Endoscopy of the auditory tube diverticulum (ATD) (see 5.3) permits inspection of the ventral aspect of the tympanic bulla and of the internal os of the eustachian tube.

The tympanic bulla is not a good subject for diagnostic radiographs because of superimposition of the petrous temporal bones. However, where the facilities are available, scintigraphic and CT scanning may produce useful images.

Temporohyoid osteoarthropathy (THO)

THO comprises a proliferative osteitis of the petrous temporal and proximal stylohyoid bones. The aetiology of the underlying disorder is not known, and the presence of infection is rarely confirmed. A degenerative inflammatory process is most likely involved. Ankylosis of the joint between the stylo-hyoid and temporal bones is a common feature of THO. The consequences of this ankylosis include pathological fractures through the middle and inner ears causing peripheral vestibular signs (see Chapter 11) or through the stylo-hyoid the effect of which is to limit the horse’s ability to move the tongue. The first sign of temporo-hyoid osteitis may be facial palsy when the facial nerve is compressed by the expanding bony lesion as it passes through the dorsal recess of the lateral compartment of the ATD. The diagnosis can be confirmed by endoscopy of the ATD, and the consequences can be relieved by osteotomy of the keratohyoid, thus pre-empting the pathological fracture.

Otitis interna/peripheral vestibular disease

The inner ear includes the end organs of hearing and proprioception, i.e. the cochlea, semi-circular canals, utricle and saccule.

Deafness is practically unrecorded in horses but whether this reflects an absolute rarity or a lack of observation by attendants is unclear.

The term otitis media should not be used to describe the state of neurological disturbance where there is head tilt, ataxia, circling and nystagmus; this is indicative of disturbance of the vestibular system, particularly the peripheral vestibular apparatus of the inner ear.

Otitis interna may arise as an extension of suppurative otitis media or be concurrent with osteitis of the petrous temporal bone (THO – see above).

The diagnosis is based on the presenting signs, the exclusion of other neuropathies such as cervical vertebral stenotic myelopathy (‘wobbler syndrome’), endoscopy of the ATDs and diagnostic imaging of the area.

5.3 Diseases of the auditory tube diverticulum (ATD) (guttural pouches)

Anatomy and function of ATDs

The ATDs are balloon-like structures lying between the base of the cranium dorsally and the pharynx and oesophagus ventrally. The volume of each pouch is approximately 300 mL, and medially the two ATDs are in contact with one another, divided only by a thin layer of areolar tissue. The stylohyoid bone divides each pouch into lateral and medial compartments.

Each pouch is in contact with the base of the skull so that those structures which enter and leave the cranium through the foramen lacerum must cross the pouch: internal carotid artery, cervical sympathetic nerve and cranial nerves IX (glossopharyngeal), X (vagus) and XI (accessory).

The facial nerve (VII) lies in the submucosa of the lateral compartment dorsally.

The internal maxillary artery and vein cross the wall of the lateral compartment, and here the pouch lies beneath Viborg’s triangle.

The walls of the ATDs are lined by ciliated columnar mucous membrane, and a dynamic clearance system removes mucus and particulate debris.

The drainage ostia are slit-like openings under cartilaginous flaps which lie on the dorso-lateral wall of the pharynx, and they are quite close together, separated by the pharyngeal recess. Thus, although slight discharges from one pouch may produce a predominantly unilateral nasal discharge, the more copious the discharge, the more likely it is to be bilateral.

Signs of ATD diseases

The signs of disorders of the guttural pouches reflect either compression of adjacent organs when they become distended or damage to the structures which cross them.

Swellings of the ATDs may be visible externally at the parotid region or will partially obstruct the pharynx leading to dyspnoea or dysphagia.

Erosion of the internal carotid artery can cause spontaneous haemorrhage at the nares which on occasions is so severe that the horse exsanguinates.

