E3419. The Frontal Recess: What the Radiologist Needs to Know?
  1. Mona Alrehaili; King Salman Bin Abdulaziz Medical City
  2. Sara Alharbi; King Salman Bin Abdulaziz Medical City
The radiologist should be familiar with the greatly variable anatomy of paranasal sinuses; in particular, recognition of the complex anatomic variants comprising the frontal sinus outflow tract is essential for successful surgical intervention. We aim to summarize the important anatomical varieties in the region of frontal recess and their impact on the outflow pathway and patency.

Educational Goals / Teaching Points
Identify the structure of frontal sinus outflow tract. Be familiar with anatomical variation of the ethmoid and accessory air cells around the frontal recess and their impact on the drainage pathway and patency. Understand the surgical importance of characterizing frontal sinus and recess anatomy.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The frontal sinus outflow tract is the functional unit for frontal sinus drainage and includes the frontal infundibulum, ostium, and recess. Being a narrow cleft within the population of anterior ethmoid cells, the frontal recess is responsible for most cases of frontal sinusitis. The patency of the frontal recess is affected by the following neighboring structures: Agger nasi cells, ethmoid bulla, uncinate process and accessory air cells in the region of the frontal recess. Agger nasi cell and ethmoid bulla form the anterior and posterior partitions of the frontal recess. The extent of their pneumatization is among the most important factors impacting the frontal sinus outflow tract. The frontal recess drains into either the middle meatus or ethmoid infundibulum depending on the superior attachment of the uncinate process. The frontal recess can be pneumatized by various cells and these cells may alter the shape and position of the frontal recess or frontal sinus ostium, the higher association with chronic sinusitis increases the importance of addressing them adequately. Insufficient dissection of air cells obstructing the frontal sinus is a common reason for endoscopic failure, therefore preoperative examination by CT is crucial for successful surgery. The variable air cells around the frontal recess can be grouped into medial and lateral pneumatization (to the frontal sinus), and anterior and posterior groups (air cells above agger nasi cell and ethmoid bulla, respectively). Medial pneumatization: Inter frontal sinus septal cell is an air cell within the intersinus septum of the fontal sinus. Lateral pneumatization: the supraorbital ethmoid air cells are ethmoid cells extending into the orbital plate of the frontal bone and are often lateral and posterior to the frontal sinus. Anterior pneumatization: frontal cells are situated above the agger nasi cells and depending on their number and extension they are divided into four types. Posterior pneumatization: the suprabulla cell as its name implies, is an air cell just superior to the ethmoid bulla.

The frontal sinus outflow tract can be affected by wide variation of ethmoid and accessory air cells. Understanding and identifying those cells is essential for safe and successful surgical approach.