Mass effect of a large frontal pneumosinus dilatans on the left frontal lobe: a case report and literature review.

Pneumosinus dilatans (PD) is a rare condition characterized by abnormal expansion of the paranasal sinus without bone destruction or significant mucosal disease. Its association with Dyke-Davidoff Masson syndrome (DDMS) is particularly uncommon. We report the case of a 54-year-old female with learning disabilities, pseudoseizures, and asthma who was referred to our clinic after an MRI performed for decreased visual acuity revealed marked dilatation of the large left frontal sinus. She denied nasal symptoms but reported frontal headaches. Endoscopic examination was unremarkable. Imaging demonstrated progressive sinus enlargement and a mass effect in the left frontal lobe. The case was reviewed in a multidisciplinary setting and diagnosed as DDMS. Despite the conservative management, the patient remained stable. This case underscores the importance of recognizing PD and its rare associations, and emphasizes the value of multidisciplinary evaluation and radiological surveillance in selected patients.