Computed tomographic findings of nasal and paranasal disease in domestic rabbits highlight maxillary sinusitis and close association with dental disease: 100 studies (2004–2024)

Nicole Mikoni Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, CA

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David Sanchez-Migallon Guzman Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California-Davis, Davis, CA

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Hugues Beaufrère Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California-Davis, Davis, CA

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Kathryn Phillips Department of Surgical and Radiological Sciences, Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, CA

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Abstract

OBJECTIVE

To describe CT findings and epidemiologic features of nasal and paranasal disease of rabbits (Oryctolagus cuniculus).

METHODS

An electronic search was performed for rabbits that underwent skull CT from 2004 to 2024 and had findings consistent with nasal/paranasal or maxillary dental disease. History, signalment, and physical examination findings were recorded and reevaluated retrospectively for evidence of changes to the nasal passages, paranasal sinuses, and nearby associated anatomy. Data were analyzed with descriptive statistics, ordinal mixed logistic regression, and correlation analysis.

RESULTS

100 studies from 69 rabbits were reviewed. Lop-eared rabbits represented 30 of 69 cases. Upper respiratory signs (48 of 69 [69.6%]) and dental-related disorders (21 of 69 [31.9%]) were primary complaints. Rhinitis (49 of 69 [71.0%]), sinusitis (50 of 69 [72.5%]), and both (40 of 69 [60.0%]) were most diagnosed, with turbinate destruction (48 of 69 [69.6%]) and alveolar bone loss of adjacent teeth (51 of 69 [73.9%]) being common findings. Sinusitis was most common in the ventral (48 of 50 [96.0%]) and dorsal (33 of 50 [66.0%]) recesses of the maxillary sinus. Multiple CT variables were significantly correlated (P < .05); of those, maxillary alveolar bone loss of the incisor teeth and the second premolar tooth were, respectively, correlated with rhinitis grade and with sinusitis and sinusitis grade within the ventral recess of the maxillary sinus (P < .001).

CONCLUSIONS

Computed tomographic evaluation allowed characterization of nasal and paranasal disease in rabbits and the association of rhinitis, sinusitis, and dental disease.

CLINICAL RELEVANCE

The correlation between the maxillary dentition, rhinitis, and sinusitis highlights the need for thorough evaluation in CT of the teeth in rabbits with upper respiratory signs.

Abstract

OBJECTIVE

To describe CT findings and epidemiologic features of nasal and paranasal disease of rabbits (Oryctolagus cuniculus).

METHODS

An electronic search was performed for rabbits that underwent skull CT from 2004 to 2024 and had findings consistent with nasal/paranasal or maxillary dental disease. History, signalment, and physical examination findings were recorded and reevaluated retrospectively for evidence of changes to the nasal passages, paranasal sinuses, and nearby associated anatomy. Data were analyzed with descriptive statistics, ordinal mixed logistic regression, and correlation analysis.

RESULTS

100 studies from 69 rabbits were reviewed. Lop-eared rabbits represented 30 of 69 cases. Upper respiratory signs (48 of 69 [69.6%]) and dental-related disorders (21 of 69 [31.9%]) were primary complaints. Rhinitis (49 of 69 [71.0%]), sinusitis (50 of 69 [72.5%]), and both (40 of 69 [60.0%]) were most diagnosed, with turbinate destruction (48 of 69 [69.6%]) and alveolar bone loss of adjacent teeth (51 of 69 [73.9%]) being common findings. Sinusitis was most common in the ventral (48 of 50 [96.0%]) and dorsal (33 of 50 [66.0%]) recesses of the maxillary sinus. Multiple CT variables were significantly correlated (P < .05); of those, maxillary alveolar bone loss of the incisor teeth and the second premolar tooth were, respectively, correlated with rhinitis grade and with sinusitis and sinusitis grade within the ventral recess of the maxillary sinus (P < .001).

CONCLUSIONS

Computed tomographic evaluation allowed characterization of nasal and paranasal disease in rabbits and the association of rhinitis, sinusitis, and dental disease.

CLINICAL RELEVANCE

The correlation between the maxillary dentition, rhinitis, and sinusitis highlights the need for thorough evaluation in CT of the teeth in rabbits with upper respiratory signs.

