Guttural pouch mycosis, don't turn a blind eye!

Guttural pouch mycosis is a disorder known to few horse lovers. The disease is gradually becoming more common in our regions and is usually fatal if it is not diagnosed in time. It is a fungal infection that affects the horse's guttural pouches, ultimately resulting in swallowing problems and an unstoppable fatal nosebleed.

What is a guttural pouch?

Each horse has two guttural pouches on either side of its throat. These guttural pouches are pocket-shaped protrusions of the Eustachian tube. This tube forms a connection between the horse's throat and ear. This guttural pouch is thus filled with air and is radiographically clearly visible as a radiolucent zone (Photo 1). The function of the air sac is controversial to date, but what is certain is that there are some very important structures that run along or through these air sacs. 

Blood vessels:

Some of the main arteries of the head run along the wall of the guttural pouch. The main artery (carotid artery) starts from the heart and carries oxygen-rich blood along the neck to the head and brain. The main artery splits at the level of the head into several large vessels that are part of the wall of the guttural pouch (internal carotid artery, external carotid artery and maxillary artery). (Photo 2)

Nerves:

The central nerves are 12 nerves that originate from the brain stem to innervate different structures. Some of these nerves (IX, X, XII) run right through the guttural pouch and, in the case of guttural pouch mycosis, can cause typical nerve symptoms. The tongue-throat nerve or glossopharyngeal nerve (IX) is responsible for the nerves of the tongue and throat. The vagus nerve (X) is an important nerve that innervates many muscles such as the vocal cords and larynx. The hypoglossal nerve (XII) mainly innervates the tongue. (Photo 2)

In addition, some nerve centres of the autonomic nervous system (sympathetic ganglia) are located in the vicinity of the guttural pouch.

Fungal infection

As the name suggests, guttural pouch mycosis is a condition in which a fungal infection manifests itself at the level of the guttural pouch. Often a typical fungus, Aspergillus Fumigatus, is isolated. Although this fungus is widespread all over the world, it only becomes established in the air sac under certain conditions. Nobody knows yet why certain horses are affected, but it seems that certain climatic factors play a role. The increasing temperatures in our region due to global warming could explain the higher prevalence of this deadly disease in recent years.

The Aspergillus fungi, once established in the air sac, will look for a place where they can multiply optimally. Fungi like warm temperatures and because there are large blood vessels in the air sac, these are ideal nesting places for the fungi. Additionally, the arteries are also the ideal source of nutrients for the fungi. In most cases the internal carotid artery will be colonised by the Aspergillus (Photo 3 a and b, Photo 4).

Symptoms

Initially the fungus will grow symptomless without the horse feeling anything and without you as a horse owner noticing anything about it. That is why this condition is so dangerous. In the end, most horses will get some nasal discharge. The problem is that many other rather innocent conditions, such as sinusitis, pharyngitis, etc., can also be accompanied by nasal discharge so that one is not immediately concerned. 

Bleeding

The most important, most typical but also the most dangerous symptom of guttural pouch mycosis is the occurrence of nasal haemorrhage. As mentioned earlier, the fungus will usually settle on the wall of the blood vessels in the guttural pouch (usually the internal carotid artery). In this process, the blood vessel wall is affected, initially causing small bleeding. The blood enters the throat through the air sac and is often seen externally as a nosebleed. 

However, these small haemorrhages do not remain harmless because the more the fungus grows, the more the blood vessel wall will be damaged. If the condition is not recognised in time, it will lead to a fatal arterial haemorrhage that is unstoppable and will lead to acute death of the horse. 

Nerve symptoms

In addition to blood vessels, the fungal infection will also affect the nerves located in the guttural pouch walls. This is accompanied by specific nervous symptoms that may or may not disappear after treatment of the disease. This depends on the severity of the damage and the duration of the symptoms.

Dysphagia: This means that a horse has difficulty eating and swallowing. Due to the impairment of the innervation of the tongue and throat muscles, affected horses will often eat slowly and with difficulty and let the food fall out of their mouths. If a horse shows such symptoms, a mouth examination is recommended, but also an endoscopic examination of the throat and guttural pouches.

Roaring: the innervation of the vocal cords and larynx is often affected by guttural pouch mycosis. The symptoms of roaring are: respiratory noise during exercise, exercise intolerance, reduced performance. The diagnosis is quickly made by an endoscopic examination. If your horse shows symptoms of roaring for inexplicable reasons, an examination of the guttural pouches is certainly recommended. (Photo 5)

Horner's syndrome: this rare syndrome is caused by damage to the 'sympathetic nerves' and is characterised by unexplained sweat patches, often on the affected side, hanging down of the upper eyelid, protrusion of the third eyelid and congested, red mucous membranes.

Other nerve symptoms may occur but are rare. In severe cases of dysphagia, horses can choke so badly that an aspiration pneumonia develops.

What can be done about this?

Any case of guttural pouch mycosis is considered an emergency. Horses that suddenly exhibit a nosebleed for an unknown reason should be examined further immediately to determine the cause of the bleeding. Through an endoscopic examination the veterinarian can determine where the blood comes from. The most common causes for a unilateral nosebleed are:

• an innocent, ruptured, small vein in the nose: usually in the summer period due to high temperatures. 
  
