Anatomical landmarks in revision sinus surgery and advanced nasal polyposis

Endoscopic sinus surgery (ESS) has been shown to be safe and effective when used appropriately for the management of chronic rhinosinusitis (CRS). However, in cases of revision surgery or advanced sinonasal polyposis or both, the usual anatomical landmarks that guide the endoscopic sinus surgeon can be distorted or obstructed from view, making dissection difficult and potentially dangerous if the surgeon does not have a method and understanding of the anatomy to navigate their way safely through the sinonasal cavity. In many cases, this results in incomplete surgery out of concern for doing harm to a patient.

ESS for CRS is indicated for patients who have failed maximal medical management. There are several goals of ESS whether it is being performed as a primary or revision surgery. One of the major goals is to open the affected sinuses to allow for improved drainage. The goal of functional ESS is to open the natural ostium of the sinus and preserve the mucosa so as to allow the natural process of mucociliary clearance to take place. However, this only applies to patients who have functional mucociliary clearance, and the goal of drainage must be approached differently in patients with cystic fibrosis and ciliary dyskinesia. In such patients, drainage relies more upon gravity and less upon the natural mucociliary clearance process. Another goal with opening the cavities is to allow easy in-office access for either debridement or taking cultures when necessary. A third goal is the removal of all diseased cells to obtain access to the last layer of mucosa. For a complete sphenoethmoidectomy, this allows access to the mucosa along the skull base and orbit. This allows access for irrigations, topical medications, and in-office surveillance. It is important to remember that ESS for CRS is only part of the overall treatment for a chronic disease. Finally, a primary goal of ESS is to do no harm. The goal of treatment is primarily to improve the quality of life for our patients, and, therefore, causing an avoidable complication is truly counterproductive.

The American Academy of Otolaryngology—Head and Neck Surgery endorses the intraoperative use of computer-aided surgery for appropriately selected cases, including revision surgery or extensive nasal polyposis. However, we must remember that this technology is a tool that may be inaccurate at times and may fail during the course of an operation. It is the hope of the authors that this article provides useful, consistent landmarks that will help to guide a surgeon through the most difficult ESS. To navigate safely, the surgeon must constantly have a reference as to the location of their instruments in a 3-dimensional space by viewing a 2-dimensional screen. Using the discussed landmarks should help the surgeon to operate confidently and safely.

When dealing with a complex case, a successful surgery begins preoperatively with a thorough evaluation of the sinus computed tomography (CT) scan in the axial, coronal, and sagittal planes. Some of the essential aspects of the imaging to note before the surgery are as follows:

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  presence of sinuses and obvious deviations (eg, aplastic frontal, contracted maxillary, and dominant right sphenoid);
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  presence and size of cells of the frontal recess and sinus (frontal cells, suprabullar cells, and agger nasi cells);
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  presence of suprabullar cell with significant supraorbital extension;
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  superior attachment of the uncinate process;
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  location of the anterior ethmoid artery (distance from the skull base);
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  distance from the inferior turbinate to the orbital floor;
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  keros classification

  ²

  • Keros P.

  Uber die praktische Bedeutung der Niveau-unter-schiede der Lamina cribrosa des Ethmoids.

  Laryngol Rhinol Otol (Stung). 1965; 41: 808-813

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  ;
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  dehiscences of the skull base, orbital wall, and bone around the carotid artery and optic nerve;
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  attachment of the sphenoid intersinus septum; and
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  presence of Onodi cell.

Sinonasal landmarks provide the surgeon with a reference point in a 3-dimensional space as one is viewing a 2-dimensional screen. They are also useful for determining the location of the ostia of the paranasal sinuses and the location of the sinuses themselves. It is important to be comfortable with using multiple landmarks, as the usual landmarks (eg, middle turbinate) may have been removed previously in cases of revision. In the following article, we focus on the landmarks that are almost always present and identifiable regardless of the number of previous surgeries or extent of nasal polyposis (Table).