Introduction

Domestic rabbits are common patients of veterinary practitioners, with an increase in worldwide popularity as household companion animals.1 Due to the elongated anatomy of the soft palate and positioning of the epiglottis dorsal to the soft palate, rabbits are obligate nasal breathers that rely on nasal airflow for adequate respiration. As a result, upper respiratory diseases are a major cause of morbidity and mortality in rabbits and can involve a variety of infectious, neoplastic, traumatic, and congenital etiologies.2 Of equal importance is the close association of the nasal passages to other nearby structures in rabbits such as the maxillary dental arcades, with processes affecting the dentition having the capacity to subsequently extend to the nasal anatomy.3,4

The nasal cavity of the rabbit is divided down its length by the nasal septum to form 2 distinct passages, with each passage being organized in an intricate array of nasal concha, meatuses, and sinuses.4,5 Both volumetric and air flow analysis studies have been performed in healthy rabbits to further characterize these anatomic structures.35 The paranasal sinuses in rabbits are divided into 4 bilateral sinus spaces: the dorsal conchal sinus, dorsal recess of the maxillary sinus, ventral recess of the maxillary sinus, and sphenoidal sinus.6 The dorsal conchal sinus has a large opening into the dorsal recess of the maxillary sinus. The dorsal and ventral recesses of the maxillary sinus are indented along the lateral margin by the nasolacrimal duct and drain into the nasal cavity with the dorsal conchal sinus (the collective space is the conchomaxillary cavity) via the maxillary sinus ostium. Caudal to the medial canthus of the eye, the dorsal and ventral recesses of the maxillary sinuses freely communicate and expand into a larger sinus. The sphenoidal sinus does not directly connect with the other paranasal sinuses and instead opens up into the nasal cavity via its own sphenoidal sinus ostium (Supplementary Figure S1).6 Rabbits presenting with disease affecting the nasal and paranasal anatomy may range from more subtle signs such as chronic nasal or ocular discharge in mild cases or marked respiratory distress in severe cases.7

Computed tomography allows for far superior evaluation of the nasal passages compared with standard radiography, as has been highlighted in previous studies.3,4,8 It also allows for evaluation of structures without superimposition of nearby anatomic structures and can be used to assess the individual sinuses and concha in both healthy (Supplementary Figure S1 and Supplementary Figure S2) and diseased individuals. While the aforementioned studies have evaluated how the rabbit nasal anatomy is organized on CT in healthy individuals, a large-scale evaluation of apparent changes in rabbits with nasal and paranasal disease has yet to be performed.

The objectives of the present study were to describe CT findings and epidemiologic features of nasal and paranasal disease of domestic rabbits. We further set out to investigate for possible relationships between nasal and paranasal disease and the closely associated maxillary dental anatomy and hypothesized that disease of the maxillary dentition would correlate with an increased prevalence of nasal disease, particularly within the maxillary sinus spaces.

Methods

Case selection

An electronic search of the medical records at the University of California-Davis William R. Pritchard Veterinary Medical Teaching Hospital was performed to identify rabbits that underwent CT of the skull from April 1, 2004, to January 31, 2024. A search was specified for lagomorphs only, and search terms included skull CT, cone-beam CT, rhinitis, sinusitis, and nasal. Rabbits with conventional multidetector fan-beam and cone-beam skull CTs available for retrospective review were included in the study regardless of the reason for CT and whether clinical signs of nasal or paranasal disease were present. Multiple CT evaluations from the same rabbit were included in the study as long as at least 1 month had passed between study dates. The decision to include multiple studies from the same individuals was elected to evaluate for changes in findings present on initial CT scans over time.

Medical records review

Information extracted from each medical record included signalment (age, breed, sex, and whether the rabbit was altered or intact), clinical signs and duration of clinical signs prior to performance of the patient’s first CT evaluation, and any attempted medical treatments prior to performance of the patient’s first CT evaluation.

Image acquisition and review

Images were acquired by use of a multidetector CT or cone-beam CT scanner, with patients being placed in sternal recumbency under sedation or general anesthesia. The preferred acquisition method included submillimeter slice thickness, with 0.62 mm from the multidetector CT scanner, though older studies performed in 2010 and earlier exhibited larger slice thickness. Cone-beam CT scans involved smaller slice thicknesses at 0.2 to 0.3 mm. Commercial computer software (Horos Project) was utilized to reevaluate CT images in the transverse plane with multiplanar reconstructions. The CT images were retrospectively reviewed by both a board-certified veterinary radiologist (KP) and an American College of Zoological Medicine residency–trained veterinarian focused on companion zoological species (NM); the reviewers were not blinded to the final diagnosis at the time of image review. The use of IV contrast medium (Iohexol; 880 mgI/kg) for the CT scans was recorded when performed. All images were additionally evaluated for the presence or absence of rhinoliths, turbinate destruction, maxillary alveolar bone loss, oronasal fistula formation, upper skull cortical bone loss (of the maxillary, nasal, facial, lacrimal, incisive, pterygoid, or sphenopalatine bones), nasal septum lysis, nasal septum deviation, sphenoidal sinus septum deviation, rhinitis, sinusitis, nasal or paranasal masses, nasolacrimal duct changes, retrobulbar disease, dental disease, otic disease, and regional lymphadenopathy. The severity of sinusitis and rhinitis was determined on the basis of the overall degree of nasal and paranasal fluid or soft tissue increased attenuation (sinusitis) or turbinate loss (rhinitis) appreciated by the 2 CT reviewers (KP and NM) for each individual rabbit study. A consensus was reached by the 2 CT reviewers for each study evaluated and categorized as none, mild, moderate, or severe on the basis of the percentage of affected nasal or paranasal regions. Mild cases were < 25% affected, moderate cases were 25% to 75% affected, and severe cases were > 75% affected within the nasal passages (rhinitis) or within at least 1 individual paranasal sinus (sinusitis).

