Acute sinusitis in the rabbit: a new rhinogenic model

Host-microbe interactions in chronic rhinosinusitis biofilms and models for investigation

Chronic rhinosinusitis (CRS) is a debilitating condition characterized by long-lasting inflammation of the paranasal sinuses. It affects a significant portion of the population, causing a considerable burden on individuals and healthcare systems. The pathogenesis of CRS is multifactorial, with bacterial infections playing a crucial role in CRS development and persistence. In recent years, the presence of biofilms has emerged as a key contributor to the chronicity of sinusitis, further complicating treatment and exacerbating symptoms. This review aims to explore the role of biofilms in CRS, focusing on the involvement of the bacterial species Staphylococcus aureus and Pseudomonas aeruginosa, their interactions in chronic infections, and model systems for studying biofilms in CRS. These species serve as an example of how microbial interplay can influence disease progression and exemplify the need for continued investigation and innovation in CRS research.

Efficacy of Low-Level Laser Therapy in a Rabbit Model of Rhinosinusitis

Little is known about alternative treatment options for rhinosinusitis (RS). We aimed to evaluate the efficacy of low-level laser therapy (LLLT) for RS in experimentally induced rabbit models of RS. A total of 18 rabbits were divided into four groups: a negative control group (n = 3), an RS group without treatment (n = 5, positive control group), an RS group with natural recovery (n = 5, natural recovery group), and an RS group with laser irradiation (n = 5, laser-treated group). Computed tomography and histopathological staining were performed for each group. mRNA and protein expression levels of local cytokines (IFN-γ, IL-17, and IL-5) were also measured. Tissue inflammation revealed a significant improvement in the laser-treated group compared with the RS and natural recovery groups (p < 0.01). In addition, sinus opacification in the CT scans and cytokine expression was reduced in the laser-treated group, though without statistical significance. LLLT could be an effective option for the management of RS concerning radiological, histological, and molecular parameters.

Unilateral Intervention in the Sinuses of Rabbits Induces Bilateral Inflammatory and Microbial Changes

Background

Chronic rhinosinusitis (CRS) is a globally prevalent inflammatory condition of the paranasal sinuses which severely impairs patients' quality of life. An animal model of unilateral sinusitis by transient sinus occlusion has been described previously in rabbits. The aim of this study was to characterise the sinusitis rabbit model by investigating temporal and bilateral changes in the bacterial community and mucosal inflammation.

Methods

Development of sinusitis was achieved by endoscopically placing Merocel ^® , a sterile nasal packing material, in the left middle meatus of six New Zealand white rabbits for four weeks. After a total period of 14 weeks, rabbits were assessed for sinusitis by endoscopic examination, magnetic resonance imaging (MRI) and histology. Swabs from the left and right middle meatus were obtained for bacterial community analysis at three time points (week 0, week 4, week 14) during the study.

Results

Endoscopic evaluation showed unilateral inflammation in all animals examined after the 4-week blocking period and at week 14. Notably, inflammatory changes were also seen in the contralateral sinus of all animals at week 4. MRI images demonstrated unilateral sinus opacification at week 4 in two rabbits, and partial unilateral sinus opacification at week 14 in one rabbit only. Histological analyses revealed substantial spatial heterogeneity of mucosal inflammation with inconsistent findings across all animals. No significant differences in mucosal inflammatory markers (such as goblet cell hyperplasia, epithelial denudation and oedema) could be identified between nostrils at week 14. The bacterial community in the rabbit sinuses was heavily dominated by Helicobacter at week 0 (baseline). At the end of the blocking period (week 4), bacterial alpha and beta diversity were significantly increased in both nostrils. The bacterial community composition at week 14 had primarily returned to baseline, reflecting the endoscopic and radiological results.

Conclusion

This study reaffirmed the ability for development of sinusitis without inoculation of any pathogens in a rabbit model. We were able to demonstrate bilateral sinonasal mucosal inflammation, by inducing unilateral sinus blockage, which resulted in significant changes to the sinonasal bacterial community. These findings may explain some of the clinical observations seen in CRS and warrant further research to reveal potential implications for its therapeutic management.

Paranasal Sinus Mucosal Regeneration: The Effect of Topical Retinoic Acid

Background

Paranasal sinus mucosa may suffer morphological and functional alterations as a result of surgical trauma. Mucosal stripping typically yields regenerated mucosa characterized by fibrosis, inflammatory infiltrate, and dysmorphic or absent cilia. The aim of this study was to determine the effect of topical retinoic acid (vitamin A) on regeneration of paranasal sinus mucosa.

