The anatomy of the frontal sinus and frontal recess can be likened to an hourglass with its waist at the frontal ostium. Perhaps the most complex anatomy in the sinonasal region lies inferior to the ostium at the frontal recess. On first inspection, there appears to be a lengthy bony duct-like structure from the frontal sinus to the middle meatus that has been referred to as the nasofrontal duct. This duct-like structure often does not have bony walls of its own, rather the walls are formed by the close relationship of bordering anatomic structures. Therefore, this region is more appropriately referred to as a recess, specifically the frontal recess. This frontal recess is highly variable and challenges even sophisticated attempts of constant anatomic description. The frontal recess is bounded anteriorly by the agger nasi, laterally by the orbit, and medially by the middle turbinate. The posterior limit of the frontal recess is more variable depending upon the relationship of the ethmoid bulla or bulla lamella to the skull base. When the bulla lamella reaches the skull base, it forms a distinct posterior boundary of the frontal recess. When it does not reach the skull base, the suprabullar recess communicates directly with the frontal recess and the anterior ethmoid artery may offer the only discrete posterior margin. The patency of the frontal recess depends upon several factors including: 1. the superior articulation of the uncinate process, 2. the agger nasi cell, 3. the presence or absence of frontal cells, 4. the supraorbital cell, and 5. the bulla lamella.

Sagittal schematic cut-away view of the sinuses shows solid black arrow directed cephalad through the frontal recess into the frontal sinus (pink). Ethmoid cells are shaded blue, maxillary sinus purple, and sphenoid sinus yellow. (Adapted from Grant's Atlas of Anatomy)	Sagittal cadaver dissection shows rather narrow frontal recess (arrowheads). Agger nasi cell lies anterior to the recess (a). In this case, the bulla lamella (arrow) reaches the skull base and forms a discrete posterior boundary of the frontal recess.	Sagittal schematic shows the “waist” of the hourglass at the frontal sinus ostium. The frontal recess in this diagram communicates with the ethmoid infundibulum. This is not a constant drainage pathway.

Coronal CT image demonstrates patent frontal recesses bilaterally (dotted lines) draining medial to agger nasi cells (a) and lateral to the vertical lamellae of the middle turbinates.	Coronal CT shows patent frontal recess on the left (dotted line) draining medial to ethmoidal bulla (b). The right frontal recess is occluded by mucosal thickening.	Sagittal CT of cadaver specimen shows patent frontal ostium, frontal recess (dashed line), and agger nasi cell (A). Broad arrow marks inferior turbinate. (Adapted from Radiologic Clinics of North America, Mafee M, ed., Jan. 1993)

Surgery of the frontal sinus and frontal recess can be most challenging given the highly variable and complex anatomy of the region. External procedures were the mainstay of treatment prior to the introduction of functional endoscopic sinus surgery. The trephination procedure is a limited external approach to frontal sinus drainage that may be performed in conjunction with endoscopic frontal sinusotomy. Most frontal sinus conditions requiring surgery however, can now be managed entirely endoscopically. The goal of endoscopic sinus surgery is to reestablish mucociliary clearance. The region of the frontal recess is highly susceptible to postoperative scarring resulting in frontal recess stenosis, thus the recess is often avoided. Surgery is initially directed at the osteomeatal complex and disease in the frontal recess and sinus generally clears following this conservative endoscopic approach. Most endoscopic procedures directed at the frontal sinus are performed in patients who have previously undergone osteomeatal complex surgery. In these patients, it is not uncommon to find scarring, osteoneogenesis, and anatomic variants that predispose the patient to frontal sinus disease. Many patients have a combination of these factors. In particular, incomplete removal of the obstructing agger nasi cells and frontal cells can lead to chronic frontal sinusitis. Advances in endoscopic surgery and the development of image-guided (computer-assisted) techniques have resulted in the increasing use of endoscopic techniques in the management of frontal sinus pathology. Endoscopic approaches are used to establish one of three types of frontal sinus drainage. The three types differ in extent of resection, however, they are alike in that the sinus remains bounded by mucosa-lined bone rather than scar tissue. The retention of the mucous membrane may result in less secondary sinus shrinkage and obstruction than occurs with external approaches. If long-term stable drainage of the frontal sinus cannot be established with an endoscopic approach or prolonged stenting of the frontal sinus ostium, an external approach with obliteration of the frontal sinus may be necessary. This exhibit will demonstrate the postoperative CT appearance of frontal sinus trephination, the three types of endoscopic frontal sinus drainage procedures directed at the frontal recess, and osteoplastic flap with obliteration.