Statistical analysis

Categorical data (presence or absence of each CT-detected change) were reported as a percentage frequency of occurrence. Descriptive statistics were calculated with commercial software (Excel; Microsoft Corp). A correlation matrix was performed with Spearman correlation coefficients for all ordinal CT interpretation variables. For serial CTs in the same patient, only data from the first CT were used for correlation analysis. Due to the number of associations, results of the correlation coefficients and P values are displayed in heat maps (Supplementary Figure S3). The effect of age, sex, reproductive status, and breed (lop vs nonlop breeds) on rhinitis and sinusitis severity was assessed with ordinal mixed logistic regression. Assumptions were checked graphically on residual plots. The assumption of proportional odds was checked with a likelihood ratio test. An ordinal mixed logistic regression model was also performed to assess the effect of maxillary alveolar bone loss on the presence of unilateral or bilateral rhinitis and sinusitis excluding normal cases. An α of .05 was used for significance. R (version 4.3.2; The R Foundation for Statistical Computing) was used for statistical analysis.

Results

Rabbits

A total of 69 client-owned rabbits with a total of 100 CT studies among them were included in the study. For individuals in which breed was specified (57 of 69), lop-eared rabbits comprised the majority of the study population (30 of 57 [52.6%]), followed by Netherland dwarf breeds (10 of 57 [17.5%]), Rex breeds (5 of 57 [9.8%]), and New Zealand Whites (5 of 57 [9.8%]). English spots (2 of 57 [3.5%]), Lionheads (2 of 57 [3.5%]), a Flemish giant (1 of 57 [1.8%]), a Silver Marten (1 of 57 [1.8%]), and a Californian (1 of 57 [1.8%]) comprised the remaining breeds. Average age of clinical presentation was 6 years, with a range of 4 months to 12 years. The study population included 38 males and 31 females; the vast majority of these animals were spayed or neutered (64 of 69 [92.8%]), with few being left unaltered (5 of 69 [7.2%]). Age, sex, reproduction status, and breed (lop vs nonlop) were not found to significantly change the odds of more severe rhinitis (all P > .05). Non–lop-eared rabbits had significantly higher odds of more severe sinusitis (proportional OR, 6.7; 95% CI, 1.5 to 31.4; P = .015) than lop-eared rabbits. Age, sex, and reproductive status did not have an effect on the odds of sinusitis (all P > .05).

History and physical examination findings

Depending on the case, rabbits were presented for the first CT evaluation between 1 day and 4 years following initial onset of clinical signs. Of the 69 rabbits presented, 48 (69.6%) were presented for evaluation of upper respiratory signs as the primary complaint. The most common associated clinical signs included nasal discharge (36 of 69 [52.2%]), sneezing (35 of 69 [50.7%]), difficulty eating (23 of 69 [33.3%]), and ocular discharge (14 of 69 [20.3%]). Less common respiratory clinical signs included dyspnea (4 of 69 [5.8%]), intermittent epistaxis (3 of 69 [4.3%]), coughing (3 of 69 [4.3%]), frequent wiping of the nose or eyes (2 of 69 [2.9%]), and ocular inflammation (1 of 69 [1.4%]). Of the 3 rabbits that presented with intermittent epistaxis, 2 (66.7%) had confirmed intranasal neoplasia (1 lymphoma and 1 adenocarcinoma). A subset of rabbits (21 of 69 [31.9%]) were presented for evaluation of nonrespiratory signs as their presenting complaint, with the majority of these complaints being associated with dental-related issues (12 of 21 [57.1%]). Almost all rabbits (62 of 69 [89.9%]) had been placed on 1 or more medications prior to presentation for CT, with the most common therapeutics being meloxicam (37 of 69 [53.6%]), enrofloxacin (32 of 69 [46.4%]), trimethoprim-sulfamethoxazole (18 of 69 [26.1%]), and procaine penicillin G (12 of 69 [17.4%]).

