Diseases of the nasal cavity and sinuses

Clinical signs and locations of sinonasal pathology

Nasal discharge

Bilateral discharge:
- Lesion is caudal to nasal septum eg: pharyngeal lesion; LRT lesion in horses
- Lesion has resulted in nasal septum destruction
  - Neoplasia
  - Fungal infection
Unilateral discharge:
- Lesion is cranial to nasal septum eg: nasal or sinus lesion; pharyngeal or guttaral pouch lesion in horses.

Type of discharge

- Serous
- Catarrhal
- Purrulent
- Haemorrhage

Clinical signs

- Sneezing - nasal
- Facial swelling - nasal, pharyngeal
- Pain - any location
- Coughing - pharynx, larynx, trachea
- Dyspnoea/altered air flow
- Respiratory noise

Functional anatomy

Mucosa

Mucosal epithelium
- Nares and epiglottis- stratified squamous
- Nasal cavity, paranasal sinuses, larynx, trachea - pseudostratified, columnar, cilliated
Submucosa
- Submucosal glands
- Lymphoid tissue
Blood vessels, lymphatics and nerves
- Very rich blood supply to nasal mucosa

Nasal chambers and turbinates

Scrolls of turbinate bone
Arrangements vary with species

Nasal septum

Full length of nasal chamber in horses
- 2 openings into pharynx
Partial length in other species
- Single opening into pharynx

Sinuses

Size, arrangement and number vary with species
Poorly developed in carnivores
- Poor communication of frontal sinus in cats with nasal cavity
  - Predisposed to frontal sinus bacterial infections
- Maxillary sinus opening very large - 'maxillary recess'
  - Maxillary sinus infections very uncommon in carnivores
- Highly developed in horses
- Slit-like, high openings in horses
- Predisposed to bacterial infections
- Cheek teeth embedded within the maxillary sinuses
- Maxillary sinusitis secondary to tooth root abscesses

Guttural pouch

Horses
- Diverticulum of the eustachian tube with a thin slit-like opening at the rostroventral aspect into the pharynx.
- Mucous secretions drain out of the pouch when the horse lowers its head
- Lined by respiratory epithelium
- Bordered by glossopharyngeal, vagus, accessory and hypoglossal nerves; sympathetic trunk; internal and external carotid arteries
Pathology
- Mycotic infections eg: Aspergillus fumigatus
  - Bacterial infections eg: Streptococcus equi var. equi ('Strangles') or S.equi var zooepidemicus
- Tympany - associated with dysfunction of the pharyngotubal opening resulting from thickening (oedema, inflammation) or obstruction by a mucosal fold (eg: foals)

Defense mechanisms

Particle deposition

Coiled nature of turbinates promotes turbulent airflow and impaction of large particles >10 μm in diameter onto the nasal mucosa

Mucociliary escalator

Cilia on the respiratory epithelium beat in a co-ordinated manner
- Cilia beat in a caudal direction in nasal cavity
- Cilia beat in a cranial direction in trachea and lower airways
- Mucus is swallowed when it reaches the nasopharynx
- Constant movement reduces chances that pathogens can adhere to the respiratory epithelium

Mucus

Produced by the goblet cells of the respiratory epithelium and the submucosal glands with contribution from lacrimal glands draining into the nose
Traps particles for transportation away and subsequent swallowing
Physical barrier against mucosal damage
Prevents dessication of the mucosal epithelium
Contains antimicrobial substances
Immunoglobulin - IgA
- IgA produced by mucosal plasma cells
- IgA can attach to specific pathogen antigens (viruses, bacteria) trapping them in the mucus for clearance
Lysosyme
- Direct action on bacterial cell walls
- Lactoferrin
  - Inhibits bacterial growth as sequesters iron, an essential co-factor for many bacteria

Commensal bacteria

The normal bacterial flora of the nasal cavity, pharynx, larynx and proximal portion of the trachea compete with potentially pathogenic bacteria and help to prevent their colonisation (competitive exclusion).
The airway environment distal to the mid-portion of the trachea is effectively sterile.

