**1. Introduction**

The sinonasal organ plays an important role in the human respiratory system, as this organ consistently encounters external irritants and is therefore one of the most frequently inflamed sites in the human body [1]. Inflammation may begin as an infectious process (acute rhinosinusitis), and, if the symptoms persist without resolution, it can lead to inflammatory consequences (chronic rhinosinusitis (CRS)) [2]. CRS is one of the most prevalent chronic diseases in modern society and is defined as the presence of more than one nasal symptom (mucopurulent drainage, nasal congestion, facial pain-pressure-fullness, and decreased sense of smell) and a documentation of inflammation for more than 12 weeks [3]. It is a heterogeneous, multifactorial disease with multiple distinct factors, including genetic, infectious, immune, anatomic, allergic, and inflammatory components [2]. The goal of CRS therapy is maximal medical treatment including oral and topical antibiotics, nasal steroids, systemic steroids, antihistamines, and saline irrigations. Functional endoscopic sinus surgery (FESS) is indicated if medical therapy fails [4].

The safety and efficacy of FESS for CRS have been strongly supported by meta-analyses from both large outcome studies and cohort studies. Improvement in both disease-specific and generic quality of life and objective measures have been demonstrated for the efficacy of FESS; however, across long-term follow-up, there is a 10–20% revision rate, which is considered to be refractory CRS [5]. Refractory CRS is defined by failure to stabilize after surgery and treatment with antibiotics, saline rinses, and topical steroid and has become a significant issue for ENT surgeons [6]. Predicting surgical outcome is crucial for evaluating the severity of CRS preoperatively, and the severity of CRS is usually defined by several factors. Temporally, the duration and frequency of symptoms and signs of CRS patients

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*Rhinosinusitis*

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cannot be precisely correlated. Spatially, the Lund-Mackay (L-M) score, which is based on CT images, is the most frequently used method to evaluate the severity of CRS; nevertheless, the L-M score represents only a snapshot of the condition [7]. A swift change in mucosal swelling is frequently observed during the subacute stage of sinusitis. Other parameters should be considered in order to define the severity of CRS and more accurately predict its prognosis.

Various factors are related to refractory CRS, including mucociliary dysfunction, the presence of mucosal biofilm, peripheral eosinophil count, mucosal eosinophilia, acute postoperative infection, ASA triad, cystic fibrosis, osteitis, hyperreactive airway, inhaled allergen, and experience of the performing surgeon [8–12]. It is important to find a simple way to evaluate the severity of CRS in order to identify an accurate prognosis for patients and determine which patients may need longterm medical treatment. The aim of the study was to determine the clinical features related to the severity of CRS that would necessitate revision surgery, by carefully eliminating surgeon bias using standardizing surgical procedures.
