A 4-year-old 3.2-kg (7-lb) spayed female mixed-breed rabbit (Oryctolagus cuniculus) was referred to a veterinary teaching hospital for evaluation because of a 3-year history of chronic sneezing and left-sided nasal discharge. Previous treatments prescribed by the referring veterinarian included tobramycin ophthalmic solution (1 drop, intranasally, q 12 h) for 2 years, enrofloxacin (10 mg/kg [4.5 mg/lb], PO, q 12 h) for 16 months, chloramphenicol (30 mg/kg [13.6 mg/lb], PO, q 12 h) for 7 months, and meloxicam (0.3 to 0.6 mg/kg [0.14 to 0.27 mg/lb], PO, q 12 h) intermittently for 2 years, with only partial improvement. A deep nasal culture performed 7 months prior to the referral examination tested positive for Bordetella bronchiseptica that was susceptible to chloramphenicol.
On physical examination, the rabbit had white dried discharge at the entry of the left nares and on the left antebrachium (attributed to frequent sneezing) as well as a left-sided head tilt. Results of a CBC were compared with expected values derived from a database” of hematologic values for 43 to 83 healthy rabbits, and no abnormalities were identified. Results of plasma biochemical analysis were within the respective reference ranges. The rabbit was sedated with butorphanolb (1.3 mg/kg [0.59 mg/lb], IM) and midazolamc (1 mg/kg [0.45 mg/lb], IM) for IV catheter placement, and anesthesia was induced with isofluraned (1.25% in oxygen) via facemask. Results of a CT scan of the skull were consistent with left-sided atrophic rhinitis and maxillary sinusitis with fluid accumulation and irregular mineralization in the dorsal and ventral recesses of the left maxillary sinus and osteolysis of the rostral part of the left maxillary bone (Figure 1). No abnormalities of the dentition or tympanic bullae were detected. On the basis of these findings, a left-sided pararhinotomy and middle meatal antrostomy of the left maxillary sinus were recommended.
Selected CT images of the head of a 4-year-old rabbit that was evaluated because of a 3-year history of chronic sneezing and unilateral (left-sided) nasal discharge. A—In the sagittal plane image, notice the fluid lines and soft tissue-attenuating material in the dorsal (white asterisk) and ventral (black asterisk) maxillary recesses. B—In the transverse-plane image obtained at the level of the mid-diastema, notice the presence of osteolysis of the left maxillary bone (white arrow) and the mineral-attenuating material inside the maxillary sinus (black arrow), in addition to the soft tissue-attenuating material in the dorsal (white asterisk) and ventral (black asterisk) maxillary recesses.
Citation: Journal of the American Veterinary Medical Association 254, 11; 10.2460/javma.254.11.1316
Selected CT images of the head of a 4-year-old rabbit that was evaluated because of a 3-year history of chronic sneezing and unilateral (left-sided) nasal discharge. A—In the sagittal plane image, notice the fluid lines and soft tissue-attenuating material in the dorsal (white asterisk) and ventral (black asterisk) maxillary recesses. B—In the transverse-plane image obtained at the level of the mid-diastema, notice the presence of osteolysis of the left maxillary bone (white arrow) and the mineral-attenuating material inside the maxillary sinus (black arrow), in addition to the soft tissue-attenuating material in the dorsal (white asterisk) and ventral (black asterisk) maxillary recesses.
Citation: Journal of the American Veterinary Medical Association 254, 11; 10.2460/javma.254.11.1316
Selected CT images of the head of a 4-year-old rabbit that was evaluated because of a 3-year history of chronic sneezing and unilateral (left-sided) nasal discharge. A—In the sagittal plane image, notice the fluid lines and soft tissue-attenuating material in the dorsal (white asterisk) and ventral (black asterisk) maxillary recesses. B—In the transverse-plane image obtained at the level of the mid-diastema, notice the presence of osteolysis of the left maxillary bone (white arrow) and the mineral-attenuating material inside the maxillary sinus (black arrow), in addition to the soft tissue-attenuating material in the dorsal (white asterisk) and ventral (black asterisk) maxillary recesses.
Citation: Journal of the American Veterinary Medical Association 254, 11; 10.2460/javma.254.11.1316
Two weeks after the CT examination, the rabbit was premedicated with midazolam (1 mg/kg, IM), oxymorphonee (0.1 mg/kg [0.05 mg/lb], IM), and glycopyrrolatef (0.01 mg/kg [0.005 mg/lb], IM). After oxygen delivery by facemask, anesthesia was induced with ketamineg (5 mg/kg [2.3 mg/lb], IV) and midazolam (0.5 mg/kg [0.23 mg/lb], IV), and the rabbit was intubated with a 3-mm uncuffed endotracheal tubeh after topical lidocainei instillation (2 mg/kg [0.91 mg/lb]) over the arytenoids. Anesthesia was maintained with isoflurane (1% to 3%) in oxygen (1 L/min). Fentanyl citratej (loading dose of 5 μg/kg, IV, followed by an IV infusion of 30 to 60 μg/kg/h [13.6 to 27.3 μg/kg/h]) was provided to reduce the minimum alveolar concentration of isoflurane, and lactated Ringer solutionk (10 mL/kg/h, IV) was administered. The rabbit was placed in right lateral recumbency, and the left maxillary region was aseptically prepared for surgery. The relevant anatomy1 is shown (Figure 2). A 5-mm horizontal linear incision was performed over the facies cribrosa (Figure 3). The soft tissues were dissected away from the underlying bone with Metzenbaum scissors.