ATD disorders provide the potential for a very wide range of neuropathies to such an extent that the possibility of guttural pouch disease should be considered practically whenever a horse is presented with a cranial nerve deficit.

Physical examination of ATDs

External palpation in the parotid area is helpful to detect swellings produced by tympany, empyema, infection of adjacent lymph nodes or neoplastic foci particularly in the parotid lymph nodes.

On occasions guttural pouch mycosis may produce painful foci deep to the base of the ear when the head of the stylohyoid bone or the tympanohyoid articulation has become involved. However, this condition rarely produces an external swelling.

Endoscopy of ATDs

The simplest way to pass an endoscope into each pouch is by using a wire leader passed through the biopsy channel of the endoscope. This channel is invariably eccentric, and thus the wire can be used to raise the cartilage flap before advancing into the duct beyond. This manoeuvre can only be successful when the ostium is approached via the ventral nasal meatus.

Apart from looking for abnormalities inside the ATDs, endoscopy should be used to examine the larynx and pharynx for extension of ATD disease into those structures.

Depression at the pharyngeal recess and partial obscuring of the larynx may result from distension within the ATD.

Pharyngeal and laryngeal hemiplegia can result from mycotic infections.

Radiographic examination of ATDs

The ATDs are normally filled by air, and the contrast thus provided makes for good diagnostic radiographs.

The erect lateral projection is used and may reveal free gas/fluid interfaces, loss of air contrast through replacement by inspissated pus or soft tissue substitution e.g. indentations from lymph node swelling in the caudal wall.

Complete occlusion of an ATD can occur in cases of chronic empyema or chondroid formation.

Topical treatment of ATDs

A 35-cm long, 30-mL Foley balloon catheter offers a suitable indwelling device for repeated topical infusion of medication. The catheter is advanced up the ventral nasal meatus using a metal stiffener slightly bent at the leading end. This is rotated under the cartilage flap of the ostium which lies on the lateral pharyngeal wall at the same level as the eye.

Long-term catheterization may lead to weakening of the ostium and erosion of the cartilage flap.

Surgical approaches to ATD

1. Hyovertebrotomy. An incision is made parallel and immediately cranial to the wing of the atlas. The parotid salivary gland is reflected forwards. An endoscope introduced into the ATD per nasum serves to illuminate the membranous lining deep in the surgical site once the loose connective tissue has been bluntly separated. When this approach is used the ATD is entered through the lateral wall of the medial compartment where it projects caudal to the stylohyoid bone.

2. Viborg’s Triangle. Access to the ATDs by this approach is very restricted except in conditions where there has been stretching of the tissues through distension of the pouch which in turn increases the overall size of Viborg’s triangle.

3. Paralaryngeal (Whitehouse) approach. With the horse in dorsal recumbency, a ventral midline incision is made over the larynx. The dissection passes lateral to the larynx, trachea and cricopharyngeal muscle to reach the pouches ventro-medially. Entry to the ATD is again made medial to the stylohyoid bone. The depth of incision limits the value of this approach.

4. Modified Whitehouse approach. The site of the incision corresponds to that used for prosthetic laryngoplasty, i.e. it lies ventral to the linguo-facial vein and then follows the same route to enter the pouch. This approach may be used in the standing sedated patient for the removal of chondroids when the horse is considered a poor risk for general anaesthesia.

5.4 Guttural pouch tympany

Aetiology: In this condition the ATD ostium acts as a non-return valve so that air can enter the pouch but cannot escape.

Clinical signs and diagnosis: This is a condition of foals which usually manifests itself within a few days of birth and it is thought to arise from a congenital malfunction of pharyngeal opening of the pouch rather than a physical obstruction.

The disorder appears to be more common in fillies than in colts and is almost invariably unilateral. Arabian horses are most susceptible.

Air accumulates and produces a tympanitic swelling in the parotid region which is initially non-painful and non-inflammatory.

