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Figure 18 Sagittal view with a probe through the inferior hiatus semilunaris into the maxillary sinus natural ostium.

Figure 19 Sagittal (a) and endoscopic (b) views after uncinate resection, illustrating the maxillary sinus natural ostium (M), the lateral (orbital) wall of the infundibulum (I), ethmoid bulla (B), and posterior fontanelle (PF) area. The uncinate tail occasionally is not completely removed and may lateralize, occluding the maxillary sinus natural ostium and preventing its visualization.

F. Middle Meatal Antrostomy (Figures 20-23)

In patients with more advanced disease and/or anatomical distortion due to prior surgery, a wider antrostomy is generally recommended (26-28,37). This immediately identifies the horizontal and vertical bony ridge of the antrostomy, the MOF, and the posterior wall of the maxillary sinus. Combining these three anatomical landmarks with simple-to-use columnellar measurements provides the surgeon with extremely accurate anatomical information that maintains the surgeon's endoscopic orientation as he or she proceeds posteriorly along the ethmoid sinus into the sphenoid sinus. This is especially important in distorted sinus cavities (see Sections G and H below, on anterior and posterior ethmoidectomy). The antrostomy ridge correctly identifies one's location within the ethmoid sinus (i.e., the anterior versus posterior ethmoid cells). The MOF helps in maintaining the correct anteroposterior trajectory as the surgeon proceeds toward the sphenoid sinus. The posterior wall of the maxillary sinus demarcates the relative level of the anterior sphenoid sinus in the coronal plane.

Figure 20 Sagittal (a) and endoscopic (b) views showing the site of blind entry into the maxillary sinus through the posterior fontanelle area (vertical line). Asterisk = horizontal portion of the middle turbinate basal lamella. MT = tail of middle turbinate. B = bulla. I = lateral (orbital) wall of the infundibulum. M = maxillary sinus natural ostium. IT = inferior turbinate.

Figure 20 Sagittal (a) and endoscopic (b) views showing the site of blind entry into the maxillary sinus through the posterior fontanelle area (vertical line). Asterisk = horizontal portion of the middle turbinate basal lamella. MT = tail of middle turbinate. B = bulla. I = lateral (orbital) wall of the infundibulum. M = maxillary sinus natural ostium. IT = inferior turbinate.

In the absence of any "normal" ostiomeatal complex landmarks, or when there is difficulty identifying the natural ostium of the maxillary sinus, the maxillary sinus should be entered through the posterior fontanelle, superior to the posterior one-third of the inferior turbinate. This approach will ensure that the surgeon remains a safe distance from the orbit floor, which rises superiorly at this level. Once the posterior wall of the maxillary sinus and MOF have been identified, by palpation with a probe and endoscopic visualization, a wide antrostomy is created by removing most of the posterior fontanelle and connecting it to the area of the maxillary natural ostium anteriorly.

When performing an antrostomy through the posterior fontanelle area, care must be taken that the nasal, as well as the medial maxillary sinus mucosa, is penetrated. Failure to do so may result in the formation of a maxillary sinus cyst, or mucocele, due to lateral elevation of the medial maxillary sinus mucosa and concomitant disruption of the natural ostium.

The site of the natural ostium is incorporated into the maxillary antrostomy to reduce the chances of circular mucus flow. When the natural ostium is not clearly visible, this is best achieved by removing tissue in a retrograde fashion following the MOF and the horizontal portion of the

Figure 21 Sagittal (a) and endoscopic (b) views showing a wide middle meatal antrostomy. The vertical line in the sagittal view denotes the approximate level of the maxillary sinus posterior wall, sphenoid sinus anterior wall, and orbital apex, in the coronal plane. These critical anatomical structures lie approximately 7 cm from the columnellar base. In advanced cases an inferior eth-moidectomy is performed, keeping within 10 mm of the horizontal and vertical antrostomy ridge as one proceeds inferomedially into the sphenoid sinus adjacent to the nasal septum (dotted arrow). S = sphenoid. PE = posterior ethmoid.

Figure 21 Sagittal (a) and endoscopic (b) views showing a wide middle meatal antrostomy. The vertical line in the sagittal view denotes the approximate level of the maxillary sinus posterior wall, sphenoid sinus anterior wall, and orbital apex, in the coronal plane. These critical anatomical structures lie approximately 7 cm from the columnellar base. In advanced cases an inferior eth-moidectomy is performed, keeping within 10 mm of the horizontal and vertical antrostomy ridge as one proceeds inferomedially into the sphenoid sinus adjacent to the nasal septum (dotted arrow). S = sphenoid. PE = posterior ethmoid.

antrostomy ridge to a point just behind the convexity of the nasolacrimal duct. At this point the MOF appears to be approximating the lamella of the inferior turbinate.