Anatomy of the left paranasal cavities in rabbits represented on left lateral (A) and oblique (left rostrodorsal-right caudoventral; B) views of a rabbit skull. Anatomic features represented include air-filled spaces of the nasal cavities (green), the dorsal conchal sinus (yellow), dorsal and ventral recesses of the maxillary sinus (dark blue and light blue, respectively), and the sphenoidal sinus (pink). A— The dashed circle corresponds to the surgical entry through the facies cribrosa into the dorsal and ventral recesses of the maxillary sinus. B—The dorsal and ventral recesses of the maxillary sinus connect through a large opening in their caudal halves (solid line), and the dorsal conchal sinus connects to the dorsal half of the dorsal recess of the maxillary sinus through a large opening, forming the conchomaxillary cavity. The conchomaxillary cavity opens into the middle nasal meatus through a slit-like opening, the maxillary sinus ostium, located in the maxillary sinus (dashed line). The sphenoidal sinus opens into the nasal cavities through its own opening (asterisk). The illustrations were created on the basis of information and images in Casteleyn C, Cornillie P, Hermens A, et al. Topography of the rabbit paranasal sinuses as a prerequisite to model human sinusitis. Rhinology 2010:48(3);300–304. Adapted with permission.
Citation: Journal of the American Veterinary Medical Association 254, 11; 10.2460/javma.254.11.1316
Anatomy of the left paranasal cavities in rabbits represented on left lateral (A) and oblique (left rostrodorsal-right caudoventral; B) views of a rabbit skull. Anatomic features represented include air-filled spaces of the nasal cavities (green), the dorsal conchal sinus (yellow), dorsal and ventral recesses of the maxillary sinus (dark blue and light blue, respectively), and the sphenoidal sinus (pink). A— The dashed circle corresponds to the surgical entry through the facies cribrosa into the dorsal and ventral recesses of the maxillary sinus. B—The dorsal and ventral recesses of the maxillary sinus connect through a large opening in their caudal halves (solid line), and the dorsal conchal sinus connects to the dorsal half of the dorsal recess of the maxillary sinus through a large opening, forming the conchomaxillary cavity. The conchomaxillary cavity opens into the middle nasal meatus through a slit-like opening, the maxillary sinus ostium, located in the maxillary sinus (dashed line). The sphenoidal sinus opens into the nasal cavities through its own opening (asterisk). The illustrations were created on the basis of information and images in Casteleyn C, Cornillie P, Hermens A, et al. Topography of the rabbit paranasal sinuses as a prerequisite to model human sinusitis. Rhinology 2010:48(3);300–304. Adapted with permission.
Citation: Journal of the American Veterinary Medical Association 254, 11; 10.2460/javma.254.11.1316
Anatomy of the left paranasal cavities in rabbits represented on left lateral (A) and oblique (left rostrodorsal-right caudoventral; B) views of a rabbit skull. Anatomic features represented include air-filled spaces of the nasal cavities (green), the dorsal conchal sinus (yellow), dorsal and ventral recesses of the maxillary sinus (dark blue and light blue, respectively), and the sphenoidal sinus (pink). A— The dashed circle corresponds to the surgical entry through the facies cribrosa into the dorsal and ventral recesses of the maxillary sinus. B—The dorsal and ventral recesses of the maxillary sinus connect through a large opening in their caudal halves (solid line), and the dorsal conchal sinus connects to the dorsal half of the dorsal recess of the maxillary sinus through a large opening, forming the conchomaxillary cavity. The conchomaxillary cavity opens into the middle nasal meatus through a slit-like opening, the maxillary sinus ostium, located in the maxillary sinus (dashed line). The sphenoidal sinus opens into the nasal cavities through its own opening (asterisk). The illustrations were created on the basis of information and images in Casteleyn C, Cornillie P, Hermens A, et al. Topography of the rabbit paranasal sinuses as a prerequisite to model human sinusitis. Rhinology 2010:48(3);300–304. Adapted with permission.
Citation: Journal of the American Veterinary Medical Association 254, 11; 10.2460/javma.254.11.1316
Intraoperative (A through E) and postoperative (F) photographs of the same rabbit as in Figure 1. Images were obtained at the time of the first surgery, performed with the rabbit in right lateral recumbency (nose to the left and the ears to the right for intraoperative images). A—A 5-mm skin incision was made horizontally over the facies cribrosa. B—Pararhinotomy through the facies cribrosa into the right maxillary sinus was performed with a curette, and the opening was widened with rongeurs. C—After suction and flushing of debris, a middle meatal antrostomy was performed with a 3-mm surgical elevator, and the opening was then expanded with Metzenbaum scissors in the anatomic location of the maxillary sinus ostium. D—Patency of the communication created between the maxillary recess and the nasal cavity was assured by temporarily passing a rubber tube through the surgical site to the naris. E—The surgical site was closed routinely in 2 layers. F—On the day after surgery, the incision site had minimal inflammation.