Diagnostic imaging findings

Most CT images were obtained with 0.62-mm slice thickness (78 of 100 [78.0%]), with just over half of these studies utilizing contrast medium (53 of 100 [53.0%]). Of the 100 studies, 2 were cone-beam CT studies. The CT findings for each item of interest were summarized by percent frequency out of the 69 initial studies from each rabbit (so as to not overrepresent findings from those rabbits with sequential CT studies), as follows: otitis in any portion of the ear canal with concurrent nasal/paranasal disease (34 of 69 [49.3%]), rhinoliths (28 of 69 [40.6%]), dental disease with concurrent nasal/paranasal disease (21 of 69 [30.4%]), detectable nasolacrimal duct anatomic changes (15 of 69 [21.7%]; 2 were unable to be confidently traced), concurrent retrobulbar disease (7 of 69 [10.1%]), oronasal fistula formation (8 of 69 [11.6%]), nasal septum lysis (6 of 69 [8.7%]), nasal septum deviation (9 of 69 [13.0%]), sphenoidal sinus septum deviation (45 of 69 [65.2%]), and an intranasal mass (5 of 69 [7.2%]). Of the rabbits with detectable nasolacrimal duct anatomic changes, 8 of 15 (53.3%) had ocular discharge appreciated clinically, while the remaining 7 of 15 (46.7%) did not. Rhinoliths were visualized within each of the paranasal sinuses (Figure 1). Four of 5 of the cases with nasal masses had diagnostic histopathology that identified 2 intranasal adenocarcinomas, an intranasal lymphoma, and a nasal osteosarcoma. Representative CT images of these neoplastic processes can be found in Figures 2 and 3. The majority of rabbits (50 of 69 [72.5%]) had concurrent disease (dental, otic, or retrobulbar) in addition to alterations in their nasal passage anatomy. Turbinate destruction was observed in 48 of 69 cases (69.6%), with destruction ranging from mild (9 of 48 [18.8%]) to moderate (5 of 48 [10.4%]) to severe (34 of 48 [70.8%]) and affecting both (32 of 48 [66.7%]) nasal passages, the left side only (10 of 48 [20.8%]), or the right side only (6 of 48 [12.5%]).

Figure 1
Figure 1

Images of rhinoliths affecting the various rabbit paranasal sinuses. A—A rhinolith (ρ) within the rostral nasal cavity with concurrent rhinitis. B—A rhinolith within the ventral recess of the maxillary sinus with concurrent sinusitis (γ), as well as a rhinolith within the dorsal recess of the maxillary sinus with concurrent sinusitis (β). The nasolacrimal duct on the normal contralateral side is additionally labeled (λ). C—Bilateral rhinoliths (ε) within the sphenoidal sinus with concurrent sinusitis. D and E—A large conglomeration of rhinoliths within the nasal cavity and dorsal conchal sinus (D). Over time, despite a prior dorsal rhinotomy and medical management, this patient developed additional rhinoliths (asterisk).

Citation: Journal of the American Veterinary Medical Association 2024; 10.2460/javma.24.05.0330

Figure 2
Figure 2

Images of intranasal neoplasia affecting various rabbits. A severe, destructive intranasal lymphoma fills the nasal cavity and all paranasal sinuses bilaterally, with cortical bone loss and a large mass protruding from the nasal cavity on the right side in a rabbit, with the mass being highlighted on the transverse plane on both precontrast (A) and postcontrast (B) CT. Sagittal (C) and transverse (D) precontrast bone algorithm and (E) postcontrast soft tissue algorithm CT images of a rabbit with diffuse unilateral intranasal adenocarcinoma. The mass is causing destruction of the nasal turbinates, fills the caudal nasal cavity and caudal continuation of the dorsal and ventral recess of the maxillary sinus, and encroaches on the caudal portion of the left dorsal conchal sinus. There is a large region of cortical bone loss dorsally in the maxilla, and the contrast-enhancing mass bulges dorsally through this defect. The body of the mass is highlighted in each image (κ).

Citation: Journal of the American Veterinary Medical Association 2024; 10.2460/javma.24.05.0330

Figure 3
Figure 3

Dorsal- (A), sagittal- (B), and transverse-view (C) CT images of a rabbit with unilateral nasal osteosarcoma with complete destruction of the affected nasal turbinates and aggressive bone lesion of the nasal bone. The most severely affected region is outlined in each image (κ).

