Guttural pouch

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Guttural pouch (labelled 97) Directions for the dissection and study of the cranial nerves and blood vessels of the horse (1913) (14593873947).jpg
Guttural pouch (labelled 97)

Guttural pouches are large, auditory-tube diverticula that contain between 300 and 600 ml of air. They are present in odd-toed mammals, some bats, hyraxes, and the American forest mouse. They are paired bilaterally just below the ears, behind the skull and connect to the nasopharynx. [1]

Contents

Due to the general inaccessibility of the pouches in horses, they can be an area of infection by fungi and bacteria, and these infections can be extremely severe and hard to treat. The condition guttural pouch tympany affects several breeds, including the Arabian horse. The condition predisposes young horses to infection, often including severe swelling and often requires surgery to correct. The guttural pouch is also the site of infection in equine strangles. [1]

Structure

The guttural pouches are located behind the cranial cavity, caudally the skull and below the wings of the atlas (C1). They are enclosed by the parotid and mandibular salivary glands, and the pterygoid muscles. The ventral portion lies on the pharynx and beginning of the esophagus, with the retropharyngeal lymph nodes located between the ventral wall and pharynx. The left and right pouches are separated by the longus capitis and rectus capitis ventralis muscles dorsomedially. Below these muscles, the two pouches fuse to form a median septum. [2]

The guttural pouches connect the middle ear to the pharynx. The opening into the pharynx is called the nasopharyngeal ostium, which is composed of the pharyngeal wall laterally and a fibrocartilaginous fold medially. This opening leads to a short soft tissue passageway into the respective guttural pouch. The openings are located rostrally to enable drainage of mucus when the head is lowered and prevent fluid build-up. [3] The plica salpingopharyngea, a mucosal fold at the caudal portion of the Eustachian tube, forms an uninterrupted channel between the medial lamina of the Eustachian tube and the lateral wall of the pharynx. The plica salpingopharyngea can sometimes act as a one-way valve trapping air in the pouch, causing guttural pouch tympany [4] . Each pouch is moulded around the stylohyoid bone which divides the medial and lateral compartments. The medial compartment is much larger, and protrudes more caudally and ventrally. [2]

The epithelium is pseudostratified and ciliated containing mucus-secreting goblet cells; lymph nodules are also present. [4] The compartments of each guttural pouch contain many important structures including several cranial nerves and arteries that lie directly against the pouch as they pass into and out of foramina in the caudal aspect of the skull. The glossopharyngeal, vagus, accessory and hypoglossal nerves;[ citation needed ] the sympathetic trunk leaving from the cranial cervical ganglion; and the internal carotid all cause a mucosal fold indent within the medial compartment, visible when viewed endoscopically. [5] The facial nerve is in contact with the dorsal part of the pouch. The external carotid artery passes ventral to the medial compartment before crossing to the lateral wall of the lateral compartment. [5] The pouch also covers the temporohyoid joint. [5]

Function

The function of the guttural pouches has been shown with experimental data to participate in the rapid cooling of arterial blood destined for the brain and surrounding structures. In other words, the horse's guttural pouches are 'brain-cooling devices', cooling blood within the internal carotid arteries during hyperthermia that occurs during heavy exercise. [6] [7] However, this proven function has been called into question by another study that neither examined the guttural pouches nor the internal carotid arteries; [8] and others have argued that a cooling function would require an unattainable high rate of inspiratory air flow partly diverted into the guttural pouches. [9]

The issue of necessary guttural pouch air flow rates, to provide rapid cooling of the internal carotid arteries, has been solved by further supporting evidence from microvascular studies of the guttural pouch mucosa. [10] Many of the guttural pouch mucosal superficial arterioles and capillaries extend outwards, forming two types of vascular plexuses surrounding the internal carotid arteries: one with capillary bundles parallel to the internal carotid arteries in the outer layer of the tunica adventitia (outer peri-arterial plexus) and the other with vein-artery-vein triads within the inner layer of the tunica adventitia (inner peri-arterial plexus). These guttural pouch microvascular plexuses, engulfing the internal carotid arteries, are typical of countercurrent heat exchangers recognised in other animal species, supporting the data that guttural pouches participate in selective brain cooling, even at lower air flow rates.