Established cases invariably show evidence of opportunistic infection because a mucopurulent nasal discharge is generally present by the time afflicted foals are submitted for corrective surgery.

The laxity of the medial septum between the ATDs may lead to swelling on the normal side, and hence false diagnoses of bilateral tympany may be made.

Dysphagia and dyspnoea may be exhibited by virtue of the size of the distension.

Occasionally ATD tympany is an acquired disorder of the adult horse.

Treatment: Three principles have been applied for the relief of ATD tympany:

1. Dilation of the pharyngeal ostium on the affected side.

2. The creation of a fistula between the normal and distended pouches by the removal of a section of the medial septum.

3. Blunt fistulation between the ATD and the pharyngeal recess.

A simple conservative technique to remedy the disorder consists of the long-term implantation of an indwelling Foley catheter placed through the defective pharyngeal ostium per nasum and left in place for up to 8 weeks.

The purpose of the medial wall fistulation technique is to facilitate the egress of air from the abnormal ATD through the pharyngeal ostium of the normal side. Transendoscopic laser surgery provides an option for non-invasive fistulation through the medial septum when this facility is available.

Prognosis: The prognosis for ATD tympany is usually favourable regardless of whether the catheterization or fistulation technique is used. Delayed treatment may lead to dyspnoea in later life if the tissues have become irreversibly over-stretched.

5.5 Diverticulitis of the guttural pouch

Aetiopathogenesis: These are poorly defined and poorly understood conditions in which inflammation of the mucous membrane lining of the ATDs occurs and which can loosely be termed ‘diverticulitis’. They include strangles infection in the lymphoid tissue of the walls of the pouches, empyema, chondroid formation and chronic diverticulitis.

A catarrhal inflammation of the ATD mucosae probably accompanies most upper respiratory tract bacterial and viral infections, and the tympany described above is also likely to be accompanied by inflammatory changes, hence the term ‘tympanitis’.

‘Strangles’

See Chapter 19.

This is an infectious condition of horses caused by Streptococcus equi which consists of a suppurative lymphadenitis, particularly of the lymph nodes, associated with the upper respiratory tract including the ATDs.

Occasionally the free movement of air through the drainage ostia of the ATDs is obstructed by the physical presence of the lymphadenopathy, and a variable degree of tympany may be exhibited.

Temporary tracheotomy is indicated for those horses which show life-threatening airway obstruction.

Chronic ATD empyema and chondroids

Empyema of the ATDs occurs when mucus and/or pus accumulates within the pouches because it fails to drain satisfactorily.

The primary aetiological factor in ATD empyema is a dysfunction of muco-ciliary clearance followed by stagnation of mucus, opportunist bacterial infection and finally purulent exudation. There is a possible aetiological association with tympany.

Regardless of the precise aetiology of empyema, pus which is stagnant within the pouch eventually becomes inspissated and progressively leads to the formation of solid concretions – chondroids.

Horses with chondroids should be regarded as carriers for Streptococcus equi infection unless proven otherwise.

• The clinical signs of empyema include a bilateral purulent nasal discharge and swelling of the parotid region.

• The distension of the affected pouch into the pharynx may produce obstructive dyspnoea. The nasal discharge is sometimes malodorous.

• Lateral radiographs confirm the loss of air contrast from within the ATD, and if the pus is still fluid, an air/fluid interface will be demonstrable.

• An indwelling self-retaining Foley balloon catheter may be used for drainage of the ATD and for long term irrigation in the management of chronic cases.

• Inspissated caseous pus/chondroids may be liquefied by a process of repeated lavage via the pharyngeal ostium aided by the instillation of acetylcysteine.

• Chondroids which do not respond to conservative management may be removed individually using trans-endoscopic grasping forceps if they are small in number; otherwise surgical removal is required to extirpate chondroids.

• Whenever chondroids are bilateral the ventral Whitehouse approach is preferred so that both pouches can be entered through the same incision.