Citation: Journal of the American Veterinary Medical Association 254, 11; 10.2460/javma.254.11.1316
Intraoperative (A through E) and postoperative (F) photographs of the same rabbit as in Figure 1. Images were obtained at the time of the first surgery, performed with the rabbit in right lateral recumbency (nose to the left and the ears to the right for intraoperative images). A—A 5-mm skin incision was made horizontally over the facies cribrosa. B—Pararhinotomy through the facies cribrosa into the right maxillary sinus was performed with a curette, and the opening was widened with rongeurs. C—After suction and flushing of debris, a middle meatal antrostomy was performed with a 3-mm surgical elevator, and the opening was then expanded with Metzenbaum scissors in the anatomic location of the maxillary sinus ostium. D—Patency of the communication created between the maxillary recess and the nasal cavity was assured by temporarily passing a rubber tube through the surgical site to the naris. E—The surgical site was closed routinely in 2 layers. F—On the day after surgery, the incision site had minimal inflammation.
Citation: Journal of the American Veterinary Medical Association 254, 11; 10.2460/javma.254.11.1316
Intraoperative (A through E) and postoperative (F) photographs of the same rabbit as in Figure 1. Images were obtained at the time of the first surgery, performed with the rabbit in right lateral recumbency (nose to the left and the ears to the right for intraoperative images). A—A 5-mm skin incision was made horizontally over the facies cribrosa. B—Pararhinotomy through the facies cribrosa into the right maxillary sinus was performed with a curette, and the opening was widened with rongeurs. C—After suction and flushing of debris, a middle meatal antrostomy was performed with a 3-mm surgical elevator, and the opening was then expanded with Metzenbaum scissors in the anatomic location of the maxillary sinus ostium. D—Patency of the communication created between the maxillary recess and the nasal cavity was assured by temporarily passing a rubber tube through the surgical site to the naris. E—The surgical site was closed routinely in 2 layers. F—On the day after surgery, the incision site had minimal inflammation.
Citation: Journal of the American Veterinary Medical Association 254, 11; 10.2460/javma.254.11.1316
Hemostasis was achieved with electrocautery and pressure applied with cotton-tipped applicators. A curette was used to create an opening through the facies cribrosa into the dorsal recess of the maxillary sinus rostral to the left maxillary second molar tooth. The opening was then expanded to an 8-mm diameter with rongeurs. Caseous material was removed by suction and flushing, and material within the maxillary sinus was collected for microbial culture and antimicrobial susceptibility testing. Although the nasal mucosa appeared grossly healthy, the ostium of the conchomaxillary cavity into the nasal cavity could not be seen. A middle meatal antrostomy was performed with a 3-mm surgical elevator in the medial wall of the dorsal and ventral recesses of the maxillary sinus, in the reported anatomic area of the ostium in rabbits, to create a fenestration into the left middle nasal meatus. This opening was then expanded to 5 mm in diameter with Metzenbaum scissors. A 3F rubber tubel was passed from the surgical site into the nasal cavity to the level of the naris to ensure its patency and was removed. The subcutaneous tissue was closed in a simple interrupted pattern, and the skin was closed in an intradermal pattern with 4-0 monofilament suture.m The rabbit was administered flumazeniln (0.1 mg/kg, SC) to reverse benzodiazepine effects, and meloxicamo (0.5 mg/kg, SC) was administered during recovery. Culture of samples from the maxillary recess revealed B bronchiseptica, undetermined fastidious nonenteric bacteria, and Streptococcus viridans; the decision was made to continue with chloramphenicol treatment on the basis of susceptibility test results for the B bronchiseptica strain. Minimal inflammation of the surgical site was present after surgery, and no signs of dyspnea were observed. The rabbit was discharged from the hospital 2 days after surgery, and the owner was instructed to administer meloxicam (0.5 mg/kg, PO, q 12 h) for 7 days, chloramphenicolp (33 mg/kg [15 mg/lb], PO, q 12 h) for 1 month, and tramadolq (15 mg/kg [6.8 mg/lb], PO, q 12 h) for 5 days. On recheck examination 10 days later by the referring veterinarian, the rabbit had complete resolution of the nasal discharge and the left-sided head tilt, although persistent sneezing was still reported.
One and a half years after the surgery, the rabbit was evaluated for recurrence of upper respiratory signs over the previous few months with increased frequency and duration of sneezing. In the week prior to this examination, meloxicam (0.5 mg/kg, PO, q 12 h) and chloramphenicol (30 mg/kg, PO, q 12 h) were prescribed by the referring veterinarian but the clinical signs did not substantially improve. Physical examination revealed bilateral serous nasal discharge, dried secretions on both antebrachia, and a static left-sided head tilt. Results of a CBC revealed a moderately high heterophil-to-lymphocyte ratioa (2.4:1 [expected value, 1:1], 2,941 heterophils/μL [expected value, 919 to 3,970 heterophils/μL], and 1,248 lymphocytes/μL [expected value, 793 to 7,809 lymphocytes/μL]). Plasma biochemical analysis results were within the reference ranges. The rabbit was sedated as previously described, and a second CT scan was performed. The results were consistent with right-sided sinusitis with accumulation of soft tissue-attenuating material in the dorsal and ventral recesses of the right maxillary sinus as well as osteolysis of the right maxillary bone (Figure 4). Moderate bilateral destruction of the nasal turbinates was noted. The nasal septum was intact, and no aural or oral abnormalities were observed. Deep nasal swab samples were collected for aerobic and anaerobic culture; the results indicated a mixed growth of Staphylococcus spp, Micrococcus spp, and Bordetella spp, with the latter susceptible to chloramphenicol.