Reflexes

Sneezing

Pathology of the upper airways

Developmental abnormalities

Palatoschisis
Nasal deviation
All brachycephalic dog and cat breeds!
- Esp. English Bulldogs - stenotic nares, wide/long soft palate, hypoplastic trachea

CIrculatory diseases

Epistaxis
- Haemorrhage from the nose
- Causes
  - Inflammation eg: ulcerative rhinitis
  - Neoplasia eg: infiltrating tumour, haemangioma
  - Trauma
  - Clotting defects
- Horse:
  - Haemorrhagic nasal polyp
    - 'Ethmoid haematoma', 'Progressive haematoma' - arise from the ethmoid region and can extend to fill the nasal cavity. They can be difficult to control as they can recur after surgery.
    - Histology - multiple areas of acute to chronic haemorrhage within a fibrous tissue stroma.
  - Exercise-induced pulmonary haemorrhage

Inflammatory disease

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Inflammation in the URT can be classified on:
- Location
  - Nasal cavity - rhinitis
  - Paranasal sinuses - sinusitis
  - Guttural pouch and eustachian tube - eustachitis
  - Pharynx - pharyngitis
- Type
  - Grossly many inflammatory processes (eg: response to viral or bacterial infection) in the URT will begin as a serous discharge, and then progress to a catarrhal exudate, and then to purulent/pseudomembranous/haemorrhagic as neutrophils are recruited
  - Serous - transparent fluid exudate (acute inflammation)
  - Catarrhal - mucous exudation (acute to subacute inflammation)
  - Pseudomembrnaous - fibrin exudation
  - Purulent - pus
  - Ulcerative
  - Haemorrhagic
  - Granulomatous (chronic inflammation)
  - Polypoid (chronic inflammation)
- Timecourse
  - Acute, subacute, chronic
- Causes
  - Infectious agent - viral, bacterial, fungal, parasitic
  - Trauma or foreign body (eg: grass seed)
  - Irritant or allergens
  - Neoplasia

Viral infections

Bovine herpesvirus -1
- Causes Infectious bovine rhinotracheitis (IBR)
- Highly infectious URT disease of cattle
- High morbidity, low mortality
- Aerosol transmission - requires close contact between animals
- BHV-1 infects the respiratory mucosal epithelial cells (intranuclear inclusion eosinophilic inclusion bodies)from nasal mucosa down to bronchioles
  - leading to neutrophilic inflammation of varying severity.... serous -> catarrhal -> purulent nasal discharge, sneezing, coughing.
  - with secondary bacterial infection (eg: Pasturella spp., Mycoplasma spp., Fusobacterium necrophorum) can lead to fibrinous to necrotizing inflammation; mucosal sloughing, ulceration... pyrexia, dyspnoea ... inhalation pneumonia... death.
- Clinical signs include coughing, discharge, lacrimation, and increased respiratory rate.
- Clinical disease most severe in young calves - can develop mucosal ulcerative lesions in the oesophagus and forestomachs and viraemia with multiorgan infection.
- Cause of abortion >5 months of gestation

Cytomegaloviruses
- Porcine cytomegalovirus
  - Causes Inclusion body rhinitis
    - Disease of suckling piglets 1-5 wks of age
    - Clinical signs: those associated with acute/subacute rhinitis (ie: serous nasal discharge, progressing to catarrhal or purulent discharge with time and secondary bacterial infections; sneezing; pyrexia)
    - Morbitity high, mortality low
    - Histology: large basophilic intranuclear inclusion bodies in the nasal and sinus respiratory epithelium with lymphocytic infiltration of the mucosa.
    - Can develop viraemic stage, with inclusions in other organs eg: renal tubular epithelium. Piglets can die during this phase.
Equine herpesvirus - 1, 4
Feline herpesvirus -1
- One of the causes of Feline viral rhinotracheitis
  - Viruses and bacteria are involved in the complex. The most frequent aetiologic agent is FHV-1, and less frequently feline calicivirus and/or Chlamydophia psittaci (NB: previously called Chlamydia psittaci var felis)
  - All three agents infect URT respiratory epithelium, although FHV-1 has the highest affinity for this epithelium
  - Feline calicivirus more frequently infects the oral mucosa -> ulcerative stomatitis
  - C.psittaci more frequently infects the conjunctival epithelium -> chronic conjunctivitis
  - Infection of the respiratory epithelium by FHV-1 results in a typical neutrophilic rhinitis with intraepitheial intranuclear eosinophilic inclusion bodies, with expected clinical signs
  - Resolution of clinical signs usually occurs by 7-14 days.
  - FHV-1 remains latent in the trigeminal ganglion, and can reactivate at times of stress. Can infect the cornea -> ulcerative keratitis.
  - Occasional mortality in kitten or immunocompromised animals usually associated with secondary bacterial infection.