Chronic ATD diverticulitis

Chronic catarrhal inflammation of the ATDs in horses may be encountered with no history to suggest previous strangles infection.

Chronic diverticulitis without the presence of empyema may present with a syndrome of neuropathies where any combination of deficits of the glossopharyngeus, vagus, facial, spinal accessory and sympathetic nerves may be present. It is assumed that the nervous pathways are damaged as an extension of the inflammatory process in the ATD walls.

The diagnosis is established by a functional assessment of the cranial nerves mentioned, combined with the endoscopic identification of a roughened thickening of the ATD lining. The nervous form of diverticulitis carries a poor prognosis.

5.6 Guttural pouch mycosis

Aetiopathogenesis: The fungal plaques of guttural pouch mycosis (GPM) are usually found in one of two characteristic sites:

• The majority on the roof of the medial compartment.

• Others on the lateral wall of the lateral compartment.

There is a close association between the predilection sites and the underlying internal carotid (ICA) and external carotid (ECA) arteries respectively.

Clinical signs:

• The development of an invasive fungal plaque on the mucosal wall of the ATD of a horse will produce consequences ranging from nil to fatal.

• Spontaneous epistaxis at rest is the most frequent sign noted by owners and usually consists of a small quantity of fresh blood at one nostril in the first instance.

• A number of further minor haemorrhages may follow but, if untreated, exsanguination is a probable final outcome.

• It is unusual for the first episode of epistaxis to be fatal, but the course of the disease from first to final haemorrhage rarely spans more than three weeks and is more likely to be a matter of days.

Pharyngeal paralysis is the most frequent neuropathy which accompanies GPM and the inclusion of ingesta in a nasal discharge from any horse is an indication to inspect both ATDs by endoscopy as well as to assess pharyngeal function.

Endoscopic evidence of pharyngeal paralysis includes persistent dorsal displacement of the palatal arch, the presence of saliva and ingesta in the nasopharynx, weak pharyngeal contractions and a failure of one or both of the pharyngeal ostia of the ATDs to dilate during deglutition (see Figure 1.2).

Laryngeal hemiplegia is the next most frequent cranial nerve deficit encountered in horses with GPM but it is rarely responsible for the only signs observed by the owner.

GPM may produce a wide range of other signs referable to the head and upper neck. These include facial palsy and Horner’s syndrome; reluctance to lower the head to the ground and stiffness in the upper neck; parotid pain; otorrhoea; epiphora and photophobia.

Abnormal head posture may be associated with pain in the atlanto-occipital joint when the mycosis has extended into this joint.

Diagnosis: The clinical signs are not specific, but whenever a horse is presented with spontaneous epistaxis the possibility of GPM should be explored because delayed treatment may result in a fatal outcome.

A definitive endoscopic diagnosis of a mycotic plaque in the ATD (Figure 5.1) is not always straightforward; two caveats should be heeded:

Figure 5.1 Guttural pouch mycosis. The mycotic plaque lies on the internal carotid artery in the dorsal region of the medial compartment of the right ATD.

• First, the stress of handling the horse may precipitate a fatal epistaxis.

• Second, endoscopic visibility within the affected pouch may be poor after a recent haemorrhage, and accurate location of the lesion will not be possible.

If the epistaxis has been recent, it is sufficient to identify the stream of blood flowing from the pharyngeal drainage ostium.

In all cases of mycosis, the contra-lateral pouch should be checked for extension of the disease through the medial septum and for concurrent bilateral mycosis.

A full endoscopic assessment of laryngeal and pharyngeal function is required for an accurate prognosis.

Treatment:

• Medical treatment of GPM, be it by the use of topical or systemically administered antimycotic drugs or by a combination of both, is likely to be unsuccessful.

• Surgical occlusion of the branches of the carotid artery is recommended.

• The treatment of choice is transarterial coil embolization.

• The internal carotid is not an end-artery and therefore the placement of a simple ligature on the cardiac side of the lesion will not always be successful because retrograde haemorrhage may occur.