Results of a CT scan of the head of the same rabbit as in Figure 1, 1.5 years after left-sided pararhinotomy and middle meatal antrostomy of the left maxillary sinus was performed. The rabbit was evaluated for recurrence of signs of upper respiratory disease, including bilateral nasal discharge. A—In the sagittal plane image, there is soft tissue-attenuating material in the dorsal (white asterisk) and ventral (black asterisk) recesses of the maxillary sinus. B—In the transverse-plane image obtained at the level of the caudal part of the diastema just rostral to the maxillary first premolar tooth, notice the focal right-sided osteolysis (arrow) in addition the soft tissue-attenuating material in the dorsal (white asterisk) and ventral (black asterisk) recesses of the right maxillary sinus.
Citation: Journal of the American Veterinary Medical Association 254, 11; 10.2460/javma.254.11.1316
Results of a CT scan of the head of the same rabbit as in Figure 1, 1.5 years after left-sided pararhinotomy and middle meatal antrostomy of the left maxillary sinus was performed. The rabbit was evaluated for recurrence of signs of upper respiratory disease, including bilateral nasal discharge. A—In the sagittal plane image, there is soft tissue-attenuating material in the dorsal (white asterisk) and ventral (black asterisk) recesses of the maxillary sinus. B—In the transverse-plane image obtained at the level of the caudal part of the diastema just rostral to the maxillary first premolar tooth, notice the focal right-sided osteolysis (arrow) in addition the soft tissue-attenuating material in the dorsal (white asterisk) and ventral (black asterisk) recesses of the right maxillary sinus.
Citation: Journal of the American Veterinary Medical Association 254, 11; 10.2460/javma.254.11.1316
Results of a CT scan of the head of the same rabbit as in Figure 1, 1.5 years after left-sided pararhinotomy and middle meatal antrostomy of the left maxillary sinus was performed. The rabbit was evaluated for recurrence of signs of upper respiratory disease, including bilateral nasal discharge. A—In the sagittal plane image, there is soft tissue-attenuating material in the dorsal (white asterisk) and ventral (black asterisk) recesses of the maxillary sinus. B—In the transverse-plane image obtained at the level of the caudal part of the diastema just rostral to the maxillary first premolar tooth, notice the focal right-sided osteolysis (arrow) in addition the soft tissue-attenuating material in the dorsal (white asterisk) and ventral (black asterisk) recesses of the right maxillary sinus.
Citation: Journal of the American Veterinary Medical Association 254, 11; 10.2460/javma.254.11.1316
A pararhinotomy of the dorsal recess of the right maxillary sinus was performed through the facies cribrosa with a right middle meatal antrostomy of the dorsal and ventral recesses of the maxillary sinus according to the same protocol described for the left side. Resected tissues of the maxillary sinus wall were submitted for aerobic and anaerobic bacterial and fungal culture and susceptibility testing, which yielded growth of B bronchiseptica susceptible to chloramphenicol, S viridans, and fastidious nonenteric bacteria. The rabbit recovered uneventfully from surgery with minimal facial swelling and no signs of dyspnea and was discharged from the hospital 2 days later. The owner was instructed to administer meloxicam (0.5 mg/kg, PO, q 12 h) for 7 days, tramadol (15 mg/kg, PO, q 12 h) for 5 days, and chloramphenicol (50 mg/kg [22.7 mg/lb], PO, q 12 h) until reevaluation. Nutritional support was also recommended. On follow-up by telephone, the owner reported complete resolution of the rabbit's nasal discharge and a marked reduction in its frequency of sneezing 8 days after surgery.
One year after the second surgery and 2.5 years after the initial referral examination, the rabbit was evaluated a third time for progressively worsening sneezing over the previous 2 to 3 months. Chloramphenicol administration had been continued at the previous dosage since the second surgery, and treatment with meloxicam (0.5 mg/kg, PO, q 12 h) had been started by the referring veterinarian the week prior to the reevaluation. On physical examination, mild bilateral serous nasal discharge was noted, with referred upper airway sounds on pulmonary auscultation as well as a mild asymmetry between the regions of the left and right facies cribrosae on palpation. A CBC revealed a moderately high heterophil-to-lymphocyte ratioa (2.3:1; 3,223 heterophils/μL and 1,400 lymphocytes/μL). Results of serum biochemical analysis were within the reference ranges. The rabbit was sedated as previously described, and a third CT scan was performed; results were consistent with persistent bilateral chronic rhinitis and sinusitis and fairly static maxillary osteomyelitis with right- and left-sided nasal turbinate destruction compatible with the previous pararhinotomy (Figure 5). Soft tissue-attenuating material that likely represented inflammatory debris and mucus was observed caudal and rostral to the previous rhinotomy site. A deep nasal swab sample was collected for microbial culture and susceptibility testing. Growth of B bronchiseptica susceptible to chloramphenicol and enrofloxacin was reported. The owner elected to continue chloramphenicol treatment and additionally had the rabbit treated with acupuncture. Three weeks after this referral visit, decreased frequency of sneezing and decreased nasal discharge were reported. One year after the last examination and 4 years after the initial rhinotomy procedure, the rabbit was still being managed with the same treatment, with minimal persistent sneezing (several times per day) and intermittent mild clear nasal discharge reported.
