Fungal rhinosinusitis is an infectious and/or allergic disease caused by fungi in the sinus and nasal cavity. Due to the warm and humid climate in Guangxi Zhuang Autonomous Region, the incidence of fungal rhinosinusitis is higher than that in other provinces. However, its physiological mechanism is not yet clear. Not every patient colonized by fungi develops a fungal infection. To a large extent, the immune status of the patient determines the nature of fungal disease in the nasal passages. The pathologic process of progression from harmless fungal colonization to fungal rhinosinusitis is unclear and has not been reported.

We report two patients, one who developed fungal rhinosinusitis 1.5 years after surgery performed to treat an inverted papilloma, and the other with a history of hypertension and cerebral infarction. Both patients recovered from their surgeries. An average time of 2.5 years elapsed from the development of maxillary sinus cysts to the development of fungal rhinosinusitis.

According to these case reports, we speculate that the progression of fungal rhinosinusitis from harmless colonization to disease onset requires approximately one to three years and that the length of the process may be related to underlying diseases, surgical treatment, deficient autoimmune status, and abuse of hormone antibiotics and hormones. Additional data are needed to conduct relevant studies to appropriately prevent and treat fungal rhinosinusitis.

Fungal rhinosinusitis is a comprehensive term that includes primarily inflammatory diseases of the nasal cavity and/or sinus caused by fungal infections. Much controversy exists regarding the classification of fungal rhinosinusitis, but the most widely accepted classification roughly divides fungal rhinosinusitis into two groups according to the histopathological findings as follows: Invasive fungal rhinosinusitis and noninvasive fungal rhinosinusitis. Invasive fungal rhinosinusitis includes three categories: Acute invasive sinusitis, chronic invasive sinusitis, and granulomatous sinusitis. There are three different clinical manifestations of noninvasive fungi: Saprophytic fungal infection, fungal ball, and allergic fungal rhinosinusitis[1,2].

Fungi are ubiquitous, and spores are inhaled with every breath. Guangxi Zhuang Autonomous Region has a subtropical monsoon climate, and the weather is warm and humid, which is more conducive to fungal growth. The incidence of fungal rhinosinusitis in Guangxi is higher than that in other provinces. A statistical analysis of total chronic sinusitis (CRS) and fungal rhinosinusitis patients in our hospital from 2009 to 2018 indicated that 2518 patients with CRS were treated in 10 years, including 471 patients with fungal rhinosinusitis, accounting for 18.71% of CRS patients. In the past 10 years, the overall fungal rhinosinusitis trend in our hospital has increased each year (Figure 1). However, its pathogenesis and causes are still unclear. Anatomical disorders, environmental exposure, microbial toxicity, genetic background, and the immune status of infected hosts are considered to be potential causes[3]. Fungi are found in the nasal mucosa and paranasal sinuses of healthy people and CRS patients. Fungal infections do not occur in every colonized patient, and the immune status of patients largely determines the nature of fungal disease in the nasal cavity[4]. However, the pathophysiological mechanism of the transformation from harmless fungal colonization to fungal rhinosinusitis in patients is still unclear, and there are no relevant literature reports at present.

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Figure 1 Annual changes in the number of fungal rhinosinusitis patients from 2009 to 2018.

In our follow-up study of fungal rhinosinusitis patients at the First Affiliated Hospital of Guangxi Medical University, we found two patients with complete progression from harmless fungal colonization to fungal rhinosinusitis. In this paper, by studying the pathogenic progression of these two patients from harmless fungal colonization to fungal rhinosinusitis, we estimated the time required for the pathological transition in these patients and examined the cause of their nasal or sinus infections, which is important for the effective prevention and treatment of fungal rhinosinusitis in the future. Below are the case reports of the two patients.

The two cases were pathologically diagnosed as maxillary sinus aspergillosis.

Transnasal endoscopic maxillary sinus surgery was performed.

After the operation, hemostasis, fluid replacement, and anti-inflammatory treatment were routinely administered.

A fungal ball is the most common noninvasive fungal sinusitis finding; it is usually located on one side of the maxillary sinus and is more common in middle-aged and elderly women[5,6]. These patients are mainly characterized by runny and stuffy nose, dried blood in the nose, headaches, and facial pain. However, as host immune function deteriorates, the fungal ball may develop into an invasive form that erodes the sinus wall, causing facial pain or obstructing the sinus opening and causing secondary bacterial infection. Currently, the clinical diagnosis of fungal rhinosinusitis relies mainly on imaging examination. On CT, fungal rhinosinusitis is characterized by microcalcification in the diseased sinus. Surgery is the first choice for treatment of symptomatic fungal spherical sinusitis, which involves minimally invasive procedures and clearing of the field. Surgery can clear the lesions, remove the obstructive factors, reconstruct the normal anatomy, protect the sinus mucosa, and return the patient to normal physiological function[7,8]. Antifungal therapy is usually not required after complete excision of the fungal ball, but removal of the fungal ball for pathological diagnosis is a common procedure[9,10].