• Occlusion of the distal segment with a balloon-tipped catheter combined with proximal ligation of the ICA is superior.

• Topical antimycotic medication as an adjunct to arterial occlusion is probably not necessary.

Prognosis: Those cases of GPM not showing neurological complications can usually be brought to a successful conclusion by arterial occlusion surgery.

Although a small proportion of horses showing pharyngeal paralysis recover normal swallowing function, destruction on humane grounds is a more likely outcome and is indicated as soon as the patient shows signs of dehydration or aspiration pneumonia. Laryngeal hemiplegia resulting from GPM can be managed as for the idiopathic form recurrent laryngeal neuropathy (see ‘Treatment’ in 5.20).

5.7 Other ATD disorders

Trauma

The rectus capitis ventralis muscles insert onto the basisphenoid bones which form a narrow bridge between the foramina lacera in the dorso-medial aspect of the ATDs.

Fractures at the junction of the basisphenoid and occipital bones may occur in horses which have sustained violent head trauma by rearing over backwards. Some patients with this injury are unable to stand but show collapse and epistaxis.

Endoscopy can be used to confirm that the origin of the epistaxis lies in the ATDs, and radiography can also make a valuable contribution to diagnosis.

Apart from blood showing as free fluid in the floor of the ATDs, a step in the base of the skull will be visible on radiographs.

The condition is irreparable, but those horses which are able to stand may make a full recovery albeit after a prolonged period. Others are rendered partly quadriplegic, and humane destruction is indicated.

Foreign body penetration into the retropharyngeal tissues by wire can occur in horses. The clinical signs include epistaxis, nasal discharge, dyspnoea, dysphagia and pain in the upper neck with restricted movement. The radiographic identification of metallic material in the caudal wall of the ATD is straightforward but projections in two planes are required for an accurate stereotactic location of the object.

Neoplasia

All regions of the horse richly endowed with lymphoreticular tissue are potential sites for lymphoma development, and this tumour can arise in the tissues abutting onto the ATDs.

Ectopic melanosis is a common feature of the mucosa of the ATD of grey horses. The usual site for this is in the lateral compartment over the internal maxillary vessels. Primary melanomas can arise here also (see 5.29).

5.8 Disorders of the external nares

Anatomical features

The nostrils contribute more than 50% to the total resistance to flow of the entire upper respiratory tract during quiet breathing. This can be reduced considerably by active dilation during exertion. The C-shaped alar cartilages, back-to-back at the midline, provide rigidity for the otherwise soft structures of the external nares. Dilation of the nostril margins is achieved through the action of the nasolabialis muscles which receive their motor supply through the dorsal buccal branches of the facial nerves. The alar folds which attach to the ventral conchus mark the dorsal margin of the airway through the nasal vestibule, although the blind pocket of the false nostril lies above this.

The nostril margins and the structures which support and dilate them are of paramount importance to the sports horse. Any disorder which leads to collapse at this level is likely to render a horse useless for athletic pursuits.

‘Wry nose’

• A congenital deformity of the nose resulting from gross foreshortening of the premaxilla on one side.

• The deformity is not thought to be genetically transmitted but may be due to abnormal positioning in utero.

• The deformity is externally obvious.

• Even radical surgery is unlikely to render the horse suitable for exercise.

• Deviation of the nasal septum is usually accompanied by a degree of wry nose which may be very subtle on occasion and is most easily recognized through incisor malocclusion.

Hypertrophy of alar folds

• It is normal for the alar folds which form the floor of the false nostril sometimes to vibrate during exhalation. This is the origin of the vibrant expiratory noise known as ‘high blowing’. Occasional horses exhibit a comparable vibrant sound during inspiration.

• Confirmation that the origin of the noise lies at the alar folds is achieved by placing full thickness mattress sutures from the skin at the dorsal aspect of the nose across the openings of the false nostrils. The technique is performed under local anaesthesia so that the noise can be compared before and after suture placement. A positive result is an indication for resection of the alar folds.

