The anatomical structure of frontal sinus and frontal recess is complex and variable, making difficult to visually expose the frontal sinus ostium and frontal sinus drainage channel, and becoming a more challenging area in endoscopic sinus surgery. In 2017, Comoglu et al. divided the development of frontal sinus into four types [
5]. In 2016, Wormald et al. proposed The International Frontal Sinus Anatomy Classification (IFAC) [
21]. This article provides a more precise and systematic nomenclature for the air cells around the frontal recess. The purpose of this study is to provide the imaging data of the development of the frontal sinus and the air cells around the frontal recess under the IFAC classification in normal Chinese adults, to propose a theoretical basis for the simulation of the flow through the frontal sinus after Draf surgery with different types of frontal sinuses. In 1991, Wolfgang Draf classified the endoscopic frontal sinus surgery into Draf1 (Remove the obstructive lesions below the frontal sinus ostium and remove the anterior ethmoid cells, mainly the agger nasi cells, which blocks the frontal sinus drainage channel. The operation does not involve the frontal sinus ostium), Draf2a (Based on draf I, the floor of the frontal sinus between the middle turbinate and the orbital cardboard and the ethmoid cells invading the frontal sinus were removed to locally enlarge the frontal sinus ostium and form a channel between the middle turbinate and the orbital cardboard. The root of the middle turbinate was not involved in the operation), Draf2b (Based on draf IIa, the root of the middle turbinate was excised inwardly so that the medial margin of the frontal sinus opening reached the nasal septum)and Draf3 (On the basis of bilateral draf II, the floor wall of the bilateral frontal sinus, the adjacent upper nasal septum, and the septum of the frontal sinus were excised, and bilateral penetrating drainage channels were established)according to the degree of frontal sinus lesions and the extent of surgical resection [
19]. This is currently the most widely used classification of the frontal sinus surgery worldwide, but going under continuous improvements. In 2013, Komser et al. proposed a new naming method such as Draf2c (On the basis of draf IIb, the middle frontal sinus septum and the upper nasal septum were removed), in order to minimize the surgical operation of Draf3 on non-diseased areas [
2]. In 2016, the International Classification of frontal sinus endoscopic surgery was further refined and divided into seven grades, although at present, Draf classification is the most commonly used in clinical practice [
15]. In recent years, computational fluid dynamics technology has been widely used in medicine. In our field of rhinology, it is mainly used to simulate the normal state, various pathological states, and the changes of nasal cavity and paranasal sinuses before and after surgery. At present, few studies are available on the distribution, pressure, nasal resistance, and velocity of the airflow in the frontal sinus after Draf surgery. Previous studies suggested that the airflow in the normal frontal sinus is very small and can be ignored, but the airflow into the frontal sinus after Draf surgery cannot be ignored. Li et al. found significant statistical differences in pressure and flow velocity between Draf III and the normal model, with the "frontal sinus T" structure as an important cause of edema after Draf III [
11]. In this study, computer fluid dynamics (CFD) was used to simulate Draf1–3 in patients with different development of frontal sinuses, and the airflow characteristics of the frontal sinus before and after Draf were compared to further explore the influence of Draf on the airflow in frontal sinuses with different development. This provide a certain reference in the design of preoperative surgical plan and the evaluation of postoperative complications. Saline nasal irrigation has been added into the guidelines as a routine treatment for patients with chronic rhinosinusitis after surgery. Early postoperative nasal irrigation can significantly prevent nasal crust and nasal adhesion, improving the course of that treatment that is at least four weeks. Saline irrigation can not only remove inflammatory factors from the nasal cavity and promote mucosal secretion of mucin, but also improve the ciliary clearance function and reduce mucosal congestion [
7]. However, few studies are available on the hydrodynamic changes brought by saline through the nasal cavity and paranasal sinuses before and after Draf surgery, especially the changes in the flow velocity, volume, and pressure of saline over time, and the changes in the fluid at different positions of the nasal cavity and paranasal sinuses. This study used CFD to simulate the process of saline irrigation before and after Draf, and the changes of transient water flow distribution in nasal cavity and paranasal sinuses were observed to provide a certain reference for the selection of the best position for nasal irrigation after frontal sinus surgery, the control of water volume and flow rate in the device used to product the nasal irrigation, and postoperative nasal drug delivery.