Fungal sinusitis: diagnosis with CT and MR imaging

Fifteen patients with surgically proven diagnosis of fungal sinusitis were examined by plain film, CT and MRI. Plain films revealed calcifications within the sinuses in 8 cases, while CT showed calcifications either in the form of a cast or of focal calcifications in 11 cases. The remaining 4 cases were false negative by CT. The attenuation of the calcifications was always above 120 HU. MR showed a characteristic signal pattern in the form of a central signal void within the sinus, representing the fungal ball surrounded by a hyperintense rim on the T2-weighted images representing the inflamed mucosa. Following contrast media injection, there was a strong enhancement of the inflamed mucosa but not of the central void or mycetoma. The void caused by the mycetoma ball may either be due to the calcifications or the presence of trace amounts of manganese and magnesium, as well as by the decreased water content of the mycetoma balls and the high concentration of its protein content, being above 40%. MRI gave an important information about the content of the sinuses allowing the differentiation of lesions which are otherwise indistinguishable by CT. Still MR seems to be not specific as the abovementioned characteristic signal pattern could be seen in patients with mucocele, acute intrasinus hemorrhage, partially aerated and inflamed paranasal sinuses, dentigerous cysts of the maxillary sinuses and postoperative sinuses with fibrosis. To differentiate between these different entities, one has to resort to CT