To determine the usefulness of CT findings of an expansile ball-like high density mass in the differential diagnosis of fungal and nonfungal sinusitis.

Paranasal sinus CT findings in 62 patients (36 males and 26 females) with pathologically proven chronic paranasal sinusitis were retrospectively analyzed. Sinusitis was fungal in 21 patients (34%) and nonfungal in 41 (66%). Bone and soft tissue window settings were reviewed by two radiologists in terms of the presence, expansibility, bilaterality, and location of the ball-like high density mass, involved sinuses, bone thickening of the sinus wall, and associated calcification.

The ball-like high density mass was more common in fungal sinusitis patients (81%), in whom it was expansile in 88% of cases and unilateral in 94% (p<0.05). In all patients, the mass was located in the maxillary sinus; in 88% of fungal cases and 90% of nonfungal, it was present in both its medial and lateral portions. Bone thickening (76%) and calcification (86%) were more common in fungal sinusitis (p<0.05).

A ball-like high density expansile mass appears to be a valuable finding in the diagnosis of fungal sinusitis.