Sinusitis in dogs – symptoms, tests and treatment

Overview

The nasal cavity and sinuses form a connected system

Sinuses are air-filled cavities lined with mucous membrane. Their mucus drains into the nose through an opening. Combined nasal and sinus inflammation is called rhinosinusitis.

In dogs, sinusitis usually accompanies nasal cavity disease. Aspergillus fungi in particular can inflame the nose and frontal sinus. A fluid-filled sinus nevertheless does not automatically mean fungal disease.

In a study of chronic idiopathic rhinitis, meaning inflammation of unknown cause, sinusitis was found in 8/13 dogs, or 62%. Another study of primary aspergillosis found frontal sinus involvement in 15/19 dogs, or 79%. These figures describe different selected patient groups, rather than disease risk for all dogs.

Causes

Inflammation can spread from the nose or involve teeth

A viral nasal infection can involve acute inflammation of the nose and sinuses. Bacterial infection can develop later after the initial viral infection. However, primary bacterial rhinitis is extremely rare in dogs. Discharge therefore does not always mean bacteria were the original cause.

An upper tooth root abscess can spread towards a nasal sinus. Dental disease or a nasal foreign body may also be found with aspergillosis. Both the fungus and local underlying factor are then considered in treatment.

Aspergillus spores are abundant in the environment and airborne. Why a particular dog develops disease is not precisely known. Disease can occur without general immune deficiency.

A blocked drainage route can collect mucus

Blockage of a sinus outflow opening has been associated with inflammation, scarring, injury and a space-occupying lesion. A mucocoele is a mucus-containing structure lined by respiratory epithelium. It can be sterile and is therefore different from bacterial sinusitis. Accumulating mucus can nevertheless raise pressure and expand the cavity. Distinguishing inflammation from a mucocoele affects treatment choice.

Risk factors

Risk factors depend on the cause. A tooth root abscess and local nasal cavity damage can be associated with sinusitis. Aspergillosis can occur in an otherwise healthy dog, although a healthy dog's risk is low.

In a case series of 8 dogs with frontal sinus mucocoeles, 7 had previous skull trauma. These dogs' signs had begun by 10 months of age. However, a mucocoele has also been described in an 8-year-old dog without a trauma history. Mucus accumulation is therefore not confined to young or previously injured dogs. These details concern mucocoeles, rather than the age distribution of all sinusitis.

Typical symptoms

Signs at home can resemble nasal cavity disease. The presentation depends partly on whether there is fungal disease, other inflammation or a lesion causing secretions to accumulate.

• Nasal discharge persists or returns.
• Discharge comes from one nostril or later both.
• Your dog sneezes or snorts.
• Discharge can change from mucus-like or pus-filled to bloody.
• Touching the muzzle is painful.
• Fungal disease can cause crusts, ulcers or loss of pigment on the nose.

An expanding frontal sinus mucocoele can change facial shape and put pressure on surrounding structures. Swelling at the inner eye corner can be a separate finding needing investigation. In one dog, mucus accumulation compressed and displaced the eyeball sideways. Such swelling is different from ordinary watery nasal discharge.

Of 30 dogs in the aspergillosis study, 17/30, or 57%, had nosebleeds. Sneezing occurred in 15/30, or 50%. These proportions are not specific to sinusitis, as not every dog in the study had sinus inflammation.

Complications and consequences

Persistent disease can damage bone and press around the eye

Fungal frontal sinusitis can involve bone erosion or new bone formation. Among dogs with aspergillosis and frontal sinusitis, 4/15, or 27%, had a cribriform plate outline defect interpreted as bone destruction or demineralisation. Cribriform plate damage can involve central nervous system signs. Fungal disease can also cause frontal sinus osteomyelitis. This area's condition affects local treatment planning.

Even a benign mucocoele can erode the surrounding bony wall and extend inside the skull. It can also extend into the eye socket or towards the skin. Imaging therefore investigates the cause and extent of facial swelling.

In the frontal sinus mucocoele case series, 4 dogs were clinically normal 10–70 months after surgery. In the other 4, mucus accumulation recurred after 1–9 months. Some needed another operation. These results concern mucocoeles, rather than the general outlook for sinusitis.

Diagnosis at the vet

Imaging and endoscopy answer different questions

Your vet reviews discharge duration, the affected side, dental problems and any injury. The mouth and tooth root region are examined as part of the nasal and sinus assessment. An ordinary mouth examination may not reveal disease confined to a root.

CT shows cavity fluid contents and bone damage. It can also reveal a tooth root lesion or old fracture. Nasal endoscopy, meanwhile, can find plant material not clearly identified on CT. The tests therefore complement each other.

In a healthy dog, the connection between the frontal sinus and nasal cavity is generally too narrow for ordinary frontal sinus endoscopy. Fungal disease can abnormally widen the opening. If CT shows a sinus lesion but the opening is not patent, procedural access may need to be created.

