ABSTRACT
The paranasal sinuses are paired, mucosalined structures contiguous with the nasal cavity, consisting of pneumatized spaces within the maxillary, ethmoid, frontal, and sphenoid bones. The frontal sinus consists of
two paired air cells within the frontal bone separated by an intersinus septum, which drain inferiorly into the middle meatus. The frontal sinus is the last to develop and is typically not present at birth; full development continues into early adulthood although 10%–12% of frontal sinuses remain underdeveloped and hypoplastic.3 The ethmoid sinuses are actually a complex of two large groups of cells that are separated by the basal or ground lamella of the middle turbinate: the anterior ethmoid air cells that drain into the middle meatus and the posterior ethmoid cells that drain into the superior meatus. These air cells are the most mature of the paranasal sinuses at birth, reaching adult dimensions by about 12 years of age. Importantly, ethmoid air cells can expand beyond the boundaries of the ethmoid bone, pneumatizing superolaterally into the sphenoid bone (sphenoethmoidal or Onodi cells) or laterally into the maxillary bone (infraorbital ethmoid or Haller cells).2
