Paranasal sinus mucocele.

Mucocele of the paranasal sinuses is a distinct clinicopathologic entity in which there is obstruction of the sinus cavity outflow tract, resulting in expansion of the sinus walls. The histologic features are quite nonspecific, requiring clinical, radiologic, and pathologic correlation. Most of these lesions result from increased pressure in the sinus due to sinus outlet obstruction, usually as a consequence of inflammatory or allergic processes. However, tumor, trauma, and previous surgery may play a role.