Results of a CT scan of the head of the same rabbit as in Figure I at the time of reevaluation for recurrence of upper respiratory signs I year after undergoing right-sided pararhinotomy and middle meatal antrostomy of the right maxillary sinus. A—Sagittal plane image of the left nasal cavity. B—Sagittal plane image of the right nasal cavity. C—Transverse plane image obtained at the level of the mid-diastema. Notice the improvement (reduced amount of soft tissue-attenuating material) in the right and left maxillary sinuses, compared with that in the previous CT images. The findings indicated that clinical signs were not associated with recurrence of obstruction at the surgical sites.
Citation: Journal of the American Veterinary Medical Association 254, 11; 10.2460/javma.254.11.1316
Results of a CT scan of the head of the same rabbit as in Figure I at the time of reevaluation for recurrence of upper respiratory signs I year after undergoing right-sided pararhinotomy and middle meatal antrostomy of the right maxillary sinus. A—Sagittal plane image of the left nasal cavity. B—Sagittal plane image of the right nasal cavity. C—Transverse plane image obtained at the level of the mid-diastema. Notice the improvement (reduced amount of soft tissue-attenuating material) in the right and left maxillary sinuses, compared with that in the previous CT images. The findings indicated that clinical signs were not associated with recurrence of obstruction at the surgical sites.
Citation: Journal of the American Veterinary Medical Association 254, 11; 10.2460/javma.254.11.1316
Results of a CT scan of the head of the same rabbit as in Figure I at the time of reevaluation for recurrence of upper respiratory signs I year after undergoing right-sided pararhinotomy and middle meatal antrostomy of the right maxillary sinus. A—Sagittal plane image of the left nasal cavity. B—Sagittal plane image of the right nasal cavity. C—Transverse plane image obtained at the level of the mid-diastema. Notice the improvement (reduced amount of soft tissue-attenuating material) in the right and left maxillary sinuses, compared with that in the previous CT images. The findings indicated that clinical signs were not associated with recurrence of obstruction at the surgical sites.
Citation: Journal of the American Veterinary Medical Association 254, 11; 10.2460/javma.254.11.1316
Discussion
Upper respiratory disease, especially chronic rhinitis, is common in companion rabbits and can become a life-threatening disease in this obligate nasal-breathing species.2 Rabbits are commonly used for research on human sinusitis because of the local anatomic similarities between the 2 species.3 The paranasal cavities of rabbits are paired and comprise a dorsal conchal sinus, a large maxillary sinus with a dorsal recess and ventral recess, and a sphenoidal sinus, and the anatomy has been described in detail elsewhere.1 However, some authors do not consider that rabbits have sinuses and refer only to the recesses.2 The maxillary sinuses are the largest paranasal cavities, each extending from the area of the facies cribrosa of the maxilla up to the rostral orbital edge.1 The dorsal recess of each maxillary sinus has an ovoid shape and is located lateral to the middle nasal meatus and ventral to the dorsal conchal sinus.1 The ventral recess of the maxillary sinus has a similar shape and is located ventral and somewhat medial to the dorsal recess, with its ventral edge against the alveolar bulla of the maxillary premolar teeth1; it also extends more caudally than the dorsal recess.1 The dorsal and ventral recesses connect to each other through a large opening in their caudal halves, and the rostral halves are crossed by the nasolacrimal duct.1 The maxillary and dorsal conchal sinuses are connected to each other by a very large opening located in the rostral half of the dorsal recess of the maxillary sinus, and these 2 structures form the conchomaxillary cavity.1 The conchomaxillary cavity opens into the middle nasal meatus through the slit-like maxillary sinus ostium, which is located in the area of the dorsal recess of the maxillary sinus.1 The ostium maintains similar pressures between the nasal cavities, and it allows ventilation of the conchomaxillary cavity and clearance through mucociliary transport, with cilia oriented toward the opening.4
Occlusion of the maxillary sinus ostium is 1 key factor in the multifactorial etiopathogenesis of maxillary sinusitis.4–6 In an experimental study, ostial obstruction and injection of virulent strains of Streptococcus pneumoniae resulted in bacterial sinusitis, whereas neither procedure alone resulted in the condition.5 Sinuses with occluded ostia initially developed positive pressure, followed by a negative pressure, compared with findings for the other nasal cavities.4 Changes in pressure may reduce mucociliary function, facilitate adherence of bacteria to the sinus mucosa, and allow development of transudates and serous secretions that might provide suitable medium for excessive growth of bacteria from the normal flora.4 Inadequate ventilation is also an important contributing factor to the development of bacterial sinusitis, and reduced oxygen tension following obstruction of the maxillary sinus ostium is suspected to facilitate the growth of facultative anaerobes.4,7 Reduced mucociliary transport in the sinus may also decrease the clearance of pathogens associated with sinusitis.4,7
Specific characteristics of some pathogens, such as the formation of bacterial biofilm by Pseudomonas aeruginosa, can contribute to the development of sinusitis in rabbits.8,9 Chronic sinusitis can be associated with advanced dental disease, traumatic injuries, neoplasia, or foreign bodies.3 Tympanic bullae are indirectly connected to the nasal cavities through the nasopharyngeal meatus and the eustachian tubes; therefore, chronic sinusitis and rhinitis can develop secondary to otitis media.10 In this case, the etiology of the bilateral sinusitis was unknown.