‘Atheroma’ of false nostril

• Epidermal inclusion cysts (sebacious cysts) occasionally develop in the lining of the false nostril.

• These are painless and can be seen at the dorsal aspect of the nose rostral to the naso-maxillary notch.

• Although the swellings can be sizeable they do not obstruct respiration and are of cosmetic significance only.

• Chemical ablation of the lining by flushing with 10% formalin solution after evacuation of the contents is usually effective. The formalin is left in situ for 5 minutes before being flushed clear with sterile saline solution.

• Otherwise removal by careful dissection from the dorsal skin surface is straightforward, and recurrence is improbable.

Facial paralysis

See Chapter 11.

Flaccidity of a nostril margin through dysfunction of the nasolabialis muscle represents an aerodynamic disaster to an athletic horse. Many cases of facial palsy are of iatrogenic origin, and during facial surgery, i.e. dental extractions, the branches of the facial nerve should be respected. Care should be taken to avoid trauma to the nerve when horses are recumbent or recovering from general anaesthesia.

Trauma

• Wounds to the nostrils are typically sustained when a horse pulls backwards having caught the margin of its nose on a hook.

• These injuries demand meticulous management in the acute stage with layer-by-layer anatomical restoration.

• Inadequately managed nostril tears lead to stricture of the nostril aperture and a major reduction in athletic capacity.

Alar cartilage necrosis

Neglected penetration injuries of the alar cartilages may be followed by the extension of suppuration into the cartilage matrix. Careful resection of the diseased tissue is required because loss of mechanical stability at this location represents a serious complication.

5.9 Diagnostic approach to nasal and paranasal sinus disease

Anatomical considerations

The paranasal sinuses are extensive air-filled spaces lined by mucoperiosteum. The normal removal of mucus is a dynamic process depending on muco-ciliary flow to the drainage ostia which do not lie at the lowest points in the sinuses. Once the nasal meati are reached mucus is lost by a combination of evaporation and further muco-ciliary flow towards the nasopharynx. The aetiopathogenesis of primary sinusitis in horses hinges on stagnation of mucus in the sinus cavities through inhibited dynamic clearance.

The five paired paranasal sinuses of the horse are:

1. Frontal/conchofrontal.

2. Caudal maxillary.

3. Rostral maxillary.

4. Ethmoidal.

5. Sphenopalatine.

The frontal sinus is divided into conchofrontal (CFS) and frontal (FS) portions. Drainage takes place through the fronto-maxillary foramen into the caudal maxillary sinus (CMS). The ethmoidal and sphenopalatine sinuses also drain via the CMS into the middle nasal meatus.

The rostral maxillary sinus (RMS) has an independent drainage ostium, again into the middle nasal meatus.

The RMS is divided into a lateral bony and a medial turbinate portion within the ventral conchus (ventral conchal sinus, VCS). They are separated by the infra-orbital canal and a sheet of bone joining it ventrally to the roots of the cheek teeth. In the young horse the lateral bony compartment is largely occupied by the roots and reserve crowns of the cheek teeth, and regardless of age, the VCS is not easily accessible for surgery other than via the CFS.

• The apices of the 4th, 5th and 6th cheek teeth (109, 110, 111, 209, 210 and 211) lie within the maxillary sinuses; they are most prominent in young horses and recede towards the floor of the sinuses with age.

• The roots of the 3rd cheek tooth (108 and 208) form the rostral wall of the RMS.

• When dental periapical suppuration is the cause of sinusitis and oral extraction is unsuccessful, surgical exodontia requires that the roots are approached through the sinuses.

• Structures such as the nasolacrimal canal, infra-orbital canal, vein and artery of the angle of the eye are vulnerable to iatrogenic insult.

