How to Flush Guttural Pouches in the Field Without the Use of an Endoscope

1. Introduction

The guttural pouch is an anatomical structure unique to perissodactyls, including equids, tapirs, a South American forest mouse, and some species of rhinoceros, bats, and hyraxes.¹  Unfortunately, it has also become a medical issue for the horse because this blind-ended sac can hold fluid, infectious debris, and fungal growths. Access to the pouch has historically been difficult for a solo practitioner because it typically requires an endoscope and involves two or three assistants. The procedure often requires sedation for safe endoscopic examination because there are numerous delicate structures contained therein that could be damaged. This paper will outline a simple way to enter the guttural pouches, without sedation in most cases, and offer the opportunity to medicate the pouch inexpensively.

Anatomy

The guttural pouch is an extension of the equine Eustachian tube that connects the pharynx to the middle ear. This pouch is located between the base of the skull dorsally and the pharynx and esophagus ventrally (Fig. 1). It is covered laterally by the pterygoid and digastricus muscles and the parotid and mandibular salivary glands. The floor lies mainly on the pharynx and also covers and molds to the retropharyngeal lymph nodes and stylohyoid bone, which presents a raised ridge within the guttural pouch and divides it into its lateral and medial compartments. The left and right guttural pouches are separated by a thin median septum. Its function is unknown, although it has been hypothesized to be associated with pressure equilibration across the tympanic membrane, contribution to air warming, a resonating chamber for vocalization, a flotation device, and for cooling of the brain of the horse.1 Internal structures of the guttural pouch will be described in further detail below.
 

Indications to Flush Guttural Pouches

Diseases involving the guttural pouch include fungal empyema, Streptococcus equi subspecies equi infection, chondroid formation, and bacterial empyema. Contamination can occur from a penetrating exterior wound. Trauma can lead to a fractured stylohyoid bone. In addition, the guttural pouch should be investigated in cases of head tilt, epistaxis, or cranial nerve dysfunction.²

Diagnosis of a problem within the guttural pouch requires endoscopic visualization. Entrance into the guttural pouch with the endoscope typically involves utilizing an assistant to manipulate the endoscope and the use of a probe or stylet passed through the endoscopic channel to lift the pharyngeal orifice of the Eustachian tube to gain entrance to the guttural pouch (Fig. 2). Using a video camera and screen makes the process easier because both participants can visualize at the same time. Without a video screen, communication between the veterinarian looking through the ocular end and the assistant passing the endoscope is paramount to give directions to the assistant.
 

Typically, the horse requires sedation to pass the probe and endoscope into the guttural pouch. The endoscope is passed in the ventral meatus until the pharyngeal orifice is visualized. At this point, the probe is passed through the scope channel and advanced beneath the flap and forward into the guttural pouch. The scope is then rotated clockwise to enter the left pouch and counterclockwise to enter the right pouch while advancing simultaneously. Once the endoscope has entered the guttural pouch, the probe is retracted back into the channel to avoid inadvertent trauma to any of the structures. At this point, a complete exam of the guttural pouch and relevant structures can be undertaken. The inside of the guttural pouch is lined with glistening epithelium and should appear as such. There is not normally any fluid, mucus, or muco-purulent or plaque-like material associated with the lining of the guttural pouch. The guttural pouch is divided into a large medial and smaller lateral compartments by the stylohyoid bone. The medial compartment is further divided into medial and lateral recesses. Structures that are associated with each compartment and that should be identified on endoscopic exam are described as one might see on endoscopic exam. On entering the guttural pouch, the dorsal aspect of the lateral recess of the medial compartment is encountered. The large stylohyoid bone is usually readily noted. Clinically relevant structures that can be seen in the medial and lateral compartments are as follows: atlanto-occipital articulation, glossopharyngeal nerve (c.n.IX), internal carotid artery, and cranial cervical ganglion (c.n.X) dorsal and medial to the internal carotid artery; other structures to note are the paracondylar (jugular) process of the occipital bone, the occipitohyoideus muscle, and the rectus and longus capitus muscles. The floor of the medial compartment should be examined for enlargement and/or drainage of the medial retropharyngeal lymph nodes that lie just below the floor of the guttural pouch. The chorda tympani (a branch of c.n.VII which joins c.n.V) is seen at the proximal extent of the stylohyoid bone, coursing dorsally and laterally within the lateral compartment of the guttural pouch. The large facial nerve (c.n.VII) can also be seen in the lateral compartment. The external carotid artery is large, coursing laterally, and can be identified by its pulsing motion; the caudal auricular artery can often be identified as a branch of the external carotid artery that courses dorsally and caudal to the facial nerve. The maxillary vein can also be identified passing behind and lateral to the external carotid artery. Though not visualized directly, c.n.XI and c.n.XII are also closely related to the guttural pouch and may be affected by disease processes involving the guttural pouch (Figs. 3 and 4).¹
 

Samples can be taken with an aspiration catheter or cytology brush, utilizing instruments that could pass through the endoscope channel. In addition, basket forceps can be used to remove chondroids, or rat-tooth grabbing forceps can be used to remove foreign bodies.  [...]