When approaching a difficult case, we must assume that the usual landmarks including the middle turbinate and sometimes the inferior turbinate are missing. The first step in any case is to identify the nasal floor and follow it to the nasopharynx. This may require removal of polyps along the floor of the nose. Regardless of the number of revision surgeries a patient has had, the ability to refer to the nasal floor and the nasopharynx serves as a constant reference. In addition, the nasal septum (or its remnant) is used to maintain the anatomical orientation of the endoscope.

The next landmark that should be identified, which also serves as a guide for the remainder of the surgery, is the antrostomy ridge and medial orbital floor (MOF). In revision cases or cases of extensive polyposis, finding the natural ostium may not be a feasible way to identify the maxillary sinus. In such cases, the safest location to enter the sinus is through the posterior fontanel just above the posterior one-third of the inferior turbinate (Figure 1). This is the area with the greatest inferosuperior distance between the inferior turbinate and the orbital floor, as the MOF rises in a superior direction as one proceeds posteriorly. From here, the posterior fontanel can be removed retrograde to incorporate the natural maxillary ostium, just posterior to the nasolacrimal convexity. We advocate identification of the natural maxillary ostium using an angled scope to ensure there are no mucosal bridges present. The nasolacrimal convexity should be identified to prevent injury to the nasolacrimal duct. This convexity can almost always be identified even in the most complex cases and serves as another important landmark, which we address later in the article. In advanced cases of CRS, we advocate a large maxillary antrostomy that allows visualization of the MOF and posterior maxillary wall. Care must be taken posteriorly to avoid injury to the contents of the greater palatine canal.

By performing this antrostomy, we have created an antrostomy ridge at the junction of the medial maxillary wall and the orbital floor. We divide this antrostomy ridge into 3 parts: horizontal, transitional, and vertical (Figure 2, Figure 3). The MOF and antrostomy ridge is essential as a landmark to have a reference in all the 3 dimensions even when no other landmarks, such as the middle turbinate, are visible. The coronal plane of the horizontal portion of the antrostomy ridge correlates with the anterior ethmoid cells, and the coronal plane of the transitional ridge correlates with the posterior ethmoid cells. The coronal plane of the posterior maxillary wall sits within a few millimeters of the coronal plane of the face of the sphenoid and orbital apex. The ability to visualize the orbital floor through the maxillary sinus gives the surgeon the vertical height of where the lamina papyracea begins. Also, staying within 1 cm of the antrostomy prevents injury to the carotid artery, the optic nerve, anterior ethmoid artery, and skull base.

The uncinate process and ethmoid bulla are often not present or are obscured in revision or polyp cases. To safely enter the ethmoid cavity, we draw an imaginary line parallel to the nasal floor from the level of the posterior MOF (transitional ridge) to the nasal septum (Figure 4). By entering through the midpoint of this line, one enters the inferior aspect of the posterior ethmoid air cells through the horizontal portion of the middle turbinate basal lamella. Even in cases of extensive polyposis, the lamina papyracea can usually be identified at this point within the posterior ethmoid cavity. Once this lamina papyracea is identified, the superior posterior ethmoid cells can be dissected to expose the fovea ethmoidalis. In advanced disease, in which the lamina papyracea or the skull base or both cannot be identified within the posterior ethmoid cavity, a sphenoidotomy can be performed first to identify the lateral and superior limits of dissection. This is discussed later.

After identification of the skull base and lamina papyracea within the posterior ethmoid cavity (or the sphenoid sinus), the ethmoid cavity can be opened in a retrograde fashion as described by Wigand, knowing that the skull base ascends as one works in an posteroanterior direction. This should be confirmed on sagittal images of the sinus CT scan. Palpation of the orbit is a critical maneuver to determine any evidence of dehiscence of the lamina papyracea and should be performed throughout the surgery. When working in a posteoanterior direction along the skull base, the surgeon should remain laterally along the thicker bone of the fovea ethmoidalis and away from the eggshell thin bone of the lateral lamella of the cribriform plate. Once the smooth white bone of the fovea ethmoidalis is identified laterally, the surgeon can carefully open the cells medially following the downsloping curvature of skull base in a lateral to medial direction.