Common presenting signs

• The clinical signs of paranasal sinus diseases almost invariably include a nasal discharge, which may be mucoid, purulent, haemorrhagic or a combination of these.

• There may also be facial swelling and obstructive dyspnoea.

• Some expansive lesions in this area displace orbital tissues resulting in exophthalmos, but it is exceptional for a sinus disorder to extend caudally into the cranium to provoke central nervous signs.

• The intranasal structures are richly vascular, and it is not surprising that trauma and destructive conditions frequently lead to epistaxis.

History

• Note should be made of possible contact with infectious respiratory disease and of the duration and nature of any nasal discharge.

• It is unusual for sinusitis to be bilateral, and it is logical that the discharge will be largely unilateral when its origin lies proximal to the caudal limit of the midline septum.

• When a horse is presented with unilateral epistaxis enquiries should be made regarding associations with exercise to eliminate a diagnosis of exercise-induced pulmonary haemorrhage (see 6.7).

• Epistaxis due to guttural pouch mycosis may be acute, and, even if episodic, the course of the history is unlikely to exceed 3 weeks (see 5.6).

• A diagnosis of progressive ethmoidal haematoma (PEH) is more likely to be correct when episodes of epistaxis span a longer period, especially if the blood is not fresh.

• A foetid nasal discharge points to suppuration, but this could arise from a wide range of chronic sinus lesions.

Physical examination

• The facial area should be inspected for evidence of deformity of the supporting bones through swelling or trauma.

• Subcutaneous emphysema may be detected after trauma in some cases where the sinus walls have been disrupted.

• Percussion of the walls of the paranasal sinuses is an unreliable technique, but increased resonance may be perceived when the walls become thin, or dullness may develop when the sinuses are completely filled by fluid or soft tissue.

• The airflow at each nostril should be checked to assess obstruction of the nasal meati.

• The clinical crowns of the cheek teeth are examined for the presence of fracture, displacement or impaction of degenerate ingesta.

• The patency of the nasolacrimal duct can be checked by catheterisation and infusion of saline solution from either end.

Endoscopy

Endoscopy of the nasal area is performed in two ways:

• First, by conventional passage of the instrument into the nasal meati.

• Second, by direct inspection of the sinus contents through small trephine holes.

The latter technique is most commonly performed into the CFS or CMS. All endoscopy of this region is best performed on the standing horse because orientation is straightforward and the nasal tissues of a recumbent horse become discoloured and engorged.

Nasal endoscopic checklist:

1. Nasal meati – are they narrowed? Compare with contralateral side.

2. Is narrowing of the meati the result of conchal distension?

• Dorsal concha – CFS.

• Ventral concha – VCS.

3. Is narrowing due to a soft-tissue mass? Does the colour of the mass indicate a PEH, cyst or tumour? Can a mass be seen extending caudal to the midline septum when the endoscope is passed via the opposite nostril?

4. Sinu-nasal drainage ostium in caudal middle meatus:

• Is there discharge/blood present?

• Is the ostium dilated or compressed?

5. Ethmoidal labyrinth:

• Is there any sign of blood/PEH?

6. Conchal mucosa, check for:

• Mycosis.

• Ulceration/haemorrhage.

• Necrosis.

7. After surgery, check for:

• Evidence of persistent infection including mycosis.

• Satisfactory sinu-nasal fistulation.

8. Direct sinus endoscopy, check for:

• Empyema.

• Dental periapical reactions.

• Mycosis.

• PEH.

Radiography

The good contrast provided between bone and air renders the nasal chambers and paranasal sinuses excellent candidates for radiographic diagnosis (Figure 5.2). Erect lateral, lateral oblique, lesion-oriented oblique and ventro-dorsal views may be required for a comprehensive investigation. The radiographic signs of sinu-nasal disease include:

Figure 5.2 Erect lateral radiograph of the paranasal sinuses showing free fluid lines (long arrows) and a soft tissue mass (short arrows).

