A fungus may be characterized by its radiologic and operative gross findings. Computed tomography (CT) revealed a rim of soft tissue attentuation of variable thickening along the bony walls of the isolated paranasal sinus, or mottled hyper-dense foci of variable size. A small amount of friable muddy mass surrounded by purulent secretions or dirty brown clay-like materials provide highly pathognomonic findings. However, these characteristics may induce clinical misdiagnosis. During the last four years we experienced 11 cases of chronic paranasal sinusitis in which pathologic examination failed to confirm fungal hypae, despite clinical suspicion of a fungus ball based on operative or CT findings. During the same period, we also experienced another 52 patients who were diagnosed with fungus ball at pathologic examination. To evaluate in sinus fungus balls, we reviewed the medical records of these 63 patients and also reviewed CT scans and operative records of another 1127 patients who received endoscopic sinus surgery for chronic rhinosinusitis. The sensitivity of CT evaluation was 62%, and specificity was 99%. The false-positive and false-negative rate were 22% and 2%, respectively. With regard to operative findings, such as clay-like inspissated mucus, the sensitivity, specificity, and predictive value positive rate were 100%, 99% and 83%, respectively. To make a diagnosis of fungus ball, a high index of suspicion is necessary and a pathologic confirmation is mandatory.