Methods

Both maxillary sinuses of 12 New Zealand white rabbits were surgically opened and stripped of mucosa. Six rabbits received 0.01% topical retinoic acid gel treatment to the stripped left maxillary sinus (low concentration group). The remaining six rabbits received 0.025% topical retinoic acid gel to the stripped left maxillary sinus (high concentration group). The stripped right maxillary sinus of all 12 rabbits served as the operated, untreated control to reflect the normal healing process. Six other animals served as unoperated controls. The sinus mucosa was examined by light microscopy after 14 days.

Results

Untreated regenerated mucosa showed expected changes of submucosal gland loss, basal lamina and lamina propria fibrosis, cellular atypia, and loss of cilia. Topical retinoic acid treatment appeared to result in better mucosal regeneration marked by less cellular atypia and fibrosis. Although the regenerated mucosa was still grossly abnormal, the degree of ciliary loss and cellular derangement was reduced. The lower-concentration retinoic acid group had more favorable morphology than the higher-concentration retinoic acid group, and both were improved when compared with no treatment.

Conclusions

In a rabbit model, topical vitamin A in the form of retinoic acid gel appears to enhance regeneration of ciliated paranasal sinus mucosa. This preliminary study suggests that topical retinoids may have applicability in promoting sinus wound healing.

Models for the study of nasal and sinus physiology in health and disease: A review of the literature

Objective

Chronic sinusitis is a very common yet poorly understood medical condition with significant morbidity. Hence, it remains an entity that is difficult to treat with unsatisfactory outcomes of current management options. This necessitates research into the etiology and pathophysiology of the condition to enhance our knowledge and the therapeutic options. Unfortunately, this kind of research is not always feasible on human subjects due to practical and ethical limitations. Therefore, an alternative model that simulates the disease had to be found in order to overcome these limitations. These models could either be in vivo or in vitro. The aim of our review is to summarize the research findings and key discoveries of both in vivo and in vitro models of chronic sinusitis that have enhanced our understanding of the condition today and have paved the way for the future research of tomorrow.

Data Sources: PubMed literature review.

Methods

A review of the literature was conducted to identify the main successful in vivo and in vitro models for chronic sinusitis.

Results

Creating a successful model for chronic sinusitis is no easy task. Over the years, both in vivo animal models and in vitro tissue culture models were proposed, with each model having its accolades and pitfalls, with the ideal model remaining elusive to this day. However, advancing three‐dimensional cell culturing techniques seems to be a promising new way to find a more accurate model.

Conclusion

None of the current models is perfect for a thorough study of chronic sinusitis. However, three‐dimensional cell cultures have the potential to bridge the gap between in vivo and in vitro studies.

Level of Evidence

NA

Effect of a combination of mometasone furoate, levofloxacin, and retinyl palmitate with an in situ gel-forming nasal delivery system on nasal mucosa damage repair in an experimental rabbit model

BACKGROUND

In this study a combination of Mometasone Furoate (MF)+Levofloxacin hemihydrate (LH)+Retinyl palmitate (RP) with an in situ gel-forming delivery system was evaluated at different stages of nasal mucosal damage repair in a rabbit maxillary sinus model.

METHODS

In this study, 28 rabbits were included and assigned randomly to four groups. In all rabbits, a standard ostium was opened in the medial wall of the maxillary sinus by using a drill. Two different subsequently prepared gels with an in situ gel-forming delivery system were used. Of these 14 nasal cavities, combination 1 (active combination) was applied daily to 5, combination 2 (placebo) to 5, while 4 did not receive any pharmaceutical treatment. The diameter of the ostium was measured. Histopathological assessment was performed.

RESULTS

After 2, 3 and 4 weeks, the ostium diameter was significantly wider in the group where gel 1 had been applied compared to both the placebo group and control group. In the group treated with gel 1, after 2, 3 and 4 weeks the presence of superficial cilia was significantly greater, surface epithelium significantly less. In the 4th week, histologic scores for fibroblastic proliferation and vascular proliferation in the group treated with gel 1 were better than in either the control group or the placebo group. With gel 1, chronic inflammation parameters were also significantly lower than in the other groups.

CONCLUSION

The MF+LH+RP mixture with an in situ gel-forming nasal delivery system applied for wound healing after FESS prevents the formation of stenosis and is favorable for proper wound healing.