• a tumour of the ethmoid
  
• a foreign body
  
• a fungal infection in the guttural pouch
  

If the horse is bleeding from both nostrils it usually comes from a deeper area and is usually pulmonary haemorrhage. This usually occurs during strenuous exercise and the blood coming from the nostrils then has a typical foaming aspect.

A full endoscopic examination of the nose, throat, guttural pouches and trachea is therefore necessary for any form of nasal bleeding to reach a correct diagnosis.

If severe guttural pouch mycosis is diagnosed, the horse must be rushed to a specialist equine clinic for ligation and thrombosis of the affected arteries. If there is no more blood flow, the horse will no longer be able to bleed. Simply ligating the main artery in the neck is insufficient because there is retrograde blood supply from the brain (circle of Willis) to these affected blood vessels in the guttural pouch. To prevent this, various techniques have been developed and applied over the years. The most efficient technique with the highest chance of success and the least complications is the coil embolisation technique. 

Surgical procedure: 'Coil embolisation technique'

At Equitom we use the latest and least invasive technique (coil embolisation). This has its origins in human medicine, namely in interventional radiology. The operation consists of inserting a catheter through the main artery in the neck (common carotid artery)and advancing it into the affected arteries (Photo 6). A contrast medium and a special imaging device, the fluoroscope, are used to find the way to the affected blood vessels. Once the catheter is correctly positioned, special coils are placed in the blood vessel to stop the blood flow (Photo 7). These coils are placed at the highest and lowest point of the guttural pouch to stop the normograde and retrograde blood flow at the level of the guttural pouch for each large artery within its wall (Photo 8).

This elegant technique drastically reduces operating time compared to older methods, is minimally invasive and highly efficient but requires expertise, precision and specific equipment.

Medical therapy

The surgical procedure protects the horse from bleeding and reduces the supply of nutrients, but is often insufficient to completely kill off the fungus. Therefore additional medical treatment is necessary. The horse is therefore treated with fungicidal medication both systemically (oral medication) and locally after the operation. In local therapy, the medication is sprayed directly onto the fungal site via the endoscope.

The treatment of guttural pouch mycosis is essential and life-saving, but even if the horse fully recovers from the fungal infection, permanent symptoms may occur. The acquired nerve damage may persist long after the fungus has been killed. Some horses fully recover over time. Other horses suffer permanent injuries such as roaring and swallowing problems. The recovery depends on the severity and duration of the fungal infection...

If necessary, the horse should be supported in the post-operative period. Horses with severe dysphagia need tube feeding to eat.

TIPS

If your horse shows one or more of the following symptoms, contact your veterinarian immediately for further examination:

Persistent nasal discharge; especially if it only comes from one nostril.

Difficulty eating, swallowing problems and possibly dropping food from the mouth: this can be due to nerve damage in the guttural pouch due to a fungal infection.

A nosebleed is an alarm that cannot be ignored! If your horse is bleeding from the nose it should be examined as soon as possible. If it comes out of the guttural pouch, an emergency admission and intervention is crucial.

DO NOT FORGET

Guttural pouch mycosis is a serious condition which, if not treated (in time), will kill your horse!

The sooner the fungal infection is diagnosed, the less damage to blood vessels and nerves and the greater the chance of full recovery. Horses that are helped too late often have permanent damage to the head nerves resulting in permanent (swallowing) problems. Some horses eventually have to be euthanised even after overcoming the fungal infection because the nerve damage is too severe and irreversible and they can no longer eat and drink. 

In some cases an acute severe nosebleed occurs which is so severe that the horse could bleed to death within 15 minutes. In such cases, immediate ligamentation of the main artery in the neck (common carotid artery) by your veterinarian can be life-saving. In many cases, however, one arrives too late. Should this succeed, the horse must then be immediately transported to a specialised clinic to thrombose the arteries in the guttural pouch by means of the 'coil technique'.

Photo 1: Radiographic image of a horse's head and throat. The radiolucent black zone shows the guttural pouch.

Photo 2: Endoscopic image of a normal guttural pouch. The hyoid (stylohyoid) is situated centrally in the air sac and divides the air sac into two compartments (lateral and medial). On the right side of the stylohyoid we see the artery (internal carotid artery) that is most commonly colonised by the fungus. Next to this artery we see a fold in which some important nerves are located.

Photo 3a and b: Endoscopic image of a guttural pouch with a mild infliction of the wall. We see a clear plaque-shaped fungal infection. In this case there is no proximity of blood vessels or nerves.

Photo 4: Very severe colonisation of the guttural pouch by fungus (Aspergillus). The complete anatomy of the guttural pouch is unrecognisable and no structure can be recognised.

Photo 5: Endoscopic image of a horse's throat with nerve symptoms at the level of the throat (roaring). The innervation of the vocal cords and the left arytenoid are damaged. The left arytenoid is clearly paralysed and will cause a roaring noise during exercise.

Photo 6: Intra-operative image in which the main artery in the neck (common carotid artery) has been exposed. A guiding catheter is then inserted into the lumen of the artery.

Photo 7: Intra-operative image. The surgeons have just inserted the coils into the right place. 

Photo 8: Fluoroscopic image of the guttural pouch region. A contrast medium is used to check whether the arteries are still passable. This is not the case, so the operation is successful.