Visible fungal deposits, or plaques, can be sampled directly. Culture can nevertheless reflect contamination, so the result is assessed alongside cytology and other findings. A negative antibody result does not exclude aspergillosis. Tissue sampling also looks for inflammation type, fungal structures and other explanatory changes.

Sinus fluid does not always mean bacterial infection

In the idiopathic rhinitis study, positive bacterial culture was not consistently associated with sinusitis. Soft tissue or fluid material in a sinus was checked endoscopically to exclude fungus and a tumour.

If a mucocoele is suspected, CT helps distinguish mucus accumulation from other cysts and tumours. With inner eye corner swelling, contrast imaging can also examine tear duct course and patency. In one mucocoele case, bacterial cultures were negative. Histology showed chronic inflammation without significant infection or malignant cells.

Treatment

Treating the cause and clearing the sinus

Treatment depends on the cause of sinus disease. Underlying tooth root disease needs local treatment. A nasal foreign body is also removed if found. Root canal treatment or professional cleaning may be needed instead of, or alongside, an antimicrobial. Medication alone therefore does not replace local dental care.

Mechanical removal of fungal plaques is central to aspergillosis treatment. Removing plaques from a sinus may require surgery. Local antifungal medication is then used. Additional benefit from systemic antifungals in local sinonasal aspergillosis is uncertain. In deep infection, however, systemic medication is essential. Your vet plans medication and procedures.

In a large aspergillosis study, after debridement considered complete, 60/112 dogs, or 54%, achieved clinical remission with the first treatment. After partial or incomplete debridement, the corresponding outcome was 6/28, or 21%. Clinical remission meant resolution of signs without continued treatment. The study concerned sinonasal aspergillosis as a whole.

Drainage routes and further care

For a frontal sinus mucocoele, a drainage route can be opened or sinus lining removed. Some cases need several operations. In fungal infection, repeated investigations and debridement may be needed, particularly with frontal sinus involvement.

Draining sinus secretions associated with idiopathic inflammation did not resolve the entire disease in a small study. Debridement and flushing can nevertheless help reveal hidden fungus or another lesion.

Adverse effects have included air accumulating beneath the skin. In an aspergillosis study, adverse effects were recorded in 97/403 dogs, or 24% of those with available adverse-effect information. Improvement in signs does not always confirm fungal clearance, so follow-up may include repeat imaging or endoscopy.

Prevention

Regular tooth brushing removes plaque and helps control periodontal disease. Tooth root problems are addressed by treating local dental disease, as a root abscess can spread towards a sinus.

Smoke and irritating gases can cause nasal and sinus signs, so exposure is reduced. Changing the environment cannot prevent every fungal case: moulds are abundant and the precise reason for disease onset is unknown. Preventing injury reduces skull impacts that can relate to later mucus accumulation.

Important for dog owners

Track changes and keep the follow-up plan

Record discharge colour, amount and side, sneezing, pain on touching the muzzle and any blood. A photograph of facial swelling helps compare changes later. Tell your vet about previous head injury, dental problems and the response to earlier medication.

Establish whether the sinuses and teeth were investigated alongside the nasal cavity, and whether tissue or fungal samples were taken. A sinus fungal deposit can be missed if the cavity cannot be reached endoscopically.

At discharge, ask what discharge is expected after the procedure and which changes mean returning to the practice. Planned follow-up may include repeat imaging and endoscopy under anaesthesia. Keep reports and agreed appointment dates. In the mucocoele case series, recurrence occurred after 1–9 months, so new facial swelling needs reassessment.

With breathing difficulty, transport your dog promptly but calmly to an emergency vet. A cool car reduces heat-induced panting. You can phone ahead so the emergency team can prepare for arrival.

Frequently asked questions

Is sinusitis the same as rhinitis?

Not quite. Rhinitis means nasal lining inflammation, whereas sinusitis affects the sinus lining. The diseases often occur together. Assessing sinus contents and bony structures generally needs imaging, while endoscopy helps look for the cause.

Does sinus fluid always mean bacterial infection?

No. An idiopathic rhinitis study found sinusitis in 8/13 dogs, or 62%. Positive bacterial culture was not associated with sinusitis. Sinus contents can also be examined to investigate fungus, a tumour or another cause.

Can a tooth cause sinusitis?

Yes. A tooth root abscess can spread towards a nasal sinus. Disease confined to a root can be missed during an ordinary mouth examination. Tooth root imaging may then help, and treatment also targets the affected tooth.

Can benign mucus accumulation be dangerous?

Yes. A mucocoele is a mucus-containing cystic lesion that, despite benign tissue structure, can erode adjacent bone and extend into surrounding spaces. A frontal sinus mucocoele can change facial shape and compress surrounding structures. Treatment may therefore require surgically opening a drainage route.

Is it enough for nasal discharge to stop after treatment?

Resolution of signs is positive, but in fungal disease it does not always confirm clearance. Follow-up may therefore include repeat CT and endoscopy under anaesthesia. Agreed monitoring helps distinguish persistent or recurrent disease from a situation where signs have eased but nasal structures still need assessment.