The first patient was found to have a mass during a physical examination in January 2016, and the tumor was surgically removed in February. In September 2017, the patient began to have headaches in the right frontal part of the head. In November, the patient visited again. A paranasal sinus CT scan showed a high-density shadow in the maxillary sinus (Figure 3), raising the possibility of maxillary sinus mycosis. The postoperative pathological diagnosis was right maxillary sinus aspergillosis. Approximately one and a half years were required for the patient to develop fungal rhinosinusitis, which may be related to the deficient immune status caused by the recurrence of the patient's inverted papilloma or to the bacterial changes caused by the invasiveness of the first surgical procedure.

The second patient underwent a physical examination in May 2016. A head CT scan showed a submucosal cyst in the right maxillary sinus. In May 2017, a CT scan of the maxillary sinus cavity showed that the cyst had disappeared. In May 2018, a head CT scan obtained during a physical examination showed new maxillary sinus inflammation. No treatment was administered for two years. In November 2018, the patient had repeated aspiration of blood sputum and was admitted to the hospital in February 2019. The postoperative pathology showed a large number of fungal colonies in the right maxillary sinus, which were PAS (+) and PASD (+) upon staining, and the diagnosis of aspergillosis was clear. The time required for progression of the maxillary sinus cyst to fungal rhinosinusitis was 2.5 years. The patient had been diagnosed with hypertension in 2004 and usually had good blood pressure control. A physical examination revealed a history of cerebral infarction in 2015. We conclude that the occurrence of fungal rhinosinusitis was associated with decreased immunity due to cardiovascular disease.

Based on the analysis of the above two cases, we speculate that the pathological transition from fungal colonization to fungal rhinosinusitis requires approximately one to three years. The duration may be related to underlying disease, surgical treatment, decreased immunity, and use of hormone antibiotics and hormones. Not every colonized patient develops fungal infection. The interaction of fungi with the host immune system determines the occurrence or disappearance of infection. Studies have shown that many factors may cause chronic fungal rhinosinusitis; 10% of patients are exposed to a harmful work environment (mining), 10% of patients smoke, and 20% have had surgery for CRS. Leszczyńska et al[11] suggested that hypertension and confirmed type 2 diabetes are predominant in patients with fungal rhinosinusitis. Successful antifungal immunity depends on the innate and adaptive immune systems. Innate immune responses to fungi are mainly orchestrated by phagocytes and the epithelium. Toxins secreted by fungi, such as candidalysin, can directly damage epithelial membranes and trigger a danger-response signaling pathway that activates epithelial immunity[12]. C-type lectin receptors (CLRs), which include Dectin-1 and Dectin-2, are essential pattern recognition receptors involved in fungal recognition and initiation of protective antifungal immunity[13]. Upon binding of its ligands, Dectin-1 activates a number of cellular responses, including phagocytosis, reactive oxygen species production, and the production of numerous cytokines via multiple signaling pathways[14]. The best characterized Dectin-1 signaling pathway is the Syk-CARD9 pathway, which leads to activation of the canonical NF-κB subunits, c-Rel, and p65 and, subsequently, production of pro-IL-1β, IL-6, IL-10, IL-23, and TNF-α[15]. Dectin-1-mediated cytokine production has been shown to influence T-cell polarization. Dectin-1^-/- mice infected intratracheally with Aspergillus fumigatus showed reduced levels of key Th17 cytokines (IL-17 and IL-23) and a dominant IL-12p40/IFN-γ-producing Th1 response, with increased lung fungal burdens relative to wild-type infected animals[16]. The importance of Th1 and Th17 immunity in antifungal defense mechanisms has been described in both mice and humans. Th1 cells secrete IFN-γ, GM-CSF, and TNF, which affect the maturation and killing ability of phagocytes as well as antigen-presenting cell function. The synergistic action of TNF with IFN-γ induces macrophage reactive oxygen species production in vitro, which is thought to contribute to in vivo growth arrest of intracellular fungal pathogens including Histoplasma capsulatum and Coccidioides immitis[17,18]. In humans, deficiencies in receptors for either IL-12 or IFN-γ have been associated with increased susceptibility to coccidioidomycosis and histoplasmosis[19,20]. Notably, IFN-γ immunotherapy has been shown to improve the outcome of patients with aspergillosis, cryptococcosis, or coccidioidomycosis[21]. Th17 cells produce cytokines, including IL-17A, IL-17F, and IL-22, that promote neutrophil trafficking and fungicidal activity and are involved in the induction of antimicrobial peptides such as S100A7, S100A8, S100A9, and β-defensins from epithelial cells and keratinocytes that defend against fungal overgrowth[22]. Th17 cells are essential for preventing mucosal fungal infections, such as chronic mucocutaneous candidiasis, and Malassezia skin infections[23]. In humans, a deficiency in the IL-17/IL-17R axis and in signaling components, including genetic defects in STAT1 and STAT3 (hyper-IgE syndrome), results in increased susceptibility to chronic mucocutaneous candidiasis[24]. CLRs have been implicated in Th2-mediated fungal allergic responses. For instance, in mice, following repeated lung exposure to Aspergillus fumigatus, CD4+ T cells produce IL-4, IL-5, and IL-13 in a Dectin-1-dependent manner (Clec7a^-/- mice)[24]. Moreover, intratracheal administration of A. versicolor spores in mice exacerbated house dust mite-induced allergic asthma through the production of IL-4 and IL-13[25].

