Page 666 - The Veterinary Care of the Horse

Causes

Infection of the paranasal sinuses may be the result of the following.
VetBooks.ir • An upper respiratory tract infection Viruses can damage the lining of the sinuses and

this can interfere with the normal clearance of mucus. Initially there is a nasal discharge
due to overflow of mucus or pus. As the lining becomes thickened as a result of

inflammation, the drainage ostia may become partially blocked and mucus collects
within the sinuses which then become infected by bacteria. This is called primary

sinusitis.
• Tooth root infection The roots of the back four molar (cheek) teeth of the upper jaw lie

within the maxillary sinuses. If a tooth root becomes infected the sinus is also involved.

• Trauma If the horse is kicked and the bone overlying the sinus is fractured and
contaminated, secondary infection of the sinus may develop.

• Cysts, tumours or an ethmoid haematoma (see page 469) Any of these within the
sinus can block the drainage of mucus and cause sinusitis.

• Fungal infection This can occur after sinus surgery if the horse is given hay and bedded

on straw. Primary fungal infections are uncommon.

Clinical signs

These will include some of the following.

• A unilateral nasal discharge This may be mucopurulent, purulent or bloody depending

on the cause of the sinus infection. A thick, foul-smelling discharge is likely to be
secondary to tooth root infection. A yellow discharge without an unpleasant odour may

be the result of primary sinusitis or a sinus cyst (Figure 15.9). Bloody discharges arise
from trauma, a haematoma or a tumour. It is uncommon but possible for the discharge to
come from both nostrils.

• Localized facial swelling on one side This occurs at the front or side of the face when

there is an enlarging mass, e.g. a cyst or tumour within the sinus. Occasionally the
swelling can block the flow of tears along the nasolacrimal duct causing tear overflow.

• A dull sound on percussion of the sinuses If an air-filled sinus is tapped with the fingers
or knuckles the sound is hollow. This becomes dull if the sinus is filled with fluid, pus or

a mass.
• Abnormal respiratory noise If the sinus is distorted it can obstruct the nasal passages

and restrict air flow. This causes a noise which is present when the horse inhales and
exhales and is constant from day to day. If the noise is present at rest, the obstruction is