Учебники / Computer-Aided Otorhinolaryngology-Head and Neck Surgery Citardi 2002

may be removed with 45-degree and 90-degree side-toside and front-to-back grasping frontal giraffe forceps. Bone fragments, which have been inadvertently pushed up into the frontal sinus, may be pulled down into the frontal recess with frontal sinus seekers. They may then be removed with giraffe forceps for removal. The frontal recess mucosa should not be grasped with forceps, as it may strip out of the frontal recess. Mucosal loss will result in scarring and possibly osteoneogenesis. Redundant pieces of mucosa may be removed with through-cutting forceps or the gentle application of curved powered dissection blades. At this point, the ostium should be open and a suction canula may be gently passed into the frontal sinus to aspirate debris for microbiological and pathological examination as well as for frontal sinus irrigation. Irrigation of the sinus can be particularly helpful to clear a bloody field, reduce edema, and allow direct visualization of bony fragments and mucosal edges. If the suction canula is also a CAS surgical navigation probe, it will demonstrate that the frontal sinus ostium is open.

Figure 14.3 demonstrates an agger nasi cell cap that is obstructing the frontal recess in a patient with recurrent frontal recess disease. The suction probe is in the obstructing cell, while the true passageway to the frontal sinus is medial to the probe. The frontal ostium is above the agger nasi cell cap, and the frontal

FIGURE 14.3 This intraoperative CAS screen capture (InstaTrak, Visualization Technology, Lawrence, MA) shows that the remnant agger nasi cap has scarred to ethmoid bulla remnant posteriorly (sagittal view). In addition, remnant cells are seen medially (coronal CT and endoscopic view). In the endoscopic view, the probe has displacing the agger nasi cell cap superiorly; this causes the crosshairs to appear in frontal sinus.

may be found posteriorly in the middle meatus. In contrast, a type III cell opens into the anterior middle meatus just behind the agger nasi cell. Frontal recess obstruction from frontal cells can occur in a similar fashion to that of the agger nasi cell; that is, edema in very small, tight drainage pathways, or iatrogenic scar may close the frontal recess [13].

The CAS computer is particularly valuable for surgical planning when these cells are present. The sagittal reconstruction will demonstrate the labyrinth of bony lamella creating various drainage pathways, while coronal and axial scans primarily demonstrate the location of the pathology. Without all three CT planes, location and removal of the cell walls is very difficult.

Frontal cell dissection is performed in the manner described for agger nasi cells. First, the cell walls that can be removed must be identified. Then, the frontal sinus curettes or through-cutting instruments are used to break down the walls. Finally, the loose bony fragments are removed with giraffe forceps. Of course, mucosal preservation must be achieved. Types II–IV frontal cells may be too far superior or lateral to be removed completely by frontal recess dissection. In those instances, the frontal recess dissection should be performed first and then a frontal sinus trephine or osteoplastic flap may be added to improve access from above.

Figure 14.5 demonstrates a type I frontal cell above an agger nasi cell on the medial orbital wall. The probe or suction tip is medial and anterior to the

FIGURE 14.5 This intraoperative CAS screen capture (InstaTrak, Visualization Technology, Lawrence, MA) shows a left type I frontal cell. The pointer is at the medial wall of frontal cell. The endoscopic image demonstrates open frontal cell.

cell. This correlates with the endoscopic image, which demonstrates the open obstructing cap of the cell. The pathway to the frontal sinus is medial to this cell (namely, between the medial cell wall and the middle turbinate attachment to skull base. In Figure 14.6A the CT demonstrates a type II frontal cell. The sagittal CT image depicts this type II frontal cell well. It could be argued that this cell is perhaps a suprabullar cell; however, the CT demonstrates two cells that are stacked in tier configuration. The corresponding endoscopic picture is the frontal recess after the cells have been dissected and the frontal ostium has been open. Note that the probe is actually below the frontal recess so that the endoscopic picture is not obscured. Figure 14.6B is the 3-month postoperative healed right frontal recess in this patient. Figure 14.7 is an excellent example of a type III frontal cell. The sagittal view demonstrates that the drainage pathway for the cell is actually back into the anterior ethmoid, behind the agger nasi cell. The probe is at the posterior skull base so that a clear view of the type III cell pneumatized above a small agger nasi cell into the frontal sinus may be obtained.

