RESUMO
Pneumosinus dilatans is a term used to describe a localized abnormal dilatation of one or more paranasal sinuses without radiological evidence of localized bone destruction, hyperostosis or mucous membrane thickening. The involvement of all paranasal sinuses and mastoid air cells has been named pneumosinus dilatans multiplex. Although the involvement of one or more paranasal sinuses has been reported widely, all paranasal sinuses and the concomitant involvement of mastoid air cells has been reported in only one case. Herein, we present three unusual cases of pneumosinus dilatans (one is a second case of pneumosinus dilatans multiplex in English literature, another is the first reported case of a frontal pneumosinus dilatans case associated with frontoethmoidal meningocele, mental retardation and facial asymmetry and the third one is pneumosinus dilatans with a huge arachnoid cyst) along with the review of relevant literature.