Ans. a (Nasal cavity with maxillary sinus). (Ref. ENT secrets 3rd ed., 100-107)Osteomeatal unit/complex (OMC) confluence# OMC is the normal aerated channel which provide airflow & mucociliary clearance for sinuses.# Anterior ethmoidal air cells, maxillary & frontal sinuses drain into it.# It is the cross road for drainage of most paranasal sinuses.# It is the key area for pathogenesis of chronic sinus diseases.# The concept that obstruction of OMC results in ethmoid, frontal & maxillary sinusitis is fundamental to FESS# Well identified on coronal CT with patient prone & head hyperextended (Coronal CT).# Thus, components of OMC include:# Middle meatus# Maxillary sinus ostium & infundibulum# Anterior & middle ethmoidal air cells ostia & ethmoidal infundibulum# Frontal recess/frontonasal duct# Bulla ethmoidalis# Hiatus semilunaris# Uncinate process# Sphenoethmoid recess & superior meatus (included by some authors)# Uncinate process is thin, curved lamina of bone from the lateral side of ethmoidal labyrinth that forms a portion of lateral nasal wall. It projects downwards & backwards & ranges from 1 to 4 mm in height and 14 to 22 mm in length. Superior edge of uncinate process is free and forms medial boundary of hiatus semilunaris.# Ethmoidal infundibulum is a trough shaped air space that is below bulla & above & lateral to uncinate process. It receives drain from anterior & middle ethmoid air cells & frontal & maxillary sinuses. The infund-ibulum may be narrowed if there is Concha bullosa &/or large Haller's cell (pneumatized middle turbinate).# Hiatus semilunaris is curvilinear opening of lateral wall that is above uncinate process & below the bulla ethmoidalis. This opening separates uncinate process from ethmoidal bulla & serves as connection between infundibulum & middle meatus.# The middle ethmoidal air cell produces a round swelling called bulla ethmoidalis on lateral wall of middle meatus.# Onodi cells are most posterior ethmoidal cells that surround optic canal.