Citation: Journal of the American Veterinary Medical Association 2024; 10.2460/javma.24.05.0330

Maxillary alveolar bone loss was present in 51 of 69 cases (73.9%), which were categorized as having 1 to 2 teeth (32 of 51 [62.7%]) or more than 2 teeth (19 of 51 [37.3%]) affected. Of the affected maxillary teeth, the second premolar was found to be most commonly diseased in 42 of 51 cases (82.4%), followed by the primary incisor tooth (22 of 51 [43.1%]), fourth premolar tooth (8 of 51 [15.7%]), second molar tooth (8 of 51 [15.7%]), first molar tooth (7 of 51 [13.7%]), third molar tooth (5 of 51 [9.8%]), and third premolar tooth (3 of 51 [5.9%]). Maxillary alveolar bone loss (dental disease) did not influence the presence of unilateral versus bilateral rhinitis or sinusitis (all P > .05). The peg teeth were not observed to be affected by maxillary alveolar bone loss in any study. Upper skull cortical bone loss was present in 15 of 69 cases (21.7%), with affected bones including the maxilla (14 of 15 [93.3%]), lacrimal (2 of 15 [13.3%]), incisive (2 of 15 [13.3%]), nasal (1 of 15 [6.7%]), pterygoid (1 of 15 [6.7%]), facial (1 of 15 [6.7%]), and sphenopalatine (1 of 24 [6.7%]) bones. This cortical lysis was associated with intranasal masses and periapical abscesses (or advanced dental disease).

Rhinitis was present in 49 of 69 cases (71.0%), sinusitis was present in 50 of 69 cases (72.5%), and concurrent rhinitis and sinusitis were present in 40 of 69 cases (57.8%). Of the rhinitis cases, 11 of 49 (22.4%) were categorized as mild, while 5 of 49 (10.2%) were categorized as moderate and 34 of 49 (69.4%) were categorized as severe. Rhinitis location was found to be bilateral in 34 of 49 cases (69.4%), primarily left sided in 9 of 49 cases (18.4%), and primarily right sided in 6 of 49 cases (12.2%). Cases of sinusitis varied in severity from mild (12 of 50 [24.0%]) to more moderate (8 of 50 [16.0%]) or severe (30 of 50 [60.0%]). Side distribution was found to be bilateral (33 of 50 [66.0%]) or either left sided (9 of 50 [18.0%]) or right sided (8 of 50 [16.0%]). Case examples of severe destructive rhinitis and severe chronic sinusitis are highlighted in Figure 4. Affected sinuses by percentage frequency included the ventral recess of the maxillary sinus most commonly at 48 of 50 (96.0%), followed by the dorsal recess of the maxillary sinus (33 of 50 [66.0%]), dorsal conchal sinus (31 of 50 [62.0%]), and sphenoidal sinus (19 of 50 [38.0%]). Sinusitis distribution among the various paranasal sinuses is illustrated in Figure 5. Of the rabbits that had > 1 sinus affected, 8 of 50 (16.0%) had 2 affected sinuses, 14 of 50 (28.0%) had 3 affected sinuses, and 17 of 50 (34.0%) had all 4 sinuses affected, while the remaining 11 of 50 (22.0%) had only 1 sinus affected.

Figure 4
Figure 4

Transverse plane CT images of 3 different rabbits with destructive rhinitis. A and B—Destructive rhinitis with varying degrees of unilateral (A) and bilateral (B) turbinate destruction and loss of normal anatomy. C—Severe diffuse rhinitis and sinusitis affecting the dorsal conchal, dorsal recess of the maxillary, and ventral recess of the maxillary sinuses bilaterally with turbinate destruction. This rabbit was later treated and made significant recovery.

Citation: Journal of the American Veterinary Medical Association 2024; 10.2460/javma.24.05.0330

Figure 5
Figure 5

Images of sinusitis affecting the paranasal sinuses in different rabbits. A and B—Transverse view (A) and sagittal view (B) of dorsal conchal sinusitis in a rabbit (α). The nasolacrimal duct is additionally labeled (λ). C and D—Transverse view (C) and dorsal view (D) of sinusitis within the dorsal recess of the maxillary sinus with concurrent rhinoliths present (β). The nasolacrimal duct is additionally labeled (λ). E—Transverse view of sinusitis within the left ventral recess of the maxillary sinus (γ). The nasolacrimal duct is additionally labeled (λ). F—Transverse view of left-sided sphenoidal sinusitis (ε).