• Free fluid interfaces in the sinuses.

• Loss of normal air contrast through substitution by fluid or soft tissue.

• Depression or elevation of the supporting bones of the face.

• Distortion of normal structures such as the tooth roots, sinus walls, midline septum and infra-orbital canals.

Other imaging modalities

• Scintigraphy.

• Computed tomography (CT).

Scintigraphy has emerged as a useful means to identify active bone turnover, often before radiographic changes are seen, and it is particularly applicable to discriminate between dental apical disease and primary sinusitis.

The complex anatomy of the equine head, with the frequent superimposition of normal and abnormal structures, renders the interpretation of radiographs difficult. CT scanning offers a precise means to locate abnormalities (Figure 5.3).

Figure 5.3 A transverse CT section through the head at the level of the first upper molars. The arrows point to three sites of progressive ethmoidal haematoma development. Courtesy of Dr Renate Weller, Royal Veterinary College.

Biopsy

Even after full endoscopic and imaging investigations, surgical exploration may be performed before a specific diagnosis has been made. Suspect tissues should be biopsied to differentiate neoplastic disorders from other disease processes.

5.10 Treatment for sinu-nasal disorders

Treatment objectives

• Accurate diagnosis of the primary sinu-nasal disorder and removal of diseased tissue.

• Restoration of the normal drainage mechanisms or the creation of alternative drainage through a sinu-nasal fistula.

• Adequate visibility within the sinuses and nasal meati for accurate diagnosis and surgery.

• Means to control haemorrhage during surgery and in the recovery period.

• A safe airway during surgery and recovery.

• Facilities for topical post-operative treatments and for monitoring progress.

• An early return to exercise.

• A pleasing cosmetic result.

Medical management

Non-surgical treatments for sinusitis include antibiotics, mucolytics, steam inhalations, volatile inhalations and continued controlled exercise. The objective is the return of normal muco-ciliary clearance. Most cases of simple primary sinusitis will be resolved either naturally or with minimal veterinary assistance provided that the necessary supportive management is instituted promptly.

Trephination

• Simple trephination also aims to restore normal sinus drainage but with the addition of irrigation and topical antibiotic infusion to clear stagnant mucus and eliminate secondary infection.

• Trephination is performed using local anaesthetic infiltration with the horse standing.

• The preferred site for trephination is into the CMS in the angle formed between the margin of the bony orbit and the facial crest.

• In-dwelling balloon catheters provide a good means for regular irrigation over a number of days until the discharge to the nostril ceases.

• The RMS is less available for simple trephination especially in young horses where the lateral compartment is largely occupied by the roots and reserve crowns of the third and fourth cheek teeth.

Facial flap surgery

In the face of chronic sinusitis, sinus cyst and PEH the natural drainage system may well be physically obstructed. Fistulae can be made by removal of the floor of the CFS and medial wall of the VCS so that there is free communication between the sinus cavities and the nasal meati. Extensive fronto-nasal flap surgery is required for this and additional drainage from the CMS is achieved by removal of the septum dividing it from the RMS.

• The bulla of the RMS may bulge caudally into the CMS when it is inflated by pus, and this is easily punctured and excised.

• This form of fistulation may be performed through a trephine hole into the CFS before introducing tubing for subsequent irrigation and drainage.

• In surgical practice the fistulae described provide convenient routes by which to lead sock-and-bandage pressure packs to the nostrils (see below).

• Fronto-nasal or maxillary flap surgery is required for extensive excisional procedures such as the removal of sinus cysts, PEHs and selected tumours as well as for the relief of chronic sinusitis and fistulation techniques.

• Radical exposure of the nasal chambers, paranasal sinuses and their contents can be achieved through the bony walls of the supporting bones.

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Tags: Equine Medicine Surgery and Reproduction

Jun 18, 2016 | Posted by admin in EQUINE MEDICINE | Comments Off

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Disorders of the ear, nose and throat

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