Diagnostic imaging modalities for evaluation of sinusitis or rhinitis in rabbits include radiography, rhinoscopy, CT, and MRI.2,10 The use of CT or MRI is considered ideal for diagnosis of pathological upper respiratory system conditions and for planning of possible surgical approaches.2,3,10 In an experimental study,11 bacterial sinusitis was induced in rabbits by reversible bilateral ostial occlusion of the maxillary sinuses, followed 5 days later by inoculation of the sinuses with Staphylococcus aureus. Images obtained by CT and MRI were independently evaluated by 2 experienced reviewers to monitor the resolution of bacterial sinusitis after reversal of the occlusion.11 The CT imaging was found to have greater interobserver consistency and was more time- and cost-effective than MRI.11 Poorer agreement between reviewers in scoring sinus opacification by MRI, compared with CT, was attributed to difficulty in defining bone anatomy and maxillary sinus detail by use of MRI.11 However, in similar experimental settings, other authors observed that CT findings did not reflect acute changes in the sinus mucosa during the early stage of experimentally induced bacterial sinusitis in rabbits, as there was no correlation between the histopathologic and CT findings 10 days after local inoculation with bacteria.12 This suggested that results should be evaluated cautiously when CT is used for assessment of acute sinusitis in rabbits. Rhinoscopy allows direct visual examination of the nasal cavities and concurrent collection of biopsy samples.13 Examination by this modality is limited to the ventral and middle meatuses and adjacent turbinates through the natural nasal openings.13 However, rhinoscopy can be used during pararhinotomy for visual examination of the structures of the affected maxillary sinus14 and possibly the maxillary sinus ostium. For the rabbit of the present report, CT was chosen because image acquisition is completed more rapidly than with MRI, which allowed the use of deep sedation rather than anesthesia. The method also allowed for appropriate surgical planning for this patient.
Culture of a deep nasal sample for aerobic and anaerobic bacteria and susceptibility testing of isolates are recommended in the management of chronic sinusitis or rhinitis in rabbits.3,10 In rabbits with experimentally induced S pneumoniae sinusitis, no bacteria were detected during histologic examination of mucosa stained with acridine orange15; therefore, samples obtained during rhinotomy or pararhinotomy should not be limited to the mucosa of the nasal structures. Results of another experimental study16 revealed that after 2 weeks, the initially inoculated S pneumoniae were replaced by nonfermentative gram-negative flora and anaerobic bacteria. This highlights the need to submit samples for both aerobic and anaerobic bacterial cultures. In an epidemiological study17 of 121 rabbits with nasal discharge and sneezing, the bacteria most commonly isolated by aerobic nasal culture of the nares were Pasteurella multocida (54.8%), B bronchiseptica (52.2%), Pseudomonas spp, (27.9%), and Staphylococcus spp (17.4%). Mixed infections were frequent, and the most frequently noted combination was P multocida and B bronchiseptica, similar to the findings in a previous study.18 Culture of samples from the rabbit of the present report repeatedly isolated B bronchiseptica; this organism is thought to be a common inhabitant of the rabbit respiratory tract and may or may not induce disease on experimental inoculation.10 The pathogenicities of the B bronchiseptica strains isolated over time from our patient were unknown. Staphylococcus spp, Streptococcus viridans, Micrococcus spp, and undetermined fastidious nonenteric bacteria were also isolated and are usually thought to be secondary invaders isolated from the nares.10
Treatment of chronic rhinitis in rabbits is often challenging and associated with frequent recurrence.3 Systemic antimicrobial treatment alone is often insufficient to resolve purulent rhinitis when a moderate to large amount of the discharge is present.2,3 In a study19 of New Zealand white rabbits with induced bacterial sinusitis and reversible ostial obstruction, the resolution of signs compatible with sinusitis by CT examination was more dependent on relief of ostial obstruction than on antimicrobial treatment. A surgical approach in association with appropriate antimicrobial administration is indicated to remove caseous material and reestablish the patency of the paranasal cavity openings.2,3 The compounding of medications in the United States is subject to state and federal regulations. The chloramphenicol for the patient of this report was prepared by a licensed pharmacist in a state-licensed pharmacy. Additional attention is required for treatment of animals that are considered food-producing species by the US FDA; treatment with certain antimicrobials, such as chloramphenicol, is prohibited in food-producing animals in the United States. The rabbit of this report was strictly a companion animal and was not destined to enter the food chain at any time.
Rhinotomy and pararhinotomy via a dorsal, lateral, or intraoral transpalatal approach have been reported for treatment of chronic purulent rhinitis in rabbits,2,3,10,20 dogs,21,22 and cats,22 and for debulking of odontomas or extraction of maxillary incisor teeth affected by odontoma in prairie dogs.23–25 A recent clinical report20 described an intraoral transpalatal approach for treatment of an odontogenic abscess obstructing the rostral nasopharynx in a rabbit. This technique was not used for the patient of the present report owing to the more dorsal and caudal location of the lesions and lack of dental involvement. The dorsal approach involves the perforation of nasal bones following deflection and reflection of associated periosteum.2,3,10 This technique allows treatment of both nasal cavities at the same time as well as creation of a larger surgical opening when extensive lesions are present in the nasal cavities.2,3,10 A lateral approach through the facies cribrosa was elected instead of a dorsal approach because it was considered a faster and less invasive technique that would result in better postoperative recovery and because the main lesions were unilateral at the time of the evaluation and were mainly located in the maxillary sinus.
