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Letters to the Editor |
Section of Radiology, Crawford Long Hospital of Emory University, 550 Peachtree Street, Northeast, Atlanta, GA 30365-2225
Editor:
I read with much interest the article by Mukherji and colleagues (1) in the May 1998 issue of Radiology on allergic fungal sinusitis.
There is one point the authors raise that confuses me. In the introduction, allergic fungal sinusitis is classified within the broader category of noninvasive fungal sinusitis, along with mycetoma. The diagnostic criteria for allergic fungal sinusitis are listed, including "the absence of fungal invasion of submucosa, blood vessels, or bone." Yet in the Results, 41 (93%) of their 45 patients demonstrated erosion of an involved sinus wall on CT scans, and nine (20%) had evidence of disease extending into adjacent structures (all in patients with bone erosion). The authors also state that "the degree of bone erosion and extension beyond a sinus may mimic aggressive sinonasal neoplasms" and later on suggest that such findings could be due to "pressure from a combination of the underlying sinonasal polyposis and the allergic mucin." Does this imply that in most patients with allergic fungal sinusitis there is substantial osseous erosion and sometimes soft-tissue extension beyond the sinus margins without actual invasion of bone, periosteum, and other adjacent soft-tissue structures? In addition, if this is the case, how would one distinguish between allergic fungal sinusitis and actual osseous invasion in a sinus already involved by polyposis (and therefore already expanded)?
References
Department of Radiology, University of North Carolina School of Medicine, 3324 Old Infirmary, CB 7510, Chapel Hill, NC 27599-7510
We thank Dr Silverstein for his interest in our work (1) and also for the opportunity to further clarify the entity of allergic fungal sinusitis. The issue of bone changes in allergic fungal sinusitis is an important and confusing topic that merits further discussion.
The diagnostic histologic features described by Katzenstein et al (2) in their original report on allergic fungal sinusitis is the presence of a characteristic type of mucin containing scattered fungal hyphae and eosinophils termed "allergic mucin." DeShazo et al (3) recently updated the classification of fungal sinusitis. Allergic fungal sinusitis was categorized as a form of noninvasive fungal sinusitis that has no histologic evidence of fungal hyphae invasion into blood vessels, submucosa, or bone. Acute (fulminant) invasive fungal sinusitis is histologically distinct, demonstrating granulomatous inflammation and necrosis, as well as direct invasion of the aforementioned structures by fungal hyphae (3). To our knowledge, these histologic findings of bone invasion and necrosis present in acute (fulminant) invasive sinusitis have not been described in allergic fungal sinusitis (3–5).
We concur with Torres et al (4), who state that the "origin of the bone erosion is poorly understood" in allergic fungal sinusitis. This is likely due to the fact that the bone margins are often not submitted after surgical resection of allergic fungal sinusitis. Thus, pathologists may not have had sufficient opportunity to fully evaluate the cause of the bony changes in allergic fungal sinusitis. We agree with previous authors (3–6) who feel that the origin of the bone changes in allergic fungal sinusitis are likely due to pressure erosion caused by the expanding sinonasal mass, as opposed to invasion by a more aggressive infection. Other authors (5–8) have suggested that this process may be aided by inflammatory mediators. Once bone erosion has occurred, it is unlikely that CT would be able to be used to distinguish between bone erosion caused by direct hyphal invasion and pressure erosion.
In our series, we found that extension beyond the sinus margin is a late finding in allergic fungal sinusitis and was probably due to progressive bone demineralization of the sinus walls by the allergic mucin. This may be due to allergic mucin alone or may be in association with underlying polyposis (6,9). Both allergic fungal sinusitis and sinonasal polyposis can have increased intrasinus attenuation, sinus expansion, and demineralization of the sinus wall. As we state in the discussion, CT may not be able to be used to distinguish between advanced allergic fungal sinusitis and advanced sinonasal polyposis with desiccated secretions (9).
References
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