The frontal and maxillary sinuses are extensions of the nasal cavity and are lined by a mucous membrane similar to the one that lines the nose. Accordingly, infections in the nasal cavity may spread to the sinuses, and vice versa. A nasal infection is called rhinitis and a sinus infection is called sinusitis.
The signs of rhinitis and sinusitis are sneezing, nasal discharge and gagging or retching from a postnasal drip. The discharge is thick, creamy, and foul smelling.
In young dogs, bacterial rhinitis and sinusitis usually do not occur unless the mucous membrane has been damaged by an upper respiratory infection, foreign body in the nasal cavity, or trauma to the nose. Respiratory infections caused by the herpesvirus, adenovirus, or parainfluenza virus are the most common causes of acute rhinitis. These infections may be followed by secondary bacterial involvement.
Canine distemper is a serious cause of secondary bacterial rhinitis. The discharge is mucoid and purulent. Other signs of distemper will be present.
In older dogs, tumors and infected teeth are the most common causes of rhinitis and sinusitis. Both are characterized by a chronic, long-standing purulent discharge from one nostril, along with sneezing and sniffling. Tumors and abscessed teeth may cause a blood-streaked discharge.
The diagnosis of rhinitis or sinusitis is based on X-rays, cultures, direct visualization of the nasal cavity using a flexible endoscope, and, in some cases, tissue biopsy.
Treatment: Bacterial rhinitis following upper respiratory infection is treated with broad-spectrum antibiotics that are continued for at least two weeks. Fungal infections usually respond to one of the newer antifungal agents, such as itraconazole or fluconazole. Antifungal drugs are given for six to eight weeks.
Chronic infections are difficult to clear up. Inflammatory debris builds up, causing further obstruction of air flow. Treatment involves using an antibiotic selected on the basis of sensitivity tests. In some cases, exploratory surgery will be required to clean out the nasal cavity and/or an infected sinus.