14.2.5 Supraorbital Ethmoid Cells

The supraorbital ethmoid cell or cells develop posterior to the agger nasi cell from the third frontal pit or groove of Schaeffer [10]. They occur along the skull base

FIGURE 14.7 This intraoperative CAS screen capture (InstaTrak, Visualization Technology, Lawrence, MA) shows a type III frontal cell, which can be best seen on the saggital CT image. The pointer is located in the posterior ethmoid.

in the frontal recess behind the frontal sinus. They may be multiple, may occur anterior or posterior to the anterior ethmoid artery, and usually are separated from the frontal sinus by the ethmoid bulla lamella. They may extend back to or even past the middle turbinate basal lamella . The important common feature of these cells is that they pneumatize laterally out over the orbit. They may also pneumatize forward from their lateral position and appear to be part of a septated frontal sinus. Understanding the spatial relationship of supraorbital ethmoid cells to the frontal sinus, orbit, and skull base is an important key to frontal recess dissection [14].

Axial scans as well as sagittal CT reconstructions are important in delineating the drainage pathway of a supraorbital ethmoid cell. It will usually drain just posterior to the frontal sinus ostium. Due to its proximity to the frontal ostium, the entrance to an extensively pneumatized supraorbital ethmoid cell can be easily confused with it, leaving the internal frontal ostium obstructed at the end of the procedure. This is especially true when viewing the area endoscopically in a bloody field. CAS CT review (particularly the sagittal view) and intraoperative CAS surgical navigation make this differentiation much easier. The CAS probe will distinguish between the supraorbital ethmoid cell opening and the frontal sinus; in doing so, the CAS system demonstrates whether additional dissection is needed.

It is important to remove the common wall between the supraorbital ethmoid cell and the internal frontal ostium as far superiorly as possible, preferably to the skull base. This will prevent recirculation of mucus at either cell ostium. When cell walls are only partially removed, mucociliary clearance may be disrupted, leading to recirculation and trapping of mucus in the frontal recess. CAS facilitates the identification and removal of this septation. Completely opening the supraorbital ethmoid cells creates a much larger common drainage pathway for the two cells. It is much less likely that this pathway will be less likely to become obstructed by edema. Figure 14.2 demonstrates an optimal intraoperative result.

It should also be noted that extensive pneumatization of a supraorbital ethmoid cell can doom frontal sinus obliteration to long-term failure. If the anterior lateral portion of a supraorbital ethmoid cell is confused with a septated frontal sinus, frontal sinus obliteration will be very difficult. Mucous membrane removal in the most lateral or posterior recesses of the cell over or behind the orbit is often impossible and will create a situation of almost certain mucocele development. Therefore, the CT scans obtained in preparation for CAS are very important in presurgical planning, since they will demonstrate a laterally pneumatized supraorbital ethmoid cell, which is a contraindication to frontal sinus obliteration.

14.2.6 Interfrontal Sinus Septal Cell

The interfrontal sinus septal cell appears less frequently than the agger nasi and supraorbital ethmoid cells. It develops in the septum between the two frontal sinuses. This cell may pneumatize to different degrees, varying from just the

lower septum all the way to the frontal sinus apex or into a pneumatized crista galli. This cell empties into one frontal recess, usually medial and anterior to the internal frontal ostium. It may also empty into one frontal sinus (rather than directly into the frontal recess). Disease in this cell can cause frontal sinus disease by creating edema and narrowing the total drainage pathway of the frontal recess. Either edema from residual interfrontal sinus septal cell disease or iatrogenic scarring can contribute to frontal recess obstruction and therefore frontal sinus disease in the previously operated patient [15].

