The main indications for rhinoscopy

The main indications for rhinoscopy are a history of unilateral nasal discharge, the known or probable entrance of a foreign body, obstructive disease indicating tumor with no conclusive radiographic findings, and severe rhinitis with suspicion of aspergillosis. In all other cases of chronic nasal disease with no significant findings by radiography, rhinoscopy might be helpful but is not always conclusive. The standard radiographic examination of the skull consists of a lateral and a dorsoventral projection. These radiographs may provide all the information that is needed or they may serve as a primary inventory examination. In examination of the nose and nasal sinuses, and special projections, such as craniocaudal radiographs, open-mouth projections, or radiographs with intraoral film, are required.

Rhinoscopy

Rhinoscopy is a relatively simple procedure in dogs and cats. It requires anesthesia and intratracheal intubation, to prevent air circulation through the nasal cavities. We prefer to perform the examination with the patient in sternal recumbency, in a sphinx-like posture. A firm pillow is placed between the head and the front legs so that the head is stabilized but not fixed. The rhinoscopic examination is preceded by a careful inspection of the oral cavity and the pharynx.

A simple otoscope can be used for visualization. It should be of good quality, having a strong light source and dark specula, in order to illuminate at least the very rostral part of the nasal cavity. The nostril is approached from the lateral side at an angle of 45° to the vertical surface of the nasal plane. The tip of the speculum is placed near the lateral limit of the nostril and is then introduced by slowly turning the otoscope until its line of vision is parallel to the nasal cavity. This movement is necessary to push the nasal ala, which obstructs the opening, into a lateral position.

Once the otoscope is introduced, visibility is often found to be disappointing. Nasal disease often causes discharge and the tip of the speculum becomes blocked by mucus. The lens of the otoscope can be slid slightly to one side, allowing the introduction of a small suction cannula, while vision through the lens is maintained. The mucus is removed under visual control and the rostral part of the nasal cavity is then examined.

The use of an otoscope is often preferable for diagnosis and removal of foreign bodies which have entered the nasal cavity via the nostril. A forceps (called a foreign body forceps) developed for use through an otoscope under visual guidance can be found in catalogs for human otoscopic instruments.

A telescope is needed for complete examination of the nasal cavity. The basic equipment includes a light source, a flexible fiberoptic cable, and a telescope with a small diameter. We prefer the 25°-vision rigid telescope that is 2.7 mm in diameter and about 15 cm long. The best instruments have a wide-angle lens, which is important for orientation and facilitates the examination. This telescope is adequate for most cats and dogs but for very small cats it is too large in diameter and a 1.2 mm diameter rigid telescope is needed. In most cats and dogs the 2.7 mm telescope can be introduced and alongside it a suction cannula (size 6) or a foreign body or biopsy forceps can be passed.

The light source for rhinoscopy can be a single-outlet model, but a combined light source and electronic flash generator is necessary to obtain photographic images. The camera should be adapted to the telescope and the timing of the flash. For teaching purposes a chip camera and a video recorder are great assets.

Additional equipment for rhinoscopy includes several suction cannulas (size 6), a vacuum source, a selection of biopsy forceps, and a small dropper bottle of 0.1 per cent adrenaline solution to stop profuse bleeding (do not use more than 1 or 2 drops at a time).

The anatomical borders that guide the inspection of the nasal cavity are the nostril rostrally, the nasal septum medially, the roof of the nasal cavity dorsally, and the bottom of the nasal cavity ventrally. The cribriform plate is part of the caudal boundary, the other part being the ventrally positioned opening to the nasal pharynx, called the choanae. The endoscopic procedure aims at bringing the greater part of the nasal cavity into view. The procedure is limited by the choanae, if not by the pathologic process. Careful maneuvering and patient repositioning of the telescope will result in a reliable impression of the normal and pathologic structures in the nasal cavity.

Fungal rhinitis

Fungal diseases involving the nasal cavity, the frontal sinuses, and the nasal plane occur in both dogs and cats. In dogs the most prevalent mycosis in the nasal cavity and frontal sinuses is caused by Aspergillus spp. The fungus is also found--although rarely--in the nasal cavity in cats. Cryptococcus neoformans is a more common cause of nasal disease in cats, and in certain areas even quite common; nasal infections also occur in dogs.

Clinical signs of aspergillosis in the nose and frontal sinus are dominated by profuse mucopurulent nasal discharge and nasal pain. Depigmentation of the nasal plane below the nostril from which there is discharge is a characteristic sign. Intermittent hemorrhagic discharge occurs and profuse nasal bleeding is not exceptional. In involvement of the frontal sinus alone, hemorrhagic discharge or profuse bleeding from the nose may be the only sign. The nasal infection is often unilateral initially, becoming bilateral later. Aspergillosis is often not suspected in its initial stage and histories of nasal discharge present for months are not uncommon. There is no apparent correlation between the duration of the initial nasal discharge and the severity or progression of signs by the time of diagnosis. Other factors such as the number of infecting spores and the resistance of the host may play a role. Depression is a prominent sign when the frontal sinus is infected.

