INTRODUCTION: Chronic rhinosinusitis (CRS) is one of the most widespread chronic diseases affecting about 10% of the world population. It is an inflammatory disease which affects the paranasal sinuses (ethmoid, sphenoidal, maxillary and frontal) and the nasal cavity. The anatomy, physiology and pathophysiology of this area is very complex and encompasses various osseous, cartilaginous, nervous and vascular structures. The general loss of human productivity due to CRS and absenteeism from work or school represent a major economic factor on a global scale. The direct cost of treating chronic rhinosinusitis is well documented, and in the United States of America, for example, the cost amounts to around $12.8 billion annually. Patients with CRS are not at risk of mortality due to their disease, but their quality of life is significantly impaired. Rhinosinusitis in adults is defined according to EPOS 2012 guidelines (European Position Paper on Rhinosinusitis and Nasal Polyps) as an inflammation of the nose and the paranasal sinuses characterized by at least two or more specific symptoms. One symptom must be either nasal obstruction or nasal discharge, while the other two are facial pain and/or reduced sense of smell. In order to confirm the diagnosis, endoscopic signs (nasal polyps, oedema, mucopurulent discharge) and/or CT changes in the nose and paranasal sinuses should be visible. According to its duration, rhinosinusitis is classified as acute and chronic rhinosinusitis. If the disease lasts for up to 12 weeks, it is called acute, whereas if it lasts for longer than 3 months, it is regarded as chronic. The aetiology of CRS can be odontogenic or non-odontogenic. Chronic non-odontogenic rhinosinusitis (CnORS) is caused by allergies, biofilm formation, anatomical variations, ciliary disfunction and others. Chronic odontogenic rhinosinusitis (CORS) is caused by pathological processes of the teeth and the surrounding tissue including oroantral fistulas, periapical processes, maxillary cysts, foreign bodies in paranasal sinuses, and complications after tooth extraction. The diagnostic criteria for CORS are the same as for CnORS, however, CORS must have a clear odontogenic cause in addition to all the criteria. Approximately 10% of all CRS have odontogenic origins. The incidence of CORS is increasing worldwide, mostly due to the neglect of dental health of those who cannot afford dental treatments. A part of the increase can be attributed to the increased number of procedures in complex reconstructive dentistry, i.e. procedures such as dental implant surgery and bone grafting. Despite its frequency, CORS is disproportionately underrepresented in the literature and there are still many questions regarding exact incidence, onset, diagnosis, differential diagnosis and treatment of the disease. CRS symptoms can be assessed by using subjective questionnaires. The most common questionnaire is the Sino-Nasal Outcome Test (SNOT-22). SNOT-22 has been widely adopted in clinical practice due to its simplicity, encompassing 22 symptoms reflecting health burden for patients with rhinologic disorders. Each item quantifies symptoms severity from 0 (no problem) to 5 (the worst symptom). The sum of all items amounts to the maximum score of 110. High score indicates poor outcome. The SNOT-22 is a validated questionnaire with disease specific and quality of life related measures of the sinonasal function. It demonstrates good reliability, validity, and responsiveness. The visual analogue scale (VAS) symptom score is also a psychometric instrument widely used in the field of rhinology to subjectively quantify a patient’s symptom severity. It consists of 16 symptoms. Although there are a variety of radiological tests available, computerised tomography (CT) is accepted as the gold standard for the anatomical pathology evaluation of paranasal sinus diseases including CRS. The Lund-Mackay score (LMS) was developed to evaluate the severity of the paranasal sinus disease. LMS is a widely used method for the radiologic staging of chronic rhinosinusitis and involves scoring six bilateral areas from 0 to 2, for a possible range of scores between 0 and 24. AIM: To compare the differences between the intensity of the symptoms and the disease severity observed on CT scans in patients with CnORS and CORS, and to correlate the symptoms with the CT scan findings. METHODS: The research was conducted from October 2019 to May 2020 at the Clinic of Otorhinolaryngology and Head and Neck Surgery of University Medical Centre Sestre Milosrdnice, the Clinical Department of Diagnostic and Interventional Radiology of University Medical Centre Sestre Milosrdnice and the Department of Oral Surgery of Univesity Hospital Dubrava. The study included 64 