma to the head, such as is caused by rearing and falling over backwards. Endoscopic

examination reveals: Compression of the nasopharynx that is asymmetric. Blood in the guttural pouch. Sub mucosal hemorrhage and swelling of the medial aspect of the medial compartment of the guttural pouch. Radiographic examination reveals ventral deviation of the dorsal pharynx and loss of the usual radiolucency associated with the guttural pouch. Treatment is conservative and consists of supportive care, monitoring the hematocrit, and administration of broad-spectrum antibiotics if there is concern of the development of secondary infection. The prognosis for complete recovery is guarded.Various neoplasms have been recorded as involving the guttural pouches. The presenting signs are: swelling of the parotid region, epistaxis, dysphagia or signs of cranial nerve disease. Neoplasms include melanoma, lymphosarcoma, hemangiosarcoma, squamous cell cardnoma and sarcoma. Diagnosis is made by physical, endoscopic and radiographic examination and biopsy. The prognosis is very poor to hopeless.

SURGICAL DRAINAGE OF THE GUTTURAL POUCH1

The following approaches can be used to open the guttural pouch for removal of pus, mycotic plaques, and foreign bodies and to establish drainage.

HyovertebrotomyA 10-cm-long incision is made 2 cm craniad to and parallel with the wing of the atlas (see Fig. 45-14). The dense parotid fascia is incised, and the parotid gland and overlying parotidoauricularis muscle are reflected cranially. The guttural pouch lining is exposed beneath a covering of areolar tissue and grasped with rat-toothed or Allis tissue forceps. It is punctured with the closed tips of scissors or a hemostat, and this opening is enlarged by spreading its edges with a hemostat or the fingers. To establish ventral drainage, the pouch is opened ventrally through an incision in Viborg’s triangle, guided by a finger within the pouch. The hyovertebrotomy can be closed or left partly open for infusion of irrigating solutions.

Viborg’s Triangle ApproachViborg’s triangle is bordered by the tendon of the sternocephalicus muscle, the linguofacial vein, and the vertical ramus of the mandible . A vertical or horizontal incision is made in this area, taking care to avoid the parotid duct and branches of the vagus nerve along the floor of the guttural pouch. The incision is usually kept open with a soft rubber drain to establish ventral drainage.

Whitehouse ApproachWith the horse in dorsal recumbency, a skin incision is made on the ventral midline over the larynx. Dissection is continued between the paired sternohyoideus and omohyoideus muscles and along the larynx to the affected guttural pouch. The guttural pouch is opened medial to the stylohyoid bone, and care is taken to avoid the pharyngeal branch of the vagus nerve and the cranial laryngeal nerve, which are close to the incision.

Modified Whitehouse ApproachIn the modified Whitehouse approach, the skin incision is made along the ventral edge of the linguofacial vein and extends rostrally for about 12 cm from the jugular vein. The underlying fascia is incised to expose the lateral aspect of the larynx, and blunt dissection is continued until the guttural pouch cavity has been entered. The major advantage of this modification is that dissection is through a natural fascial plane and does not involve an incision between the sternohyoideus and omohyoideus muscles. Advantages of both Whitehouse approaches are direct access to the roof of the guttural pouch, digital access to the lateral compartment, excellent ventral drainage, and simultaneous access through the septum to both pouches. Although both approaches involve deep dissection, they do not appear to have a higher rate of complications than other approaches.

Reference

1 Auer J.A, J.A Stick, 2006, Equine Surgery 3rd Edition, Saunder Elsivier St. Louis Missouri

2 Kumar A.,2010, Veterinary Surgical Techniqus, Vikash publishing House Pvt. Ltd. Noida U.P.

3 Radostits O.M, C.C Gay, K.W Hinchcliff, P.D Constable, 2006, Veterinary Medicine, A textbook of the diseases of cattle, Horses, sheep, pigs and goats 10th edition, Saunders Elsevier St Louis

4 Reed S.M, W.M Bayly, D.C. Sellon, 1998, Equine Internal Medicine 2nd Edition, Saunders St. Louis Missouri