The MOF and bony ridge of the antrostomy provide the correct anteroposterior trajectory as the surgeon proceeds posteriorly into the posterior ethmoid and sphenoid sinuses. The MOF must always be kept in view and be constantly referred to throughout the surgery. Failure to visualize the superior margin of the antrostomy may cause the surgeon to proceed in a more superior direction toward the skull base.

The camera alignment on the monitor screen must also be periodically checked to ensure that the camera has not been inadvertently rotated. The endonasal anatomy is aligned so that the upper border of the monitor screen corresponds to the superior direction anatomically. The opening of the antrostomy should face medially in the sagittal plane (parallel to the nasal septum), with the

horizontal portion of the antrostomy ridge and adjacent MOF projecting in an anteroposterior direction toward the orbital apex. The posterior wall of the maxillary sinus as seen through the antrostomy demarcates the approximate level of the anterior wall of the sphenoid sinus, or posterior wall of the posterior ethmoid, in the coronal plane.

Figure 22 Sagittal (a) and endoscopic (b) views showing a wide middle meatal antrostomy. The horizontal and vertical ridge of the maxillary antrostomy (arrows) and adjacent MOF correctly identify the surgeon's location within the ethmoid sinus and helps maintain the correct anteroposterior trajectory as he or she proceeds toward the sphenoid sinus. The posterior wall of the maxillary sinus (PM) demarcates the relative level of the anterior wall of the sphenoid sinus in the coronal plane. The asterisk denotes the maxillary sinus natural ostium incorporated into a wide middle meatal antrostomy. Note the location of the maxillary sinus natural ostium adjacent to the MOF and several millimeters behind the convexity of the nasolacrimal duct (oval). B = inferior wall of the ethmoid bulla. Small arrows denote infraorbital nerve coursing along the orbital floor.

Figure 22 Sagittal (a) and endoscopic (b) views showing a wide middle meatal antrostomy. The horizontal and vertical ridge of the maxillary antrostomy (arrows) and adjacent MOF correctly identify the surgeon's location within the ethmoid sinus and helps maintain the correct anteroposterior trajectory as he or she proceeds toward the sphenoid sinus. The posterior wall of the maxillary sinus (PM) demarcates the relative level of the anterior wall of the sphenoid sinus in the coronal plane. The asterisk denotes the maxillary sinus natural ostium incorporated into a wide middle meatal antrostomy. Note the location of the maxillary sinus natural ostium adjacent to the MOF and several millimeters behind the convexity of the nasolacrimal duct (oval). B = inferior wall of the ethmoid bulla. Small arrows denote infraorbital nerve coursing along the orbital floor.

Figure 23 Endoscopic view of improperly aligned camera. The camera is rotated 30 degrees counterclockwise. The solid black line points superiorly. The unsuspecting surgeon may inadvertently penetrate the orbital wall thinking he or she is dissecting "superiorly" into the ethmoid cavity on the monitor. Conversely, the roof of the ethmoid may be penetrated if one incorrectly judges the direction of dissection "medially" on the monitor.

Figure 23 Endoscopic view of improperly aligned camera. The camera is rotated 30 degrees counterclockwise. The solid black line points superiorly. The unsuspecting surgeon may inadvertently penetrate the orbital wall thinking he or she is dissecting "superiorly" into the ethmoid cavity on the monitor. Conversely, the roof of the ethmoid may be penetrated if one incorrectly judges the direction of dissection "medially" on the monitor.

G. Anterior Ethmoid Air Cells (Figures 24 and 25)

The anterior ethmoid air cells run medial to the horizontal antrostomy ridge. In advanced disease or distorted cavities, the surgeon first performs an inferior ethmoidectomy (anterior and/or posterior, depending on the extent of disease) to identify the medial orbital wall inferiorly (26,37). At this point, the surgeon must begin to regularly palpate the eye prior to exenterating any additional ethmoidal cells. By looking for movement in the orbital wall, bony dehiscence will be identified. A good exercise is to fracture or remove a small piece of bone from the lamina papyracea to illustrate this movement while palpating the eye. The orbital wall, once identified, represents the lateral limits of one's dissection and is followed posteriorly or superiorly as needed (see Sections H and I, on posterior ethmoid and sphenoid dissection).

In advanced disease, the surgeon initially maintains a safe distance of approximately 10 mm as he or she proceeds around the antrostomy ridge (37). This corresponds to the approximate size of a large upbiting forceps. The inferior posterior ethmoid and sphenoid are identified (as described below) prior to dissection of the more superior ethmoid air cells.

Figure 24 Sagittal (a) and endoscopic (b) views with ethmoid bulla opened. B = ethmoid bulla. I = lateral infundibular wall. The junction of the medial orbital floor (MOF) with the lamina papyracea makes up the superior margin of the maxillary sinus natural ostium (asterisk).

Figure 24 Sagittal (a) and endoscopic (b) views with ethmoid bulla opened. B = ethmoid bulla. I = lateral infundibular wall. The junction of the medial orbital floor (MOF) with the lamina papyracea makes up the superior margin of the maxillary sinus natural ostium (asterisk).

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