1.1
Nasal cavity and paranasal sinuses

Normal anatomy

Symmetry of the thin, scrolled nasal turbinates is an important aid to detecting abnormalities in the nasal cavities. The turbinates are more densely formed rostrally and become thicker with more interspersed airspaces caudally. The turbinates are surrounded by mucosa but are themselves thin bone. Thin collimation is required to appreciate their structure in CT images. The nasal sinuses should be air filled with a thin or undetectable mucosal lining. A comparison of CT and MRI of the normal nasal cavities and paranasal sinuses to gross cross-sectional anatomy has been reported in mesaticephalic dogs (Figures 1.1.1, 1.1.2),1 and computed tomography of the normal nasal cavity and nasolacrimal drainage system has been described in cats.2,3

Figure 1.1.1 Normal Nasal Cavity (Canine)      CT

2y MC Great Pyrenees mix. Representative transverse plane images of the nasal passages and paranasal sinuses ordered from rostral to caudal (a-f). Representative dorsal plane images ordered from dorsal to ventral (g-i). The dorsal (a: small white arrow) and ventral (a: large white arrow) nasal conchae are finely scrolled rostrally and become larger caudally as the ethmoidal conchae or ethmoturbinates (c: open arrow). The nasal septum (a: arrowhead) separates the left and right nasal cavities. The dorsal, middle, and ventral nasal meati (a: black arrows) allow airflow to the caudal nasal cavity. The nasal sinuses include the maxillary recess (c: asterisk), the frontal sinus (e: large open arrow), and the sphenoidal sinus (e: small open arrow). The nasopharyngeal meatus (c: black arrow) connects the nasal cavity to the pharynx. The cribriform plate (e,h: arrowheads) separates the nasal cavity from the calvarium.

Figure 1.1.2 Normal Nasal Cavity (Canine)      MR

MR images of the nose provide good detail of the nasal turbinates. Normal turbinates are scrolled and symmetrical. They appear moderately intense on T1 images (a) and hyperintense on T2 (c), PD (d), and T1 contrast-enhanced (b) images.

Normal nasal cycle

The nasal cycle is a normal physiologic phenomenon with a periodicity of 2-3?hours, which has been described in dogs.4,5 This frequent, alternating cycle is thought to allow nasal mucosa to recover from the minor trauma of conditioning inspired air. Many dogs with otherwise normal nasal CT or MR examinations will display asymmetry of the nasal mucosa reflected by apparent unilateral mucosal congestion (Figure 1.1.3). The asymmetry is due to unilateral vasoconstriction causing increased mucosal perfusion on the contralateral side resulting in mucosal thickening and increased resistance to airflow. In patients exhibiting the nasal cycle, the mucosal thickening on the affected side is uniform, and there is no evidence of underlying turbinate involvement.

Figure 1.1.3 Normal Nasal Cycle (Canine)      CT

Typical appearance of normal ectoturbinates in the midnasal cavity (a). The nasal cycle results in turbinate asymmetry due to nonuniform mucosal perfusion (b). This is a normal physiologic phenomenon that is thought to accelerate the rate of nasal mucosal healing from minor injury due to nasal airflow. The nasal cycle has a periodicity of 2-3?hours in dogs.

Developmental disorders

The nasal septum and turbinates can occasionally appear asymmetrical in otherwise normal dogs and cats. These anomalies are often clinically insignificant but can sometimes lead to impaired airflow or obstruction. Brachycephalic dogs and cats may also have poorly developed or malformed turbinates and paranasal sinuses that predispose them to other sinonasal disorders. The sinuses may be partially developed, asymmetrical, or absent on one or both sides. Cats occasionally have marked distortion of turbinates that may represent abnormal growth resulting from severe viral rhinitis at an early age. Early trauma while skull growth is still occurring can also lead to distortion of nasal anatomy. Such patients are often prone to recurring rhinitis as adults. In brachycephalic cats, the nasal bones become dorsally rotated and reduced in size, and the course of the nasolacrimal duct becomes altered.6

Nasopharyngeal stenosis, a narrowing of the nasopharynx caudal to the choana, occurs most commonly as a congenital condition.7 It may also be secondary to inflammation, trauma, or tumors. The regions of stenosis are very narrow and require thin-slice CT images to detect. Sagittal reformatted images are helpful for identifying and quantifying the stenosis (Figure 1.1.4).