This completes the triad of internal carotid artery cooling that protects the horse's brain from hyperthermia. The triad including the function of guttural pouches achieving arterial cooling, via both by utilizing inspiratory air cooling as well as microvascular countercurrent heat exchangers surrounding internal carotid arteries, and finally afterwards where the internal carotid arteries project upwards passing through the intracranial cavernous venous sinuses accepting cooled venous blood from the nasal sinuses. [11]

Pathology

If the drainage tract becomes blocked for any reason, the mucous secretions can accumulate and cause the pouch to distend, producing a visible and palpable protrusion behind the mandible. The exudate may become contaminated with pathogens. The bacteria Streptococcus equi, the causative agent of strangles, is commonly involved. Mycotic infections can also occur. [5] Some visible symptoms of guttural pouch disease include abnormal head and neck carriage, nasal discharge, painful swelling and occasional abnormal functioning of the structures associated with the pouch. [5] Secondary problems may include inflammation of the middle ear due to migration of the infection along the auditory tube; nasal bleeding caused by damage to the internal carotid artery; with vagus nerve involvement there may be laryngeal hemiplegia (roaring) or difficulty swallowing (also if glossopharyngeal nerve is involved); and Horner's syndrome from the involvement of sympathetic nerves. Involvement of the facial nerve is rare. [5]

As the guttural pouches are covered by respiratory epithelium and mucosa, they have the potential to be affected by all respiratory pathogens. [12] Most infections are self-limiting, requiring no or little medical intervention. Upon endoscopy, affected guttural pouches often house mucopurulent fluid that is in the process of draining. [12]

Guttural Pouch Empyema

Guttural pouch empyema is characterized by the accretion of purulent, bacteria infested exudate in the pouch. The bacteria is primarily Streptococcus equi, the infectious agent of strangles. Clinically apparent symptoms include painful swelling of the parotid area and recurrent infected nasal discharge, and in severe circumstances, difficulty breathing and abnormal head carriage may be observable. [13] Fever, anorexia, difficulty swallowing and soft palate displacement may or may not be seen. [14] Empyema is often secondary to guttural pouch tympany (distention of the pouches with air) in foals and weanlings. Arabians, in particular, are inclined to guttural pouch tympany, as many have a congenital defect in the pharyngeal orifices of the pouches. [15] The infection can also be due to the rupture of the nearby retropharyngeal lymph nodes, usually caused by an abscess. [16]

Diagnosis is established through and endoscopic examination. Radiographic examination of the area will show an opaque fluid line in the pouch and if a retropharyngeal lymph node is involved, it may reveal a mass. [13] In mild, acute cases of empyema, a saline or polyionic solution lavage is often performed via an endoscope or catheter repeatedly until the exudate drains. [16] Antimicrobial therapy without a lavage seldom remedies the infection. [13] In more complex cases, where concretions have formed, surgical intervention may be necessary to ensure appropriate drainage and removal of the hardened material. The area can be accessed surgically through the Viborg's triangle [13] ,. [16]

Guttural Pouch Tympany

Guttural pouch tympany is an uncommon ailment in which excessive amounts of air become trapped in the pouch, resulting in abnormal expansion. Tympany is usually unilateral, but in some cases can affect both pouches. It is seen most often in young foals and is more common in females than in males. [17] Tympany results in non-painful, soft swelling beneath the ear and behind the jaw. Additional symptoms may include roaring, difficulty breathing, and difficulty swallowing and/or aspiration pneumonia. [18] Diagnosis is achieved through radiography and endoscopic evaluation. The specific cause of guttural pouch tympany is not known, but it is suspected that it is more common when there are defects of the plica salpingopharyngeus, and/or the pharyngeal orifice where they act as a one-way valve that does not allow air to escape. [18] Because of the risk of secondary infection, it is crucial that tympany be treated as soon as possible. Treatment protocols may include, but are not limited to, surgical intervention and in cases where surgery is not an option, insertion of a transnasal Foley balloon catheter in an attempt to remodel the pharyngeal orifice. [19]

Guttural Pouch Mycosis

Guttural pouch mycosis (GPM) is a fungal disease that is rare but potentially life-threatening. GPM is of unknown pathogenesis currently and no predisposing factors have been identified. Fungal plaque is usually located in the medial guttural pouch, near the internal carotid artery. [13] Clinical signs include unilateral or bilateral epistaxis due to erosion of the artery walls, [13] nasal discharge and cranial nerve dysfunction. [20] GPM is a dangerous condition as spontaneous fatal hemorrhaging can occur, usually within a few days to weeks after the first bout of epistaxis [13] ,. [17] The most common fungus associated with GPM is Aspergillosis . [21]

Diagnosis is made based on the history of the animal, presenting clinical signs and endoscopic exploration. Pharmaceutical treatment is not suggested without coinciding surgery. [22] Treatment typically consists of topical as well as systemic antifungal medication, paired with surgery to occlude or embolise affected arteries. [21] Early intervention is necessary to ensure the best chance of survival. Horses that experience dysphagia or other forms of nerve dysfunction as a result of GPM have a poorer prognosis that those who have not exhibited those symptoms. [23]

See also

Related Research Articles

<span class="mw-page-title-main">Optic nerve</span> Second cranial nerve, which connects the eyes to the brain

In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells; it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus.

