Case reveal

Findings:

• The right guttural pouch is severely distended and diffusely filled with heterogenous material that has intermediate to high signal intensity on the T2-weighted sequences and is isointense to the surrounding musculature on T1 sequences (purple arrowheads). Best seen on the T2w images, in the dependent aspect of the right guttural pouch, formed small rounded to ovoid, smoothly marginated and non-contrast enhancing T2w hypointense material is seen. The lateral compartment of the right guttural pouch bulges laterally into the soft tissues caudal to the right mandibular ramus, at the level of the right parotid salivary gland, bulging the adjacent cutaneous margin. Additionally, the distended right guttural pouch extends severely across midline, extending laterally to the left stylohyoid bone (outlined in green on left). The right guttural pouch severely displaces and compresses the left guttural pouch leftward and dorsally (yellow arrowheads), and displaces the oropharynx, larynx and cranial cervical trachea ventrally and the nasopharynx dorsally. The oropharyngeal, nasopharyngeal and laryngeal lumens are focally compressed, most severely affecting the nasopharynx, where there is complete obliteration of the nasopharyngeal lumen. The wall of the distended right guttural pouch is contrast-enhancing and mildly thickened and contains multiple septated bands of tissue with low to intermediate signal intensity on T2-weighted images. Fluid-filled fingerlike projections connect between the septated regions of the right guttural pouch.

• The pharyngeal opening of the right guttural pouch can be identified; however, the right auditory tube becomes severely narrowed caudal to the oropharyngeal opening. At this site, there is an accumulation of thickened, irregularly margined and contrast-enhancing tissue.

• Additionally, within the gravity dependent aspect of the left guttural pouch (medial and lateral compartments), there is a mild amount of fluid, with intermediate to high T2 signal intensity and a well-defined air-fluid interface (magenta arrowheads).

• Within the dorsal aspect of the oropharynx just rostral to the pharyngeal opening of the auditory tubes, there is a mild amount of gravity dependent, T2 hyperintense fluid.

Conclusions:

• Severe right sided guttural pouch fluid distension, most compatible with guttural pouch empyema, and associated with the presence of chondroids, severe nasopharyngeal and oropharyngeal compression, and likely non-patent right auditory tube secondary to the presence of fibrous scar tissue and/or granulation tissue.
• Mild left guttural pouch fluid, likely empyema.
• Mild fluid accumulation in the oropharynx.

Case follow-up:

• The right guttural pouch was explored and lavaged. A communication was created between the right and left guttural pouches for drainage. Patent drainage from the left side was confirmed at the time of discharge.
• PCR was negative for Strangles. Culture grew multiple types of bacteria but not Streptococcus Equi subspecies Equi.

A little bit more…

• The guttural pouches represent diverticula of the auditory tubes and bilaterally connect the oropharynx to the middle ear (Thomas-Cancian et al., Hardy et al., Perkins et al.).
• The stylohyoid bones traverses the guttural pouches, dividing them into two compartments (larger medially than laterally) (Thomas-Cancian et al, Hardy et al.).
• Empyema is the most common disease of the guttural pouch. Usually due to a primary upper airway infection or secondary to abscessation of the retropharyngeal lymph nodes with extension of the infection into the adjacent guttural pouch. Streptococcus Equi subspecies Equi is the most causative infections agent. Infections tend to be most commonly unilateral but have sometimes affect both guttural pouches (Thomas-Cancian et al., Perkins et al.).
• Less commonly, fungal infection of the guttural pouches may occur and may be associated with more aggressive regional changes, which may potentially be fatal (Perkins et al.).
• The guttural pouch walls are in close relation to large vessels (maxillary vessels and external and internal carotid arteries) and some cranial nerves (VII, IX, X, XI and XII). Diseases of the guttural pouch (especially mycoses) can therefore affect the regional vasculature, resulting in severe hemorrhage. Additionally, horses may present with cranial nerve signs (Thomas-Cancian et al., Hardy et al., Perkins et al.).

• More severe cases of empyema can, respectively, result in osteomyelitis and myositis of the regional osseous and muscular structures, especially those of the temporohyoid apparatus and the skull base (Thomas-Cancian et al.).
• Compression of the larynx and upper esophageal opening can lead to dysphagia or respiratory distress (Hardy et al.).
• Exudative material within an infected guttural pouch can conglomerate to form chondroids (Hardy et al.).
• Endoscopy is most commonly used for the evaluation of the guttural pouches and the diagnosis of disease. Cross sectional imaging is occasionally performed to complement endoscopy as it allows for the evaluation of regional structures which cannot be fully assessed with endoscopy (Thomas-Cancian et al., Perkins et al.).
• The normal anatomy of the guttural pouches has been described in horses using computed tomography (salami et al.) and to a lesser extent using MRI (Arencibia et al.).
• MRI is of benefit for evaluation of the majority of structures of the head; however, computed tomography allows a more comprehensive evaluation of the osseous structures and detection of more subtle osseous changes (Manso‐Díaz et al.).
• With more severe disease and the presence of chondroids, drainage of the affected guttural pouch is often indicated in addition to systemic therapy (e.g. antibiotics) (Thomas-Cancian et al., Hardy et al., Perkins et al.).

References:

• Thomas-Cancian, Aurélie, et al. “Diagnostic Imaging of Diseases Affecting the Guttural Pouch.” Veterinary Sciences10.8 (2023): 525.
• Hardy, Joanne, and Renée Léveillé. “Diseases of the guttural pouches.” Veterinary Clinics: Equine Practice 19.1 (2003): 123-158.
• Perkins, Gillian A., et al. “Diagnosing guttural pouch disorders and managing guttural pouch empyema in adult horses.” Compendium 25 (2003): 966-983.
• Sasaki, Motoki, et al. “CT Examination of the Guttural Pouch (Auditory Tube Diverticulum) in Przewalski&rsque; s Horse (Equus przewalskii).” Journal of veterinary medical science61.9 (1999): 1019-1022.
• Arencibia, Alberto, et al. “Magnetic resonance imaging and cross sectional anatomy of the normal equine sinuses and nasal passages.” Veterinary Radiology & Ultrasound 41.4 (2000): 313-319.
• Manso‐Díaz, Gabriel, et al. “Magnetic resonance imaging characteristics of equine head disorders: 84 cases (2000–2013).” Veterinary Radiology & Ultrasound 56.2 (2015): 176-187.