Experimental maxillary sinus augmentation using a highly bioactive glass ceramic

Physicochemical characteristics of a biomaterial directly influence its biological behavior and fate. However, anatomical and physiological particularities of the recipient site also seem to contribute with this process. The present study aimed to evaluate bone healing of maxillary sinus augmentation using a novel bioactive glass ceramic in comparison with a bovine hydroxyapatite. Bilateral sinus augmentation was performed in adult male rabbits, divided into 4 groups according to the biomaterial used: BO-particulate bovine HA Bio-Oss(®) (BO), BO+G-particulate bovine HA + particulate autogenous bone graft (G), BS-particulate glass ceramic (180-212 μm) Biosilicate(®) (BS), and BS+G-particulate glass ceramic + G. After 45 and 90 days, animals were euthanized and the specimens prepared to be analyzed under light and polarized microscopy, immunohistochemistry, scanning electron microscopy (SEM), and micro-computed tomography (μCT). Results revealed different degradation pattern between both biomaterials, despite the association with bone graft. BS caused a more intense chronic inflammation with foreign body reaction, which led to a difficulty in bone formation. Besides this evidence, SEM and μCT confirmed direct contact between newly formed bone and biomaterial, along with osteopontin and osteocalcin immunolabeling. Bone matrix mineralization was late in BS group but became similar to BO at day 90. These results clearly indicate that further studies about Biosilicate(®) are necessary to identify the factors that resulted in an unfavorable healing response when used in maxillary sinus augmentation.

Osteitis and mucosal inflammation in a rabbit model of sinusitis

INTRODUCTION

Several experimental studies have shown osteitis after the onset of sinusitis, supporting the idea that bone involvement could participate in the dissemination and perpetuation of this inflammatory disease. However, procedures commonly performed for the induction of sinusitis, such as antrostomies, can trigger sinusitis by themselves.

OBJECTIVE

To evaluate osteitis in an animal model of sinusitis that does not violate the sinus directly and verify whether this is limited to the induction side, or if it affects the contralateral side.

METHODS

Experimental study in which sinusitis was produced by inserting an obstructing sponge into the nasal cavity of 20 rabbits. After defined intervals, the animals were euthanized and maxillary sinus samples were removed for semi-quantitative histological analysis of mucosa and bone.

RESULTS

Signs of bone and mucosal inflammation were observed, affecting both the induction and contralateral sides. Statistical analysis showed correlation between the intensity of osteitis on both sides, but not between mucosal and bone inflammation on the same side, supporting the theory that inflammation can spread through bone structures, regardless of mucosal inflammation.

CONCLUSION

This study demonstrated that in an animal model of sinusitis that does not disturb the sinus directly osteitis occurs in the affected sinus and that it also affects the contralateral side.

An experimental model of chronic rhinosinusitis in rabbits without bacterial inoculation

PURPOSE

Evaluate and compare two different experimental techniques of maxillary sinus ostium occlusion using N-butyl cyanoacrylate in developing chronic histological findings without the inoculation of pathogenic bacteria among rabbits.

METHODS

In a randomized study, sixteen New Zealand rabbits were assigned for occlusion of the right maxillary sinus through a transmaxillary approach or through the roof of the nasal cavity. The contralateral sinus served as a control. After 12 weeks, the animals were sacrificed for blinded histopathological analysis of the maxillary sinus mucosa.

RESULTS

Histopathological changes consistent with CRS were found in eight (100%) of the maxillary sinuses approached transmaxillary and three of those through the roof of the nasal cavity (37.5%), p 0.008 and 0.250, respectively, comparing with the control side. Chronic mucosal changes were significantly better induced using the transmaxillary approach (p 0.026).

CONCLUSION

It is possible to induce a model of chronic sinusitis among rabbits with transmaxillary sinus occlusion without bacterial inoculation. This model can be replicated for future cellular studies.

Review of experimental models: sinusitis in rabbits

Introduction

In order to better understand the pathophysiology of rhinosinusitis, several attempts have been made to create the disease in an animal model. Among the studied rodents each has its advantages and disadvantages. Rabbits are considered more appropriate for studies that require surgical manipulation or invasive procedures.

Objectives

To evaluate the most viable experimental model of rhinosinusitis in rabbits to be adopted in future studies.

