Sinusitis

Often undetected unless it causes facial deformity or a draining tract onto the skin
Seromucous sinuitis in not significant, often an extension of viral infection in nasal cavity
Purulent sinusitis tends to obstruct drainage -> chronic purulent sinusitis
Most important in horses due to their complex sinuses
Primary:
- Young horses are more prone as they are susceptible to Strangles
- Following transient systemic Streptococcus infection
- Rarely fungal infections
Secondary:
- Most common sequel to rhinitis
- Dental or periodontal disease (maxillary sinus)
- Penetrating infections from dehorning wounds and fractures of facial bones (frontal sinus)
- Expanding mass

Purulent inflammation of sinuses is likely to become chronic due to poor drainage
Inflammation may block the drainage of the sinuses and cause distortion of the overlying bones
May result in empyema, inspissated exudate, in horses

Infectious causes of sinusitis

.	VIRAL	BACTERIAL	FUNGAL	PARASITIC
Dogs	.	secondary	A. fumigatus	Linguatula serrata
.	.	.	.	Capillaria aerophila
Cats	Feline viral rhinotracheitis	secondary	Aspergillus fumigatus	Linguatula serrata sometimes
.	.	.	.	Capillaria aerophila
Horses	.	Strangles	Aspergillus spp.	.
.	.	Streptococcus equi subsp. zooepidemicus	.	.
Cattle	.	secondary	.	.
Sheep	.	.	.	Oestrus ovis larvae
Pigs	Inclusion body rhinitis	.	.	.

For an overview of respiratory infections see Respiratory System Inflammation - Pathology