Ostiomeatal complex (OMC)

• Patency of the maxillary ostium and ethmoid infundibulum on coronal CT
• Presence of mucosal thickening, polypoid tissue, or secretions within the middle meatus and infundibulum
• Anatomic variants that narrow the OMC pathway, such as Haller cells, concha bullosa, or medialized uncinate process
• Linked pattern of ipsilateral maxillary, anterior ethmoid, and frontal sinus opacification suggesting OMC obstruction

• The OMC is a narrow, three-dimensional drainage region in the middle meatus that serves as the functional drainage corridor for anterior paranasal sinuses and cannot be assessed as a single discrete structure.
• Core components visible on coronal CT include the maxillary sinus natural ostium, ethmoid infundibulum, uncinate process, hiatus semilunaris, ethmoid bulla, and frontal recess.
• The uncinate process forms the anterior and medial margin of the ethmoid infundibulum and separates it from the middle meatus, serving as a critical anatomic boundary.
• The hiatus semilunaris is the cleft between the uncinate process and ethmoid bulla, through which the ethmoid infundibulum communicates.
• The frontal recess serves as the variable superior drainage pathway of the frontal sinus and may communicate with the infundibulum or drain more directly into the middle meatus depending on superior uncinate attachment.
• OMC obstruction produces a characteristic linked pattern of ipsilateral maxillary sinus opacification, anterior ethmoid disease, and frontal sinus disease affecting the shared anterior drainage pathway.
• Anatomic variants narrowing the OMC include Haller cells, large agger nasi cells, concha bullosa, paradoxical middle turbinate deviation, pneumatized or medialized uncinate process, and septal deviation.
• Assessment is performed on thin-section coronal CT with axial and sagittal reformations used to clarify the front-to-back course of drainage pathways and frontal outflow tract.

• Isolated posterior ethmoid or sphenoid disease indicates pathology outside the OMC rather than OMC obstruction, helping distinguish primary sinonasal disease from OMC-related obstruction
• Accessory maxillary ostium can permit mucus recirculation and should be distinguished from the primary natural ostium to avoid misinterpreting drainage patterns
• Concha bullosa (pneumatized middle turbinate) can narrow the OMC and should be specifically assessed as a contributing anatomic variant
• Haller cells (infraorbital air cells) and enlarged agger nasi cells are common variants that narrow the pathway and must be identified on pre-operative planning

Describe OMC patency clearly on coronal images by explicitly stating whether the maxillary ostium and ethmoid infundibulum are patent or obstructed, specify the location and nature of any obstruction (mucosal thickening, polypoid tissue, mass, or variant anatomy), and document the presence of associated inflammatory disease in the maxillary, anterior ethmoid, and frontal sinuses to support the diagnosis of OMC obstruction.

• Failing to assess the OMC systematically on coronal images, which is the optimal plane for evaluating this three-dimensional drainage region
• Misinterpreting isolated posterior ethmoid or sphenoid disease as OMC obstruction, when these sinuses drain separately and indicate pathology outside the OMC
• Overlooking anatomic variants such as Haller cells, concha bullosa, or medialized uncinate process that may contribute to OMC obstruction
• Neglecting to document relationships to critical structures like the lamina papyracea and skull base, which affects surgical planning in pre-operative FESS assessment