In addition to staged bilateral pararhinotomies, this was, to the authors' knowledge, the first report of middle meatal antrostomy following pararhinotomy to restore ventilation of and clearance from the maxillary sinus in a companion rabbit with chronic sinusitis. Middle meatal antrostomy corresponds to a fenestration of the medial wall of the maxillary sinus into the middle nasal meatus and has been described for the treatment of nasal cysts in horses26,27 as well as in laboratory rabbits with experimentally induced bacterial sinusitis28–30 and in human patients with sinusitis.31–34 Failure to relieve any obstruction of the sinus ostium in people, with simultaneous creation of a middle medial antrostomy that does not include the natural ostium of the maxillary sinus, leads to recurrence of sinus disease.34 The reason for this is that the cilia of the sinus continue to beat toward the ostium in human patients, and this prevents appropriate clearance of the secretions through the obstructed natural ostium.33 In an investigation of rabbits with experimentally induced bacterial sinusitis and ostial obstruction that underwent creation of a nasoantral window, an ostioplasty with limited widening, or ostioplasty with a larger circumferential widening, limited widening of the natural ostium of the maxillary sinus was associated with the least inflammation and the greatest amount of mucociliary clearance, followed by circumferential ostial widening.30 However, in another study, no difference in morphological changes of the nasal cavities and mucociliary transport was observed in rabbits with experimentally induced sinusitis that underwent surgical removal of the sinus mucosa with or without ostial interference.35 In the rabbit of the present report, the maxillary sinus ostia were not seen, and a larger fenestration in the medial wall of the maxillary sinus was performed in the anatomic region of the ostium in each surgery. It was unknown whether the middle meatal antrostomies performed in this case included the maxillary sinus ostia; no recurrence of sinusitis in the left or right maxillary sinuses was noted on the last CT examination. The use of rhinoscopy during surgeries may have helped to identify the maxillary ostium and thus enabled performance of limited widening antrostomies, although the structures may be less visible in patients with chronic infection.
Postoperative care for our patient was uneventful, with fast recovery and minimal swelling on the face after each surgery. The rabbit continued to have occasional sneezing and mild serous nasal discharge, which was expected because of nasal turbinate destruction. Investigators of a study36 of rabbits with experimentally induced bacterial sinusitis and reversible ostial obstruction found that the ciliated epithelium of infected recesses regenerated 12 weeks after removal of the ostial obstruction but did not appear fully functional at that time. Possible long-term impaired ciliary transport could play a role in persistent upper respiratory signs in rabbits with chronic rhinitis, even after resolution of infection. Although it was not needed for the rabbit of this report, the technique described also permits percutaneous flushing of the maxillary recess to allow for better drainage and clearance of the maxillary sinus. The technique described in this report may not be indicated in patients with extensive caseous accumulation rostral to the maxillary sinus, but it is less invasive than dorsal rhinotomy.
Acknowledgments
Presented in part at the International Conference of Avian Herpetological and Exotic Mammal Medicine and Surgery, Venice, Italy, March 2017.
The authors declare that there were no conflicts of interest.
Footnotes
Database for healthy rabbits maintained in computerized files at the William M. Pritchard Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, Calif.
Torbugesic, Fort Dodge Animal Health, Fort Dodge, Iowa.
Midazolam hydrochloride injection, West-Ward Pharmaceuticals, Eatontown, NJ.
Isoflurane USP, Piramal Healthcare, Bethlehem, Pa.
Opana, Endo Pharmaceuticals Inc, Chadds Ford, Pa.
West-Ward Pharmaceuticals, Eatontown, NJ.
KetaVed, VedCo, St Joseph, Mo.
Mallinckrodt, St Louis, Mo.
Lidocaine 2%, VetOne, Boise, Idaho.
Hospira Inc, Lake Forest, Ill.
Baxter, Chicago, Ill.
Covidien, Mansfield, Mass.
Monocryl, Ethicon, Somerville, NJ.
Flumazenil Injection, West-Ward Pharmaceuticals, Eatontown, NJ.
Norbrook Laboratories, Newry, Northern Ireland.
Davis Compounding Solutions, Davis, Calif.
Amneal Pharmaceuticals, Hauppauge, NY.
References
1. Casteleyn C, Cornillie P, Hermens A, et al. Topography of the rabbit paranasal sinuses as a prerequisite to model human sinusitis. Rhinology 2010;48:300–304.
2. Capello V. Rhinostomy as surgical treatment of odontogenic rhinitis in three pet rabbits. J Exot Pet Med 2014;23:172–187.
3. Lennox AM. Rhinotomy and rhinostomy for surgical treatment of chronic rhinitis in two rabbits. J Exot Pet Med 2013;22:383–392.
4. Scharf KE, Lawson W, Shapiro JM, et al. Pressure measurements in the normal and occluded rabbit maxillary sinus. Laryngoscope 1995;105:570–574.
5. Johansson P, Kumlien J, Carlsöö B, et al. Experimental acute sinusitis in rabbits: a bacteriological and histological study. Acta Otolaryngol 1988;105:357–366.
6. Gnoy AR, Gannon PJ, Ganjian E, et al. A potential role for nasal obstruction in development of acute sinusitis: an infection study in rabbits. Am J Rhinol 1998;12:399–404.
7. Shin SH, Heo WW. Effects of unilateral naris closure on the nasal and maxillary sinus mucosa in rabbit. Auris Nasus Larynx 2005;32:139–143.
8. Fukami M, Norlander T, Stierna P, et al. Mucosal pathology of the nose and sinuses: a study in experimental maxillary sinusitis in rabbits induced by Streptococcus pneumoniae, Bacteroides fragilis, and Staphylococcus aureus. Am J Rhinol Allergy 1993;7:125–132.
