David S. Biller, DVM, DACVR
Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University
The nasal cavity is divided into symmetric halves called nasal fossae. These nasal fossae are separated by cartilaginous nasal septum rostrally and the vomer bone caudally. Sagittally a portion of the vomer bone extends dorsally from the ventral portion of the nasal cavity. The nasal fossae are filled with nasal conchae. These nasal conchae appear as fine, semiparallel radiopaque lines that extend caudally from the canine teeth to the level of the 3rd premolars. Caudally within the nasal fossae the ethmoid turbinates are present. These appear as a fine linear bony pattern fanning rostrally from the cribriform plane to their junction with the nasal conchae. The rostral portion of the nasal septum is radiolucent but its location is marked by the vomer bone. Because of its radiolucency it is difficult to assess its integrity radiographically. In the dog and cat if concurrent erosion of the vomer has not occurred, destruction of the septum may not be radiographically evidence rostral to the level of the 4th premolar.
The frontal sinuses are paired sinuses with a lateral and medial portion. The lateral portion extends over the orbit and may be partially divided by a bone septae. The medial portion communicates with the ethmoidal turbinate, and is variable in size and shape. The maxillary sinuses are lateral diverticuli of the nasal fossae. They are also referred to as the maxillary recesses, because the openings to the nasal cavities are as large as the sinuses themselves. In cats the frontal sinuses are very small (Persians may have no frontal sinuses at all) and maxillary sinuses are absent.
General anesthesia or deep tranquilization of the patient is essential, if not specifically contraindicated by the patient's physical condition, in order to obtain good diagnostic radiographs. The lack of proper patient restraint is the most common cause of nondiagnostic skull radiographs. High resolution (detail) radiographic image of the skull will be produced by use of nonscreen film or an ultra detail film/screen combination. Nonscreen film will necessitate a tenfold increase in mAs compared with the technique used for film in par speed screen cassettes.
The positioning of the patient and the number of projections needed for a complete study will depend on the area of the skull being evaluated. For evaluation of the nasal cavity and paranasal sinuses radiographic views include: 1) lateral (may or may not be helpful), 2) occlusal dorsoventral (intraoral), 3) ventrodorsal open mouth (extra oral film with a tube angled 20-30 degrees, 4) rostrocaudal/frontal (primary beam parallel to hard palate), 5) lateral oblique (right and left) to evaluate small frontal sinuses (30 degrees nose elevated and then 30 degrees oblique).
Radiograph Changes in the Nasal and Perinasal Sinuses
Both trauma and neoplasia may cause alterations in the shape and contour of the nasal and paranasal sinuses. Radiographic patterns or alterations in radiographic appearance and opacity of the nasal and paranasal sinuses are a reflection of aggressiveness and duration of disease rather than the specific etiology of the disease process. With diseases of acute etiology (bacterial or viral infections, allergies, radiolucent foreign body) the nasal cavity usually appears radiographically normal or only a slight increase in soft tissue opacity due to an increase in turbinate thickening or exudate can be appreciated. There are 5 radiographic patterns that demonstrate the aggressiveness or duration of disease rather than specific etiology: 1) no alteration in normal radiographic appearance (acute rhinitis, foreign bodies, viruses, bacteria, and allergies), 2) areas of increased soft tissue opacity superimposed over the normal turbinate pattern (chronic rhinitis, nasal exudate, hyperplastic rhinitis-swelling and proliferation of nasal mucosa, post traumatic hemorrhage), 3) areas of increased soft tissue opacity superimposed over areas of turbinate destruction (neoplasia and destructive rhinitis, 4) areas of decreased opacity due to turbinate destruction without accompanying soft tissue opacity, 5) mixed pattern with areas of turbinate destruction and superimposed soft tissue opacity interspersed with areas of turbinate destruction alone.
Most neoplasias of the nasal cavity originate from the region of the ethmoid turbinates and cribriform plate. In dogs 80% of these are malignant and 91% in cats are malignant. 60-75% are carcinoma (adenocarcinoma most common) with a mean age of diagnosis of 8-10 years of age. In cats the males are affected twice as often as females. Disruption of nasal septum (vomer bone) is seen frequently with malignant neoplasia. Soft tissue swelling from fascial bone destruction may also be seen associated with neoplasia. Rhinitis usually involves the middle and rostral segments of the nasal passages with equal or greater frequency than the middle and caudal segments. Obliteration of one of both nostrils is common and nasal discharge is also seen to be serous, mucoid or purulent. Destructive rhinitis with secondary epistaxis may be seen and is generally due to fungal infections. These animals are usually less than 4 years of age and aspergillosis is the most common cause. Cryptococcus neoformans can also cause hyperplastic rhinitis in cats. Radiographically rhinitis may occur as focal radiolucent areas of turbinate destruction. These lesions vary in size from small punctate holes to large poorly marginated areas of lysis. Erosion or deviation of the nasal septum (bony) is unusual. Opacification of the frontal sinuses associated with nasal disease is generally due to impaired sinus drainage. An alternative or differential for this increased opacity due to obstructive drainage includes neoplastic extension into the sinus itself.
Radiographic Changes of Nasal Disease
Chronic bacterial/viral Mycotic
1) Increased soft tissue opacity (uni- / bilateral)
2) Indistinct turbinate pattern
3) Soft tissue opacity of frontal sinuses
1) Focal (punctate) areas of lysis (turbinate destruction)
2) Focal areas of increased soft tissue opacity (uni-/bilaterally)
3) Soft tissue opacity of frontal sinuses
1) Early may mimic nondestructive rhinitis
2) With progression turbinate lysis and overlying fluid opacity
3) Vomer bone deviation/destruction, frontal / maxillary bone destruction, facial soft tissue swelling