From the blood test results of the patients, we found that the number of eosinophils before surgery was increased in the first patient and that the number of eosinophils before surgery was normal in the second patient. To our knowledge, the presence of prevalent eosinophilic infiltration of the inflamed mucosa is the most constant pathological finding in CRS. This feature is equally observed both in allergic and nonallergic patients. Such a pathological finding might be due to a prevalent Th2 immune response and a similar pattern of cytokines. The eosinophils in the sinus mucosa have been proposed to be mainly responsible for the initial tissue damage and can alter the epithelial innate immunity. In turn, tissue damage may promote bacterial aggression in the sinus mucosa; in particular, Staphylococcus aureus can cause superantigenic stimulation of the adaptive immune system through the production of exotoxins, and its biofilms have been associated with eosinophilic inflammation and elevated eosinophilic cationic protein and IL-5 levels[26]. CRS affects 1% to 9% of the general population and exhibits two traditional clinical phenotypes, CRS with nasal polyps (CRSwNP) and CRS without nasal polyps (CRSsNP). CRSwNP is characterized by T-helper cell type 2-skewed inflammation, whereas CRSsNP exhibits a T-helper cell type 1-mediated inflammatory response[27]. Iinuma et al[28] classified patients with CRSwNP as having non-eosinophilic chronic rhinosinusitis (NECRS) or eosinophilic CRS (ECRS). Some findings have suggested major differences in the pathophysiology of the two forms of CRSwNP. CD4+ T cells, basophils, and IgE+ mast cells could contribute to the eosinophilic infiltration and overall pathogenesis of ECRS, but this was not found for non-eosinophilic chronic rhinosinusitis[29]. Several pathological findings and clinical observations have suggested that CRS and asthma may be part of the same disease process, characterized by diffuse eosinophilic inflammation of the respiratory airways, from the nostrils to the bronchi, which constitutes the pathological basis of the so-called “United Airways Disease” theory[30]. The histological features of CRS and comorbid asthma largely overlap; both the sinuses and bronchial mucosa show eosinophilic inflammation and signs of airway remodeling. CRS and asthma may also interact via the systemic route through the release of pro-inflammatory cytokines in the blood, including IL-5 from peripheral sites; then, those mediators act on the bone marrow, leading to the maturation and mobilization of inflammatory cells, including eosinophils and basophils[26]. Some studies have shown that, following initial fungal allergen exposure of naïve mice, basophils are rapidly recruited to the airways, produce IL-4, and influence the development of the adaptive immune response[31]. The mechanism underlying eosinophil infiltration in fungal diseases has not been determined, but if a common mechanism could be identified, it would lead to a breakthrough in the treatment of many diseases.

In the above two cases, we have described in detail the pathogenic process from fungal colonization to fungal sinusitis. The pathological change in these two cases required approximately one to three years. At present, few related reports have been published on these subjects domestically or abroad. We have highlighted the central role of CLRs, such as Dectin-1, in inducing and modulating cytokine production and directing antifungal immune responses. However, many of the important mechanisms shaping these responses are yet to be fully understood. The formation of fungal rhinosinusitis may be related to the reduced immune function caused by endoscopic sinus surgery and hypertension in the above cases, which requires further discussion. Further understanding of other mechanisms that shape T-cell immunity during fungal infections is of great significance for the development of emerging therapies.

We would like to thank the two patients for allowing us to use their personal information.