<span class="mw-page-title-main">Eustachian tube</span> Tube connecting middle ear to throat

The Eustachian tube, also called the auditory tube or pharyngotympanic tube, is a tube that links the nasopharynx to the middle ear, of which it is also a part. In adult humans, the Eustachian tube is approximately 35 mm (1.4 in) long and 3 mm (0.12 in) in diameter. It is named after the sixteenth-century Italian anatomist Bartolomeo Eustachi.

<span class="mw-page-title-main">Glossopharyngeal nerve</span> Cranial nerve IX, for the tongue and pharynx

The glossopharyngeal nerve, also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper medulla, just anterior to the vagus nerve. Being a mixed nerve (sensorimotor), it carries afferent sensory and efferent motor information. The motor division of the glossopharyngeal nerve is derived from the basal plate of the embryonic medulla oblongata, whereas the sensory division originates from the cranial neural crest.

<span class="mw-page-title-main">External carotid artery</span> Major artery of the head and neck

The external carotid artery is the major artery of the head and upper neck. It arises from the common carotid artery. It terminates by splitting into the superficial temporal and maxillary artery within the parotid gland.

<span class="mw-page-title-main">Nasal cavity</span> Large, air-filled space above and behind the nose in the middle of the face

The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nasal cavity is the uppermost part of the respiratory system and provides the nasal passage for inhaled air from the nostrils to the nasopharynx and rest of the respiratory tract.

<span class="mw-page-title-main">Internal carotid artery</span> Artery supplying the brain

The internal carotid artery is an artery in the neck which supplies the anterior and middle cerebral circulation.

<span class="mw-page-title-main">Subarachnoid cisterns</span> Spaces around the brain filled with cerebrospinal fluid

The subarachnoid cisterns are spaces formed by openings in the subarachnoid space, an anatomic space in the meninges of the brain. The space is situated between the two meninges, the arachnoid mater and the pia mater. These cisterns are filled with cerebrospinal fluid (CSF).

<span class="mw-page-title-main">Common carotid artery</span> One of the two arteries that supply the head and neck with blood

In anatomy, the left and right common carotid arteries (carotids) are arteries that supply the head and neck with oxygenated blood; they divide in the neck to form the external and internal carotid arteries.

<span class="mw-page-title-main">Stylopharyngeus muscle</span> Muscle

The stylopharyngeus muscle is a muscle in the head. It originates from the temporal styloid process. Some of its fibres insert onto the thyroid cartilage, while others end by intermingling with proximal structures. It is innervated by the glossopharyngeal nerve. It acts to elevate the larynx and pharynx, and dilate the pharynx, thus facilitating swallowing.

<span class="mw-page-title-main">Cavernous sinus</span> Sinus in the human head

The cavernous sinus within the human head is one of the dural venous sinuses creating a cavity called the lateral sellar compartment bordered by the temporal bone of the skull and the sphenoid bone, lateral to the sella turcica.

<span class="mw-page-title-main">Carotid sheath</span> Part of neck anatomy

The carotid sheath is a condensation of the deep cervical fascia enveloping multiple vital neurovascular structures of the neck, including the common and internal carotid arteries, the internal jugular vein, the vagus nerve, and ansa cervicalis. The carotid sheath helps protects the structures contained therein.

<span class="mw-page-title-main">Jugular foramen</span> Opening in the base of the skull allowing many structures to pass

A jugular foramen is one of the two large foramina (openings) in the base of the skull, located behind the carotid canal. It is formed by the temporal bone and the occipital bone. It allows many structures to pass, including the inferior petrosal sinus, three cranial nerves, the sigmoid sinus, and meningeal arteries.

<span class="mw-page-title-main">Middle cranial fossa</span>

The middle cranial fossa is formed by the sphenoid bones, and the temporal bones. It lodges the temporal lobes, and the pituitary gland. It is deeper than the anterior cranial fossa, is narrow medially and widens laterally to the sides of the skull. It is separated from the posterior cranial fossa by the clivus and the petrous crest.

