Chronic Sinonasal Mucocele Manifesting as a Distinctive Collapsed Fibrous Hyalinized Cyst Wall

Chronic sinonasal mucoceles are benign expansile lesions caused by obstruction of sinus drainage, resulting in mucus accumulation and potential complications including nasal obstruction, facial pain, and visual disturbances. While their clinical aspects are well-characterized, detailed histopathologic descriptions remain limited. We conducted a retrospective clinicopathologic analysis of six patients treated for chronic sinonasal mucoceles between 2014 and 2024. Clinical data, imaging studies (computer tomography (CT) and magnetic resonance imaging (MRI)), endoscopic findings, and histopathologic features were reviewed. The cohort included four male patients and two female patients (age range: 31-85 years, mean: 61 years). Five patients presented with rhinologic symptoms; one was asymptomatic, with the lesion discovered incidentally. Anatomically, four muoceles (67%) involved the frontal-ethmoidal sinuses; the remaining two affected the sphenoid and maxillary sinuses, respectively. CT imaging revealed sinus opacification in five patients, with one showing marked mucosal and bony thickening. Histologically, all specimens exhibited collapsed fibrous walls with hyalinized stroma, sparse cellularity, and absent or denuded epithelium-finding consistent with late-stage changes from chronic pressure and reparative remodeling. Immunohistochemistry confirmed myofibroblastic differentiation of stroma cells. All patients underwent successful endoscopic management without recurrence. Chronic sinonasal mucoceles may present as pseudotumors with distinctive collapsed, hyalinized fibro-membranous walls, distinguishing them from early-stage lesions. Recognition of these characteristic histopathologic features, in conjunction with clinical and radiologic findings, is essential for accurate diagnosis and to avoid overtreatment. Endoscopic surgical management remains an effective treatment with excellent outcomes.