Citation: Journal of the American Veterinary Medical Association 2024; 10.2460/javma.24.05.0330

Multiple CT variables were significantly correlated with each other in the correlation matrix, with these variables having rs > 0.2 and P < .001 (Supplementary Figure S3). Among CT variables, turbinate destruction severity was correlated with severity of rhinitis (rs = 0.95; P < .001), severity of sinusitis (rs = 0.69; P < .001), and sinusitis within the dorsal conchal sinus (rs = 0.67; P < .001), dorsal recess of the maxillary sinus (rs = 0.62; P < .001), ventral recess of the maxillary sinus (rs = 0.56; P < .001), and sphenoidal sinus (rs = 0.50; P < .001). Maxillary alveolar bone loss affecting the incisor teeth was correlated with severity of rhinitis (rs = 0.42; P < .001). Maxillary alveolar bone loss affecting the second premolar tooth was correlated with severity of sinusitis (rs = 0.37; P < .001) and sinusitis within the ventral recess of the maxillary sinus (rs = 0.39; P < .001). The intimate relationship between maxillary alveolar bone loss of the maxillary dentition and resulting nasal and paranasal disease is highlighted in Figure 6.

Figure 6
Figure 6

Images of rhinitis and sinusitis of presumed odontogenic origin in different rabbits. A—Left-sided focal rhinitis with loss of alveolar bone support of the left maxillary incisor tooth. The nasolacrimal duct on the contralateral normal side is labeled (λ) to emphasize the close anatomic location. B and C—Sinusitis within the ventral recess of the maxillary sinus (γ) with alveolar bone loss and abscessation of the second maxillary premolar tooth (τ). D—Sphenoidal sinusitis (ε) with alveolar bone loss and abscessation of a maxillary molar tooth (τ). This rabbit additionally had a degree of mandibular odontogenic disease (not investigated for the purposes of this study).

Citation: Journal of the American Veterinary Medical Association 2024; 10.2460/javma.24.05.0330

Sequential CT findings

A total of 17 rabbits (17 of 69 [24.6%]) underwent performance of serial CT monitoring in this study population for a combined total of 31 CT studies (31 of 100 [31.0%]). Of these studies, the most performed on a single rabbit was 5 studies over a period of 6 years. Of the 31 sequential studies performed, 17 studies (54.8%) highlighted worsening of lesions appreciated on the initial CT for the individual rabbits, while 2 of 31 (6.5%) showed improvement, and 12 of 31 (38.7%) revealed largely static lesions. Months between recheck imaging varied, with the least amount of time between CT scans being 1 month and the greatest being 70 months (average time between scans, 14.48 months).

Discussion

The purpose of this study was to characterize the CT findings of nasal and paranasal disease in rabbits and describe the epidemiologic features of the affected rabbits. In the current study, lop-eared rabbits (52.6%) comprised the most common breed in the study population, with average age of presentation being 6 years and most having been treated with anti-inflammatory and/or antibiotic therapy prior to their first CT. The rabbits evaluated in this study were presented for a variety of clinical signs as their primary presenting complaints, with the majority (69.6%) being presented for evaluation of upper respiratory signs. The most frequent CT changes appreciated included the presence of maxillary alveolar bone loss (73.9%), rhinitis (71.0%), sinusitis (72.5%), turbinate destruction (69.6%), and rhinolith formation (40.6%). Concurrent otitis was present in 49.3% studies.

In this study, the most common breeds presented for nasal disease were lop-eared rabbit breeds, though interestingly they were not found to have higher odds of more severe rhinitis or sinusitis compared to the non–lop-eared rabbits in this study. This breed distribution falls in line with the rising popularity of brachycephalic rabbit breeds.9,10 Prior studies have highlighted that these breeds are often more likely to develop aural diseases compared to non–lop-eared breeds due to the variations in their cartilaginous aural anatomy,11 but data have conflicted in terms of whether these breeds are more prone to other issues such as dental disease.11,12 The results of this study found that non–lop-eared breeds had significantly higher odds of more severe sinusitis (proportional OR, 6.7; 95% CI, 1.5 to 31.4; P = .015) than lop-eared rabbits but no breed predilection in terms of severity of rhinitis. Further study on the anatomic spacing of the maxillary dentition in relation to the paranasal sinuses in non–lop-eared breeds versus lop-eared breeds would be valuable to pursue to determine whether differences in anatomic layout exist that would predispose higher instances of disease formation.