<span class="mw-page-title-main">Pharyngeal branch of vagus nerve</span> Principal motor nerve of the pharynx

The pharyngeal branch of the vagus nerve is the principal motor nerve of the pharynx. It represents the motor component of the pharyngeal plexus of vagus nerve and ultimately provides motor innervation to most of the muscles of the soft palate, and of the pharynx.

<span class="mw-page-title-main">Head and neck anatomy</span> Structure of the human head and neck

This article describes the anatomy of the head and neck of the human body, including the brain, bones, muscles, blood vessels, nerves, glands, nose, mouth, teeth, tongue, and throat.

<span class="mw-page-title-main">Clivus (anatomy)</span> Bony part of the skull base

The clivus or Blumenbach clivus is a part of the occipital bone at the base of the skull. It is a shallow depression behind the dorsum sellae of the sphenoid bone. It slopes gradually to the anterior part of the basilar occipital bone at its junction with the sphenoid bone. It extends to the foramen magnum. It is related to the pons and the abducens nerve.

<span class="mw-page-title-main">Outline of human anatomy</span> Overview of and topical guide to human anatomy

The following outline is provided as an overview of and topical guide to human anatomy:

<span class="mw-page-title-main">Pharynx</span> Part of the throat that is behind the mouth and nasal cavity

The pharynx is the part of the throat behind the mouth and nasal cavity, and above the esophagus and trachea. It is found in vertebrates and invertebrates, though its structure varies across species. The pharynx carries food to the esophagus and air to the larynx. The flap of cartilage called the epiglottis stops food from entering the larynx.

<span class="mw-page-title-main">Parapharyngeal space</span>

The parapharyngeal space, is a potential space in the head and the neck. It has clinical importance in otolaryngology due to parapharyngeal space tumours and parapharyngeal abscess developing in this area. It is also a key anatomic landmark for localizing disease processes in the surrounding spaces of the neck; the direction of its displacement indirectly reflects the site of origin for masses or infection in adjacent areas, and consequently their appropriate differential diagnosis.

A parapharyngeal abscess is a deep neck space abscess of the parapharyngeal space, which is lateral to the superior pharyngeal constrictor muscle and medial to the masseter muscle. This space is divided by the styloid process into anterior and posterior compartments. The posterior compartment contains the carotid artery, internal jugular vein, and many nerves.

