Infraorbital Ethmoid Cell (Haller's Cell).

The potential pathophysiologic importance of a Haller' s cell is clear, but the anatomic definition is not. As described by Haller in 1765, these cells grow into the bony orbital floor that constitutes the roof of the maxillary sinus, are differentiable from the bulla, and have a potential pathophysiologic relationship to a narrowed ethmoid infundibulum or maxillary sinus ostium

The ostiomeatal complex is a functional entity of the anterior ethmoid complex that represents the final common pathway for drainage and ventilation of the frontal, maxillary, and anterior ethmoid cells . Any or all cells, clefts, and ostia, with their dependent sinuses, may become diseased, thereby contributing to the symptoms and pathophysiology of sinusitis. 
 

Posterior ethmoid cells can become pneumatized far laterally and to some degree superiorly to the sphenoid sinus, in which case they are called sphenoethmoid cells(cellulae sphenoethmoidales) or Onodi cells.Pneumatization of the clinoid process in those cases may originate from the posterior ethmoid cell, also.

The optic nerve and carotid artery may be exposed in a sphenoethmoid(Onodi) cell. This is clinically significant because the sphenoid sinus is located medially and inferiorly to the most posterior cell of the posteriorethmoid complex. Consequently, attempts to use instrumentation to locate the sphenoid sinus directly behind the last cell of the posterior ethmoid complex may result in serious damage to the optic nerve or carotid artery.

The most posterior ethmoid cell may becalled a sphenoethmoid cell(Onodi cell) when it pneumatizes laterally and superiorly to the sphenoid sinus and is intimately associated with the optic nerve.