The dorsal conchal, dorsal recess of the maxillary, and ventral recess of the maxillary sinuses all communicate. The fused portions of the dorsal and ventral recesses of the maxillary sinus extend caudally near the rostral aspect of the sphenoidal sinus but does not directly connect with it.6 Given the drainage pattern of the conchomaxillary sinuses and close proximity of the sphenoidal sinus, disease processes affecting one sinus have the ability to progress more diffusely to other sinus spaces with chronicity or severe disease. This was supported by the findings of the present study, in which it was uncommon for rabbits to have only 1 sinus affected by sinusitis. Of the rabbits that had more than 1 sinus affected, 16.0% had 2 affected sinuses, 28.0% had 3 affected sinuses, and 34.0% had all 4 sinuses affected, with two-thirds of the rabbits affected having bilateral involvement. The likelihood of sinusitis to spread from one sinus space to another is an important clinical consideration for chronic disease management, and experimentally induced sinusitis has similarly documented diffusion of sinusitis beyond the region of initial disease over time.13 It is worth repeating that the sphenoidal sinus does not directly connect with the other paranasal sinuses and instead opens up into the nasal cavity via its own sphenoidal sinus ostium.6 Indeed, of the 4 paranasal sinuses, the sphenoidal sinus was found to be the least commonly affected with sinusitis (38.0%), which is suspected to be due to its lack of direct communication with the other sinus spaces.

The nasolacrimal duct is situated along the maxillary sinuses; in normal rabbit anatomy, the dorsal and ventral recesses of the maxillary sinus connect to each other through a large opening along their caudal halves, and in the rostral halves the nasolacrimal duct is located between them.6 This intimate relationship may result in alteration of the nasolacrimal duct from sinusitis within the ventral and/or dorsal recess of the maxillary sinus. Changes in the nasolacrimal duct as a consequence of nasal or paranasal disease have been documented in a prior rabbit CT study12 evaluating anatomic changes associated with dental disease. This finding was supported in this study, as 21.7% of cases exhibiting more moderate to severe sinusitis within either the dorsal or ventral recess of the maxillary sinus had concurrent compromise or destruction of the normal nasolacrimal duct anatomy. The close anatomic location of the nasolacrimal duct with the maxillary sinus is an important consideration for procedures such as lateral rhinotomy, in which this region of the nasal passage may be entered to address disease.14,15 Changes in the nasolacrimal duct as a consequence of nasal or paranasal disease have additionally been documented in a prior rabbit CT study evaluating anatomic changes associated with dental disease.12

The larger relative size of the entire maxillary sinus compared to the dorsal conchal and sphenoidal sinuses and its more intimate location to the maxillary dentition was hypothesized by the authors to contribute to its increased prevalence of sinusitis. This was supported in this study, during which sinusitis of the ventral recess of the maxillary sinus was found most commonly at 96.0% of affected sinuses, followed by that of the dorsal recess of the maxillary sinus (66.0%). There was also a correlation found between maxillary alveolar bone loss affecting the second premolar tooth and both severity of sinusitis (rs = 0.37; P < .001) and sinusitis within the ventral recess of the maxillary sinus (rs = 0.39; P < .001). As an example of the close proximity of the maxillary dentition to the maxillary sinus spaces in rabbits, prior studies have utilized the maxillary sinus as a route for dental implant placement models for humans in rabbit models.16 Rabbits presenting for maxillary premolar tooth disease (apical elongation, abscessation) in published retrospective studies or case series are similarly often found to have a degree of sinusitis in the nearby maxillary sinus recesses.12,17,18 This finding makes sense anatomically given the close proximity of the second premolar tooth apices and the ventral recess of the maxillary sinus.19

In addition to the correlation between disease of the second premolar tooth and sinusitis of the ventral recess of the maxillary sinus, we also found a correlation between maxillary alveolar bone loss of the incisor teeth with severity of rhinitis (rs = 0.42; P < .001). This anatomically makes sense, as the apices of the maxillary incisors lie just rostral to the maxillary sinus and are only separated from the nasal cavity by a thin rim of alveolar bone. A recent study20 published on CT findings of dental disease and secondary disease of the head area in domestic rabbits further supported that rhinitis and paranasal sinusitis can arise with disease of the maxillary incisor and premolar teeth, as was similarly discovered in the current study. However, the aforementioned study did not directly comment on which teeth can directly contribute to the development of sinusitis within the individual paranasal sinuses, as is proposed for the second premolar tooth’s correlation with sinusitis within the ventral recess of the maxillary sinus in this study.

One anatomic component that was not found to have a direct correlation with development of sinusitis in the rabbits in this study was the presence of nasal septum deviation. In other species such as humans, nasal septum deviation has been proposed to be a precursor to the development of maxillary sinusitis.2124 In humans affected by nasal septum deviation, up to 20% of those studied develop maxillary sinusitis over time.21 Similarly, in domestic cats, a study25 evaluating nasal septum deviation in this species found concurrent rhinitis in up to 86.7% of the cats evaluated, with a significant difference in the magnitude of nasal septum deviation between cats with and without nasal disease. In this study, only a small percentage of rabbits was found to have deviation of the nasal septum (13.0%), and this was not one of the CT variables found to be significantly correlated with the severity or presence of rhinitis or sinusitis.

