To the best of our knowledge, this is the first systematic review assessing long-term sinonasal outcomes after ESS focusing exclusively on CRSwNP. However, conducting a meta-analysis was not feasible due to the heterogeneity of the published data.

This review contributes to evaluating ESS’s role in the treatment of CRSwNP, especially considering the introduction of new therapies as mab. ESS is a safe and effective procedure [1, 6, 11, 12] however, in the coming years, its specific role in the CRSwNP treatment algorithm needs to be determined. High-quality data is very important in order to compare treatment options, short- and long-term outcomes. For example, while extended surgery seems to yield better short-term results, its long-term efficacy is less conclusive [16, 27]. Further studies are needed to clarify this specific aspect.

This review highlights the extreme need for a collective effort to obtain new high-quality long-term data. Despite CRSwNP being a highly prevalent disease and ESS being widely performed, only seven studies could be included in this review. Among them, no statistical comparisons or common analyses could be performed due to the heterogeneity in assessing the different outcomes. This also highlights the lack and urgent need to define common methods for determining outcomes. This review has been focused on different outcomes that are summarized and discussed, main findings show that SNOT-22 emerges as an easy, adequate, and efficient tool to assess outcomes, regarding olfaction the use of validated tests is recommended to evaluate treatment results and QoL. NPS should be reported before and after any treatment during follow-up, Gevaert et al. [28] publication provides guidance in this matter. The concept of recurrence should be replaced by control of disease, using specific criteria and methodology to allow comparison of results. Revision surgery in long-term follow-up was 27%. Lastly patient clustering and cofounding factors can arise in the follow-up of CRSwNP. Factors as asthma and N-ERD play a role in disease prognosis. Others as atopy, extent of surgery, presence of previous surgery and IL-5 need to be clarified and are of interest in future research.

Nasal Symptoms and QoL

Surprisingly, regardless of the outstanding importance of nasal symptoms and QoL for the otorhinolaryngologist, only 4 studies assessed these variables [16, 21, 23, 26]. Nasal symptoms are reported using numerous PROMs, making comparisons difficult. Among the different PROMs, SNOT-22 stands out as the most spread and validated. It is an outstanding tool to assess nasal symptoms and QoL associated to nasal conditions [29, 30]. Correct interpretation of SNOT-22 should be comprehensive, variables as gender and some comorbidities can influence its result [16, 26, 31].

Standardizing its use, as suggested by EPOS 2020 and the POLINA 2.0, can facilitate comparisons and treatment decisions [1, 32]. We strongly suggest performing SNOT-22 in our daily practice to have data for future long-term studies.

Olfaction

When assessing independent symptoms, olfaction stands out as one of the most influencing symptoms on QoL. Therefore, it should be a primary outcome in any CRSwNP treatment. However, only three studies [16, 21, 23] (Arancibia, Calus, Zhang) reported olfaction data after long-term follow-up, while only one single study used a validated olfaction test (BAST-24 [33]). Their data is encouraging, as all the studies included report a positive and sustained effect on long-term olfaction [16, 21, 23,24,25,26]. We strongly support performing instrumental testing in the follow-up of CRSwNP patients.

Nasal Polyp Score

Despite the main objective when treating CRSwNP is symptom control, regardless of the nasal polyp size, it is still a remarkable outcome variable. Nasal polyp size has been assessed through various scales, with the most recent being the system introduced by Meltzer in 2006 and a similar system employed in multiple clinical trials [34,35,36,37,38,39,40,41,42,43]. Efforts to establish a standardized reference for endoscopic CRSwNP scoring have been published, facilitating cross comparisons [28]. In this review, only two authors [21, 23] (Arancibia and Calus) reported the Nasal Polyp Score (NPS), but limited preoperative data precludes in-depth analysis. It’s worth noting a recent meta-analysis found no significant association between NP scoring systems and PROMs like SNOT-22, Total Nasal Symptom Score (TNSS), nasal congestion scores, and objective olfaction measurements (SIT-40) [44]. However, no long-term analysis could be performed.

Recurrence After ESS: Definition of Controlled Disease

Recurrence after long-term follow-up has been described in six studies. However, yet, there is no common criteria of what should be defined as “recurrence”. In fact, in EPOS2020 [1], CRS control is defined as: “A disease state in which the patients do not have symptoms, or the symptoms do not adversely affect quality of life, if possible combined with a healthy or almost healthy mucosa and only need for local medication”. However, this definition, despite correct is too vague and does not allow for a clear definition of recurrence or disease control. This vagueness is reflected in this review, as all the authors used a different definition of recurrence.

In fact, the concept of “recurrence” may not be suitable for CRSwNP since the absence of nasal polyps after ESS doesn’t imply the cure of the underlying inflammatory condition. The terms “Controlled,” “Partly controlled,” and “Uncontrolled” could be more suitable to categorize patients [1, 32]. POLINA [32] defines control using VAS, SNOT-22, NPS, use of oral steroids and need for surgery. We strongly suggest future publications to use a clear methodology to define illness recurrence/control.

