Why do we have paranasal sinuses?

Introduction: The paranasal sinuses, comprising the frontal, maxillary, ethmoid and sphenoid sinuses, have caused consternation and debate over their true function over the course of nearly two millennia. This review aims to define the current evidence for the role of the paranasal sinuses, and to attempt to propose an answer to the question 'why do we have paranasal sinuses?' Materials and methods: A literature review was conducted, searching Medline (1966-2007), Embase (1988-2007), the Cochrane Library and Ovid (1966-2007). Combinations of the following search terms were used: 'paranasal sinuses', 'physiology', 'anatomy', 'function', 'evolution' and 'rhinology'. Any relevant references were cascaded to increase detection of pertinent information. The current, tenable theories identified in the literature review are discussed and the evidence for them critically analysed. Results: The current, tenable theories are described. Discussion: The paranasal sinuses may act simply to improve nasal function; certainly, it has been demonstrated that they may act as an adjunct in the production of nitric oxide and in aiding the immune defences of the nasal cavity. However, there is a distinction between utility and evolutionary origin. It may still be that the sinuses arose as an aid to facial growth and architecture, or persist as residual remnants of an evolutionary structure with an as yet unknown purpose, and in doing so have found an additional role as an adjunct to the nasal cavity.