Methods

An electronic search for studies with experimental models of rhinosinusitis in rabbits published in English and Portuguese between July of 1967 and January of 2013 was conducted in Medline, Pub Med, Cochrane, and CAPES databases, using the keywords “sinusitis”, “rabbits”, and “polyps”.

Results

A total of 256 studies were retrieved, but in accordance with the inclusion and exclusion criteria, only ten studies were selected. Many different methods of response assessment were used in these studies.

Conclusion

To date, there is no ideal experimental model for induction of acute or chronic rhinosinusitis in rabbits, but the rhinogenic model appears to be the most viable option for the continuity of studies of the disease.

Comparison of Histopathological and CT Findings in Experimental Rabbit Sinusitis

The aim of this study was to investigate and compare histopathological and computerized tomographic (CT) findings of experimental acute sinusitis in an animal model. The noses of five healthy rabbits were inoculated with a gelatin sponge impregnated with a solution containing Staphylococcus aureus, and one healthy rabbit acted as the control. The animals were sacrificed on the tenth day, following the acquisition of paranasal CT scans. Specimens were obtained from the lateral nasal walls, and the ethmoid and maxillary sinuses of the animals for histopathological examination. Histopathological and CT findings were compared. Various degrees of epithelial disorganization, foci of ruptured epithelial cells, and inflammatory cell infiltration in the lamina propria were seen in the histopathological examinations of the five study rabbits, and mucosal thickening and soft tissue density were noted in their CTs. There was no correlation between the histopathological and CT findings. It was shown that CT did not reflect the acute changes in the sinus mucosa. Patients with chronic sinusitis must be evaluated for a chronic process. Computerized tomographic scans should not be obtained in acute sinusitis cases. In this way, both unnecessary radiation exposure and economic waste can be avoided.

Laser-induced microbial reduction in acute bacterial rhinosinusitis

BACKGROUND

This study was designed to assess laser-induced manipulation on bacterial load and host in an animal model of acute bacterial rhinosinusitis (ABRS). An animal study using 12 rabbits followed an elaborated efficient in vitro model. ABRS was created by packing the nose with a sponge soaked in solution containing pathogenic microorganisms. Eight infected animals were randomly allocated to two separate groups, each being exposed to different laser therapies. Two healthy animals served as treatment controls, and one animal without ABRS and treatment was observed.

METHODS

ABRS was confirmed histologically, radiologically, and bacteriologically. Two days after bacterial inoculation, packing was removed and nasal passages were treated by laser irradiation. Two laser modalities were tested. A near infrared (NIR) 940-nm diode laser with diffuser fiber tip was used in four rabbits. A photosensitizer (methylene blue 0.01 or 0.05%) and 635-nm laser combination was used in the second cohort. Nasal cultures were obtained before and after the laser treatments. Animals were killed 5-10 days after laser treatment and bacteriological/histological results were analyzed.

RESULTS

An average 2 log reduction in bacterial colony counts was achieved with both laser methods compared with control. Histological studies showed tissue integrity preservation without significant damage to nasal mucosa.

CONCLUSION

Significant bacterial reduction was achieved with both NIR laser and photograph activated therapies in an animal study of ABRS. This pilot study shows an innovative method of bacterial killing without host tissue damaging and may have potential future clinical application.

Developing a rabbit model of rhinogenic chronic rhinosinusitis

OBJECTIVE

The purpose of this study was to develop a rabbit model of rhinogenic chronic rhinosinusitis (CRS).

METHODS

New Zealand white rabbits were used and divided into two groups. In group A rabbits, a piece of Merocel (Medtronic-Xomed, Jacksonville, FL) was inserted into one nasal cavity and the other was left undisturbed as control. In group B rabbits, 1 microg phorbol 12-myristate 13-acetate (PMA) was injected into bilateral nasal lateral walls and then a piece of Merocel (Medtronic-Xomed) was inserted into one nasal cavity. At week 2, the Merocel (Medtronic-Xomed) was removed, and computed tomography (CT), nasoendoscopy, and cultures were performed. All examinations were repeated at week 12. Rabbits that had purulent discharge in nasal cavities and sinuses opacification shown in CT scans were diagnosed as having rhinosinusitis. Rabbits with CRS were randomly allocated to receive intravenous ceftriaxone (50 mg/kg/day) for 28 days or nothing. All rabbits with CRS received CT scans, nasoendoscopy, and cultures at week 16.

