Pseudoballs as a distinct endotype of sinonasal bioballs

Fungal ball has been known as a noninvasive subtype of chronic rhinosinusitis (CRS). Recently, other endotypes of sinonasal bioballs, which we reported as bacterial balls and mixed balls.

This study aimed to investigate the pseudoball as a distinct endotype of sinonassal bioballs.

This study included 41 CRS patients with suspected fungal balls who underwent functional endoscopic sinus surgery (FESS) from January 2020 to November 2022. All fungus-like biomaterials were stained with Hematoxylin-Eosin, Gomori-Methenamine-Silver (GMS), and Gram stains. Diagnosis of pseudoballs was made when both GMS and Gram staining were negative. Clinical and computed tomography (CT) findings were compared between fungal balls and pseudoballs.

Four endotypes of sinonasal bioballs were identified: fungal balls (56.1%), mixed balls (26.8%), pseudoballs (12.2%), and bacterial balls (4.9%). During FESS, the pseudoballs had heterogeneous gross features with a gel-like or semi-solid consistency and yellow-to-gray colors. Histopathology of the pseudoballs showed a matrix with thick acellular mucous material without any fungi or bacteria. When compared with fungal balls, all pseudoballs cases were immunocompetent (100%) and prone to involvement of the posterior ethmoid sinus (60%, p = 0.01) in CT scans.

The pseudoballs were dual-negative in GMS and Gram staining and showed distinct clinical and radiological characteristics as a different endotype.