Pneumosinus dilatans associated with nasal polyposis.

OBJECTIVE: Pneumosinus dilatans (PSD) and pneumocele involve the expansion of one or more paranasal sinuses. We present the first cases of frontal PSD and pneumocele associated with nasal polyposis. We also attempt to explain the development of these rare pathologies through this unexpected association. METHODS: Two cases are described. A 31-year-old man presented with chronic rhinosinusitis for many years and a left frontal protrusion. Physical examination found nasal polyposis and CT scan showed an abnormally enlarged left frontal sinus without bone destruction. The second patient was a 17-year-old man who presented with a left frontal protrusion and orbital encroachment associated with chronic rhinosinusitis. Physical examination also found nasal polyposis and CT scan showed an abnormally enlarged left frontal sinus with focal thinning of the bony sinus walls. DISCUSSION: Focal or generalized thinning of the bony sinus walls differentiates pneumocele from PSD; otherwise, these two entities share the same physiopathological and clinical courses. Many explanations have been proposed for their development including increases in intra-sinus pressure, weakening of bone by tumor invasion, intracranial hypotension, spontaneous drainage of a mucocele, and congenital or hormonal causes. Yet, its physiopathology remains unknown. These two cases support the pressure mechanism of development.