Though the overall frequency of intranasal mass-like lesions in this study was low (7.2%), the clinical signs and imaging characteristics noted in this study are worth mentioning. Of the intranasal masses that had concurrent histopathology available in this study, 2 intranasal adenocarcinomas, an intranasal lymphoma, and a nasal osteosarcoma were diagnosed, which are in line with more commonly reported spontaneous intranasal neoplasms in rabbits.2628 Of the 3 rabbits that presented with intermittent epistaxis, 66.7% had confirmed intranasal neoplasia (1 lymphoma and 1 adenocarcinoma), and though this is not a hallmark sign of intranasal neoplasia compared to a prior case series in rabbits, intranasal neoplasia was the most common cause of epistaxis in the dog29 and should therefore be considered as a differential for rabbits presenting for epistaxis. The intranasal neoplasms in this study had prominent cortical bone lysis and multisinus involvement, which has been similarly highlighted in prior rabbit intranasal neoplasm studies.2628 Evidence of either of these changes on CT should prompt further investigation including contrast-enhanced CT and tissue sampling with histopathology to evaluate for intranasal neoplasia whenever possible.

This was a retrospective study evaluating both multidetector fan-beam and cone-beam CT studies. Cone-beam CT has the advantage of increased spatial resolution and smaller slices, which makes it ideal for evaluating nasal turbinates, alveolar bone, and dental structures.30 Multidetector fan-beam or traditional CT has better contrast resolution, which facilitates evaluation of soft tissues including masses and lymph nodes in rabbits.12 Contrast medium can further facilitate distinction of tissue margins/masses and highlight regions of peripheral contrast enhancement.31,32 This is of particular importance when evaluating for regions of focal neoplasms or granuloma/abscess formation.31 In the current study, approximately half of the studies available utilized contrast medium (53.0%). Though the overall frequency of intranasal mass-like lesions in this study was low (7.2%), contrast medium was utilized in all 5 of these studies, and IV contrast administration is recommended to be applied to cases with suspicion for underlying neoplasia or intranasal granulomatous disease/abscess formation for improved lesion detection.

As with other retrospective studies, there were limitations associated with the available data. For the patient data, not all rabbits were described in terms of their breed or full duration of clinical signs prior to presentation for CT. Missing data can result in the potential for skewed results and may alter which meaningful associations are found (or not found) between variables. In this study, the most common breeds presented for nasal disease were lop-eared rabbits. Though this breed distribution does fall in line with the rising popularity of these brachycephalic breeds,9,10 13 of the rabbits utilized for this study did not have a breed listed in their patient record and therefore could have contributed to differences in the breed trends seen here. Multiple sequential CT studies from the same individual rabbit were utilized in completion of this retrospective study as well. This was chosen by the authors to evaluate the possible changes in CT associated to disease progression of rabbit nasal and paranasal disease. However, only the initial CT was considered in the epidemiologic descriptive statistics, as well as in the ordinal mixed logistic regression, and correlation matrix analyses to avoid overrepresenting data and introducing bias. An interesting finding from the sequential CT study data obtained was that 54.8% of studies highlighted worsening of lesions appreciated on the initial CT scan and 38.7% revealed largely static lesions despite active treatments. This is likely a biased finding, as individuals that clinically improved were less likely to be presented again by their owners for repeat imaging. Another limitation to consider is that not all CT studies included the use of IV contrast medium administration, which can diminish the ability to evaluate for more subtle soft tissue structures such as neoplastic masses and infectious granulomas/abscesses.

The CTs evaluated in this study allowed characterization of the imaging findings that can occur with nasal and paranasal disease in rabbits and highlighted a variety of representative images. This information can be utilized to improve CT evaluation of the nasal passages and associated structures and assess overall severity based on the number of changes present. The strong correlation between the maxillary incisor and development of rhinitis and the second maxillary premolar and sinusitis of the ventral recess of the maxillary sinus highlights the need for thorough evaluation in CT of the teeth in rabbits with upper respiratory signs.

Supplementary Materials

Supplementary materials are posted online at the journal website: avmajournals.avma.org.

Acknowledgments

A special thanks is extended to Chrisoula A. Toupadakis Skouritakis for her exceptional production and labeling of the CT scan images highlighted in this manuscript. The authors would also like to extend gratitude to the University of California-Davis Companion Exotic Animal Medicine and Surgery Service for allowing use of their patient data for completion of this study.

Disclosures

The authors have nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.

Funding

The authors have nothing to disclose.

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