Sinusitis By Marvin P Fried, MD, Montefiore Medical Center, The University Hospital of Albert Einstein College of Medicine Reviewed / Revised Dec 2021 | Modified Sep 2022 View Patient Education Etiology Pathophysiology Symptoms and Signs Diagnosis Treatment Key Points More Information Invasive Sinusitis in Immunocompromised Patients Topic Resources Pansinusitis Sinusitis Algorithm for use of antibiotics... Sinusitis is inflammation of the paranasal sinuses due to viral, bacterial, or fungal infections or allergic reactions.