Catergorization

Based on histopathologic findings, fungal rhinosinusitis can be broadly divided into two categories: the invasive and non-invasive depending on invasion of mucosal layer. Three types of fungal rhinosinusitis are tissue-invasive infectious diseases: acute necrotizing (fulminant), chronic invasive and granulomatous invasive (indolent). The two non-invasive fungal rhinosinusitis disorders are fungal ball (sinus mycetoma) and allergic fungal rhinosinusitis (AFRS) (1). Still, categorization of fungal rhinosinusitis remains controversial and is open to discussion.

Rowe-Jones and Moore-Gillon (1994) proposed a chronic destructive but non-invasive (semi-invasive) form of rhinosinusitis (2). It is categorized by sinus expansion and bony erosion, but with no histologic evidence of tissue invasion. In this state, the pathogens results in progressive, chronic inflammation intermediate between allergic, sinus mycetoma and chronic invasive state. Even though inflammation and bony erosion were evident, these cases had not progressed to produce the facial mass or proptosis associated with invasive disease. Such example of semi-invasive pulmonary aspergillosis also exists (3). However, this entity may be a variant of non-invasive type in which the fungal mass destroys the sinus wall by pressure (4). In characterizing chronic non-invasive fungal rhinosinusitis, all authors refer to fungal ball or AFRS. However, difference between this entity and the fungus ball group is that their clinical course was more violent than fungus ball; they need more extensive endoscopic operation and longer follow-up. The similarity between destructive non-invasive fungal rhinosinusitis and AFRS is the long course of disease, the erosive appearance in CT scan, the need for extensive endoscopic surgery and the long follow-up period. The differences between these two groups are the different pathological appearance, immune status and treatment. The existence of this separate entity and treatment protocol are still to be settled (5).

AFRS is considered a non-tissue invasive fungal process, representing an allergic/ hypersensitivity response to the presence of extra-mucosal fungi within the sinus cavity possibly akin to allergic broncho-pulmonary aspergillosis (ABPA). In the diagnosis of AFRS, the detection of fungi in allergic mucin is considered important, although hyphae are sparse in sinus content. This leads to confusion in categorization of this entity, especially with the description of two more closely related entities – eosinophilic fungal rhinosinusitis (EFRS) and eosinophilic mucin rhinosinusitis (EMRS) (6, 7). The confusion is further heightened by the alternative hypothesis of Ponikau et al (8), which proposes a different mechanism of AFRS and might be applied universally to encompass chronic rhinosinusitis (CRS) as well. Using detection of fungi in nasal lavage as a method of diagnosis, Ponikau et al, 1999 demonstrated the presence of fungi in specimens from 93% of patients with CRS and did not find type I hypersensitivity to be prevalent in their study group. They offer the hypothesis that CRS is cell-mediated response to fungal elements and suggested the acceptance of the new term, EFRS. Thus, the question remains whether a separate unrecognized form of non-allergic, fungal eosinophilic inflammation exists that can lead to a similar clinical presentation. Ferguson (7) claimed that eosinophilic mucin could be present and cause rhinosinusitis without the presence of fungi. The controversy regarding the definition of AFRS is further intensified with well-documented reports of histologic invasion in possible cases of AFRS (9, 10). Foci of granulomatous inflammation in a patient of AFRS with orbital apex involvement has also been reported (11). Extending the hypersensitivity process in causation of AFRS, some workers claimed the consistent presence of AFRS with allergic broncho-pulmonary mycosis in same patients and termed the process as Sino-bronchial Allergic Mycosis (SAM syndrome) (12). All those different views express the ambiguity in definition of AFRS and confirm the existence of considerable overlap between AFRS, EMRS and CRS from other causes regarding the clinical features, radiological and immunological parameters (13).

After the documentation of possible histologic invasion in AFRS cases (9, 10), it casts doubts on the discrete compartmentalization of fungal sinusitis into invasive and non-invasive. Some workers support the view that different types of fungal sinusitis represent a progressive spectrum of disease with initial colonization to semi-invasive or invasive forms (14, 15). Such a progression may be precipitated by a change of host defenses (16).

The distinction of granulomatous invasive type from chronic invasive type is also not beyond controversy. In granulomatous invasive rhinosinusitis, an enlarging mass is seen in the cheek, orbit, nose, and paranasal sinuses. Proptosis is often a prominent feature. Histopathologically, a granulomatous response is seen with considerable fibrosis. Non-caseating granuloma with foreign body or Langerhan’s type of giant cell may be seen, sometimes with vasculitis, vascular proliferation and perivascular fibrosis. Hyphae in many occasions are scanty (1, 17). A. flavus is the primary agent isolated from these cases. In contrast, chronic invasive type is characterized as dense accumulation of hyphae, presence of vascular invasion, sparse inflammatory reaction, A. fumigatus isolation and association with orbital apex syndrome, diabetes mellitus and corticosteroid treatment (1, 18). However, such distinction is not recognized by other workers (19, 20). Indeed, clinico-pathological distinctions between these two types are not sharp. Both have a chronic course and predominant orbital involvement. Isolation of different type of Aspergillus species may represent separate geographical distribution and different tissue responses may depend on host immune status. Some workers even tried to classify granulomatous invasive fungal sinusitis into two types – one that is described in Sudan, other in hypertrophic sinus disease with chronic eosinophilic–lymphocytic granuloma and concomitant AFRS (10, 21).

References

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