As mentioned previously, a sphenoidotomy is sometimes performed before the ethmoidectomy, because it is a reliable way to identify the superior (skull base) and lateral (lamina papyracea) limit of dissection. The natural sphenoid ostium can be found about 1.5-2 cm above the arch of the posterior choana, adjacent to the septum, just superior and medial to the tail of the superior turbinate (Figure 5). However, in advanced disease, anatomical distortion does not always allow adequate visualization of the superior turbinate. In such cases, the surgeon can use the MOF, which was exposed during the maxillary antrostomy. The MOF is a vital landmark during the approach to the sphenoid sinus and helps in maintaining the surgeon oriented to the correct anteroposterior trajectory. Again, an imaginary line is drawn from the posterior MOF to the septum, parallel to the nasal floor. The sphenoid sinus is entered at the medial aspect of this line adjacent to the septum, which consistently enters the sinus in the middle third (Figure 6). The ridge of the maxillary antrostomy is the general trajectory of the instrument (Figure 7).

By entering the sphenoid at this medial point, the lateral structures are protected. The sphenoid can then be opened further laterally, inferiorly, and superiorly as needed. Again, after the sphenoid sinus is opened and cleaned out, the planum sphenoidale and lateral wall of the sphenoid can be identified, which represents the level of the superior and lateral limits of ethmoid dissection as these structures are followed retrograde. It is important to note that a posterior ethmoid sinus is often confused with the sphenoid sinus. However, most of the sphenoid sinus sits below the MOF and most of the posterior ethmoid cavity sits above the orbital floor. Therefore, if the floor of the sinus is easily seen immediately after entering (without looking inferiorly with an angled scope), it is probably a posterior ethmoid cell.

Ideally, the agger nasi cell, any frontal cells, and the suprabullar cells are systematically opened until the frontal sinus is visualized. However, in advanced cases where there may be scar, extensive polyposis, and edematous mucosa, this approach is not practical.

Frontal recess dissection and frontal sinusotomy is one of the most challenging aspects of ESS, especially in cases of advanced disease owing to the complex and highly variable anatomy, the proximity to the skull base, and the potential for ostial stenosis if the mucosa is traumatized. When the frontal recess cells cannot be sequentially dissected, the nasolacrimal convexity, which marks the nasolacrimal duct, is a key landmark in identifying the frontal sinus outflow tract. Fortunately, this structure can almost always be found no matter how many revisions the patient has undergone, and polyp disease often spares the the mucosa overlying this convexity allowing it to be identified in advanced cases of nasal polyposis (Figure 8).

The nasolacrimal convexity defines the trajectory to enter the frontal sinus (Figure 9). By starting at the anterior border of the natural maxillary ostium and drawing a line parallel to the bony nasolacrimal duct, the surgeon can locate the frontal sinus infundibulum. Two other landmarks are useful in locating the frontal infundibulum. The anterior attachment of the middle turbinate sits approximately 5-10 mm anterior to the ostium. The anterior ethmoid artery is located about 1 cm posterior to the ostium and generally sits at the posterior septation of the suprabullar cell. The latter 2 landmarks are not always visible in advanced cases. Our technique for identifying the frontal sinus in cases of advanced disease involves using a long curved probe. We place the tip of the probe at the anterior aspect of the natural maxillary ostium, and then follow a line parallel to the nasolacrimal convexity. The frontal sinus can usually be entered by placing the tip of the probe adjacent to the middle turbinate and directed slightly laterally. It is important to perform this maneuver gently and without force, using only 2 fingers. The attachment of the uncinate process, noted preoperatively, is helpful in determining where to place the probe. For example, if the uncinate process attaches to the middle turbinate or skull base, then sliding the probe along the middle turbinate ends in a blind pouch and the probe needs to be directed more laterally. If a suprabullar cell with significant supraorbital extension is noted on the preoperative CT scan, the surgeon should be careful not to confuse this with the actual frontal sinus. Transillumination through the frontal sinus ostium is helpful in making this distinction.

Sinonasal landmarks are essential in keeping the surgeon oriented in 3-dimensional space while looking at a 2-dimensional screen. A thorough knowledge of such landmarks will aid the surgeon to confidently, safely, and effectively performing ESS.