The diagnosis of aspergillosis as the cause of rhinitis is made by the finding of fungus plaques and culturing of the fungus. Recognition of the fungus plaque is facilitated by the atrophy of the conchae around it, which reduces the normal obstruction to rhinoscopic vision in the caudal part of the nasal cavity. The extent of the destruction in the nasal cavities and the frontal sinuses is well demonstrated by radiography, CT, or MRI, but the diagnosis depends on finding the fungus. When the fungus is in the frontal sinus alone, radiographs reveal irregular soft tissue densities in the frontal sinus, thickening of the wall of the sinus, and sometimes reaction of the periosteum, and CT scans reveal the severity of further bony involvement. A 3-4 mm diameter trephined opening in the frontal bone on the side of the affected sinus can reveal the fungus as thick, grayish yellow material, sometimes with greenish lumps. This material should be removed and cultured. Cultures from nasal discharge are often negative because the fungus is usually located in the caudal part of the nasal cavity and is not shed in the nasal discharge. A serologic test is available for detecting antibodies to Aspergillus spp. in serum.

Treatment of sinonasal aspergillosis is topical or systemic. Topical treatment is usually with enilconazole or clotrimazole. The choice between them is arbitrary, since there has been no satisfactory clinical trial to compare them. The ongoing discussion concerns how to apply the suspensions and how long the treatment should be given. The basic idea is to flush the frontal sinus and the nasal cavity via, for example, tubes introduced through trephine holes. Our clinic experience in about 120 cases (an average of 10 per year) indicates that administration of 10 cc of a 10 per cent suspension of enilconazole per tube twice daily for 14 days is sufficient. It is unpleasant for the dog because enilconazole has a bitter taste which most dogs dislike intensely. A retrospective study of cases treated in our clinic (unpublished data) revealed success in about 95 per cent in over 100 cases. Hence 90 per cent success can be expected in treatment of a smaller number of cases. A less unpleasant systemic treatment would be much preferred, but the success rates and observed toxicities of other methods are not yet encouraging. Details on clotrimazole therapy have been published.

Cryptococcosis is found as a cause of rhinitis in dogs and cats. The clinical signs are obstructive rhinitis and mucopurulent discharge. In cats crusts sometimes occur on the nasal plane and the bridge of the nose. Some cats develop mucopurulent conjunctivitis. In fresh material from the nose placed on a slide and stained with India ink, Cryptococcus spp. organisms are recognized as thick, encapsulated, round to oval yeasts. They can be cultured on Sabouraud's agar. Ketoconazole, itraconazole, or fluconazole can be used for therapy, which should be continued for 8 weeks. Alternaria spp. are found to cause granulomatous infections with crusts on the nasal plane in cats. Antimycotic treatment may be disappointing and removal of the nasal plane, as in nasal plane squamous cell carcinoma, can be a satisfactory solution.

Tumors in the nasal cavity

Tumors occur in the nasal cavity of dogs and cats of all ages, but most often from the age of 5 years onwards. Almost all are malignant. They invade the surrounding tissue but rarely metastasize before the dog or cat is euthanized. Animals living under close observation are rarely allowed to die spontaneously from the disease. The most frequent tumors are squamous cell carcinoma and adenocarcinoma; less frequent are chondrosarcoma, osteosarcoma, and lymphosarcoma.

The clinical signs include sneezing, hemorrhagic discharge, and mucopurulent discharge. In most cases unilateral obstruction of the nasal cavity is recognized because of nasal stridor. No evidence of pain is observed and the dog or cat becomes dyspneic only when the mouth is closed, which means when sleeping. As long as the tumor is unilateral the dyspnea is moderate. When the tumor obstructs both nasal cavities, dyspnea during sleep becomes a serious hindrance, causing the animal to awaken repeatedly during the night and often be very depressed in the morning. In this country, where no therapy is offered beyond permanent tracheostomy, which is rarely accepted by the owner, recurrent nasal bleeding and dyspnea are the usual reasons for euthanasia, in both dogs and cats. Cats, however, often stop eating, which may provide a humane end point and a reason for euthanasia.

Diagnostic radiographs should be made under anesthesia. Tumor is suspected when increased density is found in one or both nasal cavities, with loss of normal maxillary and ethmoidal conchae.The extension of the tumor is considered in offering a rough estimate of the animal's life expectancy, but this is usually decided by the owner's interpretation of the quality of the animal's life. In all cases in which the radiographic diagnosis is uncertain, rhinoscopy is the next diagnostic procedure. Under rhinoscopic visualization the tumors vary greatly in shape and firmness, and their color ranges from gray to deep red. Biopsies are always taken for histological confirmation of the diagnosis. If no therapy is planned, neither CT nor MRI is indicated. Radiation therapy could be considered and details have been described.

Conclusion

Fungal disease in the nasal cavity, in particular aspergillosis, is often presented as unilateral rhinitis refractory to antibiotic treatment. Tumor in the nasal cavity in dogs has similar clinical signs, as do foreign bodies. In Aspergillus infections the nose is usually painful, whereas tumor and foreign bodies in the nasal cavity rarely cause pain. When the changes on the radiographs do not clearly differentiate among fungal disease, tumor, or foreign body in the nasal cavity, rhinoscopic examination is indicated. Better definition of the extension of the lesions can be provided by radiography, CT, and MRI. These special diagnostic procedures should be included whenever this information is expected to be of importance.

References

1.  Venker-van Haagen AJ. Diseases of the nose and nasal sinuses. In: Ettinger SJ, Feldman EC, editors. Textbook of Veterinary Internal Medicine. Missouri: Elsevier Saunders, 2005; 1186-1196.