References

  1. 1 2 Pollock, P. J. (2007). "Diagnosis and management of guttural pouch mycosis". Equine Veterinary Education. 19 (10): 522–527. doi:10.2746/095777307X240162.
  2. 1 2 "Guttural Pouches - Anatomy & Physiology - WikiVet English". en.wikivet.net. Retrieved 2017-01-11.
  3. ↑ Davis, J. Weston (2015). "The equine guttural pouch: Clinically relevant anatomy and basic treatment options for trauma" (PDF). Equine Veterinary Education. 27 (8): 403–404. doi:10.1111/eve.12399 – via AAEP.
  4. 1 2 Perkins, Gillian A.; Pease, Anthony; Crotty, Erin; Fubini, Susan L. (2003). "Diagnosing Guttural Pouch Disorders and Managing Guttural Pouch Empyema in Adult Horses". Compendium. 25: 966–973.
  5. 1 2 3 4 5 6 Dyce, Keith, M.; Wesing, C. J. G.; Sack, W. O. (2010). Textbook of Veterinary Anatomy. St. Louis, Missouri: Elsevier Inc. pp. 522–525. ISBN   978-1-4160-6607-1.{{cite book}}: CS1 maint: multiple names: authors list (link)
  6. ↑ Baptiste, Keith E.; Naylor, Jonathan M.; Bailey, Jeremy; Barber, Ernest M.; Post, Klass; Thornhill, Jim (2000-02-01). "Physiology - A function for guttural pouches in the horse". Nature. 403 (6768): 382–383. Bibcode:2000Natur.403..382B. doi:10.1038/35000284. ISSN   0028-0836. PMID   10667779. S2CID   4424682.
  7. ↑ Baptiste, Keith E. (1998). "A preliminary study on the role of the equine guttural pouches in selective brain cooling". The Veterinary Journal. 155 (2): 139–148. doi:10.1016/S1090-0233(98)80009-9. PMID   9564267.
  8. ↑ Mitchell, Graham; Fuller, Andrea; Maloney, Shane K; Rump, Nicola; Mitchell, Duncan (2006-09-22). "Guttural pouches, brain temperature and exercise in horses". Biology Letters. 2 (3): 475–477. doi:10.1098/rsbl.2006.0469. PMC   1686210 . PMID   17148434.
  9. ↑ Shane K. Maloney; Andrea Fuller; Graham Mitchell; Duncan Mitchell (March 2002). "On the guttural pouch and selective brain cooling in equids: research letter". South African Journal of Science. 98 (3). hdl: 10520/EJC97450 .
  10. ↑ Ninomiya, Hiroyoshi; Kuwano, Atsutoshi (March 2019). "Microvasculature of the Guttural Pouch Mucosa and Relationship With the Internal Carotid Artery in Horses". Journal of Equine Veterinary Science. 74: 84–89. doi:10.1016/j.jevs.2018.12.025. S2CID   80962204.
  11. ↑ FF McConaghy; JR Hales; RJ Rose; DR Hodgson (Dec 1995). "Selective brain cooling in the horse during exercise and environmental heat stress". Journal of Applied Physiology. 79 (6): 1849–1854. doi:10.1152/jappl.1995.79.6.1849. PMID   8847243.
  12. 1 2 Dixon, P. M.; James, O. A. (2016-12-01). "Equine guttural pouch empyema, why does it become chronic?" (PDF). Equine Veterinary Education. 30 (2): 80–84. doi:10.1111/eve.12707. hdl: 20.500.11820/02506108-4e72-4a2b-96fe-91637419cb5f . ISSN   2042-3292.
  13. 1 2 3 4 5 6 7 Rush, Bonnie, R. "Guttural Pouch Disease in Horses" . Retrieved 2017-01-11– via Merck Veterinary Manual.{{cite news}}: CS1 maint: multiple names: authors list (link)
  14. ↑ Perkins, Justin D.; Schumacher, Jim; Kelly, Ger; Gomez, Jorge H.; Schumacher, John (2006-10-01). "Standing surgical removal of inspissated guttural pouch exudate (chondroids) in ten horses". Veterinary Surgery. 35 (7): 658–662. doi:10.1111/j.1532-950X.2006.00204.x. ISSN   0161-3499. PMID   17026551.
  15. ↑ Lavoie, Jean-Pierre; Hinchcliff, Kenneth William (2008-01-01). Blackwell's Five-Minute Veterinary Consult: Equine. John Wiley & Sons. ISBN   9780813814872.
  16. 1 2 3 Fjeldborg, J.; Baptiste, Keith (2017-01-03). "Diseases of the Guttural Pouches" (PDF). University of Copenhagen, Denmark.
  17. 1 2 Robinson, Norman Edward; Sprayberry, Kim A. (2009-01-01). Current Therapy in Equine Medicine. Elsevier Health Sciences. ISBN   978-1416054757.
  18. 1 2 Bell, Chris (2017-01-11). "Pharyngeal neuromuscular dysfunction associated with bilateral guttural pouch tympany in a foal". The Canadian Veterinary Journal. 48 (2): 192–194. ISSN   0008-5286. PMC   1780239 . PMID   17334035.
  19. ↑ Caston, S. S.; Kersh, K. D.; Reinertson, E. L.; Cammack, S. (2015-01-01). "Treatment of guttural pouch tympany in foals with transnasal Foley catheter placement". Equine Veterinary Education. 27 (1): 28–30. doi:10.1111/eve.12244. ISSN   2042-3292.
  20. ↑ Wilson, David (2010-11-28). Clinical Veterinary Advisor: The Horse. Elsevier Health Sciences. ISBN   978-1437714494.
  21. 1 2 Lepage, O. M.; Perron, M. F.; Cadoré, J. L. (2004). "The mystery of fungal infection in the guttural pouches". The Veterinary Journal. 168 (1): 60–64. doi:10.1016/s1090-0233(03)00108-4. PMID   15158209 – via Research Gate.
  22. ↑ Dobesova, O.; Schwarz, B.; Velde, K.; Jahn, P.; Zert, Z.; Bezdekova, B. (2012). "Guttural pouch mycosis in horses: a retrospective study of 28 cases". Veterinary Record. 171 (22): 561. doi:10.1136/vr.100700. PMID   23118043. S2CID   23565276.
  23. ↑ Kentucky Equine Research Staff (2013). "Fungal Infections of the Guttural Pouch in Horses". EquiNews. Retrieved 2017-01-11– via Kentucky Equine Research.
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