Closure of the frontal sinus ostium by a block of bone: unexpected cause of frontal mucocele.

Mucoceles are benign, slow-growing lesions. Frontal sinus mucoceles are caused by the obstruction of the sinus ostium and seromucous secretions fill the inside of the cyst. The size of the cyst and the destroyed sinus walls gradually expands. Cystic mass can lead to orbital or intracranial complications when it overflows beyond the boundaries of the sinus. In this manuscript, we presented an unexpected cause of frontal mucocele in which the closure of the frontal sinus ostium is caused by a block of bone. A case of orbital complications is presented.