Paranasal sinuses mucoceles as demonstrated in this case are radiologically aggressive but histologically benign.   Bony destruction arises due to obstruction from the mucocele and it can be profound.

The frontal sinus, as in this case, is particularly prone to developing mucoceles with 2/3 occurring in this sinus.  Extension may be into the orbit, intra-cranial contents or both.

As with a good deal of head and neck imaging, CT and MRI complement each other in disease assessment.  The CT illustrates the bony details elegantly with soft tissue outlined with MRI - together they complete the complete picture.  

This was a histologically proven mucocele of the frontal sinus.