Bacterial infections

Pasturella multocida
- Atrophic rhinitis in pigs
- Pigs aged 4-12 weeks old show clinical signs
- Catarrhal nasal discharge (due to an acute rhinitis), sneezing, coughing, can progress to dyspnoea and anorexia.
- Shortening and distortion of snout, secondary to nasal turbinate bone loss (histological evidence of osteolysis)
- 2 forms of the disease
  - 'Progressive' atrophic rhinitis
    - Due to infection of the nasal turbinates by P.multocida strains carrying the toxA gene that encodes for an osteolytic toxin. P.multocida adheres poorly to mucous membranes, and therefore requires a predisposing nasal insult to assist colonisation eg: co-infection with B.bronchiseptica; or Porcine cytomegalovirus (inclusion body rhinitis)
    - Turbinate bone atrophy is permanent and progressive
  - 'Non-progressive' atrophic rhinitis
    - Due to infection of the nasal turbinates by Bordatella bronchiseptica strains alone, that carry a gene that encodes for a dermonecrotic toxin.
    - Turbinate bone can regenerate by the time of slaughter
- 'Snuffles' in rabbits
  - - Most often P.multocida and/or B.bronchiseptica infection of the nasal mucosa
    - Clinical signs (nasal discharge, sneezing) result from an acute to chronic rhinitis.

Category:RVC, Category:R(D)SVS, Category:CUVS, Category:PG,

Streptococcus equi
- Streptococcus equi subsp. equi

- - Cause of 'Strangles' in horses
  - Infection with Streptococcus equi occurs after contact with contaminated feed, water bowls or an infected carrier horse
  - Organism remains viable in environment for months
  - Possibility of other sources of infection - in pharynx of in-contact dogs?
  - Colonisation of nasopharynx causing:
  - Chronic purulent rhinitis, sinusitis, eustachitis
  - Can progress to development of nodular masses in the guttural pouch consisting of inspissated pus and viable bacteria (guttural pouch empyema) - 'carrier' state
  - Regional suppurative lymphadenitis - can rupture onto skin of neck
  - Bacteraemia with abscess formation in other organs (eg: liver, kidneys) - Bastard Strangles!
- Streptococcus equi subsp. zooepidemicus
  - Can infect the respiratory tract (nasal cavity, paranasal sinuses, trachea and bronchi/bronchioles)
  - URT infection can be indistinguishable clinically from Strangles, but does not cause suppurative lymphadenitis (cf: S.equi subsp. equi)

Fungal infections

Filamentous fungal organisms
- Aspergillus fumigatus
  - Guttural pouch infections in horses - fungal plaques form on the adventitia of the carotid arteries can lead to catastrophic haemorrhage following erosion of carotid arteries!
  - Nasal infection in dogs and cats - plaques develop on the nasal or paranasal sinus epithelium. Result in severe neutrophilic rhinitis/sinusitis. Can occur secondary to areas of mucosal compromise eg: adjacent to a space-occupying lesion.
- Mucor spp.
Yeast-like fungal organisms
- Cryptococcus neoformans
  - Most commonly in cats and dogs
  - Chronic granulomatous rhinitis
  - Can invade through adjacent structures, eg: through the cribiform plate into the brain! These cases therefore can present as a primary neurological disease.

Parasitic infections

Oestrus ovis larvae in the nasal cavity of sheep and goats = Nasal bots

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