Introduction
The study of disease has progressed from an era focused on phenotype, where all information was collected by the physician in collaboration with the patient, with or without the use of tools such as the stethoscope, endoscope, X-ray and Ct scanner. We have witnessed the incorporation of ever more sophisticated laboratory-based findings, collected via microscopy and instruments developed for biochemistry, molecular biology and immunochemistry. Information gleaned by these modern techniques can provide information on the underlying cellular and molecular mechanisms that define the endotype. The purpose of this review is to discuss the phenotypic and endotypic heterogeneity of chronic rhinosinusitis from the perspective of advancing the understanding of the pathogenesis and improvement of treatment approaches and outcomes.