Equine Guttural Pouch Diseases Study Guide

Overview and Clinical Importance

The guttural pouches are paired diverticula of the auditory (Eustachian) tubes unique to equids. Each pouch has a capacity of approximately 300-500 mL and is lined with pseudostratified ciliated epithelium containing goblet cells. The stylohyoid bone divides each pouch into a larger medial compartment and smaller lateral compartment. The intimate association of the guttural pouches with major vascular structures and cranial nerves makes diseases of these structures clinically significant and potentially life-threatening.

Guttural Pouch Anatomy

Understanding the complex anatomy of the guttural pouch is essential for interpreting clinical signs and avoiding iatrogenic injury during treatment. The guttural pouches are located behind the cranial cavity, caudal to the skull, and below the wings of the atlas (C1).

Key Anatomical Structures

Guttural Pouch Empyema

Etiology and Pathophysiology

Guttural pouch empyema is the accumulation of purulent material within one or both guttural pouches. The most common cause is Streptococcus equi subspecies equi (strangles), which accounts for the majority of cases. The infection typically develops when retropharyngeal lymph nodes abscess and rupture into the ipsilateral guttural pouch, or through direct extension from upper respiratory tract infections.

Approximately 10% of horses in strangles outbreaks develop persistent guttural pouch empyema due to failure of the normal drainage mechanism. In chronic cases, the purulent material inspissates (dries out) and forms discrete, ovoid, smooth concretions called chondroids. These chondroids harbor viable S. equi on their surface and within their core, creating persistent carrier animals that can shed bacteria for months to years.

Clinical Signs

• Intermittent bilateral purulent nasal discharge
• Painful swelling in the parotid region (throatlatch area)
• Lymphadenopathy of submandibular and retropharyngeal lymph nodes
• Fever, depression, and anorexia (variable)
• Stiff head carriage and stertorous breathing in severe cases
• Dysphagia or cranial nerve deficits (uncommon, suggests nerve involvement)

Diagnosis

Endoscopy is the gold standard for diagnosis, allowing direct visualization of both guttural pouches, assessment of purulent material or chondroids, and collection of samples for culture and PCR. Radiography reveals a characteristic fluid line within the guttural pouch and can identify retropharyngeal masses or chondroids as radio-opaque nodules.

Treatment Options

Guttural Pouch Mycosis

Etiology and Pathophysiology

Guttural pouch mycosis (GPM) is a rare but potentially fatal fungal infection, primarily affecting adult stabled horses. Aspergillus fumigatus is the most common causative organism. The fungus is angiotropic (attracted to blood vessels), attaching to arteries within the guttural pouch for nutrition. Fungal plaques form diphtheritic membranes consisting of fungal mycelia, bacteria, necrotic tissue, and cell debris.

The fungal plaques are most commonly located on the caudodorsal aspect of the medial compartment over the internal carotid artery (ICA). In approximately 30% of cases, plaques also involve the lateral compartment over the external carotid or maxillary arteries. The pathogenesis remains unknown, and no predisposing factors have been definitively identified.

Clinical Signs

Clinical signs relate to the structures damaged by the fungal plaque:

Diagnosis

Endoscopy is diagnostic, revealing characteristic fungal plaques as gray-black diphtheritic membranes, typically located over arteries. The examination also allows assessment of which vessels are involved and evaluation of cranial nerve function (larynx, pharynx). Radiography and CT can provide additional information about extent of disease and involvement of adjacent structures.

Treatment: Three-Step Approach

Step 1 - Emergency Field Management: Temporary ligation of the common carotid artery can be performed at the barn as emergency aid to reduce hemorrhage while arranging transfer to a surgical facility. Keep the horse calm and minimize stress.

Step 2 - Definitive Arterial Occlusion: The primary surgical goal is to prevent fatal hemorrhage by occluding affected arteries both proximal (cardiac side) and distal (cerebral side) to the fungal plaque. This is necessary because of the Circle of Willis, which provides collateral blood flow.

Step 3 - Supportive Care and Resolution: Once arterial blood supply is eliminated, the fungal plaque typically regresses spontaneously over 30-180 days WITHOUT additional antifungal therapy. Antifungal treatment (topical enilconazole, systemic voriconazole) may be used as adjunct but is not essential after successful arterial occlusion.

G = Gray-black fungal plaque on endoscopy

P = Primary location: Internal Carotid Artery (medial compartment)

M = Mortality 50% without treatment; Must occlude artery Both sides of lesion

Guttural Pouch Tympany

Etiology and Pathophysiology

Guttural pouch tympany is a congenital or acquired condition in which air becomes trapped within one or both guttural pouches, causing abnormal distension. The condition primarily affects foals from birth to 1 year of age and is more common in fillies than colts (ratio 2:1 to 4:1). A breed predisposition exists for Arabian and German Warmblood horses, with genetic components identified in both breeds.

The pathophysiology involves dysfunction or malformation of the plica salpingopharyngea (the mucosal fold at the pharyngeal orifice of the guttural pouch). This creates a one-way valve effect, allowing air to enter the pouch during deglutition but preventing its escape. The condition may also develop secondary to upper respiratory tract inflammation affecting the mucosal flap.

Clinical Signs

• Nonpainful, fluctuant swelling in the parotid region ("bullfrog" appearance)
• Usually unilateral, but may appear bilateral due to displacement of median septum
• Stertorous breathing, especially during nursing
• Dyspnea in severe cases (compression of nasopharynx)
• Dysphagia and aspiration pneumonia may develop
• Secondary empyema can occur if untreated

Diagnosis

Radiography reveals severely enlarged, air-filled guttural pouch(es) extending caudally to the atlas with an excessively rounded caudal border. Endoscopy confirms the diagnosis, rules out other guttural pouch disorders, and helps distinguish between unilateral and bilateral disease. An abnormal guttural pouch opening (redundant plica) is often visible.

Treatment

Arab breed predisposition

Respiratory stertor while nursing

Air trapped (one-way valve)

Bullfrog appearance

Females more affected

Infection risk if untreated

Laser fenestration for treatment

Less than 1 year of age

Yields good prognosis with surgery

Differential Diagnosis Summary