Guttural Pouches: where are we?

Traditionally, three guttural pouch diseases were recognised (empyema, mycosis & tympany). Now, guttural pouches are being recognised as associated with a growing list of other disorders, including: Otitis media/interna - Temporohyoid osteoarthropathy8 ; Dorsal displacement of the soft palate9 ; Longus/rectus capitus muscle rupture16; Pharyngeal paralysis; Neoplasia2 ; Cystic structures7 ; Atlanto-occipital arthropathy4 ; Mycotic encephalitis Hypoglossal neuritis/ lingual hemiplegia11. For guttural pouch mycosis, several surgical advances have been made including fluoroscope guided catheter placement, detachable coil devices, and a standing technique that allow for quicker, safer and accurate placement of occlusion devices at the arterial embolism site. Long-term follow-ups have shown improved survival and return to work13 .

There is an explosion of interest in guttural pouches associated with the outbreaks and management of strangles (Strep. equi). PCR technology has identified guttural pouches associated with ‘carrier’ states in greater numbers of horses than previously appreciated. Previously, chemicals of mass destruction (e.g. hydrogen peroxide, iodine) were used for the treatment of guttural pouch empyema. These were replaced with repeated saline lavages and evaluations (e.g. endoscopy, culture). Now, instilling penicillin routinely into guttural pouches has gained much acceptance owing to the marked sensitivity of penicillin against Strep. equi and the possibility of distribution of penicillin in the guttural pouch to other sites (e.g. retropharyngeal lymph nodes)10 . However, the popularity of sampling and treatment came before evidence. For example, the contagious risk of relatively ‘normal’ appearing guttural pouches to horse populations was not determined. Also, sampling guttural pouches for PCR commonly includes the use of re-usable medical devices (e.g. endoscope), as reflected in consensus statements which have not been evaluated as free from contamination. Furthermore, penicillin in guttural pouches may not be innocuous. Guttural pouches have complex natural microflora5 , that differs between horses (e.g. Pseudomonas spp.-including zoonotic types)6 . The instillation of penicillin does impact on this microflora that could lead to other complications (e.g. gram negative empyema).

Temporohyoid osteoarthropathy is associated with headshaking, ear flopping and rubbing, vestibular disease, facial paralysis and exposure corneal keratitis8 . This may be the result of trauma to the petrous temporal area, ascending respiratory tract infection, or extension of otitis externa to the middle and inner ears. The result is inflammation and fusion of the stylohyoid bone to the petrous temporal bones. Using brainstem auditory evoked response (BAER) studies has revealed that auditory dysfunction and/or loss appears to be a common manifestion that appears to be permanent regardless of medical or surgical intervention, or overall neurologic improvement/s1 . Endoscopy of the guttural pouch is a commonly performed as well as magnetic resonant imaging or computed tomography. Cytological and microbiological diagnosis of otitis media/interna can be achieved through tympanocentesis and lavage15 . Endoscopic evaluation should include: Evaluation of the stylohyoid bone for the presence of a fracture; Evaluation of the head of the stylohyoid bone for the presence of osteopathy, including bony enlargement and fusion with either the tympanic bulla or petrous temporal bones; Evaluation of the guttural pouch mucosa in the temporohyoid region (e.g. hyperemia/thickening, oedema, purulent debris); Evaluation of the internal carotid artery as it enters the base of the skull (e.g. internal carotid artery can appear compressed or out of position due to bony enlargement from the temporohyoid region). Since temporohyoid osteoarthopahy is typically unilateral, then endoscopic evaluation of the both guttural pouches (tempohyoid regions) is very important to rule out common anatomic variations. The final diagnosis is a balance of the functional neurologic deficits with changes in the temporohyoid region. The goal of treatment, includes: Resolving pain and inflammation at the temporohyoid joint (± fracture site); Antimicrobial treatment for confirmed bacterial otitis media-interna and/or meningitis; Treatment of exposure keratitis; Stabilization of the temporohyoid articulation to prevent fracture or ongoing trauma at a fractured site. Surgical procedures (partial stylohyoidectomy, ceratohyoidectomy) have been described that aim to decrease movement and abnormal biomechanical forces on the temporohyoid joint. Currently, the surgical treatment considered most effective is ceratohyoidectomy3 , with good outcomes reported3,1 .

Rupture of the longus/rectus capitus muscle/s can be a cause of guttural pouch haemorrhage and epistaxis16 . This is associated with acute trauma and may also be a sequel to guttural pouch mycosis12. Distinction between this condition and guttural pouch mycosis alone requires endoscopic examination of the entire guttural pouch, particularly at the site of insertion of the strap muscles on the base of the skull. Treatment involves conservative management, stall rest for 4-6 weeks, antibiotics, and analgesics.