RESULTS

At week 12, CRS had developed in two controlled nasal cavities, six nasal cavities inserted with Merocel (Medtronic-Xomed), six nasal cavities injected with phorbol 12-myristate 13-acetate (PMA), and seven both PMA-injected and Merocel- (Medtronic-Xomed) inserted nasal cavities. Seven of nine treated CRS sides were clear of opacification after treatment. All non-treated CRS sides had persistent diseases at week 16. There was a significant difference in the CRS incidence (P = .00043) and culture rates (P = .027) between treated and non-treated CRS nasal cavities.

CONCLUSIONS

Our study developed a rabbit model of rhinogenic CRS. This model is easily performed and is reversible by treatment.

Comparative study of several sinusitis experimental modelling techniques in rabbits

Experimental models for clinical studies of rhinosinusitis are needed. Aim: to define a reliable, solid and reproducible experimental model for inflammatory rhinosinusitis with no innoculation of infectious agents in rabbits. Study design: Experimental. Material and Method: Twenty 20 rabbits were divided into 4 groups submitted to 4 different interventions: the placement of a unilateral nasal fossa sponge, unilateral obliteration of the nasal ostium with cyanoacrylate, unilateral placement of antigens in the maxillary cavity and unilateral placement of blood in the maxillary cavity. The animals were monitored for 15 days and then anesthetized and sacrificed; the maxillary sinuses were evaluated histologicaly and results were compared with controls and between the intervention groups. Conclusion: Sponje and glue as agents of meatal obstruction and toxoid aplied in the antrum are efficient as methods for rhinosinusitis modeling. Blood was not efficient in producing sinusitis.

Animal models of sinusitis: relevance to human disease

Experimental animal models are necessary to assess the efficacy of both medical and surgical procedures. The researcher who wishes to confirm and publish his results must overcome controversies concerning the validity of his model and, therefore, needs guidelines for standardization. Various models are offered in the literature. In this article, the rabbit and murine models of experimental sinusitis and their relevance to human disease with anatomical, histopathologic, and microbiologic aspects are discussed.

Chondroitin Sulfate Hydrogel and Wound Healing in Rabbit Maxillary Sinus Mucosa

OBJECTIVES/HYPOTHESIS

Chondroitin sulfate (CS) is a glycosaminoglycan in the extracellular matrix of all vertebrates. A biocompatible, nonimmunogenic, pliable hydrogel preparation of CS has recently been produced and has shown benefit in wound healing in murine and porcine epidermis. The objective of the current experiment is to compare the wound healing properties of CS hydrogel versus no treatment in wounds of the maxillary sinus mucosa.

STUDY DESIGN

Prospective investigation in an animal model.

METHODS

A 6 mm wound was created in bilateral maxillary sinuses of 17 New Zealand white rabbits. CS hydrogel (case) and no dressing (control) were randomly assigned to one side each as wound treatment. Wounds were examined ex vivo at 2, 4, 6, 10, and 14 day postinjury intervals. Wound diameter was measured microscopically by a blinded investigator. Representative specimens were examined histologically.

RESULTS

The CS disc was partially integrated into the wounds at the 4-day interval and completely integrated by the 6-day interval. The average wound diameters for the case versus control side were similar at 2 days (3.75 mm vs. 4.42 mm) but differed significantly at 4 days (2.86 mm. vs. 3.80 mm., P =.035). At 6 days, the wounds could not be discerned on either the case or control sides. However, histologic analysis revealed accelerated healing with the CS treatment. The treated wounds displayed respiratory epithelium as opposed to the squamous epithelium exhibited on the untreated sides.

CONCLUSIONS

Despite some limitations, the New Zealand white rabbit is an effective model for the study of sinonasal wound healing. CS hydrogel accelerates wound healing in sinonasal mucosa at a 4-day endpoint. We propose that the CS hydrogel acts as a surrogate extracellular matrix, serving as a repository for cytokines and growth factors produced by the regenerating mucosa. It may also provide a structural framework for fibroblasts and epithelial regeneration. Further study is necessary to establish this relationship.

Experimental sinusitis in a rhinogenic model

OBJECTIVES/HYPOTHESIS

The objectives were to determine the optimal sinusitis induction period and to examine microbiological and histopathological changes of sinusitis recovery stage in a rhinogenic sinusitis model.