Revision Surgery

Revision surgery was reported in 4 studies included in this systematic review [16, 21, 23, 24]. Long-term revision surgery rate with pooled data was 27% out of 291 patients with CRSwNP. Revision surgery rate can be easily defined, and this data can be effortlessly compared to any other long-term CRSwNP treatment database. There has been a previous meta-analysis assessing this very topic reporting revision rates between 14 to 24% [45]. However, revision surgery in that meta-analysis was not focused on long-term, while it mixed long- and short-term results.

Patient Clustering and Confounding Factors

As with any other systematic review, the differences in the confounding factors may alter our ability to compare results from different studies. Here on, different potential confounding factors are discussed.

Type and Extent of Surgery

The first and most important confounding factor is the type of surgery. Variable definitions of surgical techniques in the literature emphasize the need for standardized terminology. This is highly relevant, as it has been shown that more extensive surgery is less prone to revision surgery [11]. The “radical surgery” concept [1] showing short- and mid-term benefits over FESS in reducing recurrence and improving symptoms and smell [16, 46,47,48,49,50]. There is an urgent need to define common terminology to define ESS. Nowadays there is the ACCESS project [51], to define whether a surgery was sufficient. Pending of publication is the LOEM classification [52], which aims at helping in accurate description of the surgery. We strongly suggest following studies to clearly define their surgeries to allow comparisons in the future.

Asthma

In long-term follow-up asthmatic patients exhibit poorer outcomes in CRSwNP, given by higher recurrence rates (symptomatic and endoscopic), increased need for medication, impaired smell, reduced QoL, increased disease burden, and elevated revision ESS rates [16, 21, 23,24,25,26, 45, 53,54,55,56]. While not all studies show statistical significance, Simmonds et al. notes a trend toward worse SNOT-22 scores [26]. Arancibia et al. highlighted significant worse results in loss of smell, symptoms, and a 100% recurrence rate at 12-year follow-up for the asthmatic group [23]. Vlaminck et al. reports significantly higher recurrence rates for asthmatics compared to non-asthmatics [24]. Smith et al. associated asthma with increased risk of 2nd and 3rd ESS (p < 0.001) [54]. Asthma may be considered a risk factor for recurrence and symptom control in CRSwNP patients treated with ESS.

Non-Steroidal Exacerbated Respiratory Disease (N-ERD)

It well known N-ERD patients exhibit elevated recurrence and revision surgery rates [55,56,57,58] as higher revision surgery in the frontal sinus [59]. Notably, Riva et al. identified a higher recurrence per year (p = 0.035), indicative of multiple recurrences [25]. Mendelsohn et al. detected earlier and increased recurrence (p < 0.001), higher secondary revision ESS (p < 0.001), and is a risk factor for nasal polyp recurrence (p < 0.01) and revision surgery (p < 0.01) [22]. Although further robust studies are essential for confirmation, N-ERD appears however as a long-term predictor of recurrence and disease burden.

Atopy (Allergen Sensitization)

Overall, the association between atopy and long-term outcomes after EES in CRSwNP is complex, with some studies suggesting a significant relationship. Skin Prick Test (SPT) or ImmunoCap do not allow to differentiate atopy (allergen sensitization) from allergic disease. In CRSwNP, interrogation for allergen related symptoms is difficult and was not specified by any of the studies. Simmonds et al. [26] links atopy better outcomes after surgery regarding SNOT-22. Vlaminck et al. [24] describes higher prevalence of atopy in recurrence group. Calus et al. [21] states allergen sensitization status as predictor for revision surgery (OR 6.1) with shorter time to ESS. Riva et al. [25] doesn’t find significant differences. Further research with comprehensive allergen testing, adequate clarification of allergic disease and larger sample sizes are needed to clarify these relationships and their impact on long-term surgical outcomes in CRSwNP.

Eosinophils

Blood eosinophil count (BEC), and other eosinophil derived measures (Eosinophil rich mucus, eosinophilic nasal cytology, Eosinophilic cationic protein) have been previously associated with extensive disease, revision surgery and recurrence [60, 49]. In long-term follow-up after ESS in CRSwNP, BEC has a moderate correlation to higher scores in PROM (T5SS) in the asthma subgroup at 12 years [23]. Recurrence rate was higher in patients with local eosinophilia and eosinophilic rich mucus(p < 0.001) [24]. In the long-term most authors did not assess nor analyze eosinophil derived outcomes. The role of eosinophils in predicting outcomes, particularly in asthmatic patients, appears noteworthy, but further research and a comprehensive analysis across various parameters are necessary for a more accurate understanding.

Interleukin 5

Concerning long-term outcomes following ESS in CRSwNP, Calus et al [21] revealed a significant association between high levels of IL-5 and patients with ESS history. Elevated IL-5 may be used as a modest predictor of revision ESS during the follow-up period (OR 1.004, 95% CI 1.001 to 1.008, P < 0.05). Although no significant association between IgE and revision ESS could be found. this finding shows a prognostic significance of IL-5 at long-term follow-up, offering insights into the potential use of mab as a preventive measure against the need for revision surgery in CRSwNP patients.

Previous ESS

Previous ESS predicts revision surgery and worse outcomes in CRSwNP, shown by higher recurrence in those with prior ESS (p < 0.004) [23, 24], and a trend towards worse SNOT-22 outcomes [26]. Senior et al. [17] noted a trend for revision surgery in patients with prior procedures, contrasting with Hopkins et al. [11], stating