The paranasal sinuses and anatomy of the equine nasopharynx
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What type of epithelium lines the paranasal sinuses?
Psuedostratified ciliated columnar epithelium with goblet cells, or respiratory epithelium
List some reasons for the clinical significance of the paranasal sinuses in the horse
- Communicate with the nasal cavity
- Can get bacterial infections, nasal tumours
- Allows access to upper cheek teeth
What are the 5 paris of sinuses recognised in the horse?
Frontal, maxillary, sphenopalatine, dorsal conchal and ventral conchal sinus
What parts is the maxillary sinus divided into? What structure divides the maxillary sins?
Rostral and caudal parts. It is divided by a bony septum.
Describe the communication between the paranasal sinuses and the nasal cavity in the horse
The dorsal conchal sinus and frontal sinus communicate (this is the conchofrontal sinus). The conchofrontal sinus communicates with the caudal maxillary sinus through the frontomaxillary opening. The sphenopalatine sinus also communicates with the caudal maxillary sinus. The caudal maxillary sinus communicates directly with the nasal cavity via the nasomaxillary opening. The ventral conchal sinus communicates with the rostral maxillary sinus, which communicates directly with the nasal cavity via the nasomaxillary opening but is separated from the caudal maxillary sinus by a bony septum.
True or false: the frontal sinus develops with age in horses?
True - in a young foal it is very small but in older animals the sinus becomes very extensive
Which cheek teeth is the rostral/caudal maxillary sinus located above?
- Rostral - 3rd and 4th upper cheek teeth
- Caudal - 5th and 6th upper cheek teeth
Why does the maxillary sinus enlarge with age?
The teeth wear and grow down and forwards thus enlarging the sinus
What canal passes through the rostral and caudal maxillary sinuses?
The infraorbital canal
Which nerve is contained within the infraorbital canal?
The infraorbital nerve
What can be done to allow drainage of infection in the paranasal sinuses?
Trephining - drilling holes in the skull
What are the clinical landmarks for trephining the maxillary sinus?
- Rostral - line through infraorbital foramen
- Caudal - transverse lien through the middle of the eye
- Dorsal - line from medial canthus of the eye to the infraorbital foramen
- Ventral - facial crest and just rostral to its end
What structures limit the surgical field for maxillary sinus trephining?
Infraorbital nerve and nasolacrimal duct
What are the clinical landmarks for trephining the frontal sinus?
- Rostral - transverse line half way between medial canthus of eye and nasoincisive notch
- Caudal - transverse line taken half way along the zygomatic arch
- Dorsal - approximately 2cm from midline
- Ventral - dorsal to line from medial canthus of eye to nasoincisive notch
True or false: the paranasal sinuses in ruminants communicate?
Which sinuses are of most importance in ruminants and pigs?
Frontal and maxillary
In the ruminant the frontal sinus is divided into rostral and caudal parts, do these communicate with each other?
Which meatus do the frontal sinuses in ruminants drain into?
The ethmoidal meatus (as opposed to the middle meatus in horses)
Why must dehorning cattle be done before 6 months?
The corneal diverticulum invades the base of the horn at 6 months. It is not safe to dehorn adult animals as you will open straight into the frontal sinus.
Is the maxillary sinus a true sinus in ruminants?
How does the maxillary sinus in ruminants communicate with the nasal cavity?
Via the nasomaxillary opening
How large is the frontal sinus in pigs?
It covers the entire dorsal surface of the skull
What is the palatopharyngeal arch? What is its physiological significance?
It is a soft cuff which surrounds the entrance to the larynx in horses. It holds the laryngeal entrance (aditus) permanently up in the nasopharynx which is why horses are obligate nasal breathers
In a normal horse, where does the soft palate sit in relation to the epiglottis?
The soft palate sits below the epiglottis
What is the pharyngeal recess?
A median recess located dorsally that has implications for passing a stomach tube
What are the guttural pouches?
Where the mucosa of the auditory tube expands into a diverticulum on each side
What structures are dorsal/lateral/ventral to the guttural pouches?
- Dorsal - base of the skull and atlas
- Ventral - pharynx and oesophagus
- Lateral - pterygoid muscle, parotid and mandibular glands, ramus of mandible
Which bone divides the guttural pouch into medial and lateral compartments?
What is the preposed function of the guttural pouch?
It may influence internal carotid artery blood pressure. It may also be a cerebral blood cooling mechanism.
Infection is common in the guttural pouches, what type of infectious agent is the most common cause?
Haemorrhage of which blood vessel that runs through the guttural pouch is fatal?
Internal carotid artery
Many cranial nerves run through the guttural pouch, what effect can an infection have on these?
Pressure on cranial nerves IX and X can lead to pharyngeal and/or laryngeal paralysis. Damage to the facial nerve is rare but can lead to facial paralysis.
Which lymph nodes are located ventral to the guttural pouches?
Retropharyngeal lymph nodes
What is an abscess in the retro-pharyngeal lymph nodes called?
How do the guttural pouches drain?
Via the auditory tubes into the nasopharynx
What are the three surgical approaches to the guttural pouch?
- Viborg's triangle - parotid duct, linguo-facial vein and lig. sternocephalic muscle
- Ventral approach - retract larynx to expose pouch
- Dorsal approach - edge of wing of atlas and reflect the parotid gland
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