Inflammations may be restricted to a single sinus or may be present in several (multisinusitis) or in all of one or both sides (pan sinusitis , unilateral or bilateral).
Acute and chronic non-specific infections occur with the production of either suppurative or non-suppurative forms.
A sinusitis is said to be (closed) if the contained inflammatory exudate can not escape, either through the viscosity of the exudate or through closure of the ostium by oedema. It is said to be (open) if ciliary action and overflow permit escape of the exudate. Specific infections are rare.