METHODS

A synthetic sponge was inserted into the right-side nasal cavities of rabbits. The sponge was impregnated with a Streptococcus pneumoniae strain in group 1 and with sterile saline solution in groups 2 and 3. After the fourth day of sponge insertion, sinuses were examined by coronal computed tomography scans at two-day intervals until any radiological evidence of sinusitis was observed. When sinusitis was detected radiologically, five rabbits each from groups 1 and 2 were killed for histological examination. To determine the recovery period of sinusitis, sponges were removed from the rest of the rabbits in groups 1 and 2. Rabbits were selected randomly and killed on the 15th and the 30th days of the recovery period, immediately after radiological examinations. Group 3 was considered a sham group.

RESULTS

Sinusitis induction was performed in all rabbits in groups 1 and 2 until the 8th day. After the sponges were removed, inflammation persisted until the 30th day of the study.

CONCLUSION

In a rhinogenic sinusitis model, although histological features of sinusitis were demonstrated, further studies are required to standardize this model and to examine whether or not the studied bacterial strain spreads from nasal cavity into sinus.

Pathology of the Olfactory Mucosa: Implications for the Treatment of Olfactory Dysfunction

OBJECTIVE

The pathology of the olfactory mucosa is poorly understood; however, most cases of hyposmia and anosmia appear to be associated with a decline in the number of functioning mature olfactory sensory neurons (OSNs). Under normal conditions, OSNs undergo apoptotic cell death at a baseline rate likely secondary to their exposed location in the nose. Regeneration of mature OSNs from precursors in the epithelium allows the animal to maintain an adequate number of neurons necessary for olfactory sensation. In many cases of olfactory dysfunction, this balance is apparently disturbed, with a net loss of OSNs. The current study will examine normal and diseased olfactory tissue for the presence of data demonstrating that the preferred mechanism of OSN cell death is apoptotic in both health and disease. The potential therapeutic implications will be discussed.

STUDY DESIGN

Histologic analysis of human and animal olfactory tissue.

METHODS

Normal and diseased human and animal olfactory mucosa were assessed for immunohistochemical evidence of apoptosis.

RESULTS

Increased activity of the apoptotic effector enzyme caspase-3 was demonstrated in diseased olfactory mucosa in comparison with normal controls.

CONCLUSION

These results indicate that a common pathway may mediate OSN cell death from a diverse set of pathologic insults including aging, trauma, and sinusitis. Interference with this pathway of cell death is currently the subject of intense pharmacotherapeutic research for the management of stroke and meningitis. These drugs may ultimately prove useful in the treatment of clinical olfactory dysfunction.

Association of bronchopneumonia with sinusitis due to Bordetella bronchiseptica in an experimental rabbit model

An animal model for rhinogenic sinusitis was developed in rabbits naturally colonized with Bordetella bronchiseptica. It was found that ostial occlusion predisposes the sinus to invasion with this opportunistic bacterium and subsequent sinusitis as a result of reduced local host defense. In addition to the inflammatory lesions in the sinus, bronchitis and pneumonia were found in 84% of the experimental rabbits, suggesting that ostial dysfunction can also contribute to infectious disease of the lower respiratory tract. In such a model it is possible to study the significance of asymptomatic carriage of potential pathogens after ostial occlusion.

Acute sinusitis in the rabbit model: histologic analysis

OBJECTIVES

Characterize the histology of the rhinogenic model of sinusitis and compare this with existing models of sinusitis.

STUDY DESIGN

Prospective controlled trial in animals.

METHODS

New Zealand white rabbits were implanted with a synthetic sponge, which was then impregnated with Streptococcus pneumoniae bacteria. After a specified time the animals were sacrificed, and whole-mount sectioning of both the infected and noninfected sinuses was performed. The sinuses were carefully examined for evidence of inflammatory changes.

RESULTS

This model produced a sinus infection that is characterized by luminal exudates of neutrophils and eosinophils, mucosal infiltration with lymphocytes and plasma cells, and epithelial degeneration. In addition, discrete lymphoid follicles were identified in both the implanted and nonimplanted sides that in the implanted sides appear to hypertrophy and liberate leukocytes into the sinus lumen. Other areas were observed where luminal exudates seem to act on and degrade mucosa that has little or no underlying inflammation. In severely infected sinuses submucosal vacuole formation with overlying granulation tissue was observed.

CONCLUSIONS

The rhinogenic model of sinusitis demonstrates features typical of other known models of sinusitis. In addition, there appear to be unique features of this model, specifically the identification of discrete lymphoid aggregates, which suggest that this model has the potential to be valuable for the study of the immune response of the sinuses.