Figure 1.1.4 Nasopharyngeal Stenosis (Canine)      CT

1y F Italian Greyhound with chronic nasal discharge. There is focal occlusion of the nasopharyngeal lumen near the level of the pterygoid processes and 1 cm caudal to the caudal margin of the hard palate (b,d: arrow). The pharyngeal lumen rostral and caudal to this focal lesion appears normal (a,c: arrow). The soft tissues associated with the occlusive lesion mildly contrast enhance (b). Nasopharyngeal stenosis was confirmed rhinoscopically, and biopsy revealed moderate chronic active neutrophilic, eosinophilic, and lymphoplasmacytic pharyngitis and rhinitis.

Inflammatory disorders

Foreign body rhinitis

Imaging diagnosis of nasal foreign body rhinitis often depends on whether the foreign object can be directly visualized. When the object is not seen, as is often the case with plant awns or small wood fragments, diagnostic features include focal turbinate destruction, hyperplasia of the remaining overlying nasal mucosa, and regional accumulation of fluid or mucoid exudates.8 Foreign body rhinitis is usually unilateral except when multiple foreign bodies are present, which can occur with plant awn inhalation. The severity of the secondary imaging findings can be related to the chronicity of the disorder as well as the inertness of the foreign material. In most patients, imaging abnormalities are limited to the nasal cavity or nasopharynx and do not usually involve the paranasal sinuses (Figures 1.1.5, 1.1.6, 1.1.7).9

Figure 1.1.5 Foreign Body Rhinitis-Plant Awn (Canine)      CT

9y FS Labrador Retriever. The transverse plane image reveals unilateral regional nasal turbinate destruction. The fluid-attenuating mass represents a combination of remaining turbinates, mucosa, and accumulated exudate. The fragmented gas pattern suggests this is not a solid mass. A plant awn (foxtail foreign body) was removed at the time of rhinoscopy. Plant awns are usually not detected on CT or MRI, although the focal or regional inflammatory response is characteristic.

Figure 1.1.6 Foreign Body Rhinitis-Tooth Fragment (Feline)      CT

16y MC Domestic Longhair with chronic right-sided nasal discharge, chronic renal failure, and multiple missing teeth (a,c). An irregularly margined mineral-attenuating mass is present in the rostral aspect of the right nasal cavity. This is associated with adjacent turbinate destruction and increased soft-tissue opacity, consistent with mucosal proliferation and exudates. There is also distortion of the right maxillary bone (a: arrow) that likely results from chronic rhinitis and concurrent metabolic bone disease due to chronic renal failure. Resorption of the right maxillary bone (a: arrow) and the hard palate caudal to the mass is also evident (b: arrow). The mineral opacity was a retained migrated tooth root with peripheral cementum proliferation. This cat also has many missing teeth, pronounced periodontal bone resorption, and proliferative bone remodeling seen with chronic dental disease (a: arrowheads).

Figure 1.1.7 Wood Foreign Body (Canine)      CT

5y FS Australian Shepherd with reverse sneezing and respiratory distress. On unenhanced images, there is hyperattenuating material in the right caudal nasopharynx surrounded by soft tissue (a: arrow). On contrast-enhanced images, the soft tissue surrounding the foreign material is strongly enhancing (b), representing inflammation and granulomatous tissue. The material extends into the soft palate, which appears as a hyperattenuating structure (c). Endoscopy revealed a wood foreign body (stick) in the caudal nasopharynx (d). The stick was removed via endoscopy.

Nonspecific rhinitis

Nonspecific rhinitis is a general term that includes inflammatory nasal disorders from viral, bacterial, parasitic, or allergic causes. Rhinitis may also occur as an extension of severe periodontal disease. The most common biopsy diagnosis in this category of disease is lymphocytic-plasmocytic rhinitis, which may also have a neutrophilic or predominantly eosinophilic component (Figures 1.1.8, 1.1.9). Rhinitis may also occur secondary...