Haller cells

• Air-filled cells extending from the anterior ethmoid sinus inferiorly into the maxillary sinus at the orbital floor level
• Location lateral to the maxillo-ethmoidal suture along the medial orbital wall
• Size assessment relative to the ostiomeatal complex to determine if they cause obstruction

• Haller cells are anterior ethmoid air cells that pneumatize inferiorly into the maxillary sinus along the floor of the orbit, appearing as loculated low-density (air-filled) spaces on CT.
• They are located lateral to the maxillo-ethmoidal suture and represent infraorbital ethmoidal pneumatization.
• On coronal CT imaging, they are best visualized as air-filled cells at the medial aspect of the orbital floor between the maxillary sinus and orbital contents.
• Large Haller cells can narrow the ipsilateral ostiomeatal complex (OMC), potentially obstructing normal maxillary sinus ventilation.
• The presence and size of Haller cells should be documented preoperatively as they may be encountered and potentially violated during endoscopic sinus surgery.

• Maxillary sinus mucocele: unlike Haller cells, mucoceles show opacification and expansion of the maxillary sinus rather than air-filled infraorbital cells
• Orbital floor fracture: fractures present as cortical discontinuity and associated hematoma or soft tissue findings rather than pneumatized ethmoid cells
• Nasolacrimal duct cyst: arises at the nasolacrimal canal opening and is usually solitary, distinct from the multiple small air cells of Haller pneumatization
• Infundibular stenosis: narrowing of the infundibulum without associated infraorbital air cells, and does not have the characteristic location lateral to the maxillo-ethmoidal suture

When reporting Haller cells, clearly document their presence, size, and relationship to the ostiomeatal complex. State whether they are large enough to potentially obstruct maxillary sinus drainage, and alert the surgeon if they are prominent and may be at risk during endoscopic manipulation. Example: "Bilateral infraorbital ethmoidal (Haller) cells noted, right larger than left. The right Haller cell narrows the ipsilateral ostiomeatal complex."

• Failing to recognize Haller cells as a normal variant and mistakenly attributing sinusitis to their presence when they are likely incidental.
• Underestimating the size and extent of Haller cells on axial imaging alone; coronal and sagittal multiplanar review is essential for complete assessment.
• Not communicating the presence of prominent Haller cells to the surgeon preoperatively, which can lead to inadvertent orbital entry during endoscopic sinus surgery.
• Confusing Haller cells with other infraorbital masses or cysts; correlation with their characteristic air-density appearance and location is key to avoiding misdiagnosis.