adult patients, 32 with CnORS in the first group and 32 patients with CnORS in the second group. Patient data were collected according to the principle of matching pairs between the two groups, according to age (+/- five years) and gender. The diagnosis of CRS was made according to the diagnostic criteria of the EPOS 2012 guidelines. Since the finding of inflammatory changes on a CT scan was mandatory for the patient to be included in the study, the endoscopy finding was not necessary for the diagnosis of CRS and was used to visually exclude the presence of nasal polyps. CT scan was performed as a diagnostic or preoperative procedure carried out by an otorhinolaryngology specialist, after which the patient gave informed consent and was subsequently included in the study. The patient then completed two health-related quality of life questionnaires, SNOT-22 and VAS. VAS included additional questions regarding the presence of asthma, acetylsalicylic acid (ASA) intolerance, allergic rhinitis, smoking, previous sinus surgery, nasal corticosteroid use, as well as antihistaminic and antibiotic use. The CT scan was reviewed and scored (according to the LMS) exclusively by a radiology specialist - a neuroradiology subspecialist. Patients were assigned to a certain group only after they had undergone a detailed clinical examination by an otorhinolaryngologist and an oral surgeon, and after the CT scan had been evaluated by a radiologist. For the disease to be declared odontogenic, the CT findings had to show pathology related to the teeth of the upper jaw or the surrounding structures, which necessarily implies the involvement of the Schneiderian membrane. The following patients were excluded from the participation in the study: patients under the age of eighteen, patients with nasal and sinus polyposis, patients with a previous sinus injury or a sinus tumour process, pregnant women, and patients with cystic fibrosis, granulomatosis with polyangiitis and primary ciliary dyskinesia. Patients with a nasal septum deviation angle greater than 10 degrees diagnosed by an imaging test and patients whose CT scan was of poor quality (e.g. artifacts) were also excluded from the study. The case-control matching procedure between the two groups (CnORS and CORS) was used to randomly match patients according to gender and age (+/−five years). The normality of data distribution for continuous data has been checked with Kolmogorov-Smirnov's test and due to the test results an appropriate non-parametric data analysis has been used in the following analyses. Fisher's exact test has been used to assess differences in categorical clinical variables between the investigated groups. The Mann-Whitney U test was used for differences in quantitative clinical variables (specific VAS symptoms, SNOT-22, and LMS) between the study groups. Spearman’s Rho correlation coefficients were calculated to compare the association between the individual VAS and SNOT-22 symptoms with the LMS for the individual study groups. All P values below 0.05 were considered significant. RESULTS: Patients with CORS and CnORS matched by age and gender in this study did not show a statistically significant difference in any of the following: acetylsalicylic acid intolerance, allergic rhinitis, smoking, previous sinus surgery, use of nasal corticosteroids, antihistamines and antibiotics. The most common cause of CORS is the first molar disease, and the most common cause of odontogenic pathology is the periapical process. A statistically significant difference in individual symptoms was observed. CORS patients had a statistically significant higher self-reported values of thick nasal discharge, halitosis and temperature compared to CnORS patients. There was no statistically significant difference in other symptoms or in the overall SNOT-22 score. Furthermore, no statistically significant difference was found when the LMS was compared. A positive correlation between the LMS and thick nasal secretion and frustration levels was present in the CORS patients. The CnORS group showed a positive correlation between the runny nose, the loss of smell/taste and the LMSs. The overall SNOT-22 score did not show a correlation with the LMS in either of the two groups. CONCLUSION: Thick nasal secretion, halitosis and fever are more intense in patients with CORS, which is valuable information for the everyday clinical practice. The LMS is not statistically significantly different between the two groups and is not a good predictor of a chronic odontogenic disease. Individual symptoms show a positive correlation between the LMS in both groups, specifically between runny nose and loss of smell/taste in the CnORS group, and thick nasal secretions and frustration levels in the CORS group.