Diseases of the guttural pouches

Guttural pouches are large diverticula of the eustachian tubes that connect the pharynx to the middle ear. They are present in perissodactyls, such as equids, tapirs, some species of rhinoceros (except for the white rhinoceros), some bats, a South American forest mouse, and hyraxes [1–3]. Each pouch has a capacity of approximately 300 to 500 mL and is lined with a pseudostratified ciliated epithelium containing goblet cells [4]. Several mucous glands as well as lymphoid nodules are present in the young horse. Each guttural pouch is separated into a medial and lateral compartment by the ipsilateral stylohyoid bone, over which each pouch is draped. The epithelium overlies several vascular, neural, and lymphoid structures, and knowledge of these structures is important in understanding the clinical signs of guttural pouch disease. The medial compartment, the larger one of the two, is in contact with the internal carotid artery (ICA); the cranial cervical ganglion; the vagus; glossopharyngeal, hypoglossal, and spinal accessory nerves; and sympathetic nerves. Cranial nerves IX, X, XI, and XII are clearly visible under a mucosal fold. Ventrally, the medial compartment overlies the retropharyngeal lymph nodes, the pharyngeal branch of the vagus, and the recurrent laryngeal nerve, with this last structure being located in a mucosal fold (Fig. 1). The external carotid artery (ECA) can be seen coursing in a ventrodorsal direction on the lateral wall of the medial compartment (Fig. 2). The lateral compartment is approximately one third of the capacity of the medial compartment and laterally overlies the digastricus muscle and the parotid and mandibular glands. These structures limit lateral expansion of the pouch such that distention principally affects the medial compartment [5]. Vet Clin Equine 19 (2003) 123–158