9. Perloff JR, Palmer JN. Evidence of bacterial biofilms in a rabbit model of sinusitis. Am J Rhinol 2005;19:1–6.
10. Lennox AM. Respiratory disease and pasteurellosis. In: Quesenberry K, Carpenter J, eds. Ferrets, rabbits, and rodents: clinical medicine and surgery. 3rd ed. St Louis: Saunders, 2012;205–216.
11. Kerschner JE, Cruz MJ, Beste DJ, et al. Computed tomography vs. magnetic resonance imaging of acute bacterial sinusitis: a rabbit model. Am J Otolaryngol 2000;21:298–305.
12. Ozcan KM, Ozcan I, Selcuk A, et al. Comparison of histopathological and CT findings in experimental rabbit sinusitis. Indian J Otolaryngol Head Neck Surg 2011;63:56–59.
13. Divers SJ. Endoscopy equipment and instrumentation for use in exotic animal medicine. Vet Clin North Am Exot Anim Pract 2010;13:171–185.
14. Divers SJ. Exotic mammal diagnostic endoscopy and endosurgery. Vet Clin North Am Exot Anim Pract 2010;13:255–272.
15. Drettner B, Johansson P, Kumlien J. Experimental acute sinusitis in rabbit. A study of mucosal blood flow. Acta Otolaryngol 1987;103:432–434.
16. Westrin KM, Stierna P, Kumlien J, et al. Induction, course, and recovery of maxillary sinusitis: a bacteriological and histological study in rabbits. Am J Rhinol Allergy 1990;4:61–64.
17. Rougier S, Galland D, Boucher S, et al. Epidemiology and susceptibility of pathogenic bacteria responsible for upper respiratory tract infections in pet rabbits. Vet Microbiol 2006;115:192–198.
18. Deeb BJ, DiGiacomo RF, Bernard BL, et al. Pasteurella multocida and Bordetella bronchiseptica infections in rabbits. J Clin Microbiol 1990;28:70–75.
19. Beste DJ, Capper DT, Shaffer K, et al. Antimicrobial effect on rabbit sinusitis after temporary ostial occlusion. Am J Rhinol 1997;11:485–489.
20. Brown T, Beaufrère H, Brisson B, et al. Ventral rhinotomy in a pet rabbit (Oryctolagus cuniculus) with an odontogenic abscess and sub-obstructive rhinitis. Can Vet J 2016;57:873–878.
21. Weeden AM, Degner DA. Surgical approaches to the nasal cavity and sinuses. Vet Clin North Am Small Anim Pract 2016;46:719–733.
22. Fossum TW, Curtis C, Horn C. Surgery of the upper respiratory system. In: Fossum TW, Curtis C, Horn C, et al, eds. Small animal surgery. 4th ed. St Louis: Elsevier-Mosby, 2013;906–957.
23. Wagner R, Johnson D. Rhinotomy for treatment of odontoma in prairie dogs. Exot DVM 2001;3:29–34.
24. Capello V, Lennox AM. Small mammal dentistry. In: Quesenberry K, Carpenter JW, eds. Ferrets, rabbits and rodents: clinical medicine and surgery. St Louis: Elsevier, 2011;452–471.
25. Bulliot C, Mentré V. Original rhinostomy technique for the treatment of pseudo-odontoma in a prairie dog (Cynomys ludovicianus). J Exot Pet Med 2013;22:76–81.
26. Tremaine WH, Dixon PM. A long-term study of 277 cases of equine sinonasal disease. Part 2: treatments and results of treatments. Equine Vet J 2001;33:283–289.
27. Lane JG, Longstaffe JA, Gibbs C. Equine paranasal sinus cysts: a report of 15 cases. Equine Vet J 1987;19:537–544.
28. Forsgren K, Westrin KM, Fukami M, et al. Effects of surgery on mucosal pathologic changes following experimental sinusitis in rabbit. Ann Otol Rhinol Laryngol 1998;107:155–163.
29. Benninger MS, Kaczor J, Stone C, et al. Natural ostiotomy vs. inferior antrostomy in the management of sinusitis: an animal model. Otolaryngol Head Neck Surg 1993;109:1034–1042.
30. Hassab MH, Kennedy DW. Maxillary sinus ostioplasty versus nasal-antral window in maxillary sinusitis: an experimental study. Am J Rhinol Allergy 1996;10:357–363.
31. Lund VJ. Fundamental considerations of the design and function of intranasal antrostomies. Rhinology 1985;23:231–236.
32. Davis WE, Templer JW, Lamear WR, et al. Middle meatus anstrostomy: patency rates and risk factors. Otolaryngol Head Neck Surg 1991;104:467–472.
33. King E. A clinical study of the functioning of the maxillary sinus mucosa. Ann Otol Rhinol Laryngol 1935;44:480–482.
34. Parsons DS, Stivers FE, Talbot AR. The missed ostium sequence and the surgical approach to revision functional endoscopic sinus surgery. Otolaryngol Clin North Am 1996;29:169–183.
35. Min YG, Kim IT, Park SH. Mucociliary activity and ultrastructural abnormalities of regenerated sinus mucosa in rabbits. Laryngoscope 1994;104:1482–1486.
36. Kim YM, Lee CH, Won TB, et al. Functional recovery of rabbit maxillary sinus mucosa in two different experimental injury models. Laryngoscope 2008;118:541–545.