CAS is important for intraoperative identification of this cell. Thin-cut coronal scans usually identify its position and contribution to pathology. The interfrontal sinus septal cell’s opening and its common wall with the larger frontal recess are difficult to identify. They are best identified by using the 30and 70degree telescopes after frontal recess dissection in combination with the CAS probe. Once the frontal recess has been cleared, the common wall between the interfrontal sinus septal cell and the frontal sinus should be removed as far superiorly as possible. One method is to place a frontal sinus 90-degree curette into the interfrontal sinus septal cell and break the intervening wall laterally. However, it is more important to recognize the existence of an interfrontal sinus septal cell and open it inferiorly than it is to remove the entire common wall. Once the cell

FIGURE 14.8. This intraoperative CAS screen capture (InstaTrak, Visualization Technology, Lawrence, MA) shows an interfrontal sinus septal cell and a left supraorbital ethmoid cell.

is open and draining into a large and disease-free frontal recess, rarely will it play a role in recurrent frontal sinus disease.

The coronal view in Figure 14.8 demonstrates an interfrontal septal cell that has pneumatized into the lower interfrontal sinus septum. The suction probe is at the most anterior part of the endoscopic image, which demonstrates the open frontal ostium. Its tip is in the cell between the frontal sinuses. The coronal view from the same patient (Figure 14.9) demonstrates that the interfrontal sinus septal cell opens into the left frontal recess. The supraorbital ethmoid cell is also extensively pneumatized. The endoscopic images in Figures 14.8 and 14.9 demonstrate a complete frontal recess dissection, including an open supraorbital ethmoid cell laterally. The common partition between the supraorbital ethmoid cell and the frontal sinus has been resected as close to the skull base as possible.

14.2.7 Suprabullar Cell

The suprabullar cell is found above the ethmoid bulla. This cell occurs in the ethmoid bulla lamella or pneumatizes forward through it. This is the only ethmoid cell, which closes the frontal recess from posterior. The suprabullar cell is well visualized only on sagittal CT [14]. CAS is necessary to remove it. Without

FIGURE 14.9 This intraoperative CAS screen capture (InstaTrak, Visualization Technology, Lawrence, MA) shows that the left frontal ostium and supraorbital ethmoid cell open into frontal recess. The common partition has been resected to skull base in the endoscopic view. The frontal ostium is anterior and the supraorbital ethmoid cell is posterior to the suction tip.

CAS, it is impossible to differentiate the walls of the cell from the skull base endoscopically. Due to its position along the skull base, delicate dissection using the frontal sinus seekers, curettes, and CAS suction tips are required to first break the cap of the cell from anterior to posterior and then remove it. Once the cell walls are broken, they are best meticulously removed in a similar fashion to agger nasi cell caps.

Figure 14.10 demonstrates a right supraorbital ethmoid cell that has pneumatized out over the orbit and a suprabullar cell medially at the skull base.

14.2.8 Recessus Terminalis

If the uncinate process inserts on the medial orbital wall, the ethmoid infundibulum will end in a blind pocket. This blind pocket is called the recessus terminalis. This anatomical variation forces the frontal sinus drainage pathway down the medial surface of the uncinate and thereby directly into the middle meatus. This variant occurs more commonly than often thought (as much as 50%) [7]. The recessus terminalis is important in the surgical approach to the frontal sinus. Complete uncinate removal at its medial orbital wall attachment is the goal when dealing with a recessus terminalis.

FIGURE 14.10 This intraoperative CAS screen capture (InstaTrak, Visualization Technology, Lawrence, MA) demonstrates a suprabullar cell. In the endoscopic view, the probe tip is within the suprabullar cell. Intraoperative surgical navigation was necessary to differentiate this cell from the skull base.