The Effect of Intra-sinus Application of Betamethasone Dipropionate Nasal Cream on Patients with Chronic Rhinosinusitis Post Functional Endoscopic Sinus Surgery (FESS)

Inclusion Criteria: * Adult patients with a clinically confirmed diagnosis of CRS by an otolaryngologist (ENT) undergoing maximal medical therapy as part of their standard of care. * Having undergone functional endoscopic sinus surgery (FESS) at least 6 months prior to enrolment. * For each nostril, an endoscopic nasal polyp score of 0, 1, or 2 out of a maximum score of - (where 0= No polyps, 1= small polyps in the middle meatus not reaching below the inferior border of the middle turbinate , 2= nasal polyps reaching below the border of the middle turbinate, 3= large nasal polyps reaching the lower border of the inferior turbinate or nasal polyps medial to the middle turbinate, 4= large nasal polyps causing almost complete obstruction of the inferior nasal cavity) (Gevaert et al, 2023). * Visible middle turbinates and access to the ethmoid sinuses for dosing as established via endoscopic examination. * Participants must have a \> 2 on the disease severity visual analogue scale (VAS) at screening and pre-treatment. * Body weight: A minimum body weight \>=40 kilograms (kg) and a BMI of ≤ 39 at the screening visit. * Individuals of childbearing potential must use adequate birth control methods and not plan to get pregnant during the study. * Informed consent: Willingness to give written informed consent and willingness to participate in and comply with the study. * Age ≥18 but \<80 years. Exclusion Criteria: * Subjects with known hypersensitivity or contraindications to betamethasone dipropionate, mometasone, or topical anaesthesia. * Subjects with sino-nasal abnormalities, disease, or implanted devices that prevents the application of the therapy. * Previous enrolment in this study. * Subjects currently receiving systemic corticosteroid or have received systemic corticosteroid in the prior 4 weeks or receiving biologic therapy. * Subjects with a history of glaucoma or cataracts or have an abnormal intraocular pressure (IOP) at screening or pre-treatment (abnormal IOP is defined as greater than 21 mm Hg). * Subjects with acute sinusitis. * Subjects with known immunodeficiency. * Subjects with diabetes (Type 1). * Subjects with cystic fibrosis. * Pregnant subjects or subjects trying to get pregnant or currently lactating as the effect on human pregnancy is unknown. * Subjects who are unable to give an informed consent because of mental illness, dementia or communication difficulties. * Subjects with a Cushing's disease diagnosis within the previous 12 months. * Severe septal deviation and or previous total resection of the middle turbinate. * Any lab abnormality or underlying medical condition which, in the Investigator's opinion, should exclude the participant. * Subjects who are unlikely to comply with study procedures, restrictions and requirements as determined by the investigator.