Magnetic resonance imaging [18]
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MRI also can provide information useful in preoperative identification of allergic fungal mucin, but it usually is not necessary when making the diagnosis unless the disease has extended into the intracranial cavity or confusion exists with the diagnosis. Som and Curtin have pointed out that protein concentrations exceeding 28% cause a decreased signal on T1- and T2-weighted MRI images because of protein cross-linking and slower macromolecular motion. This effect is more pronounced on T2-weighted images because of prolonged magnetic field relaxation times. The high protein and low water concentration of allergic fungal mucin, coupled with the high water content within surrounding edematous paranasal sinus mucosa, gives rise to rather specific MRI characteristics, as depicted in the image below.
Coronal MRI showing expansion of the sinuses with allergic mucin and polypoid disease; the hypointense black areas in the nasal cavities are the actual fungal elements and debris. The density above the right eye is the mucocele. The fungal elements and allergic mucin in allergic fungal sinusitis always look hypointense on MRI scanning and can be mistaken for absence of disease.
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In a series of 10 patients with allergic fungal sinusitis (AFS), Manning et al demonstrated that hypointense central T1 signal, central T2 signal void, and the presence of increased peripheral T1/T2 enhancement were highly specific for allergic fungal sinusitis (AFS) when compared to other forms of fungal sinusitis (invasive fungal sinusitis, fungal ball) and mucocele. On MRI, the hypointense signal looks black and can be mistaken for absence of disease in the paranasal sinuses because a black signal in the sinuses on CT scan indicates the absence of disease. Compare the two images below. The combined CT scan and MRI findings provided a radiographic appearance that was highly specific for allergic fungal sinusitis (AFS).
Coronal CT scan showing extensive allergic fungal sinusitis involving the right side with mucocele above the right orbit and expansion of the sinuses on the right.
Coronal MRI showing expansion of the sinuses with allergic mucin and polypoid disease; the hypointense black areas in the nasal cavities are the actual fungal elements and debris. The density above the right eye is the mucocele. The fungal elements and allergic mucin in allergic fungal sinusitis always look hypointense on MRI scanning and can be mistaken for absence of disease.
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Left middle meatus with suctioning of thick allergic mucin from the ethmoid bulla in the center of the picture; the end of the suction is in the inferior portion of the picture.
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The viscosity of a thick allergic mucin being suctioned from the nasal cavity and vestibule in a patient with allergic fungal sinusitis.
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View just inside the nasal vestibule showing diffused polyposis extending into the anterior nasal cavity and vestibule; the septum is on the right, and the right lateral vestibular wall (nasal ala) is on the left. The polyps all are in the center. The polyps almost hang out of the nasal vestibule.
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A 15-year-old boy with allergic fungal sinusitis causing right proptosis, telecanthus, and malar flattening; the position of his eyes is asymmetrical, and his nasal ala on the right is pushed inferiorly compared to the left.
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A 9-year-old girl with allergic fungal sinusitis displaying telecanthus and asymmetrical positioning of her eyes and globes.
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Coronal CT scan showing extensive allergic fungal sinusitis involving the right side with mucocele above the right orbit and expansion of the sinuses on the right.
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Typical view of a middle meatus in a patient with allergic fungal sinusitis with expansion of the ethmoid complex and extension of the middle turbinate more inferiorly. This is a postoperative view.
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Coronal CT scan showing typical unilateral appearance of allergic fungal sinusitis with hyperintense areas and inhomogeneity of the sinus opacification; the hyperintense areas appear whitish in the center of the allergic mucin.
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Coronal MRI showing expansion of the sinuses with allergic mucin and polypoid disease; the hypointense black areas in the nasal cavities are the actual fungal elements and debris. The density above the right eye is the mucocele. The fungal elements and allergic mucin in allergic fungal sinusitis always look hypointense on MRI scanning and can be mistaken for absence of disease.
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Immediate postoperative 30° angled view showing the complete removal of polyps with a widened frontal sinus recess superiorly and widened ethmoid cavity in the mid portion. The middle turbinate is on the right, pushed against the septum. The lateral nasal wall is on the left.
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Fungal ball in the right maxillary sinus.
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Fungal debris being removed from the ethmoid complex. A suction device is seen in the right lower corner of the picture.
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Allergic mucin, fungal debris, and polyps are shown after removal from the patient. The scale is in inches.
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Coronal CT scan showing the postoperative view following removal of disease after significant disease recurred on both the right and left sides of the nasal cavity and sinuses; mild mucosal thickening of all involved sinuses is present, with some moderate thickening of the left maxillary sinus. All disease, even the lateral mucocele, was removed or drained endoscopically.
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Two-week postoperative endoscopic picture showing polypoid thickening already in the ethmoid cavities while the patient was still on tapering steroids; on the left is the lateral nasal wall. The right shows the middle turbinate next to the septum.
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A polypoid recurrence in the center of the ethmoid cavity. The septum is on the left.
