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[[Image:Mucoid rhinitis.jpg|right|thumb|100px|<small><center>Mucoid rhinitis (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
[[Image:Mucoid rhinitis.jpg|right|thumb|100px|<small><center>Mucoid rhinitis (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
Rhinitis can be acute or chronic.
Its aetiology can be:
:Infectious
:Allergic
:Toxic
:Traumatic e.g. foreign bodies
Serous cells are usually the first to respond to a noxious agent, releasing secretions into the mucocilliary blanket.
Different forms of rhinitis can be described:
'''Serous rhinitis''' - typical mild 'runny nose'
There is loss of cilia and hydropic degeneration of epithelial cells. The epithelium becomes susceptible to secondary bacterial infections, including overgrowth of resident nasopharyngeal flora. Goblet cells become stimulated, changing the secretions into a thick opaque mucus
'''Catarrhal rhinitis''' can follow serous rhinitis
It contains mucus, emigrating leukocytes and few sloughed epithelial cells
'''Mucopurulent''' and then '''purulent rhinitis'''
This occurs when secondary bacterial infection is severe, migrating [[Neutrophils|neutrophils]] are present in the exudate.
More severe damage to the nasal mucosa causes vascular permeability and seepage of large molecular weight proteins, including fibrinogen, into the exudate leading to '''fibrinopurulent''' and '''fibrinous rhinitis'''
'''Fibronecrotic''' and '''ulcerative rhinitis''' are manifestations of very severe damage to the nasal mucosa
==Chronic rhinitis==
==Chronic rhinitis==
This occurs when acute rhinitis fails to resolve and is common in most species.
It is typically catarrhal or purulent in nature.
In chronic purulent rhinitis there is extensive fibrosis of the lamina propria, atrophy of the nasal glands and squamous cell [[Cell Growth Disorders#Metaplasia|metaplasia]]. These all result in impaired local defences.
Usually, the superficial fibrinous membrane can be peeled off without leaving damaged tissue underneath.
Deeper fibronecrotic lesions associated with [[Fusobacterium necrophorum|''Fusobacterium necrophorum'']] appear as a yellowish fibronecrotic membrane, which when removed leaves an ulcerated surface.
Chronic rhinitis may manifest as [[Nasal Cavity Hyperplastic and Neoplastic - Pathology#Nasal polyps|nasal polyps]], [[Nasal Cavity Hyperplastic and Neoplastic - Pathology#Progressive ethmoidal haematoma|progressive haematoma]] in horses and [[Nasopharyngeal Polyp|nasopharyngeal polyps]] of cats.
==Allergic rhinitis==
==Allergic rhinitis==
This occurs in dogs, cats and horses, and may occur seasonally in cattle, especially Channel Island breeds.
There are similar inflammatory changes as above, due to hypersensitivity to inhaled allergens. Eosinophils tend to be the dominant infiltrating leukocytes
Grossly: the nasal mucosa is pale, thick and oedematous.
Histologically: the nasal epithelium is hyperplastic and eroded with an eosinophil infiltrate.
If the condition is chronic it may become a '''Nasal granuloma''', which extends caudally, even to the larynx and proximal trachea.
Grossly there is granular hyperplastic epithelium with multiple nodules covered by normal epithelium.
Histologically there is a centre of [[Granulation Tissue|granulation tissue]] surrounded by oedematous lamina propria covered by hyperplastic epithelium, goblet cell hyperplasia and eosinophil infiltration.
[[Category:Respiratory System - Inflammatory Pathology]]
[[Category:Respiratory System - Inflammatory Pathology]]
[[Category:Nasal Cavity - Inflammatory Pathology]]
[[Category:Nasal Cavity - Inflammatory Pathology]]
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