Laboratory Studies
Laboratory studies are of limited value in fungal sinusitis. Elevated serum fungus-specific IgE concentrations are often found in patients with allergic fungal rhinosinusitis, as this disease is mediated through an IgE type I hypersensitivity immune reaction to the fungal elements. This is not the case in patients with sinus fungal ball who have normal serum IgE levels.
Using enzyme-linked immunosorbent assays, one study examined the sinonasal tissue and secretions in patients with chronic rhinosinusitis for the presence of mycotoxins (ie, aflatoxin, deoxynivalenol, zearalenone, ochratoxin, fumonisin) to determine their possible role, if any, in chronic rhinosinusitis. No mycotoxins were found, except ochratoxin in four of 18 samples. The clinical significance of these results has not been determined. [16]
In patients with acute invasive fungal sinusitis, measurements of the immune status (eg, absolute neutrophil count, blood glucose level) are important. A study by Payne et al of 41 patients with acute invasive fungal rhinosinusitis reported that predictive variables for the disease include an absolute neutrophil count below 500/μL (sensitivity of 78%), abnormalities of the septal mucosa (specificity of 97%), and necrosis and mucosal abnormalities of the middle turbinate (specificities of 97% and 88%, respectively). [17]
Serum galactomannan Aspergillus antigen is under investigation as a screening test for invasive fungal sinusitis. A study by Melancon et al showed that this test is highly specific (100%), with high positive predictive value (100%). [18] However, its sensitivity is low (44.8%), likely because it only detects cases caused by Aspergillus species.
Imaging Studies
CT scanning of the paranasal sinuses in coronal views is essential to the evaluation of patients suspected of having fungal sinusitis. [9, 10]
In acute invasive fungal sinusitis, CT scan characteristics include mucosal thickening, soft tissue and fat infiltration, bone erosion, and involvement of the orbit, pterygopalatine fossa, and CNS.
Middlebrooks et al devised a seven-variable, CT scan–based diagnostic model for patients at risk of acute invasive fungal rhinosinusitis. They reported that an abnormality associated with one of the model’s variables—which consist of periantral fat infiltration, bone dehiscence, orbital invasion, septal ulceration, and involvement of the pterygopalatine fossa, nasolacrimal duct, and lacrimal sac—has a positive predictive value of 87%, a negative predictive value of 95%, a sensitivity of 95%, and a specificity of 86%; the involvement of two variables gives the model a specificity of 100% and a positive predictive value of 100%. [19]
MRI is useful in evaluating orbital and intracranial involvement in acute invasive fungal sinusitis.
In patients with sinus fungal ball, CT scanning shows unilateral sinus opacification with dense hyperattenuations. These hyperdensities or calcifications result from a dense collection of hyphae inside the sinus. A retrospective study by Cha et al indicated that other CT scan characteristics can be used to help identify sinus fungal balls. Those include a “sinus fuzzy appearance and sinus full haziness with mass effect.” [20] MRI is rarely necessary in the workup of sinus fungal balls, but when obtained, fungal balls can be suggested by the presence of an isointense signal within the fungal mass on T1, in conjunction with dark-signal lesions surrounded by high-signal enhancement of the mucosal walls on T2. [21]
In allergic fungal rhinosinusitis, both CT scanning and MRI are helpful in making an accurate diagnosis. Allergic fungal rhinosinusitis can occur unilaterally in up to 20% of patients but typically involves multiple sinuses. CT scan characteristics include fully opacified and expanded sinuses, bony demineralization and erosion, displacement of adjacent structures (eg, orbit, skull base), and hyperdensities within the sinuses. MRI may show hypointensity within the sinus (dense fungal elements), with enhancement of the sinus periphery (mucosal inflammation) on T1 and T2 signals.
Histologic Findings
In allergic fungal rhinosinusitis, eosinophilic mucin contains intact and degenerated eosinophils, Charcot-Leyden crystals, cellular debris, and sparse hyphae. The sinus mucosa has mixed cellular infiltrate of eosinophils, plasma cells, and lymphocytes. The mucus membrane is not invaded by fungi.
No eosinophilic mucin is present in sinus fungal ball. However, the sinus contains dense material that consists of hyphae separate from but adjacent to the mucosa. The sinus mucosa is not invaded.
Histopathologic studies in acute invasive fungal sinusitis reveal hyphal invasion of the mucosa, submucosa, nerves, and blood vessels, including the carotid arteries and cavernous sinuses; vasculitis with thrombosis; hemorrhage; and tissue infarction.
Necrosis of the mucosa, submucosa, and blood vessels, with low-grade inflammation, is observed in chronic invasive fungal sinusitis.
Granuloma with multinucleated giant cells with pressure necrosis and erosion is observed in granulomatous invasive fungal sinusitis.
A retrospective study by Melancon and Clinger indicated that in the diagnosis of acute invasive fungal sinusitis, frozen section biopsies have a positive predictive value of 100%, a sensitivity of 87.5%, and a specificity of 100% and are therefore important in the early diagnosis of this disease. [22]
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Axial CT scan of sinuses shows a right fungal maxillary sinusitis with an expanding mass (possibly aspergillosis).
